 Joint Session |
Quantitative proteomic analysis of a bean rust fungus and its host
B. COOPER (1)
(1) USDA-ARS, Beltsville, MD, USA
Uromyces appendiculatus is a rust fungus that causes disease on the economically important dry bean plant Phaseolus vulgaris. To better understand bean rust biology, we have employed high-throughput liquid chromatography tandem mass spectrometry to compare the proteins from germinating spores and infected leaves. The comparative analysis between the two helped differentiate a set of 24 U. appendiculatus proteins targeted for secretion that were specifically found in infected beans and a set of 34 U. appendiculatus proteins targeted for secretion that were found in germinated spores and infected beans. The proteins specific to infected beans included family 26 and family 76 glycoside hydrolases that may contribute to degrading plant cell walls. There were also several types of proteins with structural motifs that may aid in stabilizing the specialized fungal haustorium cell that interfaces the plant cell membrane during infection. In addition, we have analyzed more than 3,000 proteins from infected bean leaves. By statistically comparing the amounts of proteins detected in a single plant variety that is either susceptible to infection or resistant, depending on the fungal strains introduced, we have distinguished resistance from susceptibility at a proteomic level. Several of the plant proteomic responses appear to favor the pathogen during the course of infection. These results provide a basic foundation for rust fungal biology.
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Fungicide efficacy and biomass yield loss attributed to rust on switchgrass
A. HAGAN (1), K. Bowen (1)
(1) Auburn University, Auburn, AL, USA
Impact of rust (Puccinia emaculata) on switchgrass aboveground biomass (ADM) yield is unknown. Cloud 9 switchgrass was planted in January 2011. In 2011, 2012, and 2013, azoxystrobin, chlorothalonil, chlorothalonil + propiconazole, myclobutanil, propiconazole, cyprodinil + fludioxonil, and thiophanate-methyl were applied at 2-wk intervals from June to September. Rust intensity was noted monthly on a 1 to 10 scale. Relative AUDPC (rAUC) was calculated each year for each treatment. Shoots were cut in January 2 in. above the soil line and weighed. Samples were weighed wet, dried, and reweighed to determine ADM yield. A higher rAUC was noted in 2012 than 2011 or 2013, the latter had the least rust. While all fungicides reduced rAUC compared to the control, azoxystrobin and myclobutanil gave the best and cyprodinil + fludioxonil the least rust control. Similarly high ADM yield was seen in all years with azoxystrobin and myclobutanil than most fungicides and the control, which had equally low ADM yield. Rust reduced ADM by 40, 50, and 42% in 2011, 2012, and 2013, respectively. When rAUC was regressed against ADM, R2 values were 0.33, 0.59, and 0.38 for 2011, 2012, and 2013, respectively.
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Inheritance of brown and orange rust resistance in progenies from self- crosses of sugarcane
S. SOOD (1), P. Zhao (2), J. Comstock (1)
(1) Sugarcane Field Station, USDA-ARS, Canal Point, FL, USA; (2) Yunnan Sugarcane Research Institute, Yunnan Academy of Agricultural Sciences, Kaiyuan City, China
Brown rust caused by Puccinia melanocephala Sydow & P. Sydow and orange rust caused by P. kuehnii (W. Krüger) EJ Butler are economically important diseases of sugarcane in Florida. Durable resistance to rust has been difficult to obtain. The purpose of this research is to determine the frequency of rust resistant progeny from self-crosses of parental clones that have different rust reactions. Fourteen clones were self-crossed and the rust reactions of individual progeny were obtained in a manner that individual progeny was tracked in seedling flats. Progeny of each cross was divided into two sets. One set of the progeny was sprayed with brown rust spores suspension and the other set was sprayed with orange rust spores suspension. Rust data were collected four weeks after inoculation. Seedlings without any symptoms were separated and inoculated again to verify their resistant reaction and to eliminate any possibility of an escape from a successful inoculation. Progeny of self-crossed orange rust resistant clones, CP00-1825 and CP92-1167, produced orange rust resistant progenies. Interestingly, CP92-1167 was the female parent of CP00-1825. Progenies of brown rust resistant CP84-1591, CP94-2059 and Ho94-856 were predominately resistant to brown rust. All the parents used in the self-crossing except CP84-1591 lack Bru 1 gene. Further research is needed to evaluate the significance of self-crosses to achieve resistance to these rust diseases.
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Integrated Pest Information Platform for Extension and Education (iPiPE): Progress Thru Sharing
S. ISARD (1), J. VanKirk (2)
(1) Departments of Plant Pathology and Environmental Microbiology and Department of Meteorology, Pennsylvania State University, University Park, PA, USA; (2) NCSU Center for IPM, Raleigh, NC, USA
Food security is best served by a national infrastructure of private and public professionals who routinely monitor crop health and pest incidence then translate this knowledge to a shared platform enabling rapid dissemination of mitigation measures to limit crop loss. The iPiPE CAP, funded by a 2015 USDA AFRI 5-yr $7 million grant, provides such an infrastructure with cyberage tools, information products and expert commentary for detection and management of pests that threaten U.S. crops. Over the past decade, the focus of the PIPE system has expanded from a single pathogen in one crop (soybean rust), to a variety cereal rusts, and into a platform for sharing observations on a wide range of important pests in a variety of cropping systems. By categorizing pests, data, and users, iPiPE enables sharing observations while protecting privacy of individuals, companies, and government agencies. In 2016, fourteen iPiPE Crop-Pest Programs (CPPs) will incentivize growers and consultants to submit observations on target pests, including rusts in corn, soybean and sunflower, by providing tools and information for timely management decisions. Coordinated by extension professionals from across the nation, programs provide undergraduate students with hands-on extension and diagnostic experiences. Risk-based research will prioritize detection efforts for target pests and direct in-field scouting. Observations housed in a national pest observation depository will enable future research using geographically extensive, multi-year databases. iPiPE success is measured by numbers of CPPs, participating stakeholders and trained students. The iPiPE CAP will fund7 new CPPs in both 2017 and 2018.
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From Select Agent to an Established Pathogen: The Response to Phakopsora pachyrhizi (Soybean Rust) in North America
H. KELLY (1), N. Dufault (2), D. Walker (3), S. Isard (4), R. Schneider (5), L. Giesler (6), D. Wright (2), J. Marois (2), G. Hartman (3)
(1) University of Tennessee, Knoxville, TN, USA; (2) University of Florida, Gainesville, FL, USA; (3) USDA-ARS, University of Illinois, Champaign, IL, USA; (4) Pennsylvania State University, University Park, PA, USA; (5) Louisiana State University, Baton Rouge, LA, USA; (6) University of Nebraska-Lincoln, Lincoln, NE, USA
The pathogen causing soybean rust, Phakopsora pachyrhizi, was first described in Japan in 1902. The disease was important in the Eastern Hemisphere for many decades before the fungus was reported in Hawaii in 1994, which was followed by reports from countries in Africa and South America. In 2004, P. pachyrhizi was confirmed in Louisiana, making it the first report in the continental United States. Based on yield losses from countries in Asia, Africa, and South America, it was clear that this pathogen could have a major economic impact on the yield of 30 million ha of soybean in the United States. The response by agencies within the United States Department of Agriculture, industry, soybean check-off boards, and universities was immediate and complex. The impacts of some of these activities will be described in this presentation. The net result has been that the once dreaded disease, which caused substantial losses in other parts of the world, is now better understood and effectively managed in the United States. The disease continues to be monitored yearly for changes in spatial and temporal distribution so that soybean growers can continue to benefit by knowing where soybean rust is occurring during the growing season.
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| Poster Session |
Fungicides as Management Tools for Sugarcane Orange Rust
R. RAID (1), B. Chaulagain (1), S. Sanjel (1), J. Comstock (2), M. Hincapie (1), P. Rott (1)
(1) University of Florida, Belle Glade, FL, USA; (2) USDA Sugarcane Field Station, Canal Point, FL, USA
Sugarcane orange rust, caused by Puccinia kuehnii, was initially observed in Florida in 2007. Since that time, it has affected several commercially important cultivars, notably CP 80-1743, CP 72-2086, CP 89-2143, CP 88-1762, and CP 78-1628. Currently, orange rust susceptible cultivars account for over 70% of Florida’s sugarcane holdings. With host-plant resistance a long term goal, the sugarcane industry is in desperate need of additional rust management tools. A series of fungicide trials have been conducted to investigate the feasibility of fungicides serving as a viable, economic means of control. Fungicide treatments consisted of select candidates from three major classes of fungicides, the strobilurins (FRAC group 11), the triazoles (FRAC group 3), and the carboxamides (FRAC group 7), alone and in combination and/or alternation. Results indicate that the strobilurin fungicides provided the best control, followed by strobilurin/triazole and strobilurin/carboxamide combinations, and finally, the triazole fungicides alone. Fungicides have been demonstrated capable of reducing orange rust losses by as much as 40%. While economic factors will ultimately be an important consideration, levels of orange rust control obtained in these studies show promise regarding prospects for fungicides as a potential management tool.
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Evaluation of Fungicides for Management of Pea Rust
J. HALVORSON (1), S. Fitterer (2), D. Carruth (2), S. Meyer (1), J. Jordahl (1), B. Berghuis (1), S. Haugen (1), C. Schuh (1), R. Humann (1), S. Markell (1)
(1) North Dakota State University, Fargo, ND, USA; (2) BASF North Dakota Research Farm, Davenport, ND, USA
Pea rust, caused by Uromyces viciae-fabae (Pers.) Schroet., can be a yield-limiting disease. In Montana and North Dakota, reports of the disease are becoming more frequent since first reported in the 1980’s. Although yield losses have not yet been documented in North Dakota, a proactive evaluation of management tools is warranted. The objective of this study was to evaluate fungicide efficacy for management of pea rust. In 2015, two fungicide trials were conducted in Fargo and Leonard, ND. Trials were arranged in a randomized complete block design with four replicates. Treatment plots were artificially inoculated with fresh U. viciae-fabae urediniospores suspended in a soltrol solution applied with a modified backpack mounted leaf blower when a conducive environment for infection was forecasted. Ten fungicides with four different modes of action were applied at the first sign of disease. The Fargo trial was rated weekly three times, beginning one week post-fungicide application, by visually assessing rust severity on 10 leaves from 10 plants. The Leonard trial was rated once at the R5-R6 growth stage by visually assessing rust severity of stems, leaves, and whole plots. Statistical separation of disease ratings occurred between some treatments and the non-treated control at both locations. Prothioconazole, azoxystrobin, and pyraclostrobin were among the more efficacious treatments. Statistical differences in yield were not detected in the Fargo trial; the Leonard trial was not harvested. The identification of the most efficacious fungicides will provide growers important management information should pea rust become an economically important disease in North Dakota and Montana.
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Efficacy of fungicides for the management of oat crown rust (Puccinia coronata)
S. HAUGEN (1), S. Fitterer (2), D. Carruth (2), J. Halvorson (1), S. Meyer (1), A. Friskop (1)
(1) North Dakota State University, Fargo, ND, USA; (2) BASF North Dakota Research Farm, Davenport, ND, USA
Oat crown rust, caused by the macrocyclic heteroecious pathogen Puccinia coronata, is the most important disease in oat production throughout the Northern Great Plains. Due to variability in the pathogen, durable host resistance has been difficult to achieve leaving fungicides as an important management tool. In an effort to develop fungicide management information for oat producers, three fungicide efficacy trials were established at two locations in North Dakota in 2014 and 2015. Trials were conducted in a randomized complete block design with four replicates. Fungicide groups evaluated were DMI, QoI, and SDHI. All fungicides were applied at growth stage Feekes 9 (flag leaf) using a backpack sprayer. Trials were not artificially inoculated and relied on a natural inoculum source. High levels of disease developed at all three locations, and disease incidence and flag leaf severity ratings were recorded at several times throughout the growing season. At one location in 2015, normalized difference vegetation index (NDVI) ratings were conducted three times using the Crop Circle ACS-430 Crop Canopy Sensor. Yield was obtained at two of the three trials. Data indicated that all fungicide treatments had statistically lower disease values than the non-treated control. Also, yield values from fungicide treated plots were statistically higher than the non-treated control. Results of the trial will help develop fungicide recommendations for oat producers in the Northern Great Plains.
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Evaluation of Fungicides for Management of Common Bean Rust
E. CRANE (1), L. Olson (2), J. Jordahl (1), S. Meyer (1), J. Halvorson (1), B. Berghuis (1), R. Humann (1), F. Mathew (3), S. Markell (1)
(1) North Dakota State University, Fargo, ND, USA; (2) North Dakota State University, Fargo, , USA; (3) South Dakota State University, Brookings, SD, USA
Common bean rust, caused by Uromyces appendiculatus, can cause yield losses in pinto, navy, and other dry edible bean market types grown in the North Central state of North Dakota. Since the identification of U. appendiculatus race 20-3 in 2008, which confers virulence to the most commonly deployed effective resistance gene (Ur-3), all commonly grown bean varieties need to be considered susceptible to rust. Research conducted between 2009 and 2011 demonstrated that several fungicide modes of action had efficacy on rust. However, continued evaluation of fungicide efficacy is necessary to refine management recommendations. Fungicide efficacy trials were conducted at the North Dakota Agricultural Experiment Station in Fargo, ND between 2012 and 2015. Trials were sown to Othello pinto or Avalanche navy beans in eight-row plots arranged in a randomized complete block design with four to six replicates. Trials were inoculated with U. appendiculatus urediniospores suspended in a soltrol solution using a modified backpack leaf blower to incite an epidemic. Fungicide treatments were applied to the center four rows approximately one week after pustules were first observed in plots. Rust severity was determined by visually evaluating 10 arbitrarily selected trifoliates in the center two rows of each plot. In general, most fungicide-treated plots had significantly lower disease severity than did non-treated plots. Fungicides in FRAC groups 3 and 11 tended to be more effective in reducing rust severity than other FRAC groups tested. Further evaluation of fungicides is necessary as additional chemicals are labeled for use on dry edible beans.
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Yield Response and Efficacy of Fungicides for the Control of Southern Rust in Corn
A. HAGAN (1), K. Bowen (1), L. Campbell (1), H. Miller (2)
(1) Auburn University, Auburn, AL, USA; (2) Auburn University, Brewton, AL, USA
Destructive outbreaks of southern rust (Puccinia polysora) occur in South Alabama in early corn (Zea mays L.) every 3 to 4 years. Efficacy of registered fungicides was assessed at a southwest Alabama site in 2014 and 2015 on irrigated Pioneer 2023YHR and Pioneer 1637VYHR corn, respectively. Fungicides were applied at growth stage (GS) VT (tassel) and R2 (blister) at 15 gpa to 4-row plots arranged in a randomized complete block. Rust was assessed on a 1 to 11 scale on the ear leaf of five plants per plot at GS R6 (black layer). Rust severity and yield differed by year and fungicide. Tilt and Muscle reduced rust in 2015 but not in 2014. All other fungicides had lower rust ratings than the non-treated control in both years. Lower rust ratings were also recorded for all fungicides except for Headline AMP in 2015 than 2014. Quilt Xcel gave the best rust control over the two-year study period. While Quilt Xcel, Priaxor, and Headline AMP has similarly high yields in 2014, the former fungicide gave the highest yield gains compared with the non-treated control in 2015. Yields recorded for Muscle and Tilt did not differ from the non-treated control in one and both study years, respectively.
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Evaluation of fungicides for management of sunflower rust
M. GILLEY (1), S. Fitterer (2), D. Carruth (2), J. Caroline (3), B. Benson (3), J. Halvorson (1), S. Haugen (1), B. Berghuis (1), C. Schuh (1), R. Humann (1), S. Markell (1)
(1) North Dakota State University, Fargo, ND, USA; (2) BASF North Dakota Research Farm, Davenport, ND, USA; (3) Mycogen Seeds, Breckenridge, MN, USA
Sunflower rust, caused by Puccinia helianthi Schwein, is one of the most economically important diseases of sunflower. Fungicides are frequently used to prevent yield loss when susceptible (S) hybrids are planted, but the impact of rust on moderately resistant (MR) hybrids is unclear. Recently, additional fungicides, including generic tebuconazoles and mixes, have been labeled for use. The objective of this study was to evaluate these fungicides on S and MR hybrids. In May 2015, fungicide trials were established in North Dakota and Minnesota. S and MR hybrids were planted in four-row plots and arranged in a randomized complete block design with four replicates. To facilitate infection, urediniospores suspended in a soltrol solution were applied twice between R2 and R4 using a modified leaf blower. FRAC 3 (DeMethylation inhibitors), FRAC 7 (Succinate dehydrogenase inhibitors) and FRAC 11 (Quinone outside inhibitors) fungicides were applied to the middle two rows of plots at R5.3. Disease severity was determined by evaluating the upper four leaves of ten arbitrarily selected plants at growth stage R7. Disease severity was homogeneous between locations and therefore data were combined. All fungicides treatments on the MR hybrid had statistically lower disease severity than the non-treated control (NTC), but differences among fungicides were not observed. All fungicides treatments on the S hybrid also had statistically lower disease severity than the NTC. Disease severity in plots treated with generic tebuconazoles (FRAC 3) alone were all statistically the same and tended to be lower than fungicides in other FRAC groups.
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Fungicide Effectiveness on Soybean Diseases in the Southeastern United States: A Meta-Analysis
M. DELANEY (1), E. Sikora (1), A. ArchMiller (2), D. Delaney (3), A. Wilson (4)
(1) Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, USA; (2) Department of Fisheries, Wildlife, and Conservation Biology, University of Minnesota, Minneapolis, MN, USA; (3) Department of Crop, Soil and Environmental Science, Auburn University, Auburn, AL, USA; (4) School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL, USA
The study objective was to evaluate the efficacy of fungicide use through quantitative meta-analysis of data compiled from 76 soybean trials across the southern United States from 2004 through 2014. We hypothesized that fungicide would decrease the severity of Phakopsora pachyrhiza (soybean rust), Cercospora kukuchii (Cercospora leaf blight; CLB), and Corynespora cassiicola (target spot) thus increasing soybean yield and 100seed-weight. The effect of fungicide was also tested for individual moderator categories such as fungicide classes, the number of applications, and the application growth stage. After fungicide treatment, yield and 100 seed-weight increased 6.2-7.8 bu/A and 0.1-0.3 g, respectively, and disease severity decreased by 10 to 36 % on average. Fungicide efficacy increased for fungicides with mixed active ingredients or modes of action and generally with more than one application. The optimal growth stage for fungicide application varied between yield, 100 seed-weight, and disease severity. This study suggests that fungicide use helps control soybean disease severity and improve yield and 100 seed-weight, however application recommendations depend upon the main management objectives.
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Identifying Soybean Rust-resistant and Susceptible Kudzu Populations to Increase Rust Monitoring Efficiency.
E. SIKORA (1), M. Delaney (1)
(1) Department of Entomology and Plant Pathology, Auburn University, Auburn, AL, USA
Soybean rust (SBR) caused by Phakopsora pachyrhizi, is one of the most damaging diseases of soybean worldwide. Monitoring for SBR in Alabama is accomplished by scouting soybean sentinel plots and kudzu patches biweekly beginning in January. Early season detection of SBR is critical to avoid significant yield losses. However, this method is laborious, time consuming and costly. The purpose of this study was to determine locations of kudzu in South Alabama that were either susceptible or resistant to SBR. Knowing which kudzu sites are resistant can increase efficiency and reduce cost by allowing scouts to avoid monitoring sites where the disease will not develop. GPS coordinates were recorded and leaves were collected from each site, transferred to the laboratory, and inoculated with uredinospores of SBR in petrie dishes containing water agar. After incubating for 2-4 weeks, samples were examined for the presence of SBR lesions. From 2012-2015, approximately 25% of the 153 kudzu sites tested were determined to be resistant to SBR. Developing a map using the GPS coordinates for each resistant and susceptible site will allow scouts to avoid kudzu patches known to be resistant to the pathogen and to concentrate on known susceptible patches, increasing efficiency of our monitoring efforts.
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Progress of Sugarcane Orange Rust and Brown Rust During Two Crop Seasons in Florida
S. SANJEL (1), M. Hincapie (1), B. Chaulagain (1), J. Comstock (2), R. Raid (1), P. Rott (1)
(1) University of Florida, Everglades Research and Education Center, Belle Glade, FL, USA; (2) USDA-ARS, Sugarcane Field Station, Canal Point, FL, USA
Orange rust (caused by Puccinia kuehnii) and brown rust (caused by P. melanocephala) are currently the two most damaging fungal diseases of sugarcane in Florida. To better understand epidemiology of these diseases, rust severity was monitored using orange rust susceptible cultivar CL85-1040 and brown rust susceptible cultivar CL90-4725 in the field, under natural infection, during the 2014 and 2015 crop seasons. Orange rust symptoms were observed all year round, but sporulation intensity and percent diseased leaf area peaked from mid-May to early August. Later on, disease severity was low until October when another significant increase of orange rust occurred until the end of the year. This pattern of orange rust progress was similar during both crop seasons. Brown rust symptoms were mainly observed from mid-March to mid-July in 2014 and from mid-April to mid-August in 2015. Sporulation intensity and percent diseased leaf area was highest in May-June 2014 but this period shifted to June-July in 2015. These data will be useful to determine environmental conditions conducive to orange and brown rust progress, and to improve timing for chemical control of these diseases in Florida.
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Mapping of leaf rust resistances in a tetraploid wild relative derivative of durum wheat
A. CABRAL (1), K. Ammar (2), A. Loladze (2), J. Huerta-Espino (3), S. Dreisigacker (2), K. Boyle (1), J. Schmidt (1), J. Condie (1), A. Sharpe (1), W. Zhang (1), P. Fobert (4)
(1) National Research Council of Canada, Saskatoon, SK, Canada; (2) CIMMYT, El Batan, , Mexico; (3) INIFAP, Chapingo, , Mexico; (4) National Research Council of Canada, Ottawa, ON, Canada
Leaf rust caused by the fungus Puccinia triticina Eriks. is a destructive disease of bread and durum wheat (T. turgidum L. ssp. durum). In Canada, durum wheat is the fourth-largest grain crop bringing in ~$1.5 billion in gross annual revenues. Leaf rust resistance genes (Lr genes) expressed at the seedling stage or major genes, are effective in controlling the pathogen. However, with time, many of these seedling genes are overcome by evolving, more virulent races of the pathogen, creating a constant need for new/novel resistances. Increase and/or shifts in virulence among races of the pathogen have resulted in leaf rust epidemics in Mexico in 2001 and 2008. Given these occurrences, there is an urgent need to be proactive in identifying and deploying novel resistances in durums, should virulent races migrate into Canada via the North American rust corridor. A durum F7 RIL population of 198 progeny lines derived from a cross Sooty_9/Rascon_37 x T. Dic 1460/Mexi75, developed at CIMMYT, was phenotyped with rust race BBG/BP in Mexico and assayed with the 90K Infinium iSelect Custom Wheat SNP Beadchip. Preliminary genetic SNP maps were constructed using published tetraploid maps as reference, and Lr major genes were mapped on chromosomes 1B, 2A and 6B. Identified Lr genes will be characterized, fine mapped and evaluated for suitability of use in Canadian and international durum breeding programs.
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Use of precision agriculture methods to quantify brown rust variability and yield loss in commercial sugarcane fields
M. GRISHAM (1), R. Johnson (1)
(1) USDA, ARS, Sugarcane Research Unit, Houma, LA, USA
Techniques commonly used in the study and application of precision agriculture were used to study the incidence and severity of brown rust (Puccinia melanocephala) infestations in five commercial sugarcane fields. A handheld computer equipped with a GPS (global positioning system) receiver and mapping software was used to determine experimental field boundaries and establish grid-sampling points. Field size varied from 0.7 to 8.9 hectares, and grid size varied from 0.02 to 0.4 hectares. At each grid-sampling point, soil samples were taken and rust ratings were recorded weekly for six or seven weeks. Experimental plots were harvested green utilizing a single-row, chopper harvester. Total cane weight of from each plot was determined using a single-axle, high-dump billet wagon containing three electronic load sensors and equipped with a device to collect a billet sub-sample from each plot for sucrose quality analysis. Soil properties, rust ratings, and cane yield varied significantly among the sampling points within fields and also between fields. In addition, overall fertility levels of each location were variable. Rust ratings were found to be positively correlated with several soil properties, most notably phosphorus and sulfur. These correlations were even more pronounced when phosphorus and sulfur was present at excessive levels. Sucrose and cane yields were negatively correlated to the rust ratings, with higher rust levels causing reduced yields even in areas of excess nutrition. These combined data suggest that sugarcane growers that apply fertilizer at rates exceeding plant requirements will increase the incidence and severity of rust infestations in their fields.
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Virulence changes of Puccinia striiformis f. sp. tritici in 1968-2015 in the US
X. CHEN (1), T. Liu (2), A. Wan (3)
(1) USDA-ARS, Wheat Health, Genetics, and Qulity Research Unit, Pullman, WA, USA; (2) Department of Plant Pathology, Pullman, WA, USA; (3) Department of Plant Pathology, Washington State University, Pullman, WA, USA
Puccinia striiformis f. sp. tritici causes wheat stripe rust, an important disease in the US. Races of the pathogen were identified using various numbers of wheat differential cultivars from 1968 to 2009 and using a set of 18 Yr single-gene lines since 2010. To study virulence changes, races identified using the new differential set in 1968-2009 were compared with those in 2010-15. A total of 184 races were identified, including 96 races detected in 1968-2009 but not in 2010-15 and 13 races detected only after 2010. The number of races identified in each year had a trend of increasing, ranging from 5 in 1986 to 41 in 2010, and the number of virulences per race also increased over the years. Most races developed from previously existing races through single-step mutation, and some races formed through virulence combinations. Multiple introductions of races were detected. Virulences to Yr1, Yr6, Yr7, Yr17, Yr32, Yr44, and YrExp2 were detected throughout the 48 years. Virulences to Yr10 and Yr24 were first detected in 1970, Yr27 in 1971, Yr43 in 1974, YrSP and YrTye in 1972, YrTr1 in 1975, and Yr8 and Yr9 in 1999. No virulences were detected for Yr5 and Yr15.
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Impact of a flag leaf fungicide application in hard red spring wheat on management of stripe rust and protection of yield in greenhouse trials
C. SCHUH (1), J. Jordahl (1), A. Friskop (1)
(1) North Dakota State University, Fargo, ND, USA
Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an economically important disease throughout the world. Although it is commonly observed in North Dakota, stripe rust levels tend to remain low and are often more severe in hard red winter wheat fields. In 2015, an early arrival of the stripe rust pathogen and a conducive environment resulted in a higher incidence in hard red spring wheat fields in ND. Since most popular spring wheat varieties are moderately susceptible or susceptible to stripe rust, fungicides are important tools in stripe rust management. The objective of this research was to determine the impact of a flag leaf fungicide application on yield in four hard red spring wheat varieties varying in levels of stripe rust resistance. Greenhouse trials were arranged in a split-split-plot using a randomized complete block design and four replicates. Inoculation served as the main plot, fungicide application served as the subplot and variety as the sub-sub plot. The fungicide pyraclostrobin + fluxapyroxad (Priaxor, BASF) was applied at Feekes 9 for each respective treatment. Disease severity and incidence was recorded twice and yield assessments were made at crop maturity. Results from this experiment will help develop stripe rust fungicide recommendations for hard red spring wheat growers in the Northern Great Plains.
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Integrated Management of Wheat Leaf Rust in Durum Wheat in El-Minya, Egypt
A. ABDELRHIM (1), H. Abd-Allah (2), C. Cowger (3), A. El-Bana (2), M. Ismail (2)
(1) PhD. student, Plant Pathology Department, College of Agriculture, Minia University., El-Minya, , Egypt; (2) Professor, Plant Pathology Department, College od Agriculture, Minia University, Egypt., El-Minya, , Egypt; (3) USDA-ARS, Department of Plant Pathology, North Carolina State University, Raleigh, NC, USA
El-Minya is the governorate (analogous to a state) in Upper Egypt with the largest wheat area in that region or the adjacent Middle Egypt. Recently, a high incidence of leaf rust has been observed in durum wheat fields in El-Minya. To date, few studies have been done on wheat leaf rust in Egypt, especially in this governorate. As part of an ongoing study, integrated management practices were applied to the BaniSweaf 5 durum wheat cultivar, to study their influence on leaf rust severity. During the 2013-2014 and 2014-2015 growing seasons, a field experiment was implemented using a randomized complete block design. The early sowing date of 15 November resulted in the lowest area under the leaf rust progress curve (AULRPC) compared with later sowing dates of 7 December and 1 January. While adding compost to wheat fields before planting had no significant effect on AULRPC, two other practices were effective: (1) soaking wheat seeds 24hr before sowing in a resistance-eliciting compound (200 ppm ascorbic acid, 200 ppm salicylic acid and 200 ppm benzothiadiazole (BTH)); and (2) treating adult wheat plants with Plant-Guard a bio-fungicide. Both treatments significantly reduced AULRPC, as compared with a control, whether mixed or applied separately. However, both treatments had no significant effect compared with Sumi 8, a systemic fungicide. Dusting wheat seedlings with agricultural sulfur. Integration of the above factors (early sowing date, soaking seeds in resistance elicitors, treating adult plants with Plant-Guard, and dusting wheat plants by agricultural sulfur) had a highly significant effect on leaf rust severity in both growing seasons.
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Soybean Rust Research in Illinois
J. HAUDENSHIELD (1), G. Hartman (1)
(1) USDA-ARS, Urbana, IL, USA
Soybean rust (SBR), caused by Phakopsora pachyrhizi, was first reported in the continental USA in November 2004, and in October 2006 was found in Illinois. Although not known to overwinter in IL, the disease can survive on the alternative host Pueraria lobata in southern states, and return to IL during the subsequent growing season via windborne urediniospores; human-mediated transport was also demonstrated. There is no known telial host. Illinois researchers began host-resistance and fungicide trials as early as 2002 in Paraguay, where SBR was already established, and evaluated soybean germplasm for sources of resistance and tested fungicides for control. Subsequently, extraction and qPCR methods were optimized to detect and quantify SBR in passive spore traps located across the southern and midwestern US. Antibodies were prepared which detected SBR, and vital dyes were used to determine viability of urediniospores. A collection of SBR isolates from the USA—and eventually worldwide—locations was established and maintained by detached-leaf culture and cryopreservation. An evaluation of the genetic diversity of SBR isolates from US and African fields was performed, using simple sequence repeat markers. In order to assess the global migration patterns, archival dried-leaf herbarium specimens bearing signs and symptoms of SBR were PCR-amplified and identified. More recent collaborations with industry partners have determined isolate responses on host-differential sets and the potential efficacy of biological agents as alternatives to fungicides in the control of propagule production.
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Evaluation of Northern Great Plains hard red spring wheat genotypes for resistance to the local population of Puccinia striiformis (wheat stripe rust)
B. HALLEY (1), M. Breiland (1), A. Friskop (1), M. Acevedo (1)
(1) North Dakota State University, Fargo, ND, USA
Wheat growers in the Northern Great Plains region of the United States have increased their focus on stripe rust, caused by the pathogen Puccinia striiformis f. sp. tritici (Pst). Since 2000, an increase in the number of Pst races adapted to warmer climates has made identifying stripe rust resistance genes in North Dakota (ND) wheat a priority. In the 2015 growing season, a higher level of stripe rust was reported in several fields across ND. The objective of this research was to determine prevalence of Pst races in ND, and to evaluate the response of spring wheat genotypes including advance breeding lines and spring wheat cultivars for stripe rust resistance. Single-pustule isolates were derived from six stripe rust samples collected across North Dakota in 2015. Virulence phenotypes were obtained using the standard Pst differential lines. All isolates were identified to be the same race, Pstv37. A collection of spring wheat breeding lines and cultivars grown in ND, SD, and MN region were evaluated for resistance to race Pstv37. Of the 204 wheat genotypes evaluated, only two experimental lines, NDSW0703 and NDSW0702, were resistant at the seedling stage. Future work will focus on the evaluation of the wheat lines for adult-plant stage resistance, and the identification and introduction of new or underutilized Pst resistance genes into the adapted germplasm.
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Identification of SNP markers linked to orange rust resistance genes in sugarcane (Saccharum spp.)
X. YANG (1), S. Sood (2), N. Neil (3), J. Comstock (2), J. Wang (4)
(1) University of Florida, Gainesville, FL, USA; (2) Sugarcane Field Station, USDA, Canal Point, FL, USA; (3) Syngenta Seeds, Inc, Longmont, CO, USA; (4) University of Florida, Gaineville, FL, USA
Orange rust of sugarcane has impacted the Florida Sugarcane Industry since its discovery in 2007. Genetic resistance is the most efficient way to control the disease. Selection of resistant cultivars can be enhanced through markers linked to disease tolerance which in turn depends on development of genetic map. The objectives of this research are 1) to establish a high density genetic map in sugarcane and 2) to identify markers linked to sugarcane orange rust resistance genes. To establish the genetic map, we used a genotyping by sequencing (GBS) approach to genotype a biparental population and its reciprocal population derived from the cross between a resistant cultivar ‘CP95-1039’ and a susceptible cultivar ‘CP88-1762’. The phenotypic reaction of the populations to rust was determined in the field and greenhouse in multiple years between 2010 and 2015. Both populations were segregating in orange rust resistance. High quality single nucleotide polymorphisms (SNPs) were called through six different SNP-calling pipelines, and a total of 40,166 SNPs were called, among which, 2,758 were single dose (SD) markers after Chi-square test (P value ≤ 0.02). Of the 2,758 SD markers, 1,345 formed 121 linkage groups using JoinMap3.0. Linkage analysis between SD SNPs and resistance to orange rust were conducted using the Windows QTL Cartographer 2.5 to identify the markers linked to the disease resistance. The high density genetic map and linked SNPs markers will greatly facilitate the sugarcane breeding program for disease resistant cultivar development.
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Evaluation of Aegilops umbellulata Germplasm Collection for Wheat Leaf Rust Resistance
M. BREILAND (1), M. Acevedo (2)
(1) North Dakota State University, Fargo, ND, USA; (2) , Fargo, ND, USA
Wheat leaf rust, caused by Puccinia triticina, is one of the most prevalent diseases of wheat in the world causing significant reduction in crop quality and yields. Wild relatives of wheat represent a rich reservoir of genetic diversity, including disease resistance genes, which can be utilized in breeding efforts to enhance disease resistance. Lr9 is the only characterized leaf rust resistance gene from Aegilops umbellulata that has been deployed in wheat cultivars, and more rust resistance genes may be present in this population. The objective of this study is to evaluate a collection of A. umbellualata accessions maintained at the USDA-ARS National Small Grain Collection for their seedling response to leaf rust pathotypes from the US Northern Great Plains to identify accessions carrying resistance genes conferred by genes different than Lr9. A total of 64 A. umbelullata accessions were evaluated for resistance to leaf rust race TNBJ which carries virulence on Lr9. Additionally, the accessions were screened to race TDBJ, which is a common race in ND. Race TDBJ is avirulent on Lr9 but virulent to multiple genes utilized in cultivars currently grown in the US Northern Great Plains region. Results of the experiments indicated twenty five accessions were resistant to race TNBJ while 48 were resistant to race TDBJ. Of accessions resistant to TNBJ, 23 were also resistant to TDBJ. This data suggests that alternative sources of leaf rust resistance may be present in A. umbellulata besides the Lr9 gene that could be exploited for use in wheat breeding.
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Somatic Recombination in the Stripe Rust Pathogen Puccinia striiformis
X. CHEN (1), Y. Lei (2), M. Wan (2), A. Wan (3)
(1) USDA-ARS, Pullman, WA, USA; (2) Department of Plant Pathology, Washington State University, Pullman, WA, USA; (3) Department of Plant Pathology, Pullman, WA, USA
Puccinia striiformis causes stripe rust on wheat, barley and grasses. Natural population studies have indicated that mutation plays a major role, sexual recombination no role and somatic recombination a possible role in the pathogen variation. To determine if somatic recombination occurs, susceptible wheat or barley plants were inoculated with mixed urediniopsores of paired isolates, and progeny isolates were selected by passing through a series of inoculations and compared with the parental isolates on the set of wheat and/or barley differentials for virulence changes and tested with SSR and SNP markers. All 9 combinations produced possible recombinants. From 68 possible recombinants based on virulence tests, 50 were proven by at least one marker locus. Various types of recombinants were obtained, including lost virulence from both virulent parental isolates, gained virulence from both avirulent isolates, combined virulences from both parents, and inherited virulence from one parent and avirulence from another. Marker data indicated that most of the recombinants were produced through chromosome re-assortment and cross-over after the hybridization of two parental cells.
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Linking metabolites to functionality of the wheat Lr34 rust resistance gene
N. RAJAGOPALAN (1), Y. Lu (1), E. Reimer (2), W. McNabb (2), C. Gruenke (2), B. McCallum (2), M. Loewen (3)
(1) National Research Council of Canada, Saskatoon, , Canada; (2) Agriculture and Agri-Food Canada, Morden, , Canada; (3) National Research Council of Canada, Ottawa, , Canada
Plant breeders use naturally occurring resistance genes to fight plant diseases. However, new fungal strains rapidly emerge and defeat these genes. For almost a century, the wheat Lr34 gene has conferred a degree of stable resistance to the wheat rusts, making it one of the most important resistance genes. While sequence homology of the cloned Lr34 gene predicted that it encodes a putative ATP binding cassette (ABC) transporter protein belonging to the ABC G subfamily (also known as Pleiotropic Drug Resistance or PDR), its target transport substrate and mechanism of action remains enigmatic. Our previous efforts to understand the mechanism of this transporter demonstrated transport of metabolites from wheat chlorophyll catabolite (CC) extracts by the Lr34Sus protein, but not the Lr34Res protein. Here we report CC metabolite profiling of wheat flag leaf tissue, showing unique accumulation of select CC metabolites in a Thatcher-Lr34RES line compared to Thatcher-Tc. Biochemical characterization of these metabolites suggests they are in the same CC family as those putatively transported by Lr34Sus in vitro. Finally, preliminary results highlighting the effect of application of this same wheat CC extract, on rust spores germination will be presented. Metabolite profiling of the flag leaves of additional rust resistant lines is ongoing.
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Gene expression profile of Hemileia vastatrix (race XXXIII) in interaction with Coffea arabica
R. FREITAS-LOPES (1), E. Caixeta (2), T. Maciel (1), D. Lelis (1), E. Zambolim (1), N. Sakiyama (1), M. Resende (3), L. Zambolim (1)
(1) Universidade Federal de Viçosa, Viçosa, , Brazil; (2) Embrapa/UFV, Viçosa, , Brazil; (3) Universidade Federal de Lavras, Lavras, , Brazil
The race XXXIII of Hemileia vastatrix was identified in coffee plants resistant to leaf rust in Brazil. To study the interaction between coffee plants and this race we evaluated the fungal gene expression during the infection (12, 24, 96 hours and 17 days post-inoculation). Leaves of a resistant (Hibrido de Timor CIFC 832/1) and a susceptible (Caturra CIFC 19/1) coffee genotype were inoculated with spores of the fungus and the RNA was sequenced by Illumina MiSeq generating 206,000,000 reads. The data showed many genes of H. vastatrix similar to coffee genes. The genes not conserved between the organisms were evaluated for their expression. We found many common genes in the compatible and incompatible interactions, but the majority did not show differential expression, especially in the early stages of the infection. The major differences between interactions occurred at 17 dpi, consisting mainly of genes with no similarity to protein databases. Those sequences might correspond to H. vastatrix specific genes. The knowledge of gene expression during the infection process may contribute to understanding the molecular mechanisms that lead to the breakdown of resistance by new races.
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Sequencing, assembly and annotation of Hemileia vastatrix genome
B. PORTO (1), M. Resende (2), T. Maia (3), E. Zambolim (4), E. Caixeta (5), L. Zambolim (4), N. Donofrio (6)
(1) Universidade Federal de Lavras, Lavras, , Brazil; (2) Plant Pathology Department, Universidade Federal de Lavras, Lavras, , Brazil; (3) Biotechnology Institute, Universidade Federal de Viçosa, Viçosa, , Brazil; (4) Plant Pathology Department, Universidade Federal de Viçosa, Viçosa, , Brazil; (5) Embrapa Café/Universidade Federal de Viçosa, Viçosa, , Brazil; (6) Plant and Soil Science Department,University of Delaware, Newark, DE, USA
Hemileia vastatrix (Hv) is the agent of coffee rust, the most serious disease of this crop worldwide. Our goal is to sequence the genome of Hv and identify genes that might contribute to pathogenicity, as part of a joint project including University of Delaware and Brazilian Institutions. Using a hybrid assembly strategy and two next generation sequencing platforms, named Pacific Biosciences (PacBio RS II) and Illumina (HiSeq 2500), we obtained a partial genome of the isolate Hv-02 (race XXXIII) of the fungus with 576 Mb of size. It was found that 96.37% of conserved eukaryotic genes were present in the annotated Hv genome, indicating a high level of integrity during the assembly process. 13,034 genes that encode proteins. The analysis of the similarity between the predicted proteins in the Hv genome and protein sequences of other fungi deposited in public databases showed 74% hits within Puccinales order, especially with P. graminis f. sp. tritici and M. larici-populina. From the total data, 12% showed no similarity (no-hit) with any protein described in databanks analyzed. They were considered unique to H. vastatrix because they have not been described yet.
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Prediction of secretome and validation of Hemileia vastatrix effectors
B. PORTO (1), E. Caixeta (2), P. Vidigal (3), E. Zambolim (4), L. Zambolim (4), M. Resende (5)
(1) Universidade Federal de Lavras, Lavras, , Brazil; (2) Embrapa Café/Universidade Federal de Viçosa, Viçosa, , Brazil; (3) Biotechnology Institute, Universidade Federal de Viçosa, Viçosa, , Brazil; (4) Plant Pathology Department, Universidade Federal de Viçosa, Viçosa, , Brazil; (5) Plant Pathology Department, Universidade Federal de Lavras, Lavras, , Brazil
Hemileia vastatrix (Hv), the coffee leaf rust agent, has the capability to secrete proteins known as effectors, which are able to change the physiology of the host, suppressing defense responses. Some of these effectors are recognized by resistance proteins, which triggers plant defense responses against infection by the pathogen. One approach that may be performed in order to detect these proteins is the analysis of the fungus secretome using bioinformatics tools to identify candidate effector genes. The objective of this work was to predict secreted proteins of Hv race XXXIII and to identify and validate effector candidate genes by real time PCR. Out of the 13,034 predicted proteins found in the genome of the race XXXIII, 615 were identified containing the signal peptide located in the secretion pathway and with no transmembrane domains. From the obtained secretome, 111 proteins were considered candidates for specific effectors of Hv. We selected 17 genes (EHv33) to be validated by real time PCR. Analyses of the expression of these genes (EHv33) showed a wide expression pattern throughout the different times (12, 24, 48 and 72 hours after inoculation) and at different interactions (incompatible and compatible). It was observed that 11 of these genes were significantly over-expressed during the early hours at the incompatible interaction and were considered pre-haustorial effector candidate genes. Only six EHv33 genes were significantly over-expressed after the formation of haustoria at the compatible interaction.
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A new rust disease on wild coffee (Psychotria nervosa) caused by Puccinia mysuruensis sp. nov.
S. MAHADEVAKUMAR (1), L. Szabo (2), T. Eilam (3), Y. Anikster (3), G. Janardhana (1)
(1) University of Mysore, Mysuru, , India; (2) USDA-ARS, St. Paul, MN, USA; (3) Tel Aviv University, Ramat Aviv, , Israel
Psychotria nervosa, commonly called “wild coffee” (Rubiaceae) is an important ethno-medicinal plant in India. In 2010 a new rust disease of P. nervosa was observed in three regions of Mysore District, Karnataka (India) with disease incidence ranging from 58% to 63%. Typical symptoms of the rust disease on wild coffee were prominently visible during the early monsoon season (May-June) with chlorotic spots on the adaxial and black pustules (telia) on the abaxial leaf surface, respectively. Telia produced abundant teliospores, which were bi-celled, pedicillate and measured 33-45 x 19-30 μm. The germination of teliospores produced a typical metabasidium bearing four basidiospores each containing two haploid nuclei. Spore stages of the wild coffee rust pathogen were studied using artificially inoculated healthy wild coffee plants with germinated teliospores. Only telia were observed on the inoculated plants indicating that this rust fungus has an abbreviated microcyclic life cycle that includes only teliospores and basidiospores. Phylogenetic analysis based on ITS and partial LSU sequence data showed that the wild coffee rust pathogen is related to Macruropyxis. fraxini, Puccinia bartholomaei, P. choridis, and P. sparganioidis. Based on molecular and morphological data, the rust pathogen causing wild coffee rust was determined to be a new species, P. mysuruensis.
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| Session 1A: Genetics and Genomics I |
Evaluation of wild Helianthus germplasm for resistance to Puccinia helianthi (rust)
R. HUMANN (1), T. Gulya (2), L. Marek (3), J. Jordahl (1), S. Meyer (1), M. Acevedo (1), S. Markell (1)
(1) North Dakota State University- Plant Pathology, Fargo, ND, USA; (2) USDA ARS- Sunflower Unit, Fargo, ND, USA; (3) USDA ARS- North Central Regional Plant Introduction Station, Ames, IA, USA
Sunflower rust, caused by Puccinia helianthi Schwein, is an economically important disease that occurs in all sunflower producing regions of the United States. Especially in the Northern Great Plains, where yield losses as high as 80 percent have been documented. One effective tool for managing rust is genetic resistance, which is often overcome due to frequent race changes that occur when P. helianthi undergoes sexual recombination. As a result of this, new sources of rust resistance are needed. In the past, wild Helianthus species have provided novel sources of resistance. Interestingly, a disproportionate amount of resistance genes have been identified in germplasm originating from Texas. The objective of this study was to evaluate Helianthus germplasm derived from Texas for new potential sources of resistance to P. helianthi. Thirty-three H. argophyllus and 182 H. annuus accessions were obtained from the USDA North Central Regional Plant Introduction Station in Ames, Iowa. All accessions were screened to different races of P. helianthi in a greenhouse environment. Plants were inoculated with fresh urediniospores 14 days after planting and infection types were visibly evaluated 14 days post-inoculation. Thirty-three H. argophyllus and 71 H. annuus accessions were resistant to commonly detected P. helianthi races, of which, five H. argophyllus and 41 H. annuus accessions were resistant to highly virulent races. The identification of such a large number of accessions resistant to rust provides opportunity for future cultivar improvements. Future work will focus on evaluating germplasm for resistance to other pathogens and characterizing the genes conferring resistance.
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Towards Identifying the Physical and Molecular Components Involved in Resistance to the Wheat Leaf Rust pathogen Puccinia triticina
S. DUGYALA (1), P. Borowicz (1), M. Acevedo (1)
(1) North Dakota State University, Fargo, ND, USA
Use of genetic resistance is the preferred method to reduce yield losses caused by many diseases including wheat leaf rust. For decades, scientists have tried and continue trying to understand the genetics and physical mechanisms involved in durable host resistance. Wheat- Puccinia triticina (Pt) incompatible interactions can be classified into pre-haustorial and post-haustorial. Post-haustorial resistance tends to be involved in race specific resistance and is commonly characterized by presence of hypersensitive reaction (HR) while, pre-haustorial resistance do not generally involve an HR response. Histochemical and gene expression studies were used to determine if necrosis associated with pre- and post-haustorial resistance was the product of H2O2 accumulation. Susceptible cultivar Thatcher near isogenic lines (NILs) carrying different Lr genes were evaluated in a time course experiment. Pt inoculated leaf tissue was collected at 0, 6, 12, 18, 24, 48, 72, 96 hpi and 7 dpi. In Both NILs Tc-Lr9 and Tc-Lr21 HR was observed before (6hpi) and after (24hpi) haustoria formation and involved H2O2 accumulation. In the Tc-Lr9 NIL, upregulation of hypersensitive induced resistance genes TaHIR 1 and TaHIR 2 was observed before and after haustoria formation. However, upregulation of these two genes was also observed in susceptible cv. Thatcher. In the Tc-Lr21 NIL, Lr21 gene was only upregulated after haustoria formation. The data obtained from this study provide opportunities to assess components of different resistance mechanisms and suggest that some previous assumptions about plant-pathogen interaction in host and non-host systems involving pre-haustorial resistance should be revisited.
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Identification of Stem Rust Resistance Genes in the Wheat Landrace PI 362698
J. ZURN (1), M. Rouse (2), S. Chao (3), M. Aoun (1), G. Macharia (4), Z. Pretorius (5), J. Bonman (6), M. Acevedo (1)
(1) North Dakota State University, Department of Plant Pathology, Fargo, ND, USA; (2) USDA-ARS, Cereal Disease Laboratory, St. Paul, MN, USA; (3) USDA-ARS, Cereal Crops Research Unit, Fargo, ND, USA; (4) Kenya Agricultural and Livestock Research Organization, Njoro, , Kenya; (5) University of the Free State, Department of Plant Sciences, Bloemfontein, , South Africa; (6) USDA-ARS, Small Grains and Potato Germplasm Research Unit, Aberdeen, ID, USA
The emergence of new races of wheat stem rust, caused by Puccinia graminis f. sp. tritici (Pgt), continues to be a threat to global food security. The deployment of resistant varieties is the most cost-effective way to manage the disease and new resistance sources are needed. Previously, the Montenegrin spring wheat landrace PI 362698 was identified as resistant to the Ug99-lineage of Pgt. In subsequent seedling trials, PI 362698 exhibited resistance to multiple races. A recombinant inbred population was developed by crossing PI 362698 to the susceptible line LMPG-6. QTL analysis was performed using the 90K iSelect assay and disease response to multiple Pgt races at seedling stages and field trials in Kenya. Significant QTLs were identified on chromosomes 1A, 2B, 3B, 6A, and 6D. The QTL on chromosome 3B was identified in trials using Ug99-lineage races and corresponds to an allele of Sr12 or a previously unknown resistance gene. The QTL on chromosome 1A confers susceptibility to Pgt and was identified during the 2014 field trial in Kenya. The Lr34/Sr57/Yr18 adult-plant resistance gene is known to be present in PI 362698; however no significant QTLs were identified at this locus during field trials. Significant resistance loci identified on chromosomes 2B, 6A, and 6D using different Pgt races are thought to be Sr16, Sr8a, and Sr5, respectively. Thus, broad resistance conferred by PI 362698 is the product of multiple resistance genes.
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Unraveling the broad resistance in common bean cultivar Mexico 235 to Uromyces appendiculatus
O. HURTADO-GONZALES (1), T. Gilio (1), G. Valentini (1), M. Pastor-Corrales (1)
(1) Beltsville Agricultural Research Center, ARS-USDA, Beltsville, MD, USA
The Mesoamerican common bean Mexico 235 has broad spectrum resistance to the hypervirulent bean rust pathogen (Uromyces appendiculatus). It is resistant to 83 of 94 races of this pathogen maintained at Beltsville, MD. Resistance to rust in Mexico 235 is conferred by the Ur-3 and one or possibly two other genes. The objective of this study was to elucidate the inheritance of resistance in Mexico 235. To accomplish this, 253 F2 plants from the cross Pinto 114 (S) x Mexico 235 (R) were inoculated with four different races (41, 53, 49, and 67) of U. appendiculatus. The bean cultivar Aurora, the original source of the Ur-3 gene, was included in this study. Mexico 235 was resistant to all four races while Aurora was susceptible to races 49 and 67. Races 41 and 53 were used to confirm the presence of the Ur-3 in Mexico 235 and Aurora. The rust phenotypes with these races fit a 3R:1S ratio indicating that Ur-3 is indeed present in Mexico 235. Races 49 and 67 identified the other resistance genes in Mexico 235. The inheritance of resistance with these races best fits a 13R:3S ratio, suggesting that this cultivar has two other rust resistant genes. A strategy that combines the evaluation of F2:3 families, additional crosses, bulk segregant analysis, and a large set of SNP DNA markers will be used to identify the two newly discovered genes and SSR DNA markers linked to them.
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| Session 1B: Epidemiology and Integrated Pest Management I |
The effect of age and leaf position on susceptibility of wheat to infection by Puccinia striiformis f. sp. tritici
D. FARBER (1), C. Mundt (2)
(1) Oregon State University, Corvallis, OR, USA; (2) Oregon State University, Corvallis, , USA
Understanding the spread of pathogens in space and time can aid in efforts to control epidemics. Epidemics requires virulent pathogens, susceptible hosts, and a conducive environment, so it is imperative to understand not just the aerial dispersal of pathogen propagules, but also the resulting pattern of infections. We inoculated single wheat leaves with freshly harvested urediniospores of Puccinia striiformis f.sp. tritici, the causal agent of wheat stripe rust (WSR). We sampled all wheat leaves within two intersecting 0.3 m by 3.0 m transects in eight replicates and three-dimensionally mapped the lesions on the uppermost three leaves. A greater proportion of the resulting infections were observed on leaves of the same position or higher than the source leaf. To examine relative susceptibility of wheat leaves of different ages and leaf positions, 3-, 4-, and 5-week-old wheat plants were inoculated with equal quantities of P. striiformis urediniospores. Disease severity on each leaf was assessed and linearly regressed as a function of leaf position and plant age. Younger plants had significantly greater disease severity than older plants, and this effect was greater on leaves higher on the plant. Within same-aged plants, younger leaves higher on the plant had significantly greater disease severity than older leaves lower on the plant. The mean disease severity was 31.8, 26.1, and 7.45% on the uppermost, second, and third leaf, respectively. These results corroborate field data suggesting the vertical distribution of lesions was due more to differences in host susceptibility than to propagule dispersal.
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Evaluating the association of local weather, soil moisture, climate variables and remotely sensed canopy characteristics with leaf rust epidemics in Kansas canopy characteristics with leaf rust epidemics in Kansas.
B. GRABOW (1), E. DeWolf (1)
(1) Kansas State University, Manhattan, KS, USA
Leaf rust (Puccinia triticina) of wheat is an economically important disease in Kansas. In 2005, 2007, and 2008 Kansas experienced 2, 14, and 4.7 percent statewide yield losses, respectively. The objectives of this research are to identify environmental conditions that are conducive for leaf rust epidemics in the central Great Plains region of the U.S., and to develop predictive models for Kansas. The analysis was divided into two phases. The first phase identified the monthly variables associated with leaf rust epidemics (yield loss >1%). The second phase of the analysis considered the monthly variables that were associated with high yield loss (yield loss >5%) within epidemic years. Correlation analysis and classification trees were used to identify monthly variables associated with leaf rust epidemics in Kansas. Variables identified in the variable selection procedure were used to develop preliminary models for leaf rust. The preliminary models indicate that leaf rust epidemics are influenced by soil moisture conditions and remote sensing variables describing greenness in the southern Great Plains during winter and early spring. The preliminary models also indicate that extended periods of favorable temperature and high relative humidity in May are most associated with severe yield losses in epidemics years. These results suggest that it should be possible to predict wheat leaf rust epidemics in Kansas prior to producer fungicide decisions.
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Susceptibility of biofuel switchgrasses to rust in Nebraska and other northcentral states
G. YUEN (1), Y. Ma (1), C. Jochum (1), R. Mitchell (2)
(1) University of Nebraska, Lincoln, NE, USA; (2) USDA ARS, Lincoln, NE, USA
Rust, caused by Uromyces graminicola and Puccinia emaculata, is problematic on some switchgrass (Panicum virgatum) cultivars planted for forage, but switchgrass populations being developed as biofuel feedstocks have not been investigated extensively for susceptibility to these pathogens. New biofuel and older forage populations planted in trials replicated across five northcentral states (IL, IN, MO, NE and WI) were evaluated in 2014 and 2015 for rust severity and the causal agent. Rust severity varied considerably across locations and between years in certain locations. In general, lowland ecotype populations exhibited lower rust severity than upland ecotype populations. Populations derived from crosses between ‘Kanlow’ (lowland) and ‘Summer’ (upland) exhibited intermediate disease levels. Based on teliospore morphology, P. emaculata was identified in all locations and was the sole causal agent in IL, IN, and MO, whereas U. graminicola was observed commonly in NE and sporadically in WI. In NE, most populations (e.g. ‘Kanlow’, ‘Summer’, and Kanlow X Summer derivatives) were infected solely or predominantly by P. emaculata, while Kanlow N2, derived from ‘Kanlow’, and ‘Sunburst’ (upland) also were infected by U. graminicola to considerable levels. While recent surveys in southern states revealed P. emaculata to be the sole rust species infecting switchgrass, our findings indicate U. graminicola also has the potential to cause rust epidemics depending upon the switchgrass population and the location. Therefore, further development of switchgrass for biofuel must take into account the local environmental conditions and pathogen populations in the regions where the switchgrass might be grown.
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Application of SNP Genotyping Tools for Population Genetics and Molecular Diagnostics of the Wheat Stem Rust Pathogen
L. SZABO (1), J. Johnson (1), D. Hodson (2), R. Wanyera (3), P. Olivera (4), Y. Jin (1)
(1) USDA Agricultural Research Service, St. Paul, MN, USA; (2) CIMMYT-Ethiopia, Addis Ababa, , Ethiopia; (3) Kenya Agricultural and Livestock Research Organization, Njoro, , Kenya; (4) University of Minnesota, St. Paul, MN, USA
Over the last decade stem rust epidemics have destroyed wheat fields in Africa and the incidence of stem rust has increased across Europe, Middle East and Central Asia. Understanding the causes of these epidemics and the mitigation of future ones requires a better understanding of the global population and the monitoring of critical races of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici). The recent sequencing of the P. graminis f. sp. tritici genome has allowed the development of SNP genotyping tools. Two high-throughput SNP arrays (PgtSNP 1.5k and PgtSNP3.0k chips) are currently being used to characterize regional and global populations of the wheat stem rust pathogen. Genotyping has shown that the highly virulent P. graminis f. sp. tritici race group (Ug99), which is the primary cause of epidemics in Africa, is a relatively new lineage that appears to be unique to Africa. In contrast, the 2013/14 wheat rust epidemic in southern Ethiopia caused by P. graminis f. sp. tritici race TKTTF, is part of a more complex lineage that is widely distributed in Europe and Central Asia. Mining the P. graminis f. sp. tritici SNP database has allowed the development of sets of SNP markers that are diagnostic for specific lineages and are currently being used to monitor Ug99 and TKTTF race groups. These genotyping tools provides the wheat rust community powerful new tools for characterizing and monitoring P. graminis f. sp. tritici.
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First Report of Pistachio Rust in Pakistan
A. ISHAQ (1), M. Aime (2), N. Afshan (3), A. Niazi (1), A. Khalid (1)
(1) Department of Botany, University of the Punjab, Lahore, , Pakistan; (2) Botany and Plant Pathology, Purdue University, West Lafayette, IN, USA; (3) Center for Undergraduate Studies, University of the Punjab, Lahore, , Pakistan
The rare Genus Pileolaria (Pucciniaceae, Uredinales, Basidiomycota) is reported for the first time from Pakistan. The fungus was collected from Thandiani, District Abbottabad (34°13'6 N 73°22'E) on leaves of genus Pistacia (Anacardiaceae) in October 2014. Based on infection pattern, distinct spore morphology and sequence of the 28S subunit of the nuclear ribosomal DNA the rust is conspecific with Pileolaria terebinthi. The finding of this disease in Pakistan confirms further spread of the fungi within country and the need for research to develop more effective management options to reduce the impact of this rust on onion Pistachio trees.
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| Session 2A: Genetics and Genomics II |
Susceptibility and Race Specific Wheat Genes Induced by Six Puccinia triticina Races
K. NEUGEBAUER (1), M. Bruce (2), H. Trick (3)
(1) PhD Candidate, Manhattan, KS, USA; (2) Post-Doctoral, Manhattan, KS, USA; (3) Professor of Plant Pathology, Manhattan, KS, USA
Puccinia triticina, the casual agent of wheat leaf rust, is a devastating disease that can cause up to 40% yield loss. During fungal infection the host plant recognizes proteins, secreted effectors, and other molecules, which trigger a host defense response. Changes in the pathogen effectors and strong varietal selection pressure are responsible for the rapid development of new rust races. The objectives of this study are to identify and characterize wheat genes that are utilized by specific races throughout infection and to identify potential susceptibility genes. Six leaf rust races were evaluated on a single susceptible variety of wheat at six days post inoculation. RNA was sequenced and 63 wheat genes were identified that showed varying expression in response to the different leaf rust races. Out of the 63 total genes, 54 wheat genes were characterized for expression patterns during the first seven days of infection using a time course study. Race specific gene expression was found in two wheat genes that are affected by race shifts on Lr2A, Lr2C, and Lr17A. Potential susceptibility genes were also identified. RNAi was used to silence nine wheat genes to further understand their role in leaf rust infection. Transgenic plants were inoculated and observed for changes in susceptibility. Gene expression data was obtained to show gene knock down in the transgenic plants.
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Infection of switchgrass leaves by Puccinia emaculata urediniospores and the expression of putative effectors
G. ORQUERA-TORNAKIAN (1), C. Garzon (1), B. Tyler (2), B. Kronmiller (2), B. Zhao (3), T. Frazier (3), S. Marek (1)
(1) Oklahoma State University, Stillwater, OK, USA; (2) Oregon State University, Corvallis, OR, USA; (3) Virginia Tech, Blacksburg, VA, USA
Switchgrass (Panicum virgatum) is a potential feedstock crop for biofuel production. Switchgrass rust, caused by Puccinia emaculata, reduces switchgrass biomass yields and feedstock quality. Macroscopically, rust-inoculated switchgrass plants initially produce chlorotic flecks, in which uredinial pustules eventually form. Lowland switchgrass ecotypes and cultivars often display rust resistance reactions, including cholorotic flecking and reduced sporulation. The cytology of this interaction has not been studied in detail in the switchgrass rust pathosystem. This study examines the early infection process of P. emaculata on detached leaves of susceptible and resistant switchgrass genotypes using fluorescent microscopy and assessed expression of putative effectors. Detached switchgrass leaves were inoculated with urediniospores from single pustules and inoculated leaves placed on water agar supplemented with phytohormones. At 24, 48, and 72 hours post inoculation (hpi), leaves were stained with fluorescein-labelled wheat germ agglutinin. At 24 hpi, germ tube formation and appressorial penetration through stomatal openings was observed. At 48 and 72 hpi, further appressoria formation and hyphal proliferation within tissues were observed. Hyphal growth was restricted in resistant switchgrass genotypes and associated with host cell autofluorescence and chlorotic flecking. Putative effectors with homology to effector sequences from other rust fungi were identified in RNA-seq data from urediniospores and rust-infected switchgrass leaves. Seven of these putative effectors were shown by RT-PCR to be expressed by P. emaculata during infection of switchgrass leaves. Future studies will focus on correlating the development of infection structures to the expression of specific P. emaculata effectors.
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Identification of resistance related genes in soybean to Phakopsora pachyrhizi infection
D. HU (1), S. Park (2), Z. Chen (1)
(1) Department of Plant Pathology and Crop Physiology, Louisiana State University Agricultural Center, BATON ROUGE, LA, USA; (2) USDA-ARS Arid Land Agricultural Research Center, Phenix, AZ, USA
Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, was first reported in Louisiana in 2004. Currently, the only available method to manage this disease is through fungicide application due to that all U.S. commercial soybean cultivars are susceptible to P. pachyrhizi. A list of differentially expressed proteins and genes were identified in previous proteomics and RNAseq studies, including the genes that encode pathogenesis-related protein PR-10 (GmPR10), chalcone flavanone isomerase (GmCHI), ascorbate peroxidase (GmAPX), and glycolate oxidase (GmGOX). A BPMV-based virus-induced gene silencing (VIGS) approach was used to further evaluate the roles of these genes in soybean resistance to rust disease. Compared with empty vector control, the expression levels of GmPR10, GmCHI, GmAPX, GmGox in silenced plants were reduced by 81%, 60.4%, 51.8%, and 64.9% respectively. These target-gene silenced plants were then inoculated with uredospores of P. pachyrhizi and it was found there was a significant increase in fungal growth in gene silenced plants. The levels of P. pachyrhizi α-tubulin in target-gene silenced soybean plants increased 5.39 fold (GmPR10) and 5.84 fold (GmAPX) compared to the empty vector controls, demonstrating the importance of these genes in soybean resistance to P. pachyrhizi infection.
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Genetic Analysis of Leaf Rust Resistance in Durum Wheat
M. AOUN (1), M. Acevedo (2)
(1) , Fargo, ND, USA; (2) North Dakota State University, Fargo, ND, USA
Leaf rust, caused by Puccinia triticina Eriks, is increasingly limiting durum wheat (Triticum turgidum L. var. durum) production in many areas worldwide. P. triticina race BBBQD, highly virulent on durum wheat, was detected in Kansas in 2013. This race may spread, via the “Puccinia pathway”, into the Northern Great Plains, where most of the U.S. durum is produced. The objective of this study was to determine the inheritance and the genomic locations of leaf rust resistance genes to race BBBQD using durum wheat bi-parental populations. Six resistant genotypes from the USDA-ARS National Small Grain Collection were crossed to two susceptible durum cultivars, Divide and Rusty. The resulting F1, F2, and F3 progenies were evaluated for leaf rust reactions at seedling stage under greenhouse conditions. In addition, bulk sergeant analysis (BSA) was performed using the 9K iSelect wheat assay to determine the chromosomal location of the leaf rust resistance (Lr) genes in these populations. The BSA and the inheritance study indicated that PI 244061, PI 192051, and PI 209274 carried single dominant resistance genes on 2BL, 4AL, and 6BS, respectively. Chromosome arms 2BL and 4AL are not known to carry previously characterized Lr genes. Based on mapping position, the gene on 6BS is probably Lr61. For the remaining populations, the resistance appears to be the result of epistatic gene interactions. The research is ongoing to delimit the genomic regions of the identified genes. These findings are a significant step to broaden the relatively narrow leaf rust resistance in durum wheat germplasm.
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| Session 2B: Epidemiology and Integrated Pest Management II |
Wheat Stripe Rust Integrated Control Based on Forecasting, Monitoring, and Resistance
X. CHEN (1), K. Evans (1), M. Wang (2), A. Wan (2), Y. Liu (2)
(1) USDA-ARS, Wheat Health, Genetics, and Quality Research Unit, Pullman, WA, USA; (2) Department of Plant Pathology, Washington State University, Pullman, WA, USA
Stripe rust (caused by Puccinia striiformis f. sp. tritici) is a destructive disease of wheat. To improve the integrated control of the disease, resistant wheat cultivars are developed, and their resistances are monitored in fields under natural infection and in greenhouse with selected races. Yield losses and responses to fungicide application are estimated for major cultivars every year in fields, and the data are used for making decisions for fungicide application on individual cultivars. New and registered chemicals are evaluated for their efficacy, dosage, timing and effective duration on susceptible cultivars, and the data are used to register new fungicides and choose fungicides for rust control. A series of forecast models have been developed based on historical weather and yield loss data and used to predict stripe rust for each growth season. Field surveys are conducted before and after winter and throughout the remaining crop season, and rust updates and recommendations are made based on forecasts, monitoring data, disease pressure, and weather forecasts. The integrated control program saves growers millions of dollars every year.
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The control of Asian Soybean Rust by biologicals alone and in combination with fungicides at AgBiome
M. TWIZEYIMANA (1)
(1) AgBiome Inc., Research Triangle Park, NC, USA
At AgBiome, we are building a core collection of sequenced microbes from plant-related environmental sources. We employ both the microbes and their sequences in the discovery of new trait and biological products for disease and pest control in crops. Each environmental isolate is screened in high-throughput assays against a broad range of fungal pathogens, insect pests, and plant-parasitic nematodes. Isolate sequences are analyzed for known families of proteins active against plant pests, and these proteins are assayed in bacterial expression systems and transgenic crops. Successful biological and trait candidates are tested, and confirmed active biologicals proceed to the fermentation and formulation pipeline. Our lead product candidate AFS009 (Howler), a biological with high efficacy against multiple fungal pathogens, is currently undergoing field-testing in multiple locations, as well as fermentation and formulation optimization. Asian Soybean Rust (Phakopsora pachyrhizi) control is a major product goal for AgBiome; many bacterial strains have been screened for their activity to control or reduce rust infection in soybeans. The initial screening is done using leaf disks and hits are confirmed on whole-plants in growth chambers. Selected leads undergo mouse toxicity test and scale up by fermentation and formulation before they are evaluated in greenhouse and field.
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Effects of Foliar Applications of Micronutrients on Severity of Rust in Soybean
E. SILVA (1), B. Ward (1), C. Robertson (1), R. Scneider (1)
(1) Plant Pathology & Crop Physiology Department, LSU Agricultural Center, Baton Rouge, LA, USA
Since soybean rust (SBR), caused by Phakopsora pachyrhizi, was first reported in the United States in south Louisiana in 2004, numerous research projects have been conducted ranging from fungicide efficacy tests to molecular mechanisms of pathogenicity and resistance. SBR can cause yield losses of up to 80%. Since resistant cultivars are not available, management of this disease has been achieved primarily with fungicides. The use of foliar-applied micronutrients to suppress SBR had not been examined in detail. The objective of this work was to evaluate foliar application of selected reagent grade and commercial micronutrient formulations for their effects on disease severity. Field experiments were conducted annually from 2008-2014. Treatments were arranged in randomized complete block designs with four replications. Plots were four rows wide on 30 inch centers by 40 feet long, and the center two rows of each plot were rated quantitatively for disease severity. Numerous reagent grade minor elements as well as two rates of commercial products containing Fe, Mo, Mn, B, Zn and Al (Brandt Consolidated, Inc.) were applied with a boom sprayer at the R3 and R5 growth stages. Disease severity was significantly reduced with high rates of Fe, B, B plus Mo, and Mn. Low rates of B increased SBR severity. There was a significant relationship between leaf tissue concentrations of B, Fe and Mn and disease severity. Tissue analyses showed a low coefficient of correlation between SBR severity and levels of B below 60 ppm. However, above this threshold, B effectively suppressed SBR.
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Effects of O3 and CO2 concentration, exposure timing and duration on the disease components of stem rust on winter wheat.
A. MASHAHEET (1), D. Marshall (2), K. Burkey (3)
(1) PhD Candidate, Raleigh, NC, USA; (2) Professor of Plant Pathology and Crop Science, Raleigh, NC, USA; (3) USDA-ARS Plant Physiologist and Professor of Crop Science and Botany, Raleigh, NC, USA
Elevated O3 and CO2 concentrations associated with climate change may affect wheat plant growth and the wheat stem rust interaction. Most of the current knowledge in this area is based on studies that used relatively high concentrations of both gases. We conducted studies to elucidate the effects of current and projected future concentrations of both gases on wheat stem rust. We studied the effects of ozone concentration (charcoal-filtered (CF) control, 50, 70 and 90 ppb), exposure timing (prior or post-inoculation) and exposure duration (6, 3, 2 or 1 week) on disease severity, receptivity and pustule size of stem rust race QFCSC on the O3-sensitive, stem rust susceptible winter wheat cultivar ‘Coker 9553’. Results showed that stem rust severity increased 3-fold at 50 ppb O3 relative to the CF control while disease symptoms declined to control levels or less at 70 and 90 ppb O3 concentrations, respectively. These results suggest that O3 concentrations typical of present day ambient conditions stimulate wheat stem rust severity. Effects of O3 (10, 50 ppb) and CO2 (400, 570 ppm) combinations on wheat stem rust were also studied. Results confirmed that 50 ppb O3 increased disease severity 2.7-fold and 2.6-fold relative to the CF control, when gas treatment was imposed either for the entire 6-week experiment or for the 3 weeks prior to inoculation, respectively. This indicates predisposition rather than post-inoculation effects. Elevation of CO2 singly and in combination did not significantly affect disease severity relative to the CF control.
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Solatenol Fungicide: A new tool for rust control.
A. TALLY (1)
(1) Syngenta Crop Protection, Greensboro, NC, USA
Solatenol Fungicide (ISO name benzovindiflupyr) has been recently registered by the USEPA and will be sold in 2016 as four different products: Aprovia (solo), Aprovia Top (plus difenoconazole), Elatus (plus azoxystrobin), and Trivapro (plus propiconazole and azoxystrobin). One of the key strengths of Solatenol is the outstanding activity on rust diseases. It has good residual control as well as crop safety. Globally the key use is for soybean rust in Brazil and other countries in South America. Use rates range from 30-75 g ai/ha – among the lowest of many fungicides. Solatenol Fungicide also has excellent activity on other soil-borne and foliar pathogens.
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