June 22-24, 2002 - San Jose, California
Posted online August 1, 2002
Management of gray mold of pomegranates caused by Botrytis cinerea using two reduced-risk fungicides, fludioxonil and fenhexamid. J. E. Adaskaveg and H. FÖRSTER. Dept. Plant Pathology, Univ. of California, Riverside, CA 92521. Publication no. P-2003-0001-PCA.
Postharvest decay caused by Botrytis cinerea is the primary limiting factor for long-term storage and marketing of pomegranates in California. Initial infections of stamens and pistils remain quiescent until postharvest storage when senescing fruit tissues favor growth of the fungus. No postharvest fungicides are currently registered for use on pomegranates. Thus, we evaluated new treatments for decay control. Fenhexamid (900 mg/L) and fludioxonil (600 mg/L) were used as dip as opposed to spray treatments because the fruit crown covers the infected blossom tissues. Natural incidence of gray mold decay was significantly reduced after 2 or 5 (2/5) months of storage at 10 C from 69.4%/97.4% in the control to 0%/8% in the fludioxonil-treated and 1.4%/30.2% in the fenhexamid-treated fruit. Because single-fungicide treatments may select for resistance, sanitation treatments with chlorine in high-volume washes and in fungicide dips were shown to inactivate the pathogen in wash or dip solutions. Registration of different fungicide classes and the use of chlorine will allow for tank mixtures as part of a resistant management strategy.
Survival of Verticillium dahliae in lettuce seeds and weeds. R. G. BHAT (1), S. T. Koike (2), and K. V. Subbarao (1). (1) Dept. Plant Pathology, UC Davis, Salinas, CA 93905; (2) UC Cooperative Extension, Salinas, CA 93901. Publication no. P-2003-0002-PCA.
Verticillium wilt poses a threat to production of lettuce. Survival of V. dahliae in seeds of lettuce at different storage temperatures and on common weeds was studied. Infested seed lots were incubated at -20, -15, -10, 0, 5, 10, 15, and about 23 C. Incubated seeds were plated on Sorensen’s NP-10 medium at monthly intervals. Four weeks after plating, seeds yielding colonies of V. dahliae were counted. The percentage of seeds yielding V. dahliae was reduced to less than 40% after 6 months in seed samples incubated at room temperature (about 23 C). Other incubation temperatures had no effect on viability of V. dahliae. Symptomatic plants of 11 weed species growing in and around lettuce fields were sampled and tissues were plated on NP-10 medium. V. dahliae was isolated from all shepherds purse and hairy nightshade plants and from 30% of sowthistle and groundsel plants. The remaining weed species were free of V. dahliae. Regardless of the storage temperature, V. dahliae can survive in infested seeds for at least 6 months and several weed species common in lettuce fields can serve as inoculum reservoirs for V. dahliae.
Increased incidence of seed transmission of high plains disease observed in sweet corn. T. D. Blunt and W. M. Brown. Department of Bioagricultural Sciences and Pest Management, Colorado State University, Fort Collins, CO 80523-1177. Publication no. P-2003-0003-PCA.
High Plains Virus (HPV) was first discovered in the Central and Western U.S. in 1993. Symptoms in susceptible sweet corn may include severe stunting, chlorotic flecking and/or streaking, yellowing and little or no ear set. The pathogen is now considered to be a new virus. HPV is often found in conjunction with Wheat Streak Mosaic Virus (WSMV) and is vectored by the Wheat Curl Mite, Aceria tosichella Keifer (Acari: Eriophyidae). HPV has also been reported to be a seed-borne virus but at very low incidences. Observations of a field in Colorado in 2001 indicated that the agent was seed-borne at a very high incidence. ELISA tests (indirect method) using sweet corn seed from the same seed lot as that used to plant the infected field showed positive results that indicate much higher seed transmission than previously reported.
Upright fruiting habit of Puget Summer strawberry related to reduced fruit rot. P. R. BRISTOW and P. P. Moore. Washington State University, Puyallup Research and Extension Center, Puyallup, WA 98371. Publication no. P-2003-0004-PCA.
Puget Summer (WSU 2310) consistently had a lower incidence of gray mold fruit rot (Botrytis cinerea) than Totem the main cultivar grown in the Pacific Northwest. Field trials were undertaken to see if physical cultivar traits might be involved in disease reduction. The position of flowers and berries in the canopy was recorded every few days from early bloom through harvest. Totem flowers opened on long scapes high in the canopy. In contrast, scapes of Puget Summer were shorter and flowers were rarely visible. When Totem berries reached mid-sized, but still green, the scapes to fell over leaving the berries to ripen among dead leaves or on the soil. The stouter scapes of Puget Summer did not collapse under the weight of ripening berries. The weight of fruit per scape was the same for both cultivars. In a second trial, scapes were pinned down to the soil at full bloom, while others were fastened to a wire stakes to hold the flowers/berries off the soil. For both cultivars, the trend was for a lower incidence of fruit rot when berries held above the ground ripened. Upright fruiting habit appears to be one factor in reducing losses to B. cinerea.
Controlling Botrytis cinerea on fruit and canes of red raspberry with fungicides. P. R. BRISTOW and G. E. Windom. Washington State University, Puyallup, WA 98371. Publication no. P-2003-0005-PCA.
Gray mold is the most serious pre and post harvest fruit disease of red raspberry in western Washington. The pathogen also causes lesions on canes. The newer fungicides Elevate, Serenade, Switch and Zerotol were compared to a water check and to three registered products Benlate, Captan and Rovral. The three were tested alone and in a standard treatment where they were alternated and tank-mixed. The standard treatment with and without the addition of foliar nutrients (NPK) was also tested. The trial was conducted in a commercial planting (cv Meeker). An over-the-row boom sprayer was used to make six applications of each treatment between early bloom and mid harvest. Only Switch and Elevate significantly increased (23.7 and 13.8%, respectively) yields of machine harvested berries over the water check under conditions of high disease pressure. Both significantly reduced post harvest fruit rot. Switch and Elevate lowered the incidence of Botrytis lesions on the fruiting laterals; and both products along with Benlate and the standard program reduced disease incidence on primocanes. The addition of foliar nutrients to the standard program did not alter its performance.
Effect of controlling Melampsora medusae f. sp. deltoidae on the productivity of hybrid poplar stool beds. G. A. CHASTAGNER. Washington State University, Puyallup, WA 98371. Publication no. P-2003-0006-PCA.
A field trial was established to determine the impact of leaf rust on the productivity of hybrid poplar stool beds in western Washington. Six pairs of previously untreated 3-year-old stools of clone 47-174 were used. Foliar applications of triadimefon were applied to one stool in each pair during the 1996, 1997 and 1998 growing seasons to control leaf rust. During each winter, the number and weights of shoots produced by each stool were recorded. There was no difference in the productivity of the stools following 1996 sprays. By the end of 1997, shoot numbers for the two treatments were similar, but the weight of shoots from sprayed stools was significantly higher than the shoots from unsprayed stools. By the end of 1998, the sprayed stools produced 50% more shoots and about three times the biomass as the unsprayed stools. During the 1998 winter, dormant cuttings from the stools that had been treated in 1996 and 1997 were also grown in a greenhouse to determine if leaf rust control affected their growth. Cuttings from the sprayed stools initiated growth earlier and produced more shoot and root biomass than cuttings from the unsprayed stools.
Update of new and pending trifloxystrobin and tebuconazole registrations in the United States. L. FOUGHT, D. Scott, and A. Scoggan. Bayer Corp., Kansas City, MO 64120. Publication no. P-2003-0007-PCA.
New uses and products containing trifloxystrobin, a broad-spectrum strobilurin fungicide from Bayer Corp., have continued to be added since the initial registration in North America in 1999. Three trifloxystrobin-containing products will be commercialized by 2002: Flint, Stratego, and Gem. Flint will be registered for use in grapes, pome fruit, cucurbits, fruiting vegetables, hops, nut crops, and stone fruits. Gem will be registered in rice, sugar beets, and citrus. Stratego will be registered for use in peanuts, wheat, rice, corn, and pecans. Tebuconazole is a triazole compound first registered for select crops in North America in 1994. It is presently marketed under the trade names Raxil, Folicur, and Elite. Raxil is registered for use as a seed treatment in wheat, barley, and oats. Folicur is presently registered for use in peanuts and grasses grown for seed, while Elite is registered for use in grapes, selected stone fruits, and bananas/plantains. Many additional crops are pending registration and will be discussed.
Effects on growth of the pitch canker pathogen by the monoterpene constituents of pine sap resin. C. J. FRIEL and T. R. Gordon. Dept. Plant Pathology, University of California, One Shields Ave., Davis, CA 95616. Publication no. P-2003-0008-PCA.
Isolates of Fusarium circinatum, the causal agent of pitch canker on conifers, are known to differ in virulence. One factor that might limit their ability to induce lesions on their host is tolerance for the components of pine resin. Monoterpene components of pine resin are known to inhibit the growth of some fungal pathogens by as much as 50%. In this study the inhibitory effects of pine needles, pine resin, and the monoterpenes alpha-pinene, beta-pinene, limonene and myrcene were evaluated against F. circinatum. Three treatments were assessed: pine needles incorporated directly into potato dextrose agar (PDA), pitch from trees of known susceptibility placed directly on PDA, and the four monoterpenes placed in wells centered in petri dishes of PDA. Strains of the pathogen with varying virulence were grown in the presence of all treatments. On the pine needle medium, there was little differential growth between the isolates of differing virulence, and there was no significant inhibition of growth when compared to the control.
Sensitivity to iprodione, vinclozolin, and tebuconazole and characters of iprodione-resistant isolates of Alternaria spp. from pistachio. T. H. Lim (1), B. M. Pryor (2), D. P. Morgan (1), and T. J. MICHAILIDES (1). Dept. Plant Pathology, (1) Univ. of California Davis, Kearney Agric. Center, Parlier 93648, and (2) Univ. of Arizona, Tucson 85721. Publication no. P-2003-0009-PCA.
Among 60 isolates of Alternaria spp. collected from pistachio, only one (25C2) had high resistance to iprodione and vinclozolin. The EC(50) of 25C2 was 146 µg a.i. iprodione and 70.4 µg a.i. vinclozolin/ml. The EC(50) of the other 59 isolates ranged from 0.1 - 1.4 µg a.i. iprodione/ml, 1.8 - 5.8 µg a.i. vinclozolin/ml, and 0.02 - 1.8 µg a.i. tebuconazole/ml. Isolates with laboratory induced iprodione resistance (IIR) had EC(50) of 447.6 and 205 µg a.i. iprodione/ml and had cross resistance to vinclozolin. Both IIR and field iprodione resistant (FIR) isolates showed higher osmotic sensitivity than the sensitive (S) isolates. The EC(50) of IIR and FIR isolates declined, after successive sub-culturing on fungicide-free PDA medium, and their fitness was similar to that of S isolates. Application of 100 µg a.i. iprodione/ml solution controlled only the S isolates. Although iprodione-resistant isolates are rare in the field, the results suggest that these Alternaria isolates may eventually be a problem in pistachios.
Thermal time requirements for embryogenesis of the sting nematode. D. LUO, J. Smith-Becker, and J. O. Becker. Dept. of Nematology, University of California, Riverside, CA 92521. Publication no. P-2003-0010-PCA.
Belonolaimus longicaudatus is an ectoparasitic nematode with a wide host range and considerable damage potential. Embryonic development of the sting nematode was monitored on water agar plates at temperatures between 20 C and 30 C. Initial cell cleavage occurred within 1-2 hours at each temperature tested. At 20 C, the development to the blastula and gastrula stage required at least 2 days and 4 days, respectively, whereas at 28 C development to the gastrula stage was completed within 2 days. B. longicaudatus completed its embryogenic development in 3-11 days. The first-stage larvae were fully developed after 2-7 days. The first molt to second-stage larvae was initiated in the egg and was completed at hatching. The rate of development was nearly linear between 20 C and 30 C. At 32 C, the average development rate began to decline and ceased at 34 C. The lower threshold temperature for development was estimated to be 13.1 C by back projection of the linear regression line to the intercept of the temperature axis. The minimal thermal time requirement for embryogenesis, determined as the reciprocal of the slope, was approximately 64.3 degree days.
A preliminary decision support system for IPM of brown rot of dried plum. Y. LUO and T. J. Michailides. Dept. Plant Pathology, University of California Davis, Kearney Agricultural Center, Parlier 93648. Publication no. P-2003-0011-PCA.
Brown rot caused by Monilinia fructicola is an important disease of stone fruits. IPM of this disease aims to reduce fungicide application(s) in combination with appropriate cultural practices. Data of multi-year laboratory and field experiments were analyzed and used to establish a preliminary decision support system for IPM of brown rot of dried plum in California (DSS-DPBR). The DSS-DPBR currently contains two subsystems for decision supports on fungicide application to reduce risks of blossom blight and latent infection. Based on the inputs by the system users that include weather forecast for the following 5 days, an estimate of inoculum potential, and the current blossom stage, the system could provide spray recommendations at bloom. Based on an estimation of proportion of fruit with latent infection and the corresponding calendar date, the system could provide decision supports on fungicide spray for the mid-season. This system, as well as extension topics relevant to IPM of brown rot of stone fruits, is now available (http://tjm.uckac.edu) and open to suggestions for improvement.
Spatiotemporal genetic structure of Botryosphaeria dothidea from pistachio in California. Z. MA, Y. Luo, and T. J. Michailides. Dept. of Plant Pathology, University of California, Kearney Agricultural Center, Parlier, CA 93648. Publication no. P-2003-0012-PCA.
Spatiotemporal genetic structure of Botryosphaeria dothidea, the causal agent of Botryosphaeria blight of pistachio, was analyzed by microsatellite-primed (MP)-PCR. We surveyed 389 isolates of which 377 were recovered from pistachio at six Counties in California from 1990 to 2001, and 12 outgroup isolates from peach, apple, and other hosts in other states. Six microsatellite primers generated a total of 116 polymorphic DNA bands. Based on the MP-PCR data set, we observed little genetic variation (haplotypic diversity [Hs] less than 0.0243) among B. dothidea isolates collected from commercial pistachio orchards with only one female cultivar Kerman. However, relatively high diversity (Hs = 0.0886) was detected among the isolates from the Chico USDA Germplasm Repository, where more than 20 cultivars of Pistacia were planted. The lack of population differentiation among isolates collected in different years at different commercial orchards indicated that the B. dothidea populations from commercial pistachio orchards are temporally and spatially stable. The genetically uniform populations of B. dothidea pose a threat to the susceptible pistachio cultivar Kerman in California.
Role of host ethylene expression on the development of fusarium wilt symptoms. R. M. MARTIN (1) and D. J. Nevins (2). (1) Dept. Biology, Southern Utah University, Cedar City, UT 84720; (2) Dept. Vegetable Crops, University of California Davis, Davis, CA 95616. Publication no. P-2003-0013-PCA.
The observation that senescence-like symptoms of fusarium wilt can be prevented by fruit removal, combined with the observation that leaf senescence does not occur in transgenic, antisense ACC oxidase (alphaACO) tomato lines, suggests that ethylene may regulate the development of wilt symptoms. The role of ethylene in the development of the senescence-like symptoms of fusarium wilt was investigated firstly, by inoculating both wildtype and transgenic, antisense ACC oxidase (alphaACO) tomato lines with F. oxysporum. Resultant infection and colonization of vascular systems was equivalent in both wildtype and alphaACO lines. However, wilt symptoms occurred only in wildtype lines. Secondly, seedlings were infected with F. oxysporum and then exposed to 2,000 ppm of the gaseous, ethylene-binding inhibitor, nobanadien (NBD). NBD did not prevent fungal colonization of the seedling vascular systems but did prevent the development of wilt symptoms. Removal of infected seedlings after one week from NBD chambers resulted in the immediately appearance wilt symptoms in wildtype plants, which died within hours. But alphaACO plants remained healthy. These results suggest that senescence-like, fusarium wilt symptoms are a result of pathogen-induced ethylene production by host tissue.
Suppression of Phytophthora cinnamomi in avocado soils. V. T. MCDONALD, J. A. Menge, E. Pond, and M. Crowley. Dept. Plant Pathology, University of California, Riverside, CA 92521. Publication no. P-2003-0014-PCA.
Four Southern California avocado soils were evaluated four times per year for suppression of P. cinnamomi, the cause of avocado root rot and the major limiting factor of avocado production in California. In laboratory studies, infected root segments and hyphal mats of P. cinnamomi were buried in each avocado soil and, after eight days, evaluated for chlamydospore formation and survival. The soil from Somis, CA, showed a seasonal inhibition of the pathogen. Chlamydospore inhibition was low in January, higher in April, highest in July, and low again in October. This trend was also reflected in colony formation when P. cinnamomi mats and infected roots, which had been buried in the soil, were blended and plated on selective agar. In soil inoculation studies, avocado seedlings cv. Topa Topa, were planted in each natural soil or in soil that was autoclaved. After three months, roots of seedlings in the natural Somis soil had significantly less root rot as compared to seedlings in the autoclaved soil, indicating a suppressive effect of microbial origin. Additional studies showed that the Somis soil was suppressive to P. cinnamomi even if only one part natural soil was added to 99 parts fumigated soil.
Nitrogen stable isotope ratios: hosts and parasites. C. NISCHWITZ and G. Newcombe. Dept. of Forest Resources, University of Idaho, Moscow, ID 83844-1133. Publication no. P-2003-0015-PCA.
By definition, a parasite is one trophic level above its host. The higher the trophic level within marine food chains the higher the ratio of nitrogen isotopes, (^15)N and (^14)N. However, it is currently unknown whether this discrete shift in ratio is seen in terrestrial food chains. We are thus starting with known parasites of terrestrial primary producers (i.e., plants). (^15)N and (^14)N of plant and parasite samples were measured with a mass spectrometer and the nitrogen isotope ratio, delta (^15)N, was then calculated. In the initial study a T-test showed that plant parasites (p = 0.001) had a significantly higher nitrogen isotope ratio than their host plants. The differences in the ratios between host plants and parasites ranged from 0.02 per mil to 4.22 per mil. We will use this method to test fungi growing on plant pathogenic fungi and mistletoes. These fungi are assumed to be hyperparasitic. If such fungi are truly hyperparasitic, they should be one discrete trophic level above their hosts.
Quantitative comparison of methods for recovery of root-knot nematode eggs from plant roots. K. C. RADEWALD (1), J. Darsow (2), M. E. Stanghellini (1), and J. O. Becker (2). Depts. of Nematology (2) and Plant Pathology (1), University of California, Riverside, CA 92521. Publication no. P-2003-0016-PCA.
Traditionally, eggs of root-knot nematodes have been recovered by macerating roots in a blender and passing the resulting suspension through nested sieves. Using modifications of the paint shaker method (Wofford & Gray, J. Nematol 19:30-37, 1981) we improved upon the blender method. Whole root systems were placed into either a vortex mixer with a capacity of 4 liters or an agitator-type mixer for volumes up to 20 liters. A sufficient amount of 0.525% NaClO was added to cover the roots, and the containers were shaken for 2 min. The resulting suspension had a greatly reduced organic debris content allowing more rapid passage of samples through sieves compared to the blender method. Use of commercial paint mixers improved the efficiency of recovery up to 300%, and reduced the time for processing each sample up to 1000%. The paint mixer method allows evaluation of bulk root samples (i.e., up to 30 root systems tested), as from field trials, to evaluate treatment effects on nematode reproduction. Results correlated well with root ratings and number of second stage juveniles.
In vitro changes in the major structural components of wood cell walls during decay by Eutypa lata. P. E. ROLSHAUSEN (1), J. M. Labavitch (2), L. C. Greve (2), and W. D. Gubler (1). (1) Dept. Plant Pathology, University of California, Davis, CA 95616; (2) Dept. Pomolgy, University of California, Davis, CA 95616. Publication no. P-2003-0017-PCA.
Eutypa lata causes a dieback disease that poses an important economic threat to the grapevine industry in California. E. lata ascospores are released after rainfall events, infect pruning wounds and develop in woody tissue. The biochemical nature of the dieback was determined on the susceptible cultivar Cabernet Sauvignon in vitro on homogeneous grape wood blocks. Composition of lignin, pectin, cellulose and hemicellulose was determined on healthy wood tissue and 6, 12 and 18 months after infection by the pathogen. Pycnidia bearing conidia of E. lata were observed after 12 months on grape wood blocks. Infected wood blocks lost 13, 17 and 23% of their initial dry weight after 6, 12 and 18 months, respectively. The data suggest no selective degradation of lignin, pectin and cellulose over the 18 months period. However, glucose was determined to be the primary target of fungal attack.
First report of the teleomorph of Phaeoacremonium spp., the cause of esca and decline of grapevines. S. N. ROONEY, A. Eskalen, and W. D. Gubler. Dept of Plant Pathology, University of California, Davis 95616. Publication no. P-2003-0018-PCA.
Phaeoacremonium inflatipes and Phaeoacremonium aleophilum are recognized causal agents of esca and decline of grapevines. Teleomorphs of these mitosporic fungi have not previously been reported. Crosses were made by pairing different isolates, identified as Pm. inflatipes or Pm. aleophilum, on water agar. All possible pairings, within and between the two species, were made. Sterilized cane shavings were then placed on the agar surfaces between the two isolates. After five weeks, small, dark, globose perithecia formed on shavings and in agar. Perithecia were superficial to embedded, formed solitarily or in small groups and ranged in diameter from (160-) 186-294 (-350) micrometers (µm). Perithecial necks ranged in length from (200-) 311-539 (-680) µm and held white spore masses at their tips. Ascospores were hyaline, ellipsoidal to allantoid, and ranged in size from (3.5-) 3.7-4.9 (-6.0) × (1.0-) 1.0-1.2 (-1.5) µm. When cultured on media, ascospores germinated to form colonies typical of Phaeoacremonium spp. This is the first report of the teleomorph of Phaeoacremonium spp. and is important in the understanding of the biology, epidemiology and species concepts of these pathogens.
Root-lesion nematode associated with reduced wheat yield in the Pacific Northwest. R. W. SMILEY and D. A. Ball. Oregon State University, Columbia Basin Agric. Res. Center, Pendleton, OR 97801. Publication no. P-2003-0019-PCA.
High densities of Pratylenchus neglectus and/or P. thornei (root-lesion nematode, RLN) were detected in roots from 56 of 128 annually cropped nonirrigated fields sampled in semiarid eastern Oregon and Washington. Maximum densities were 4,369 per g fresh-weight root and 35,960 per kg soil. Possible associations between RLN and wheat yield were examined in two experiments. RLN densities were inversely correlated with yield in an experiment that had crop rotation, tillage and weed management variables for five years and then planted to winter wheat during the sixth year (1999); yield = 53.4 - 11.1 log P. neglectus per g root; R(^2) = 0.56; p = 0.002. Possible differences in soil water (not measured) may also have influenced yield. In 2001, five spring wheat varieties with differing yield potential were compared in paired plots that were treated or not with aldicarb (4.2 kg per ha, as Temik 15G) applied in the seed row at the time of planting. Yield was inversely correlated with RLN in roots (R(^2) = 0.21, p = 0.01), and the association was strengthened by regressing wheat yield against RLN plus percentage of plants infested with Hessian fly (R(^2) = 0.50, p = 0.001).
Winter wheat genotype reaction to Fusarium crown rot (F. pseudograminearum). R. W. SMILEY (1) and C. J. Peterson (2). Oregon State University, (1) Columbia Basin Agric. Res. Center, Pendleton, OR; (2) Dept. of Crop and Soil Science, Corvallis, OR 98701. Publication no. P-2003-0020-PCA.
Fusarium pseudograminearum is part of the complex causing Fusarium crown rot (dryland foot rot, Fusarium root rot) of winter and spring wheat in semiarid eastern Oregon and Washington. Winter wheat genotypes (69) were evaluated over 2 years in inoculated or non-inoculated paired plots. Five pathogen isolates on millet-seed substrate were mixed and dispensed 1-inch above wheat seed at planting; 140 millet seed (0.7 g) per linear foot. Wheat seed treated with benlate to suppress damping-off was planted (23-25 per square foot) into 5 × 20 foot plots by a John Deere HZ drill with cone-seeder and 14-inch row spacing. Disease incidence and severity, plant stand, growth, yield, test weight and kernel weight were measured. Inoculation reduced grain yield 2 to 28% (11% mean) during 1999-2000 and 0 to 22% (12% mean) during 2000-2001. More hard red and durum genotypes were severely damaged than soft white, hard white and red genotypes. Entries were identified with yield constraints less than 5% or more than 15% each year, or with high variability.
Evaluation of resistant trap crop mustard and oil radish cultivars and a resistant sugar beet cultivar for sugar beet nematode, Heterodera schachtii, control. H. J. SMITH (1), F. A. Gray (1), D. W. Koch (1), J. M. Krall (1), and L. J. Held (2). (1) Dept. Plant Sci.; (2) Dept. Ag. & Applied Econ., Univ. of Wyoming, Laramie, WY 82071. Publication no. P-2003-0021-PCA.
The sugar beet nematode (SBN), Heterodera schachtii (Hs), is a serious pest in sugar beets (SB) worldwide. Hs-resistant radish (R) and mustard (M) cvs. have shown to decrease soil populations of Hs when planted following malting barley in Wyoming. Four new R cvs., standard R cv. Adagio, five new M cvs., standard M cv. Metex, and Hs-resistant SB cv. Nematop were evaluated in two tests for SBN suppression under controlled environment, with SB cvs. HH50 and HM9155 as susceptible checks. In both tests, Hs populations several months after inoculation were significantly greater in the two susceptible SB cvs. than in all of the other entries. New trap crop R and M cvs. showed similar resistance as standard trap crop cvs. Hs populations in test I were as low in Nematop as in all of the trap crop entries while in test II, Nematop had significantly higher Hs populations than all the trap crop cvs. In both tests, Hs populations were significantly higher in susceptible HH50 than in HM9155, indicating possible tolerance to Hs in a US SB cv.
Managing peach rust in California using new fungicides and an inoculum-precipitation based application strategy. A. SOTO-ESTRADA and J. E. Adaskaveg. Dept. Plant Pathology, Univ. of California, Riverside, CA 92521. Publication no. P-2003-0022-PCA.
In greenhouse and field studies, peach rust caused by Tranzschelia discolor f. sp. persicae was significantly reduced on leaves and fruit as compared to non-treated controls by foliar applications with wettable sulfur, myclobutanil, propiconazole, tebuconazole, azoxystrobin, chlorothalonil, thiophanate-methyl, and an agricultural oil. Dormant treatments with selected fungicides were ineffective in reducing the disease on two peach cultivars the following season. Timing of applications in the spring was a significant factor. Protective and post-infection programs with fungicides applied after stem canker emergence (ACE) and before or after a forecasted rain using wettable sulfur, tebuconazole, or azoxystrobin were highly effective. Furthermore, under highly conducive field environments for disease, single applications of azoxystrobin or tebuconazole at ACE were significantly more efficacious than sulfur. Efficacy data from these studies supported registration labels of myclobutanil, propiconazole, tebuconazole, and azoxystrobin for management of rust on stone fruit crops in the United States.
Digital quantification techniques for the assessment of damage caused by Typhula spp. on turf. B. M. SWAN, W. M. Brown, and S. Sakadzic. Plant Pathology, Colorado State University, Fort Collins, CO 80523. Publication no. P-2003-0023-PCA.
Quantitative assessment of damage caused by fungi on turfgrass holds challenges and obstacles unique to turfgrass disease field research. The assessment of treatment efficacy in field research has relied upon visual assessment and a rating scale. Although visual ratings are very subjective, this method has become the industry standard. The objectives of this study were to develop new quantification techniques for evaluating damage caused by Typhula spp. on turf. Two digital systems for capturing images were developed. Digital images of field plots and customized computer software were used for quantifying diseased areas. Visual evaluations with a modified Horsfall-Barrett scale were also employed. There were no significant differences in the average disease ratings obtained from the two digital systems. Visual evaluations were significantly lower than both digital systems. The image capture and computer analysis approach to disease quantification provides permanent records of field trial plots, has a higher level of sensitivity, and generates exact percentages as opposed to a range of percentages.
Discovery of a second Eutypa species pathogenic to grapevine in California. F. P. TROUILLAS, P. E. Rolshausen, and W. D. Gubler. Dept of Plant Pathology, Univ. of California, Davis, CA 95616. Publication no. P-2003-0024-PCA.
Eutypa dieback is a serious canker disease of grapevine and apricots in California and throughout the world. The fungus Eutypa lata is known to be responsible for this disease but recent molecular work on fungi associated with grapevine cankers in California vineyards suggested the existence of a second pathogenic species of Eutypa (Richard et al., 1999). During the year 2000, surveys were made in northern California to find the perithecia of E. lata and sources of vineyard infections. Typical eutypoid stromata were collected from grape and other hosts and examined in the lab. Even though the teleomorph of E. lata was found on a wide range of host plants and in many locations in northern California, observations of some ascocarps collected on bay laurel, big leaf maple, ash and grapevine showed a different species of Eutypa. The two Eutypa species were separated by their morphological and molecular divergences. Koch’s postulates on grapevine of the newly discovered species were confirmed for isolates obtained from grape, laurel and maple. Taxonomically, initial studies indicate that the new species is closely related to E. leptoplaca.
Septoria leaf spot of Banana poka induced by lei-inoculum in forest of Hawaii. E. E. TRUJILLO (1), S. Bergfeld (2), and D. Nelson (3). (1) Plant & Environmental Protection Sciences Dept., University of Hawaii, 3190 Maile Way, Honolulu 96822; (2) Hawaii Dept. Land & Natural Resources, Honolulu 96813; (3) USDA-Forest Service, Hilo 96720. Publication no. P-2003-0025-PCA.
Leis strung with 25 senesced leaves of Passiflora tarminiana infected with Septoria passiflorae were used to distribute inoculum of this banana poka pathogen to vine areas with no disease, and succesfully established the disease at all inoculated sites at Hilo Forest Reserve, Hawaii. Pycniospores produced abundantly by pycnidia present on Septoria leaf spots of senesced leaves constituting the lei, induced disease symptoms a month after leis were place under healthy banana poka vines. Test under simulated rain showed a single lei to release from 1 × 10(^5) - 5.9 × 10(^5) pycniospores per lei over a 48 hr period, and their viability ranged from 81-93%. Lei-inoculum stored at -10ºC produced viable pycniospores for more than 358 days. However, spore viability decreased almost 50% after a year of storage. Biannual monitoring of 11 sites at 1096-1442 m elevations located on Blair Road showed weed biomass reduction of 1-3%, 15-50% and 50-100% at 6 month, 1 and 2 years after lei placement, respectively.
Development of dot blot technique and biological control of Botrytis cinerea on greenhouse tomatoes. R. UTKHEDE and S. Mathur. Agriculture and Agri-Food Canada, P. O. Box 1000, Agassiz, British Columbia, Canada V0M 1A0. Publication no. P-2003-0026-PCA.
Stem canker of tomato plants caused by Botrytis cinerea is a serious disease in commercial greenhouses worldwide. A dot blot assay was developed for rapid diagnosis and identification of B. cinerea. DNA from fungal cultures and from diseased plant tissue was extracted, amplified by PCR using primers specific to septate fungi, and fixed to nylon membranes. Using sequence information obtained from the GenBank database, specific oligonucleotides were designed and after labelling with digoxigenin-d-UTP, were used as probes in dot blot hybridization procedure. Probe Bot1 gave a positive reaction with all isolates of B. cinerea and with fresh or frozen diseased plant tissue. Experiments were also conducted to develop biological control of Botrytis stem canker on tomato plants grown in sawdust. Post-inoculation sprays of RootShield© and strain S33 of Rhodosporidium diobovatum have the potential to reduce lesion lengths and a preventative spray of Prestop© and strain S33 of R. diobovatum potentially prevents the occurrence of B. cinerea stem canker of tomato under near-commercial greenhouse conditions.
A strategy to delay horizontal spread of Ilarviruses to new peach orchards. J. K. UYEMOTO and L. R. Bulluck, III. USDA-ARS and Dept. Plant Pathology, University of California, Davis, CA 95616. Publication no. P-2003-0027-PCA.
The Ilarviruses, Prune dwarf (PDV) and Prunus necrotic ring spot viruses (PNRSV) had moved rapidly within and between neighboring ‘Carson’ peach orchards. When healthy test trees of six peach cultivars (including ‘Carson’) were planted amongst mature diseased ‘Carson’ trees (10 per cultivar in completely randomized block design and five replications) and assayed by sero- and bio-assays, some trees of ‘Andross’, ‘Carson’, and ‘Halford’ were positive for PDV at 2nd leaf growth stage, indicating virus transmissions at first bloom of newly planted trees. Infected test trees were removed when detected to minimize secondary pollen sources. In cultivars ‘Dr. Davis’, ‘Loadel’, and ‘Ross’, infections occurred in the 3rd- to 5th-leaf stages. Statistical analysis showed significant differences in cumulative transmission of PDV but not of PNRSV by the 4th-leaf stage (p=0.002). Clear differences in PDV infections were apparent in test trees of ‘Carson” from all other cultivars. Based on these findings and to allow two or more years of tree development before infections occur, growers should avoid planting the same cultivars near infected ones.
Elevational effects on the distribution of Phaeocryptopus gaeumannii in Idaho. R. VAN AELST-BOUMA, K. Kavanagh, and G. Newcombe. Dept. of Forest Resources, University of Idaho, Moscow, ID 83844-1133. Publication no. P-2003-0028-PCA.
Native to the Pacific Northwest of North America, Pseudotsuga menziesii (Mirb.) Franco, or Douglas-fir, consists of two natural varieties, one on either side of the Cascade Range. In Oregon, the coastal variety is exhibiting poor growth and early loss of needles associated with the unusual abundance of Phaeocryptopus gaeumannii (Rohde) Petrak fruiting within stomata. Virtually nothing is known of this fungus and its distribution on the interior variety of Douglas-fir. Our purpose was to provide an indication of the distribution of P. gaeumannii in the Northern Rocky Mountains. In particular, we investigated the effect of elevation on pseudothecial density of P. gaeumannii and the relationship between severity and needle loss. Incidence was determined by recording presence or absence of pseudothecia. In the cases of positive incidence, severity was categorically estimated based on the amount of pseudothecia present on the needles of trees sampled along elevational transects within Idaho. Site, elevation, and their interaction were found to affect both incidence and severity of P. gaeumannii. On occasion, fungi other than P. gaeumannii were found fruiting in stomata. In addition, severity appeared to affect variation in needle loss.
Production of apothecia by Sclerotinia sclerotiorum in the Salinas valley. B. M. WU, R. G. Bhat, Z. Kabir, and K. V. Subbarao. Dept. Plant Pathology, UC Davis, 1636 E. Alisal St., Salinas, CA 93905. Publication no. P-2003-0029-PCA.
It has been thought that Sclerotinia sclerotiorum can infect lettuce via ascospores in the central valley of California, but only via direct germination in the Salinas valley. However, apothecia of S. sclerotiorum were observed during field surveys in the Salinas valley. The number of apothecia that a sclerotium can produce was related to its size and burial depth. The larger the sclerotia, the more apothecia they produced (R(^2)=0.551) with an average of 2.75 apothecia per sclerotium. In the field, about 61% of apothecia were produced by sclerotia in the top 1-cm soil, and the vertical distribution could be fitted with a negative exponential model (R(^2)=0.997). Experiments demonstrated that production of apothecia by S. sclerotiorum requires continuous soil moisture for about 35 days under greenhouse conditions. Drying for more than 10 days interrupted the production of apothecia, but even a 40-day dry period did not prevent the resumption of apothecial production following rewetting. Ascospores of S. sclerotiorum may play an important role in disease cycle of lettuce drop in the Salinas valley.
