Oat blue dwarf virus (OBDV) is a marafivirus present throughout the North American Great Plains and is found at low incidence levels in barley, oats, and flax in the Upper Midwest United States. Cropping patterns in this region have changed considerably in recent years, with much greater acreages devoted to maize in areas historically planted to small grains. Considering that OBDV is endemic in small grains in this region and that its aster leafhopper vector (Macrosteles quadrilineatus) is commonly detected in maize (2), we questioned whether maize might be a host for OBDV. Although Westdal (4) reported that maize was not a host for OBDV, it is the primary host for the related Maize rayado fino virus (MRFV) transmitted by Dalbulus maidis. MRFV is the type member of the marafiviruses and ranges from South America to the southern United States. To reevaluate the ability of maize to serve as a host for OBDV, viruliferous aster leafhoppers were allowed to feed on young maize seedlings for a 7-day inoculation access period. Plants were assayed for the presence of OBDV by ELISA 21 days after leafhopper removal. Initially, open-pollinated Sunglow sweet corn was tested in three experiments, with infection rates of 17 to 100%. A test of hybrid Sunglow resulted in 63% infection. These are comparable to transmission levels obtained when oat and barley plants are fed upon by viruliferous leafhoppers. Subsequently, 10 additional varieties of sweet and field corn were tested to determine if they could serve as hosts for OBDV. Sweet corn included Silver Queen, Peaches and Cream, Morning Star, Sugar Dots, Kandy Korn, and Golden Cross Bantam. Field corn included four lines provided by the maize breeding program of M. Carena at North Dakota State University (056640, 056643, 056612, and 056652). At least one plant was infected in all sweet and field corn varieties except 056612. Infected plants were largely asymptomatic, although a very faint stipple-striping was observed on some plants. To determine whether leafhoppers could acquire OBDV from infected maize and transmit the virus to other hosts, healthy leafhoppers were fed upon detached leaves of infected maize for 4 days (approximately 30 days after initial infection) and subsequently transferred three times at weekly intervals to barley and oats. Infection rates of 42 to 55% were observed in target plants, indicating efficient transmission from maize to other cereal hosts. The extent of natural infection of maize by OBDV or economic loss, if any, remains to be determined. This discovery extends the host range of OBDV to include maize and suggests that maize has the potential to serve as a natural reservoir for OBDV. The identification of hosts for known and new marafiviruses, such as those recently detected in citrus (3) and grape (1), will expand our understanding of the ecology and epidemiology of viruses within this group.
References: (1) M. Al Rwahnih. Virology 387:395, 2009. (2) J. L. Capinera. Page 320 in: Encyclopedia of Entomology. 2nd ed. Springer Publishing, New York, NY, 2008. (3) W. Maccheroni et al. J. Virol. 79:3028, 2005. (4) P. Westdal. Can. J. Bot. 46:1431, 1968.
