Screening for Bird Cherry-Oat Aphid Resistance In Barley.

Bird cherry-oat aphid (BCOA), Rhopalosiphum padi (L.), has been reported to cause yield loss in small grains both through its role as an efficient vector of the PAV strain of Barley yellow dwarf virus (BYDV) and by actual feeding damage to winter and spring small grains by aviruliferous BCOAs.  Barley accessions have been reported to have BCOA resistance based on the antibiotic effect of seedlings on the aphids. Whether this antibiosis translates to resistance in terms of grain yield has yet to be shown.  Screening for BCOA resistance at the seedling stage has been difficult due to lack of visual symptoms on seedlings infested with BCOA using traditional greenhouse screening methods. Years of attempts to develop a seedling screening technique for BCOA by the USDA-ARS in Stillwater, OK has resulted in the development of a 1-4 visual rating scale, and the identification of resistant and susceptible checks. Eleven barleys, reported to be antibiotic to BCOA, and Morex were screened with aviruliferous BCOA using traditional seedling screening methods under high temperature and long days.  Identical flats were kept aphid free with insecticide application. Seedlings were visually rated using a 1-4 scale (1= resistant and 4= dead).  Surviving seedlings from each rating of 1-3 were rescued and transplanted in pots in the greenhouse side by side with their respective non-infested controls in a randomized complete block design.  Plant height from the soil to the tip of the longest leaf and leaf number were measured at the time of rescue and   plant height, yield and yield components were measured at maturity. Analysis was conducted to validate the rating scale in terms of grain yield.