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. In an attempt to develop a seedling screening technique for BCOA many variables were evaluated including flat type, soil type, infestation date, infestation rate, and screening conditions, (temperature and day length).  In 2005, 78 barleys, reported to be antibiotic to BCOA, were screened with aviruliferous BCOA using traditional seedling screening methods under high temperature and long days and compared to non-infested controls.  Seedlings were rated on a newly defined visual scale of 1 to 7 (1= resistant and 7= dead).  Potential resistant and susceptible checks were identified.  A replicated (2X) screening of a 960 accession subset of the Barley Core Collection was conducted using this technique.   Seedlings from 284 accessions survived screening and were transplanted to pots in the greenhouse.  Based on seedling survival percentages, the rating scale appeared to be valid.  Seedlings from the surviving accessions were screened again in 2007 and an identical set of non-infested controls was grown.  Surviving seedlings and their respective non-infested controls were rated, rescued, and transplanted to pots side by side in the greenhouse.  Plant height, yield and yield components were measured to validate the rating scale.