Technical Abstract:
Bird cherry-oat aphid (BCOA), Rhopalosiphum padi (L.), has been reported to cause yield loss in small grains through its role as a vector of the PAV strain of Barley yellow dwarf virus (BYDV) and by feeding damage to winter and spring small grains.  Barley accessions have been reported to have BCOA resistance based on antibiotic effect of seedlings on BCOA.  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 using traditional greenhouse screening methods.  In an attempt to develop a seedling screening technique for BCOA we varied flat type, soil type, infestation date, infestation rate, temperature, and day length.  Seventy-eight barleys, reported to be antibiotic to BCOA, were screened with aviruliferous BCOA using traditional seedling screening methods under high temperature and long days.  Seedlings were rated visually on a scale of 1 to 7 (1= resistant and 7= dead).  Potential resistant and susceptible checks were identified.  In this study, a replicated (2X) screening of the Barley Core Collection was conducted using this technique and rating scale.  Surviving seedlings were rescued and transplanted to pots in the greenhouse.  The second screening was more severe than the first.  The first screening had 5 and 54% survival of the susceptible and resistant checks respectively while the second screening had 0.4 and 11% survival of susceptible and resistant checks.  Accession seedling survival was 95, 81, 79, 65, 45, and 27% for ratings of 1, 2, 3, 4, 5, and 6 respectively for the first screen and 93, 40, 77, 61, 59, and 47 respectively for the second screening.  Resistance was found in 266 and 279 accessions for the first and second screening respectively.  If seedling survival translates to field resistance in terms of grain yield, this seedling screening technique will be useful for identification of BCOA resistance.