Field Variants of Barley Yellow Dwarf Virus: Detection and Fluctuation During Twenty Years

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Abstract
All 181 isolates of barley yellow dwarf virus (BYDV) that were recovered from field-collected oats, wheat or barley during 1975 and 1976 resembled one of 5 characterized isolates found previously. Most of them resembled PAV, an isolate of BYDV which is transmitted nonspecifically by Rhopalosiphum padi, Macrosiphum avenae and Schizaphis graminum. More than 1 variant of BYDV was recovered from 9 of 57 winter grain plants. Only 1 mixed infection was detected among 114 spring oat samples. Since these tests complete 20 consecutive years of evaluation of BYDV isolates in New York [USA], a compilation was made of the yearly results. Identification of 1055 BYDV isolates from spring oats showed that isolates similar to 4 of 5 characterized ones were present almost every year. A gradual change in predominating isolate type has occurred in the 20 yr, from isolates similar to the vector-specific MAV (specifically transmitted by M. avenae) to those similar to PAV. A similar pattern was detected in tests of winter grains during the same period. Mixed infections by more than 1 isolate of BYDV were common in winter grains but rare in oats during most years. Further evaluations based upon 2 kinds of serological tests confirmed the identifications of 39 isolates of BYDV. One test was a neutralization of infectivity based on serological blocking of aphid transmission from treated virus preparations. The other was the enzyme-linked immunosorbent assay procedure, which has many advantages and shows promise for future work.