Yield effects of Barley yellow dwarf virus in soft red winter wheat

Three cultivars of soft red winter wheat were evaluated to determine the re lationship between the incidence and time of infection by Barley yellow dwa rf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a s plit-plot design with six replicates at sites in Indiana and Illinois. Yiel d plots were infested with different amounts of viruliferous aphids, and th e incidence of BYDV in each plot was measured. In a 2-year study in Illinoi s with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed follo wing aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression anal yses to relate incidence of infection and yield with data from fall and ear ly spring infections provided R-2 values of 0.89 and 0.51 for the 1996 to 1 997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark , Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with d ecreases in yield, with R2 values of 0.80, 0.78, and 0.90 for the three cul tivars, respectively. Estimated yield losses in both studies and all cultiv ars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase i n virus infection. In a third study over a 2-year period in Indiana with th e same three wheat genotypes and a second BYDV isolate (PAV-P), BYDV treatm ents resulted in significant reductions in yield, but yield loss and the in cidence of BYDV were not linearly correlated. Given the differences in yiel d reductions caused by the two BYDV isolates, PAV-P may be an attenuated st rain of BYDV and may cross-protect plants from naturally occurring strains of the virus.