Effect of wheat spindle streak mosaic virus on yield of winter wheat in New York

In 1987-88 and 1988-89, field plot experiments were undertaken to assess the effects of wheat spindle streak mosaic virus (WSSMV), a soilborne virus transmitted by Polymyxa graminis, on winter wheat yields in New York. Two experimental approaches, reinfestation of fumigated plots with nonfumigated soil and a natural gradient of disease incidence, were used to produce different levels of disease. To minimize problems of covarying soil factors, yields of susceptible cultivars were compared with resistant cultivars in each experiment. The most reliable estimates of WSSMV effect were obtained with the disease gradient method when average disease incidence varied greatly between blocks and replication was high (12 blocks). Based on this approach, the grain yield of the susceptible cultivar Frankenmuth was reduced by an average of 14 kg/ha for every 1 percent increase in plants infected by WSSMV, a 1.4-t/ha (32%) reduction when all plants were infected. Yields of the breeding line NY6432-10 did not decline, despite a high incidence of plants infected with the virus in both years. When data from 1980-1989 regional yield trials were compared with temperature data, significant correlations were detected between long spring periods of temperatures conducive to WSSMV and lower yields of the susceptible cultivars Frankenmuth and Augusta relative to the yield of the highly resistant cultivar Geneva. Relative yield of Frankenmuth decreased by an average of 0.45% per day as net days in the optimal temperature range (2-11 C) increased from 20 to 45. Yield reductions for other cultivars screened over the past decade closely paralleled their relative resistance to, or tolerance of, WSSMV as demonstrated in field plot experiments. These results indicate that WSSMV has significantly reduced the yield of susceptible cultivars in New York over the past decade and that yield reduction is related to the percentage of plants infected with the virus and the duration of spring temperatures conducive to disease development.