EFFECTS OF PLANTING DATE AND INOCULATION DATE ON SEVERITY OF WHEAT STREAK MOSAIC IN HARD RED WINTER-WHEAT CULTIVARS

Hard red winter wheat cultivars were inoculated with wheat streak mosaic virus (WSMV) in the fall or spring and then were evaluated in the spring for severity of wheat streak mosaic symptoms, detection of WSMV by enzyme-linked immunosorbent assay (ELISA), fertile tiller production, yield, and thousand kernel weight (TKW). On the basis of these parameters, seven cultivars (Century, Chisholm, Pioneer 2157, Siouxland, Tam 108, Triumph 64, and Vona) were considered susceptible when inoculated with WSMV in the fall. The maximum percent reductions for these seven cultivars over 2 yr of tests in fertile tillers, yield, and TKW were 75, 87, and 48%, respectively. One cultivar, Rall, had some resistance to wheat streak mosaic if planted in the fall during the time recommended for north central Oklahoma. The maximum percent reductions in fertile tillers, yield, and TKW for Rall were 22, 20, and 11%, respectively. Spring inoculation with WSMV of wheat planted early in the fall (September or October) did not consistently result in symptoms, ELISA values positive for WSMV, or significant reductions in yield or TKW. However, spring inoculation of wheat planted late in the fall (November) resulted in symptoms, ELISA values positive for WSMV, and significant reductions in yield and TKW. Thus, the maturity of plants at the time of infection may affect severity of wheat streak mosaic because wheat planted in November was less mature (Feekes' growth stage 5) at the time of inoculation the next spring than wheat planted in September or October (Feekes' growth stage 6).