Assessing the resistance of winter wheat to wheat spindle streak mosaic bymovirus

Management of Wheat spindle streak mosaic virus (WSSMV), a bymovirus, relies on resistant cultivars. We compared the results from mechanical inoculation with virus-infected plant sap with those of a previous study from natural infection in field trials. The six cultivars tested (Century, Wichita, TAM 200, Geneva, Harus, and Augusta) became infected via mechanical inoculation of leaves, ruling out resistance to virus replication in leaves as the basis for resistance in the cultivars considered resistant in field trials. 'Augusta' (susceptible), 'Geneva' (resistant), and germplasm KS92WGRC22 (highly resistant) were compared in field plots for numbers of symptomatic versus asymptomatic tillers. Individual plants having both infected and uninfected tillers were found only in the two resistant wheats. Resistance in 'Geneva' and KS92WGRC22 could be due to uneven movement of virus front roots into tillers or to reduced virus replication in roots. If reduced virus replication in roots is the source of resistance in a cultivar, then cropping with such a cultivar would contribute less to the inoculum potential of soil than cropping with susceptible cultivars. Soil transmission of virus occurred in field soil gathered from the root zone of symptomatic 'Augusta', but not in field soil from the root zone of asymptomatic KS92WGRC22. These results suggest that infected plants can, in a single crop cycle, contribute significantly to the soil reservoir of WSSMV.