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Temperature-sensitive resistance breaking mechanism of Wsm1 and Wsm2 genes against Wheat streak mosaic virus and Triticum mosaic virus in wheat

Satyanarayana Tatineni: USDA-ARS

<div>Non-allelic single-dominant <em>Wsm1</em> and <em>Wsm2</em> genes have been deployed for management of viral diseases in wheat. Wheat cultivars Mace, carrying the <em>Wsm1</em> gene, is resistant to both <em>Wheat streak mosaic virus</em> (WSMV) and <em>Triticum mosaic virus</em> (TriMV), and Snowmass, with <em>Wsm2</em>, is resistant only to WSMV. <em>Wsm</em>-based resistance in both cultivars is temperature sensitive and, in growth chamber studies, is effective at 18°C or below but resistance breaks at higher temperatures. The underlying temperature-sensitive resistance breaking mechanism of <em>Wsm1</em> and <em>Wsm2</em> genes in wheat cultivars was examined using fluorescent protein-tagged WSMV and TriMV. Both viruses elicited foci that were approximately similar in number and size at 18 and 24°C on inoculated leaves of resistant and susceptible wheat cultivars, suggesting that resistant wheat cultivars still permit cell-to-cell movement at both temperatures. Additionally, WSMV and TriMV efficiently replicated in inoculated leaves of resistant wheat cultivars at 18°C but failed to establish systemic infection, suggesting that <em>Wsm1</em>- and <em>Wsm2</em>-mediated resistance debilitated viral long-distance transport. Furthermore, neither virus was able to enter the leaf sheaths of inoculated leaves or crowns of resistant wheat cultivars at 18°C but both were able to do so at 24°C. These data suggest that <em>Wsm1-</em> and <em>Wsm2-</em>based resistance breaks at high temperatures by permitting virus entry into the vasculature for long-distance transport in resistant wheat cultivars.</div>