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A new gene for resistance to Triticum isolates of Pyricularia oryzae stacked with Rmg8 in a local landrace of common wheat

Wang Shizhen: Kobe University

<div><em>Pyricularia oryzae</em>, the causal agent of wheat blast, first arose in Brazil in 1985 and recently spread to Asia (Bangladesh in 2016 and India in 2017). Resistance genes against this new pathogen are very rare in common wheat populations. We screened ~520 local landraces of common wheat collected worldwide with Br48, a <em>Triticum</em> isolate collected in Brazil, and found a highly resistant, unique accession, GR119. Spikes of GR119 were moderately resistant to a hybrid culture 200R54 lacking <em>AVR-Rmg8</em> (an avirulence gene corresponding to <em>Rmg8</em>), and highly resistant to its transformant carrying<em> AVR-Rmg8</em>. When F<sub>2 </sub>seedlings derived from a cross between GR119 and Chinese Spring (CS, susceptible control) were inoculated with Br48, resistant and susceptible seedlings segregated in a 15:1 ratio, suggesting that GR119 carries two resistance genes. When the F<sub>2</sub> seedlings were inoculated with Br48△A8 carrying a disrupted <em>AVR-Rmg8</em>, however, the segregation fitted a 3:1 ratio. These results suggests that one of the two genes in GR119 was <em>Rmg8</em>. The other, novel gene was designated tentatively as <em>RmgGR119</em>. <em>Rmg8</em> and <em>RmgGR119</em> had complementary modes of actions on fungal infection. The strong resistance of GR119 was attributed to the combined effects of <em>Rmg8</em> and <em>RmgGR119</em>.</div>