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Merging foundational and field research: Lessons from the ancient and emerging blast diseases on rice and wheat

Barbara Valent: Kansas State University

<div>Rice blast disease, caused by the <em>Oryza </em>pathotype (MoO) of <em>Magnaporthe oryzae </em>(synonym of<em> Pyricularia oryzae</em>), continues to threaten global rice production. At the same time, rice blast has become a model for understanding the molecular mechanisms of fungal pathogenicity and host specificity. This hemibiotrophic fungus repeatedly invades living rice cells as it spreads within rice tissue for the first 4 to 5 days before macroscopic symptoms appear. MoO biotrophic rice cell invasion requires hyphal dimorphism, a specialized interfacial structure (the Biotrophic Interfacial Complex, BIC) and specialized mechanisms for delivering effector proteins inside living rice cells. Since 1985, wheat blast disease, caused by the <em>Triticum </em>pathotype (MoT) of <em>M. oryzae</em>, emerged as an explosive new disease in S. America and S. Asia. Wheat blast differs in key aspects of its field biology relative to rice blast. For example, wheat head blast and not foliar blast is the major disease symptom in the field, and resistance appears rare in wheat relative to resistance in rice. This raised the question of whether the MoT fungus undergoes the same biotrophic invasion strategy as MoO strains. We report that MoO and MoT have conserved effectors, and they share common effector dynamics and biotrophic invasion strategies. We report new understanding of the mechanisms by which blast effectors are translocated inside living rice cells, which will ultimately impact wheat blast control as well.</div>

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