Suppression of wheat blast resistance by an effector of Pyricularia oryzae is counteracted by a host specificity resistance gene in wheat

Summary Wheat blast caused by the Triticum pathotype of Pyricularia oryzae poses a serious threat to wheat production in South America and Asia and is now becoming a pandemic disease. Here, we show that Rmg8 , a promising wheat gene for resistance breeding, is suppressed by PWT4 , an effector gene of P. oryzae , and in turn that the suppression is counteracted by Rwt4 , a wheat gene recognizing PWT4 . When PWT4 was introduced into a wheat blast isolate carrying AVR‐Rmg8 (an avirulence gene corresponding to Rmg8 ), PWT4 suppressed wheat resistance conferred by Rmg8 . PWT4 did not alter the expression of AVR‐Rmg8 , but higher expression of PWT4 led to more efficient suppression. This suppression was observed in rwt4 carriers, but not in Rwt4 carriers, indicating that it is counteracted by Rwt4 . PWT4 was assumed to have been horizontally transferred from a weed‐associated cryptic species, P. pennisetigena , to an Avena isolate of P. oryzae in Brazil. This implies a potential risk of the acquisition of PWT4 by the wheat blast fungus and the ‘breakdown’ of Rmg8 . We suggest that Rmg8 should be introduced together with Rwt4 into a wheat cultivar when it is used for resistance breeding.