Recovery Plan for Wheat Blast Caused by Magnaporthe oryzae Pathotype Triticum

Abstract

Wheat blast is an explosive new fungal disease of wheat caused by an Magnaporthe oryzae (synonym of Pyricularia oryzae) host-adapted subpopulation, the M. oryzae Triticum pathotype (MoT). MoT has been found in South America, South Asia, and Africa, but not in the United States. Wheat blast caused by the MoT fungus was first reported in Brazil in 1985 and subsequently spread to Bolivia, Paraguay, and Argentina in the 1990s and 2000s. The disease first appeared in Bangladesh in 2016 and in Zambia in 2017. The MoT fungus is seedborne, and the most likely route for movement across oceans was though grain trade. Wheat head (spike) blast is the predominant form of the disease in the field, although foliar and stem blast also occurs. The disease has proven hard to control when weather conditions are conducive, often resulting in devastating yield and quality losses. The only currently effective resistance, contained in the 2NvS translocation from the wild wheat relative Aegilops ventricosa, confers partial resistance that is variable depending on the genetic background of the specific wheat variety. Fungicides are not fully effective in controlling wheat head blast if warm, humid weather occurs during the heading stage. A major disease management strategy in areas where the disease occurs involves timing the wheat planting date so that heading does not coincide with warm rainy weather. A climate suitability model for the United States indicates that all of U.S. soft red winter wheat and about half of the hard red winter wheat are at risk.