Continuous surveillance by the international differential system showed the spatiotemporal dynamics in rice blast pathogenicity in Vietnam

The fungus Magnaporthe oryzae (syn. Pyricularia oryzae Cavara) causes rice blast, which is one of the most destructive rice diseases worldwide. Herein, we added 474 new blast isolates to our rice blast pathogens that we had previously collected and analyzed. By investigating their pathogenicity using the international differential system, we compared the pathogenicity characteristics observed before 2016 with those observed after 2017. The frequency of virulent isolates against each differential variety (DV) increased and the diversity of the blast races also increased. Particularly, the resistance genes Pish and Pita lost their effectiveness in northern Vietnam. Temporal-spatial analysis of pathogenicity scores showed that the resistance genes were categorized into four representative types: resistance breakdown, stable resistance, regional resistance breakdown, and others. Additionally, we showed that the breakdown of resistance observed in Thien Uu 8 in Ha Tinh Province was caused by the breakdown of the Pita2 resistance gene. These results are highly valuable for breeding suitable rice varieties that contribute to durable resistance, depending on regional variations in blast pathogenicity.