The Risk of Wheat Blast in Rice-Wheat Co-Planting Regions in China: MoO Strains of Pyricularia oryzae Cause Typical Symptom and Host Reaction on Both Wheat Leaves and Spikes

The Triticum pathotype of Magnaporthe oryzae (syn. Pyricularia oryzae) causes wheat blast, which has recently spread to Asia. To assess the potential risk of wheat blast in rice-wheat growing regions, we investigated the pathogenicity of 14 isolates of P. oryzae on 32 wheat cultivars, among which Oryzae pathotype of P. oryzae (MoO) isolates were completely avirulent on the wheat cultivars at 22 degrees C but caused various degrees of infection 25 degrees C. These reactions at 25 degrees C were isolate and cultivar dependent, like race-cultivar specificity, which was also recognized at the heading stage and caused typical blast symptoms on spikes. Microscopic analyses indicated that a compatible MoO isolate produced appressoria and infection hyphae on wheat as on rice. When we compared transcriptomes in wheat-MoO interactions, the bulk of pathogen-related genes were upregulated or downregulated in compatible and incompatible patterns, but changes in gene transcription were more significant in a compatible pattern. These results indicate that temperature could influence the infection ratio of wheat with MoO, and some MoO strains could be potential pathogens that increase the risk of wheat blast outbreaks in wheat-rice growing regions with global warming. In addition, certain wheat cultivars exhibited resistance and are assumed to carry resistance-promoting genes to the MoO strains.