Identification of Elite R -Gene Combinations against Blast Disease in Geng Rice Varieties.

Rice blast, caused by the fungus, is one of the most devastating rice diseases worldwide. Developing resistant varieties by pyramiding different blast resistance () genes is an effective approach to control the disease. However, due to complex interactions among genes and crop genetic backgrounds, different -gene combinations may have varying effects on resistance. Here, we report the identification of two core -gene combinations that will benefit the improvement of () rice blast resistance. We first evaluated 68 rice cultivars at seedling stage by challenging with 58 isolates. To evaluate panicle blast resistance, we inoculated 190 rice cultivars at boosting stage with five groups of mixed conidial suspensions (MCSs), with each containing 5-6 isolates. More than 60% cultivars displayed moderate or lower levels of susceptibility to panicle blast against the five MCSs. Most cultivars contained two to six genes detected by the functional markers corresponding to 18 known genes. Through multinomial logistics regression analysis, we found that , , , and loci contributed significantly to seedling blast resistance, and , , , and contributed significantly to panicle blast resistance. For gene combinations, + and + yielded more stable pyramiding effects on panicle blast resistance against all five MCSs and were designated as core -gene combinations. Up to 51.6% cultivars in the Jiangsu area contained , but less than 30% harbored either or , leading to less cultivars containing + (15.8%) or + (5.8%). Only a few varieties simultaneously contained and , implying the opportunity to use hybrid breeding procedures to efficiently generate varieties with either + or +. This study provides valuable information for breeders to develop rice cultivars with high resistance to blast, especially panicle blast.