Surveillance of Rice Blast Resistance Effectiveness and Emerging Virulent Isolates in Taiwan.

Rice blast caused by is a dangerous threat to rice production and food security worldwide. Breeding and proper deployment of resistant varieties are effective and environmentally friendly strategies to manage this notorious disease. However, a highly dynamic and quickly evolved rice blast pathogen population in the field has made disease control with resistance germplasms more challenging. Therefore, continued monitoring of pathogen dynamics and application of effective resistance varieties are critical tasks to prolong or sustain field resistance. Here, we report a team project that involved evaluation of rice blast resistance genes and surveillance of field populations in Taiwan. A set of International Rice Research Institute-bred blast-resistant lines (IRBLs) carrying single blast resistance genes was utilized to monitor the field effectiveness of rice blast resistance. Resistance genes such as (formerly ) and exhibited the best and most durable resistance against the rice blast fungus population in Taiwan. Interestingly, line IRBLb-B harboring the gene with good field protection has recently shown susceptible lesions in some locations. To dissect the genotypic features of virulent isolates against the resistance gene, isolates were collected and analyzed. Screening of the locus revealed that the majority of field isolates still maintained the wild-type status but eight virulent genotypes were found. Pot3 insertion appeared to be a major way to disrupt the avirulence function. Interestingly, a novel double-allele genotype among virulent isolates was first identified. Pot2 repetitive element-based polymerase chain reaction (rep-PCR) fingerprinting analysis indicated that mutation events may occur independently among different lineages in different geographic locations of Taiwan. This study provides our surveillance experience of rice blast disease and serves as the foundation to sustain rice production.