Rice blast disease is one of the major causes of yield loss. The most economical method to manage rice blast disease is to cultivate resistant rice varieties. However, the rapid evolution of the rice blast fungus Magnaporthe oryzae makes the introduction of various resistant genes into rice varieties a never-ending challenge for rice breeders. 'Ilpum' rice known for its excellent taste, has been mainly cultivated in the Gyeongbuk province of South Korea since its development in 1990, for 30 years. However, 'Ilpum' is susceptible to rice blast disease and bacterial leaf blight. To address this, 'Saeilpum' was developed from a cross with 'Ilpum' and 'SR30064-B2-B1-B8-20-2-1-61-21' lines. 'Ilpum' exhibited a score of 5 (susceptibility) in the blast nursery test, while 'Saeilpum' showed strong resistance with a score of 2. 'Saeilpum' is resistant to all Korean bacterial leaf blight races, K1, K2, K3, and K3a (data not shown).
For the identification of blast disease resistance genes in the 'Saeilpum', a target capture sequencing panel containing 2565 SNPs, including 1225 SNPs informative for japonica and 1339 SNPs informative for indica, was utilized with 94 lines in F5 generation derived from crosses between 'Ilpum' and 'Saeilpum'. Only 125 SNPs were observed between the parental lines with 68 SNPs located in the 0.3~15.2Mb region on chromosome 12 and the 21 SNPs in 24.4~28.9Mb region on chromosome 11. Interestingly, the bacterial leaf blight resistance gene, Xa4 was located in the end of chromosom 11, suggesting an improvement in bacterial leaf blight resistance in 'Saeilpum.' The blast resistance of 94 F5 and F6 lines was evaluated in a blast nursery test in 2022 and 2023. Using the resistance score of 94 F5 lines, a QTL was detected near 10Mb on chromosome 12. Analysis of variance showed that the chr12_10607554' marker linked with Pita2 was strongly associated with blast disease with the phenotypic variance of 80% (p<0.001). Therefore, Pita2 was suggested to be the blast resistance gene in 'Saeilpum'. These results will be beneficial for breeding of blast resistance rice in Korea. The research was funded by the Rural Development Administration(RDA) of South Korea, grant number PJ01683002.