Rice blast caused by the fungus Magnaporthe grisea (anamorphic: Pyricularia oryzae) is an important disease in rice and development of resistant varieties to blast is one of the most important goals in rice breeding programs. A japonica rice variety, Palgong, has shown resistance to the Korean blast pathogen since it was developed in 1996. Nine blast resistance quantitative trait loci (QTLs) in Palgong alleles were identified on chromosomes 2, 4, 7, and 11. Four QTLs of qBn2.3, qBn4.2, qBn11.1, and qBn11.2 explained 28–56.7% of total phenotypic variation, while five QTLs of qBn2.2, qBn2.4, qBn4.1, qBn7.1, and qBn7.2 explained 9.7–18.8%. In a previous study, one to four resistance genes were located on the loci qBn2.2, qBn2.3, qBn4.2, qBn11.1, and qBn11.2, however, resistance genes were not located on the loci qBn2.4, qBn4.1, and qBn7.1. A major QTL, qBn11.2, explaining 56.7% of total phenotypic variation was related to the durable resistance of Palgong. Additionally, rice stripe virus resistance of Palgong was assumed to be based on the Stvb-i gene, which is located on a major QTL qBn11.2.

Blast resistance of 29 rice cultivars confirmed as a durable resistance in the evaluation of sequential planting from 2004 to 2006 was evaluated to nursery screening in 14 test sites during 11 years in Korea. The average disease severity (ADS) of 29 rice varieties against rice blast showed 3.5 degree; however, the difference of disease severity among the varieties was from 1.9 to 4.8. The 29 varieties were grouped into resistance less than 3.0 ADS degree including 12 varieties and moderate resistance over 3.1 ADS degree including 17 varieties. Among the 12 rice cultivars presented low ADS, 4 rice cultivars, Ungwang, Pungmi 1, Sinunbong 1, and Dasan 1 were constantly appeared high resistant reaction during 11 years in all test sites and the others were showed various diseases severity across the test years and the test sites. Twenty-one rice cultivars including Gopum were more variable among the test sites while the others were higher variable among the test years. These results indicated that durable resistance test against rice blast using sequential planting is a very efficient screening method to predict durability and nursery test for long periods and also useful method to predict indirectly durable resistance of rice cultivars.