Sequential evaluation for field assessment of partial resistance to rice blast

High partial resistance is one of the commonly observed features of the cultivars with durable blast resistance. Proper assessment of partial resistance is essential for improving genetic resistance to rice blast. Blast evaluation by sequential planting aims to assess the dynamic consequence of population interaction between host genotype and virulent blast isolates over a prolonged polycyclic association. Nine Tongil-type cultivars developed in Korea were evaluated using sequential evaluation technique in five successive plantings under upland conditions, IRRI, Philippines. The partial resistance of the cultivars having similar reaction to blast in conventional nursery test was clearly differentiated in this experiment. Blast on Taebaeg rapidly increased in the second planting and onwards, while that on Iri 387 increased gradually. The partial resistance of Samgang and Jungweon is comparable to that of IR36, a known cultivar with high partial resistance. Singwang has a slightly lower partial resistance than Samgang. Jangseong, Yongmoon, Yongju and Pungsan have a low partial resistance. Distinct blast populations having different virulence were developed in each cultivar, indicating a selective build-up of virulent isolates in each sequential planting. Sequential planting is suitable for a critical evaluation of partial resistance of test materials in reduced number.