Phenotypic Characterization of the Rice Blast Resistance GenePi-2(t)

Abstract

The spectrum of resistance conditioned by the blast resistance gene Pi-2(t) in rice was characterized. Near-isogenic line (NIL) C101A51 carrying Pi-2(t) in the genetic background of the indica rice cultivar CO39 was resistant to 455 Philippine isolates of Pyricularia grisea when inoculated in greenhouse tests. The P. grisea isolates, collected mainly from 1983 to 1992, represented at least 18 lineages based on DNA fingerprinting data. The NIL C101A51 was planted at two sites used by the International Rice Research Institute for the evaluation of blast resistance, and for which the P. grisea populations had been analyzed by DNA fingerprinting. After initial resistance at the two sites, C101A51 eventually showed susceptible lesions. All isolates (n = 60) collected from C101A51 at the two sites were identified as belonging to a single lineage (more than 95% band similarity using the repetitive DNA probe MGR586), distinct (less than 80% band similarity) from the approximately 2,000 Philippine isolates previously subjected to DNA fingerprinting. The group of isolates, designated lineage 44, was inoculated to a set of NILs in the CO39 genetic background in greenhouse tests. Lineage 44 was found to be compatible to lines carrying Pi-2(t) (in C101A51 and 5173, the donor of Pi-2(t)), Pi-4 a (t) (in C102PKT), Pi-4 a (t) + Pi-? (in C105TTP-4-L23), and CO39. C101A51 was found to be resistant in nursery tests at 24 of the 40 sites in 16 countries in which it was tested during 1991 to 1993 through the International Network for the Genetic Evaluation of Rice. These results suggested that Pi-2(t) could condition resistance to many lineages of P. grisea and could be useful if pyramided or otherwise deployed with genes that condition resistance to lineage 44.