Identification of three major R genes responsible for broad-spectrum blast resistance in an indica rice accession

An indica rice accession HR4 was found to exhibit good resistance to rice blast in previous research. Inoculation with 116 different M. oryzae isolates revealed that HR4 has the broadest resistance spectrum of the six rice cultivars used in this study, which included two well characterized broad-spectrum resistance sources. To uncover the genetic mechanism of the broad-spectrum resistance in HR4, genetic analysis was carried out with three stable isolates. The results showed that a single dominant gene controlled its resistance to isolates GD93286 and GD00193, whereas two independent dominant genes were responsible for its resistance to isolate GD08T4. The resistance (R) gene in HR4 corresponding to isolate GD93286, named Pi-h1(t), was found to reside in a region of ~235.9 kb on the long arm of chromosome 11, while the other two R genes identified with isolate GD08T4, named Pi-h2(t) and Pi-h3(t), were linked to markers on chromosomes 1 and 12, respectively. The results indicated that the broad-spectrum resistance to rice blast in HR4 could be ascribed to multiple R genes. Identification of such multiple R genes will allow us to use markers more effectively for resistance improvement in rice breeding programs.