Characterization of Rice Blast Isolates by the Differential System and their Application for Mapping a Resistance Gene,Pi19(t)

To facilitate resistance gene characterization in the present study, the pathogenicities of newly collected blast isolates from rice fields in the Philippines were characterized using international blast differential varieties consisting of 31 monogenic lines that target 24 resistance genes. To classify and designate the blast isolates, we used a new international blast designation system, which has been proposed as a suitable naming system for comparing blast races among different studies. A total of 23 rice blast isolates collected from the Philippines were classified into 16 pathotypes, which showed reaction patterns different from those seen in the standard isolates. Among the blast pathotypes, 11 had differentiating ability for four Pik alleles (Pik, Pik‐m, Pik‐h, and Pik‐p) and Pi1, whereas the standard blast isolates from the Philippines were not able to differentiate these genes. In addition, several blast isolates were avirulent to IRBLt‐K59, IRBL19‐A, and Lijiangxintuanheigu, although the standard differential blast isolates were virulent to these lines. Moreover, two blast isolates were virulent to a monogenic line, IRBL9‐W, which harbours Pi9 and was resistant to all standard differential blast isolates. By using the isolates avirulent to IRBL19‐A, Pi19(t) was successfully mapped in the centromeric region on chromosome 12 with simple sequence repeat markers RM27937 and RM1337. These markers are useful for marker‐assisted Pi19(t) introgression worldwide.