Phenotypic virulence analysis of Pyricularia grisea isolates from Brazilian upland rice cultivars

Abstract

Phenotypic virulence analysis was made on population of Pyricularia grisea isolates collected from 10 upland cultivars in three distinct rice breeding sites, with the objective of studying the degree of similarity in the phenotypic virulence among the isolates, the composition of races, and their virulence pattern. Sixteen races were identified based on the reaction type on eight standard international differentials, the predominant ones being IB-9 and IB-41. The virulence frequency was high on IAC 47 and IAC 165 among medium and early maturing cultivars, respectively. The frequency of isolates virulent was greater on upland rice cultivars (51.1%) than on irrigated rice cultivars (21.8%). Both virulent and avirulent isolates were present in the population of P. grisea to the known genes in the near isogenic lines. Of 72 test isolates, 94.4% were virulent for genes Pi-3 and Pi-4a. The virulence frequencies were relatively lower in decreasing order on Pi-1, Pi-4b and Pi-2. The coefficient of similarity ranged from 0.28 to 1.0 among the isolates pertaining to different races, while within the race IB-9, it varied from 0.56 to 1.0. Considering the coefficient of similarity of 0.81, 72% of isolates of race IB-9 exhibited similar pattern of virulence.