Genetic and phenotypic characterization of isolates of Pyricularia grisea from the rice cultivars epagri 108 and 109 in the State of Tocantins

Abstract

An epidemic of rice (Oryza sativa) blast occurred on cultivars Epagri 108 and 109 in the municipalities of Lagoa da Confusão and Duerê in the State of Tocantins, during the rice-growing season 1998-99. DNA fingerprinting and virulence phenotype analysis were utilized to determine the diversity of Pyricularia grisea isolates collected from these cultivars in one epidemic year. Rep-PCR analysis of isolates was done by using two primer sequences from Pot2. Two distinct fingerprint groups or lineages were identified among 53 isolates collected from nine different commercial fields. The virulence pattern of isolates retrieved from these two cultivars was analyzed in artificial inoculation tests utilizing 32 genotypes in the greenhouse. A dendrogram constructed from virulence phenotype data showed a single group considering 77% similarity level. The predominant pathotype IB-45 was represented by 47 of the 53 isolates corresponding to 83%. Four other pathotypes (IB-1, IB-9, IB-13 and IB-41) were identified at random among the isolates from these cultivars. There was no relation between rep-PCR grouping and pathotypes. The results showed that the isolates of P. grisea recovered from cultivars Epagri108 and 109 in farmers' fields had narrow phenotypic and genetic diversity. The blast outbreak on these two cultivars one year after their introduction could be attributed to the new pathotype IB-45 or its increase, which was hitherto existing in low frequency.

Use of local rice cultivars as additional differentials to identify pathotypes of Pyricularia oryzae

“…The isolates of P. oryzae showing susceptible reaction on BRS Jaburu belong to TA group (128 reaction patterns) similar to the international group IA, and the numbers following the group letters indicate the pathotype number. Similar system was adopted for identifying Brazilian pathotypes in upland rice (Prabhu et al, 2002b).…”

“…Utilizing Brazilian differentials the 14 isolates of pathotype IB-1 could be further classified into eight local pathotypes. Some of the Brazilian pathotypes that showed differential reaction on commercial rice cultivars such as Primavera and Maravilha could be utilized for incorporating resistance genes in susceptible cultivars using Brazilian pathoypes (Prabhu et al, 2002b). In a recent study for identifying pathotypes in upland rice, the Brazilian differentials showed greater differential ability than with the international differentials (Silva et al, 2007).…”

Estimation of phenotypic diversity in field populations of Magnaporthe grisea from two upland rice cultivars

“…A set of eight commercial Brazilian rice cultivars was utilized as additional differentials for describing the pathotype diversity of M. grisea. Isolates virulent and avirulent to 'Primavera' were found within the pathotype IB-1 utilizing Brazilian differentials (Prabhu et al, 2002b). In another study, it has been shown that 46 isolates of M. grisea, collected from 'Primavera' during 1997-2001, belonged to 11 international and 15 Brazilian pathotypes (Prabhu et al, 2003).…”

“…Virulence and phenotypic diversity are commonly determined based on the identification of pathogenic races or pathotypes affecting diverse genotypes in breeders' plots. Virulence in the field also preexists in low frequencies for resistance genes, which have not so far been utilized in the resistance breeding of rice cultivars (Prabhu et al, 2002b). The detection of rare pathotypes has great value in predicting the effectiveness of the resistance genes in newly released cultivars.…”

“…Of 12 monosporic isolates collected from two leaf lesions of 'Primavera' in two urban areas of Lagomar and Uberlandia, in Minas Gerais State, four races IA-1, 1C-9, IB-1 and IC-65 were identified (Cornelio, 2001). International races representing the majority of the race groups were earlier reported from the upland rice growing States (Malavolta & Souza, 1992;Prabhu et al, 2002b). Pathogenic diversity is generally very high in experimental fields and at cultivar breeding sites where the conditions are highly favorable for disease development (Correa-Victoria & Zeigler, 1993;Zeigler et al, 1995;).…”