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

Abstract

The phenotypic diversity of Magnaporthe grisea was evaluated based on leaf samples with blast lesions collected from eight commercial fields of the upland rice cultivars 'BRS Primavera' and 'BRS Bonança', during the growing seasons of 2001/2002 and 2002/2003, in Goias State. The number of M. grisea isolates from each field utilized for virulence testing varied from 28 to 47. Three different indices were used based on reaction type in the eight standard international differentials and eight Brazilian differentials. The M. grisea subpopulations of ´Primavera' and 'Bonança', as measured by Simpson, Shannon and Gleason indices, showed similar phenotypic diversities. The Simpson index was more sensitive relation than those of Shannon and Gleason for pathotype number and standard deviation utilizing Brazilian differentials. However, the Gleason index was sensitive to standard deviation for international differentials. The sample size did not significantly influence the diversity index. The two sets of differential cultivars used in this study distinguished phenotypic diversity in different ways in all of the eight subpopulations analyzed. The phenotypic diversity determined based on eight differential Brazilian cultivars was lower in commercial rice fields of 'Primavera' than in the fields of 'Bonança,' independent of the diversity index utilized, year and location. Considering the Brazilian differentials, the four subpopulations of 'BRS Primavera' did not show evenness in distribution and only one pathotype dominated in the populations. The even distribution of pathotype was observed in three subpopulations of 'BRS Bonança'. The pathotype diversity of M. grisea was determined with more precision using Brazilian differentials and Simpson index.

Polymorphism Detection by Microsatellite Markers in a Magnaporthe oryzae Population From Different Geographical Areas of Brazil

“…The structure of the pathogen population refers to the amount of genetic and phenotypic variation among and within the populations, and it is divided in time and space and may be influenced by the cultivar origin, location, size of the planted area and field isolation by cultivar (Silva et al. ). In Brazil, phenotypic characterization studies of M. oryzae populations have been focussed on the determination of pathotypes and their frequency and respective compatibility with resistance genes in commercial cultivars and international differentials (Cornelio et al.…”