VARIATION ON in vitro CULTURAL CHARACTERISTICS OF Macrophomina phaseolina ISOLATES AND ITS VIRULENCE ON COMMON BEAN

Abstract

Variation on in vitro cultural characteristics and virulence in common beans (Phaseolus vulgaris L.) of 15 Macrophomina phaseolina isolates obtained from different hosts and geographical areas of Mexico were determined. In vitro variation was evaluated through the culture of isolates in Petri dishes with Potato-Dextrose-Agar culture medium during 96 h at 30±1 °C in an incubator. Virulence was evaluated in BAT 477 (tolerant) and Pinto UI-114 (susceptible) bean genotypes grown in a soil inoculated with 2 % (w/w) of sorghum (Sorghum bicolor L. Moench) seed colonized by the fungi. There was a significative variation among M. phaseolina isolates in development and in vitro cultural characteristics, as well as in their virulence in bean. Quantitative characteristics, as in vitro relative growth rate of the colony, are an appropiate tool to characterize its development. M. phaseolina isolates obtained from hosts different from bean, as sesame (Sesamum indicum L.), sorghum, maize (Zea mays L.), and soybean (Glycine max L. Merr.) infected bean, indicating the non-specificity of the pathogen. Severity of disease and percentage of dead plants in pre-emergence could be a useful criteria for selecting resistant bean germplasm to M. phaseolina in early stages of growth.