Characterization of Mexican and non-Mexican isolates of Macrophomina phaseolina based on morphological characteristics, pathogenicity on bean seeds and endoglucanase genes

The diversity patterns of 30 isolates of the fungal pathogen Macrophomina phaseolina, 15 from Mexico and 15 from other countries were analyzed based on morphological characteristics, pathogenicity on bean seeds and presence or absence of endoglucanase genes. The anastomosis frequencies among all isolates were determined under in vitro conditions and finally, two endoglucanases (egl1 and egl2) were investigated by Southern analysis. No relationship between microsclerotia size and pathogenicity was found. The most aggressive isolates on bean seeds were from Mexico, although they exhibited the lowest microsclerotia sizes and growth rate on in vitro conditions. A low frequency (less than 24%) of successful anastomosis among M. phaseolina isolates was found, while egl1 and egl2 were detected in 29 and 20 isolates, respectively. The results obtained indicate a different virulence between Mexican and non-Mexican isolates, but no clear differences between isolates were found when they were compared based on anastomosis capability or presence/absence of endoglucanase genes. Thus, we suggest that pathogenic specialization of M. phaseolina is related to the geographic origin of the isolates, whereas specialization could not be explained by analyses of pathogenicity genes or anastomosis frequencies.