Soybean-Macrophomina phaseolina-Specific Interactions and Identification of a Novel Source of Resistance.

Charcoal rot, caused by the fungus Macrophomina phaseolina, is an economically important disease of soybean (Glycine max) worldwide. Objectives of the present research were to (i) study the genetic and pathogenic diversity in a collection of M. phaseolina isolates from Argentina and Paraguay and (ii) develop an improved in vitro phenotyping method to evaluate disease response of soybean genotypes to M. phaseolina isolates. Cluster analysis showed no clear association among simple sequence repeat profiles, year of collection, pathogenicity, and geographical origin of the isolates from Argentina and Paraguay. Subsequently, the response of four soybean genotypes against seven M. phaseolina isolates was evaluated in the field and the results were confirmed using the in vitro assay developed. This assay, which is based on root disease development on soybean seedlings, allowed the detection of a differential level of aggressiveness among the isolates on four soybean genotypes. The results suggest the existence of specific interactions among soybean genotypes and M. phaseolina isolates. In addition, cultivar Munasqa RR showed a superior response against M. phaseolina compared with DT 97-4290 (moderately resistant), thus becoming a novel source of resistance to charcoal rot.