IDENTIFICATION OF PATHOGENIC DIVERSITY IN Phomopsis sp. CAUSING STEM BLIGHT IN SOYBEANS (Glycine max) BY MOLECULAR MARKERS

Abstract

Phomopsis longicolla (Plo) and P. phaseoli var. sojae (Pps) are causal agents of stem blight (SB) and seed decays (SD) in soybean (Glycine max). The objective was to study genetic and pathogenic variability of Phomopsis in interactions with cultivars of varied resistance or susceptibility, and to study the association between molecular and pathogenic profiles in the analyzed interactions. The hypothesis was that the existence of genetic variability in both fungus and plant materials increases the biodiversity in specific reactions during the development of SB. For contrasting this hypothesis, a new approach of the widely known statistical methods GGE Biplot was proposed for measuring the correlation among pathogenic attributes (phenotypic expression of the plant pathology) and molecular markers. Six isolates of Plo and one of Pps were inoculated to six soybean cultivars. Genetic variability in the fungi was evaluated at the molecular level by RAPD and ITS markers and at the phenotypic level by their pathogenic performance through the severity (S%) of the pathology caused in soybean cultivars. Molecular characterization separated the Plo isolates from the Pps isolate. Specific interaction between each isolate´cultivar combination evidenced differential pathogenic performances in respect to resistance/susceptibility. The study identified associations between the molecular variability of pathogens and the differential behavior observed in the set of soybean cultivars that interacted with Phomopsis isolates that cause TTV in G. max.