Phytophthora sojae and other pathogens on soybean (Glycine max L. Merrill) detected in Bulgaria

Abstract

Soybean (Glycine max L.) production is increasingly threatened by a complex of pathogens, whose occurrence and impact remain insufficiently characterized under Bulgarian field conditions. During the 2020 and 2021 growing seasons, symptomatic soybean plants and soil samples were collected from the Soybean Experimental Station in Pavlikeni, Central Northern Bulgaria for identification of associated pathogens. Isolation and rhizosphere soil baiting assays yielded bacterial, fungal and oomycete isolates, which were identified using molecular sequencing of the ITS regions and comparison with reference sequences in the NCBI GenBank database. The pathogens identified included Phytophthora sojae, Globisporangium ultimum, Alternaria alternata, as well as bacterial pathogen Curtobacterium flaccumfaciens pv. flaccumfaciens. Here we report for the first time the association of C. flaccumfaciens pv. flaccumfaciens with soybean in Bulgaria. Morphological, physiological, and pathogenicity assays confirmed the identity of P. sojae and demonstrated differences in cultivar susceptibility, with cultivar Isidor showing high resistance and Srebrina and Daniela exhibiting high susceptibility. These findings highlight the complex etiology of soybean diseases in Bulgaria and underscore the importance of pathogen monitoring and the use of resistant cultivars as key components of sustainable disease management strategies.