Morphological and Molecular Characterization of Didymella pinodella Causing Foot Rot and Black Stem on Field Pea

Abstract

Foot rot and black stem symptoms observed on field pea (Pisum sativum L.) were investigated to identify the causal pathogen and characterize its morphological and molecular attributes. Field surveys in pea-growing regions revealed characteristic symptoms including root and collar rot, blackening of basal stems, vascular discoloration, and progressive plant wilting under humid and cool soil conditions. Fungal isolates recovered from infected tissues produced slow-growing colonies with gray to dark olivaceous pigmentation and abundant pycnidia on potato dextrose agar. Microscopic examination revealed hyaline, ellipsoid to fusiform conidia consistent with Didymella pinodella. Pathogenicity tests conducted under controlled greenhouse conditions successfully reproduced foot rot and black stem symptoms on healthy pea seedlings, confirming virulence and fulfilling Koch’s postulates. Molecular identification using ITS rDNA, β-tubulin, and LSU gene sequencing confirmed the isolates as D. pinodella, showing high similarity with reference sequences in global databases. Phylogenetic analysis placed all isolates within a well-supported clade corresponding to D. pinodella, indicating limited intraspecific variation among populations from different geographic locations. Observed minor sequence polymorphisms suggest potential adaptation to local agro-climatic conditions. Disease development was strongly associated with excessive soil moisture and poor drainage, which favored pathogen survival and infection. The study highlights the increasing importance of D. pinodella as a soil- and residue-borne pathogen in field pea production systems and emphasizes the need for accurate molecular diagnostics for early detection. Integrated disease management strategies, including crop rotation, resistant cultivars, and improved drainage, are recommended to reduce disease incidence and ensure sustainable pea production.