Morphological and Molecular Identification of Phomopsis spp. Causing Stem Canker and Seed Decay of Soybean

Abstract

Soybean is an economically important oilseed and protein-rich crop cultivated worldwide; however, its productivity is significantly constrained by fungal diseases affecting both field performance and seed quality. Among these, stem canker and seed decay caused by Phomopsis spp. are major diseases leading to stem lesions, seed discoloration, reduced germination, poor seed quality, and considerable yield losses. Accurate identification of the causal pathogens is essential for effective disease diagnosis and management. The present study was conducted to investigate the morphological and molecular characteristics of Phomopsis species associated with stem canker and seed decay of soybean. Diseased stem tissues and infected seeds exhibiting characteristic symptoms were collected from soybean-growing regions, and fungal isolates were obtained using standard isolation and culturing techniques. Morphological characterization was performed based on colony appearance, pigmentation, pycnidial formation, and microscopic examination of conidia. Molecular identification was carried out through polymerase chain reaction (PCR) amplification and sequencing of conserved genomic regions, followed by phylogenetic analysis to determine species identity and genetic relationships among isolates. Pathogenicity assays were conducted on healthy soybean plants and seeds under controlled conditions to confirm the disease-causing ability of the isolates. The results confirmed the association of multiple Phomopsis isolates with soybean stem canker and seed decay symptoms. Morphological observations revealed variation in colony growth and conidial characteristics among isolates, while molecular analysis demonstrated high genetic similarity with previously reported pathogenic Phomopsis species affecting soybean crops worldwide.