Morphological and Molecular Characterization of Diaporthe spp. Causing Stem Canker on Soybean

Abstract

Stem canker of soybean caused by Diaporthe spp. is an emerging constraint in soybean-producing regions, leading to reduced plant vigor, premature defoliation, and significant yield losses. Accurate identification of the causal agents is essential due to the high genetic and morphological variability within the genus Diaporthe. The present study aimed to characterize Diaporthe spp. associated with soybean stem canker using morphological and molecular approaches. Diseased soybean stems exhibiting canker lesions, vascular discoloration, and necrotic symptoms were collected from different fields, and fungal isolates were obtained through standard isolation procedures. Morphological characterization was performed based on colony features, conidial morphology, pycnidia development, and cultural characteristics on selective media. Considerable variation was observed among isolates, suggesting the presence of multiple Diaporthe species associated with stem canker symptoms. Molecular identification was conducted using ITS region sequencing along with additional gene markers, followed by phylogenetic analysis to resolve species-level relationships. The results confirmed that soybean stem canker is associated with a complex of Diaporthe species exhibiting both genetic and morphological diversity. Phylogenetic clustering revealed distinct lineages corresponding to different species complexes, some of which showed regional distribution patterns. Molecular data improved resolution of cryptic species that could not be reliably distinguished based on morphology alone. The study highlights the importance of integrated taxonomic approaches for accurate identification of Diaporthe spp. in soybean ecosystems. These findings provide valuable insights into the diversity and epidemiology of stem canker pathogens and support the development of effective disease management strategies for sustainable soybean production.