Morpho-cultural variability, aggressiveness patterns, and ITS-based molecular characterisation of Colletotrichum truncatum across Indian soybean ecosystems

Colletotrichum truncatum causes anthracnose in soybean and remains a major constraint to soybean production. A total of sixty C. truncatum isolates collected from eight soybean-growing agro-ecological zones of India were characterised for morpho-cultural variability, pathogenic aggressiveness, and molecular identification using internal transcribed spacer (ITS) sequence analysis. The isolates showed significant variability in morpho-cultural traits and disease severity, with a strong contribution of host genotype to variation in disease responses. The identification of aggressive (CT-58, CT-17, CT-18, CT-32), stable (CT-41, CT-45, CT-29, CT-8, CT-52), and discriminative (CT-6, CT-7, CT-9, CT-13, CT-15, CT-22, CT-39, CT-59) isolates provides a valuable resource for resistance screening and for identifying quantitative trait loci (QTLs) associated with durable anthracnose resistance. Multivariate analyses indicated that the aggressiveness of the populations showed no significant association with morphocultural traits. ITS-based phylogeny confirmed the identity of isolates as C. truncatum but revealed low sequence divergence.