Anthracnose triggers diosgenin biosynthesis via CYP90 modulation in Dioscorea composita

Anthracnose, caused by species within the Colletotrichum genus, poses a significant biotic threat to Dioscorea composita, a medicinally important yam species known for its high diosgenin content. This study characterizes three Colletotrichum isolates (PP1, PP2, and PP3) obtained from infected D. composita leaves using multilocus sequencing of ITS1-5.8S-ITS2 and β-tubulin regions. Molecular identification revealed that isolate PP1 shares 99 % sequence similarity with Colletotrichum gloeosporioides, while PP2 and PP3 are closely related to Colletotrichum siamense. Pathogenicity assays confirmed all isolates as virulent, with PP3 inducing the most severe symptoms. Biochemical profiling under pathogen stress revealed treatment-specific modulation of secondary metabolites. Notably, PP2 elicited the highest diosgenin (181.6 μg/g) and phenolic accumulation, while PP1 significantly enhanced flavonoid content, indicating distinct metabolic fluxes triggered by each isolate. Expression analysis of CYP90, a key enzyme in steroidal saponin biosynthesis, revealed differential regulation: mild upregulation by PP1, slight downregulation by PP2, and strong suppression by the highly virulent PP3, suggesting a trade-off between pathogenic stress intensity and diosgenin biosynthetic gene expression. These findings highlight the dualistic role of Colletotrichum as both a pathogen and a potential metabolic elicitor, demonstrating that moderate biotic stress can activate specialized metabolite pathways in D. composita. This study offers the first comprehensive link between anthracnose severity, CYP90 regulation, and diosgenin biosynthesis, providing novel insights for leveraging pathogen-induced elicitation in plant metabolic engineering and sustainable pharmaceutical crop production.