Elucidation of defense-related biochemical mechanisms in clusterbean against Agrothelia rolfsii-incited stem rot

Cluster bean, a vital legume for arid regions, faces significant yield constraints from stem rot disease caused by the soil-borne fungus Agrothelia rolfsii. While the pathogen is known, a comprehensive understanding of the biochemical defense mechanisms it triggers in cluster bean remains limited. This study investigated the impact of A. rolfsii infection on key biochemical components—sugars, soluble proteins, and phenols—across three cluster bean varieties (RGC-936, RGC-1003, and RGC-1033). Biochemical analyses conducted 45 days after sowing revealed a significant shift in host metabolism induced by the pathogen. A consistent and significant depletion of carbohydrate reserves was observed, with total, reducing, and non-reducing sugars decreasing most markedly in the susceptible variety RGC-936. Conversely, the infection elicited a robust defense response, characterized by a significant accumulation of soluble proteins and phenolic compounds. The variety RGC-1033 exhibited the most pronounced induction of these defense biomarkers, with increases of 1.88 mg g⁻¹ FW in soluble protein and 0.10 mg g⁻¹ FW in total phenols. The results demonstrate that A. rolfsii infection disrupts primary carbohydrate metabolism while simultaneously activating the synthesis of defense-related proteins and phenolics. The varietal differences in the magnitude of these responses suggest a link between biochemical resilience and potential tolerance, providing crucial insights for developing stem rot-resistant cluster bean cultivars.