Resistance of Cucumber Genotypes to Sphaerotheca fuliginea Causing Powdery Mildew: Biochemical and Histological Study

Abstract

Powdery mildew caused by Sphaerotheca fuliginea is a major foliar disease of cucumber, leading to reduced photosynthetic efficiency and significant yield losses under both field and protected cultivation systems. The present study evaluates the resistance of different cucumber genotypes to powdery mildew through biochemical and histological approaches. Genotypes were screened under natural and artificial inoculation conditions, and disease severity was recorded based on lesion development and fungal coverage. Biochemical analyses were conducted to quantify defense-related compounds, including phenols, flavonoids, peroxidase, polyphenol oxidase, and catalase activity. Results revealed significant variation in resistance levels among genotypes, indicating differential activation of defense mechanisms. Resistant genotypes exhibited higher accumulation of phenolic compounds and enhanced activity of antioxidant enzymes compared to susceptible ones. Histological studies showed restricted fungal penetration, reduced hyphal growth, and rapid host cell wall reinforcement in resistant genotypes, while susceptible genotypes supported extensive mycelial colonization and tissue disruption. Structural defense responses such as papilla formation, lignification, and callose deposition were more prominent in resistant genotypes, contributing to reduced disease progression. A positive correlation was observed between biochemical defense responses and reduced disease severity, highlighting the role of induced resistance mechanisms. The study demonstrates that both preformed and induced biochemical and structural defenses contribute to cucumber resistance against powdery mildew. Overall, the findings provide valuable insights into host–pathogen interactions and emphasize the importance of biochemical and histological traits in identifying resistant cucumber genotypes. These results can be effectively utilized in breeding programs aimed at developing powdery mildew-resistant cucumber cultivars for sustainable disease management in agroecosystems.