Powdery mildew pathogen [Erysiphe necator (Schw.) Burrill.] induced physiological and biochemical alterations in leaf tissue of grapevines (Vitis spp.).

Grapevine serves as a host for an array of pathogenic agents, among which powdery mildew (PM), a fungal disease, stands as a major threat under changing climate and erratic weather patterns. The study aimed to examine the physiological, biochemical responses and microscopic examinations of diverse grapevine genotypes including the 42 Vitis species to powdery mildew infection caused by Erysiphe necator (Schw.) Burrill. Significant reductions were observed in leaf gas exchange parameters like net photosynthetic rate (33.09 %) and transpiration rate (32.36 %) in the infected leaves of susceptible genotypes compared to resistant and moderate genotype groups. Susceptible genotypes had higher intercellular CO 2 concentration (4.01 %). Chlorophyll fluorescence analysis revealed a decrease in the maximum quantum efficiency of photosystem-II in PM-infected leaves across the genotype groups. Furthermore, PM infection led to a decrease in chlorophyll content, particularly in susceptible plants, along with a notable reduction in total chlorophyll (25.86 %) and total carotenoids (3.58 %) contents. The ascorbic acid/dehydroascorbic ascorbic acid ratio was observed to be increased by 50 % in the susceptible genotypes due to PM infection. The higher potassium content was registered in healthy leaves of resistant genotypes compared to PM infection stage. This clearly demonstrated the genotype-specific ability to withstand biotic stress. Antioxidant enzyme activities, including glutathione reductase (1.27-fold), polyphenol oxidase (1.15-fold), phenylalanine ammonia-lyase (1.02-fold) and peroxidase (1.21-fold), were enhanced in PM infected plants, suggesting the activation of different defence mechanisms against oxidative stress induced due to pathogen. Scanning electron microscopy revealed prominent differences in fungal hyphae growth between susceptible and resistant genotypes, which showed restricted tissue growth and host cell necrosis. [Display omitted] • This study elucidates the complex response of grapevine germplasm to PM infection, highlighting the genotype-specific differences in disease susceptibility and defense mechanisms. • Changes in different groups of genotypes revealed major alterations in secondary metabolites due to defence response of leaf tissue to E. necator. • Susceptible genotypes showed significant reduction in gas exchange parameters, chlorophyll fluorescence and chlorophyll content in infected leaves compared to the resistant genotypes. • Antioxidant activities were found to be enhanced in the infected plants, suggesting their role in the defence mechanisms against oxidative stress. • The AA/DHA ratio was observed to be increased by 50 % in the susceptible genotypes after PM infection resulting in altered redox state. [ABSTRACT FROM AUTHOR]