Screening of cucumber genotypes against downy mildew disease and its relationship with biochemical parameters

摘要

Abstract Downy mildew caused by Pseudoperonosporacubensis (Berk. and Curt.) Rostow, is an important disease of cucumber in the Gangetic plains of eastern India. It reduces the effective photosynthetic leaf area which leads to significant yield loss. Among the management strategies available for this disease, host plant resistance is considered to be the most suitable one. To identify resistant sources against the disease, 11 cucumber genotypes were screened under open field conditions. The role of biochemical parameters viz., peroxidase (POD), polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL) activities, total phenol (TP), total sugar (TS) and total protein (TP) contents of leaves, in imparting resistance against downy mildew in cucumber was also evaluated. None of the genotypes exhibited resistant reaction against downy mildew pathogen. However, two genotypes Padmini (10.30%) and Debstar (13.34%) showed lowest disease severity and were categorised as moderately resistant to this pathogen. Moderately resistant and susceptible genotypes exhibited significant differences in the biochemical parameters evaluated. Higher enzymatic activities and phenol and protein contents were observed in moderately resistant varieties in comparison to the susceptible varieties both before and after inoculation. All the biochemical parameters, except total sugar content, increased significantly after inoculation in resistant varieties as compared to susceptible varieties. It can be inferred that pathogen infection led to increased activities of POD, PPO, and PAL as well as higher phenol and protein contents, which in turn might be responsible for reduced sporangial multiplication and pathogen inhibition. The findings of the study indicate that the evaluated biochemical parameters might be used as reliable biochemical markers for early selection of resistant genotype against downy mildew. The moderately resistant genotypes identified in this study could also be utilized as donor parents in breeding programs aimed at enhancing cucumber resistance to downy mildew disease.