Screening and Biochemical Studies on Grape Genotypes for Powdery Mildew Infection under Sub-Tropical Conditions

Abstract

Thirty two grape genotype (12 parents and 20 hybrids) were evaluated for natural incidence of powdery mildew during 2012 and 2013 during the peak disease incidence in vineyard and by artificial inoculation of leaves. Leaves were sampled during April (healthy phase) and first week of November (peak disease occurrence) for estimation of different biochemical parameters, namely, total phenols, total chlorophyll, total sugars, malondialdehyde (MDA) content, peroxidase (POD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) activities. Vitis parviflora and Male Hybrid were rated as extremely resistant (DSI = 0.37) and highly resistant (DSI = 7.25), respectively, while, Hybrid Seedless was rated as extremely susceptible (DSI = >85) type. The resistant genotypes had higher phenols, coupled with higher POD, PPO and PAL activities in both healthy and diseased leaves. Negative correlations were estimated for DSI and biochemical parameters like total phenols (r =-0.768**), POD (r =-0.682**), PPO (r =-0.665**) and PAL (r =-0.706**). Positive correlations were reported among DSI and MDA content (r = 0.753**) and total sugars (r = 0.628**). Hence, these parameters can be employed as biochemical markers for screening of grape germplasm against powdery mildew.