The accumulation of phenolic compounds and increased activities of related enzymes contribute to early defense against walnut blight

Abstract

Xanthomonas arboricola pv. juglandis (Xaj) is the causal pathogen of walnut blight. This work evaluates the correlations between selected biochemical responses to Xaj and the degree of blight sensitivity in ten genotypes. Activity of superoxide dismutase (SOD), peroxidase (POX), l-phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO), and content of phenolic compounds and malondialdehyde (MDA) significantly increased in all walnut genotypes after inoculation by Xaj while Catalase (CAT) activity varied between genotypes. Genotype's blight sensitivity was correlated with relative increases in phenolic compound content and PAL, PPO and POX activity at the initial stage of inoculation. The results show both similarities and distinct features in defense response in genotypes, suggesting that the metabolism of phenolic compounds may play a more important role in initial stages of inoculation than originally thought.