Biochemical defense mechanism in rapeseed-mustard genotypes against Alternaria blight disease

Abstract

The present study deals with biochemical defense response in rapeseed-mustard genotypes infected with
Alternaria brassicae (Berk.) Sacc. causing blight at different growth stage. Three genotypes viz. Brassica
juncea cv. Varuna (susceptible), B. juncea cv. PAB-9534 (moderately resistant) and B. alba (tolerant)
were selected. The results revealed that all the genotypes showed variable disease severity. It was observed
that in all stages of pathogen infection, disease severity and characteristic symptoms were more prominent in
susceptible genotype than the other two. The biochemical analysis of leaves of different varieties of mustard
revealed that total phenol, o-dihydroxy phenol, total sugar, reducing sugar, chlorophyll content and flavonol
contents were observed to be more in resistant genotype (B. alba) than others. With progress of infection
total phenol, o-dihydroxy phenol and protein content increased in all three genotypes while the chlorophyll,
total sugar, reducing sugar and flavonol content decreased. The results indicated that factors conditioning the
host response to A. brassicae might be the outcome of complex biochemical changes operated in host
genotypes.