Blister blight disease, caused by an obligate biotrophic fungal pathogen, Exobasidium vexans Massee is posing a serious threat for
tea cultivation in Asia. As the use of chemical pesticides on
tea leaves substantially increases the toxic risks of
tea consumption, serious attempts are being made to control such pathogens by boosting the intrinsic natural defense responses against invading pathogens in
tea plants. In this study, the nature and durability of resistance offered by
chitosan and the possible mechanism of
chitosan-induced defense induction in Camellia sinensis (L.) O. Kuntze plants against
blister blight disease were investigated. Foliar application of 0.01%
chitosan solution at 15 days interval not only reduced the
blister blight incidence for two seasons, but also maintained the induced expressions of different defense related
enzymes and total
phenol content compared to the control. Defense responses induced by
chitosan were found to be down regulated under
nitric oxide (NO) deficient conditions in vivo, indicating that the observed
chitosan-induced resistance is probably activated via NO signaling. Such role of NO in host defense response was further established by application of the NO donor,
sodium nitroprusside (SNP), which produced similar defense responses accomplished through
chitosan treatment. Taken together, our results suggest that increased production of NO in
chitosan-treated
tea plants may play a critical role in triggering the innate defense responses effective against plant pathogens, including that causing the
blister blight disease.