Bio-efficacy of a chitosan based elicitor onAlternaria solaniandXanthomonas vesicatoriainfections in tomato under tropical conditions

Abstract

With increasing problems of decreased efficacy, toxicity and environmental degradation due to the use of chemical fungicides, there is urgent need for developing alternative strategies for managing crop diseases. One approach currently being explored is the application of safe organic-based compounds to prime the defence systems of plants in order to prevent or limit infections by pathogens. Chitosan, a deacylated derivative of chitin, is one of the compounds known to promote plant defence and growth, but the mechanisms by which it is able to do so are still unclear. This study investigated the ability of a commercial chitosan extract (Armour-Zen®) to reduce disease incidence and induce the production of enzymes and expression of marker genes involved in plant defences for two important tomato pathogens, Alternaria solani and Xanthomonas vesicatoria. Foliar spray applications of the chitosan extract significantly reduced the incidences of both diseases in greenhouse and field grown tomato plants and also displayed a positive effect on growth and yields of tomato fruits. Chitosan-treated plants recorded elevated levels of defence enzymes and upregulation of the PIN II marker gene for defence signalling pathways when compared to the control. It was therefore proposed that chitosan would able to provide broad-range protection through induced systemic resistance mechanisms.