STUDY ON THE EFFECT OF SALT STRESS ON CITRUS CANKER CAUSED BY XANTHOMONAS AXONOPODlS PV. ClTRl AND EFFICACY OF SOME PHYTOHORMONES IN INDUCING RESISTANCE AGAINST THE DISEASE

Abstract

Citrus canker caused by Xanthomonas axonopodis pv. cirri (Xac) is currently the most prominent disease impacting world citrus production. A study was conducted to investigate the effect of salt stress on bacterial canker pathogen and the efficacy of some selected phytohonnones in inducing resistance against canker disease of citrus. The study was conducted during the period of January to December, 2015 in the experimental site of department of Plant Pathology at Sher-e-Bangla Agricultural University. The putative causal organism of citrus canker was identified as Xanthomonas axonopodis pv. cirri on the basis of morphological, biochemical and cultural features. Citrus plants were exposed to salt stress by irrigating with SO mM, 100 mM, 150 mM, and 200 mM salt concentration on weekly basis and inoculated with Xac. Abiotic stress influenced the defense response to pathogen and thus lesion number and size, disease incidence and severity were gradually increased with the increase of salt concentration. At the same time physiological performance of the . plant such as net assimilation rate, chlorophyll content, stomatal conductance and transpiration rate were increased while intercellular C02 concentration was decreased up to 30 days after inoculation (DAI) at 100 mM salt concentration. Beyond this range bacterial performance to modulate plant homeostasis was reduced. Application of five selected phytohonnones viz. salicylic acid (SA), jasmonic acid (lA), 3indoleacetonitrile (lAN), folic acid (FA) and nicotinic acid (NA) curtailed disease development. Among the chemicals SA showed the highest performance in case of increasing latent period and decreasing lesion number and size, disease incidence and severity followed by JA, IAN, FA and NA compared to control. None of these phytohonnones showed in-vitro antibacterial properties against Xac bacterium. SA treated plants showed the highest accumulation of endogenous total phenolic compound and potassium content in leaves cell followed by lA, INA, FA and NA compared to control. This provides evidence that the phytohonnones had the ability to induce resistance against bacterial canker pathogen.