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.
Description:
A Thesis
Submitted to the Faculty of Agriculture,
Sher-e-Bangla Agricultural University, Dhaka
in Partial fulfillment of the requirements
for the degree of
MASTER OF SCIENCE (MS)
IN
PLANT PATHOLOGY
