Host Susceptibility and Disease Mechanism of Chilli Bacterial Leaf Spot Disease, caused by Xanthomonas euvesicatoria

Plant disease resistance is crucial to sustainable agriculture. Chilli (Capsicum frutescens) is an
important crop which is consumed fresh or as a spice. Bacterial Leaf Spot (BLS), caused by the
bacterium Xanthomonas euvesicatoria, is a serious production problem for chilli. This study used
the pin prick method to assess virulence of six X. euvesicatoria isolates against two capsium
cultivars, Hugo and Warlock, which are known to be susceptible and resistant respectively.
Symptom expression was observed and the most virulent strain, BRIP62403, was selected to
screen plant reactions for a further 24 cultivars. DNA was extracted seven days after inoculation
and the number of bacteria present was estimated using qPCR targeting the pathogen. Using this
method, one cultivar was considered resistant, while 20 cultivars were intermediate and three
cultivars were susceptible. This method offers promise for early screening of cultivar susceptibility
for plant improvement programs.

Funding: Australia Awards Scholarship John Allwright Fellowship - ACIAR (Australian Centre for
International Agricultural Research)