Assessment Of Genetic And Chemical Control Of Bacterial Spot In Barbados

Research conducted on the bacterial spot disease caused by Xanthomonas campestris pv. vesicatoria on tomato, bell pepper and hot pepper in Barbados assessed prospects for genetic and chemical control of the disease on the island. Race and chemical resistance profiles of the pathogen, effectiveness of deployment of bacterial spot resistance genes in the field and the genetic basis for pathogen population changes with respect to pathogenicity and sensitivity to copper bactericides were examined. Twenty-four races of X. campestris pv. vesicatoria, 20 of which were previously unreported on bell pepper and tomato in Barbados, were identified. Race specific host selection, mutation and exchange of genetic material are postulated to explain the evolution of the pathogen population in Barbados. The research also reported the disease on hot pepper for the first time, with the most abundant bacterial races isolated being capable of overcoming resistance conferred by most available bacterial spot resistance genes in bell pepper. Chemical resistance profiles of isolates of X. campestris pv .vesicatoria indicated that 18.3 and 78.1 percent of the population were resistant to copper and zinc, respectively. Differentially resistant bell pepper and tomato were shown to succumb to the disease at significantly lower frequencies than susceptible cultivars grown alongside them. Copper resistance of X. campestris pv. vesicatoria was generally associated with the presence of a 0.6-0.9 kb plasmid which was transferable between strains. Reversion from copper resistance to sensitivity occurred at high frequencies in the absence of copper. The successful management of bacterial spot will require a multi-faceted approach including deployment of mixtures of resistance genes and exploitation of the bactericide resistance status of individual pepper and tomato fields.