Microbial Pathogenicity Research Group, Department of Biology, University of the West Indies, P.O. Box 64, Bridgetown, Barbados
The role of the avrBs1 avirulence gene of Xanthomonas campestris pv. vesicatoria in survival of the bacterium was investigated by testing two strains that differ in the structure and function of the gene in 37 different soil types of Barbados and detached leaf tissue of four pepper genotypes. One strain carried a mutation in the avrBs1 gene and lacked avirulence activity, while the other expressed wild-type avrBs1 activity. In 30 to 32 soil types and all leaf tissue tested, the mutant strain persisted longer and more abundantly than the wild-type strain over a 2- to 6-week period. During this time, the mutant strain generally replaced the wild-type strain completely in soil initially infested with a mixture of equal amounts of each strain and by a factor of 6.7 in similarly infested pepper leaves. Nine selected soil factors, namely pH, clay and cation content, and percent nitrogen, carbonates, carbon, K+, Na+, and Ca2+ did not affect bacterial survival significantly.
bacterial spot of pepper.