Races of Xanthomonas campestris pv. vesicatoria overcoming the gene Bs2 for bacterial spot resistance in pepper, prevalent on Capsicum chinense in Barbados and Grenada and weakly pathogenic on bell pepper and tomato in the field     

O'Garro  Gore  & Ferguson 《Plant pathology》1999,48(5):588-594

A total of 404 isolates of Xanthomonas campestris pv. vesicatoria , obtained from Capsicum chinense cv. West Indian Red grown in Barbados and Grenada, were differentiated into pathogenic races, and of these, 96 were tested also for selected taxonomic group phenotypes. The response of C. chinense to infection by several X. campestris pv. vesicatoria races and the contribution of races isolated from this cultivar to severity of bacterial spot of bell pepper and tomato were also investigated. P4T2, P5T2 and P6T2 were the predominant races of X. campestris pv. vesicatoria isolated from C. chinense grown in Grenada, whereas nine races (T1, P4, P6, P0T2, P1T2, P4T1, P4T2, P6T1 and P6T2) were isolated in Barbados. Race P4T2 comprised 46.0 and 71.4% of the isolates from Barbados and Grenada, respectively. The 96 isolates, all of which overcame resistance conferred by the gene Bs2 , shared taxonomic group B strain characteristics, including the presence of the β-protein band, positive amylolytic activity and inability to oxidize cis -aconitate. The C. chinense cv. West Indian Red was susceptible only to races of X. campestris pv. vesicatoria that can overcome Bs2 gene resistance. Of six such races identified in Barbados, only P4T1, P4T2 and P6T1 affected bacterial spot-susceptible bell pepper or tomato in the field, and they amounted to only 1.5–2.1% of each sample of isolates from these plant species. Moreover, they were confined to the smallest bacterial spot lesions. Bell pepper was most severely affected by combinations of races T1 with P3T2 and T2 with P0T1, and tomato by race T1 only and combinations of races P0T1 with P0T2 and P1T1 with P1T0, all of which prevailed in the field despite selection against them by C. chinense cv. West Indian Red.  相似文献   

Mutation in the avrBs1 Avirulence Gene of Xanthomonas campestris pv. vesicatoria Influences Survival of the Bacterium in Soil and Detached Leaf Tissue     

O'Garro LW  Gibbs H  Newton A 《Phytopathology》1997,87(9):960-966

ABSTRACT 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 Ca(2+) did not affect bacterial survival significantly.  相似文献