H. Bouzar

Systematic analysis of xanthomonads (Xanthomonas spp.) associated with pepper and tomato lesions.

The taxonomy and evolutionary relationships among members of the genus Xanthomonas associated with tomato and pepper have been a matter of considerable controversy since their original description in 1921. These bacteria, which are a major affliction of tomato and pepper crops in warm and humid regions, were originally described as a single species, but subsequent research has shown the existence of at least two genetic groups differentiated by physiological, biochemical and pathological characteristics. This work synthesizes the findings from several approaches, including pathogenicity tests, enzymic activity, restriction fragment analysis of the entire genome, DNA-DNA hybridization and RNA sequence comparisons based on a 2097 base sequence comprising the 16S rRNA gene, the intergenic spacer located between the 16S and 23S rRNA genes and a small region of the 23S rRNA gene. Within the group of xanthomonads pathogenic on pepper and tomato four distinct phenotypic groups exist, of which three form distinct genomic species. These include Xanthomonas axonopodis pv. vesicatoria (A and C group), Xanthomonas vesicatoria (B group) and Xanthomonas gardneri (D group). On the basis of phenotypic and genotypic differences between A- and C-group strains, the C strains should be considered as a subspecies within Xanthomonas axonopodis pv. vesicatoria.

Two genetically diverse groups of strains are included in Xanthomonas campestris pv. vesicatoria.

Two genetically diverse groups of strains were identified among cultures of Xanthomonas campestris pv. vesicatoria isolated from plants with bacterial spot of pepper and tomato. Group A strains do not pit pectate gels or hydrolyze starch, whereas group B strains are strongly positive for these reactions. Group A strains cause a hypersensitive reaction in plants of tomato breeding line Hawaii 7998, but group B strains do not. Other differences between the two groups of strains were discovered in tests for utilization of carbon compounds, serology, fatty acid profiles, silver-stained protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels, and DNA restriction enzyme digestion profiles. The levels of DNA homology between strains belonging to the same group were more than 74%, but the levels of DNA homology between strains belonging to different groups were less than 46%. The two groups of strains have different genetic backgrounds, but cause essentially the same disease of tomato and pepper.

A third tomato race of Xanthomonas campestris pv. vesicatoria

Strains of Xanthomonas campestris pv. vesicatoria were isolated from several tomato fields in Florida that differed from tomato race 1 (T1) strains commonly found in Florida. The strains produced a compatible reaction on tomato genotype Hawaii 7998 (H7998), were amylolytic and pectolytic, and were classified originally as T2 strains. However, these strains produced a rapid hypersensitive response when infiltrated into the tomato genotypes Hawaii 7981 (H7981), PI 126932, and PI 128216, whereas T2 strains produced a compatible reaction. In an experiment where electrolyte leakage was determined in leaflets of tomato cv. Bonny Best (compatible with all tomato strains), H7998 (resistant to T1 strains), and the two PIs, a member of these new strains induced a rapid hypersensitive response in the three tomato genotypes, whereas a T2 strain did not. After low concentrations of bacteria were infiltrated into the mesophyll of leaflets of PI 126932, PI 128216, H7998, and cv. Walter (compatible with all tomato strains), internal populations of the amylolytic, pectolytic Florida strain were reduced when tested in the first two genotypes but not in the latter two genotypes. Populations of the T1 strain were reduced only in H7998. These new strains are designated tomato race 3 (T3). When the T3 strains were compared with a representative group of T1 and T2 strains by fatty acid analysis and carbon substrate utilization patterns, the new T3 strains clustered distinctly from representative T1 and T2 strains. The evidence suggests the T3 strain is a recent introduction to Florida. An amylolytic, pectolytic strain isolated from seed grown in Thailand reacted similarly to the T3 strains on the tomato differentials. It also clustered with the T3 strains in the fatty acid and carbon substrate utilization dendrograms

Evidence for the preemptive nature of tomato race 3 of Xanthomonas campestris pv. vesicatoria in Florida

ABSTRACT Until recently, tomato race 1 (T1) of Xanthomonas campestris pv. vesicatoria was the only race causing bacterial spot of tomato in Florida. In 1991, tomato race 3 (T3) was first identified in 3 of 13 tomato production fields surveyed. By 1994, T3 was observed in 21 of 28 fields and was the only race identified in 14 fields. In field studies, tomato genotypes with resistance to either T1 or T3 or susceptibility to both were co-inoculated with strains of both races. Lesions on 10 plants in each of three replications for each genotype were sampled three times during the experiment; bacterial isolations were made from each lesion, and tomato race identifications were made for each strain. At the third sampling date, T3 was isolated from 97% of the lesions on the susceptible genotype Walter and the T1-resistant genotype Hawaii 7998, while T3 was isolated from 23% of the lesions and T1 from the remaining 77% on the T3-resistant genotypes PI 128216 and PI 126932. In surface population studies done in growth rooms, suspensions of T1 and T3 were applied alone and in combination to the leaf surfaces of susceptible and resistant genotypes. T1 populations were reduced more than 10-fold when applied in combination with T3, compared with populations that developed when T1 was applied alone. T3 populations were not affected when applied in combination with a T1 strain. In greenhouse studies with the T3-resistant genotype Hawaii 7981, disease was significantly reduced in plants inoculated with T3 in combination with T1, compared with plants inoculated with T1 alone. These results clearly demonstrate the competitive nature of T3 in the presence of T1 and help explain the emergence of T3 as a prevalent race in Florida.

The chrysopine family of amadori-type crown gall opines

Abstract Crown gall tumours induced by four groups of Agrobacterium tumefaciens isolates, derived from galls from four different locations in North and South America and Europe, were found to contain mannityl opine-related metabolites derived from condensation of glucose with glutamine followed by Amadori rearrangement. The opines were characterized spectroscopically as N- (1′-deoxy- d -fructos-1′-yl)-5-oxo- l -proline , N α - (1′-deoxy- d -fructos-1′-yl)- l -glutamine and its spiropyranosyl lactone, chrysopine. Tumours induced by A. tumefaciens strain 2788 and by Ficus strains also contained nopaline, while those induced by A. tumefaciens K224, K289 and Chry9 contained l , and an unidentified opine, pseudo-nopaline.