Inheritance of resistance to bacterial spot in tomato

A herança da resistência do tomateiro (Lycopersicon esculentum) à mancha-bacteriana (Xanthomonas campestris pv. vesicatoria, raça T2) foi estudada, em condições de campo, cruzando-se os genótipos resistentes 'Ohio 8245' e 'Hawaii 7998' com os genótipos suscetíveis 'CNPH 401-08' e 'CNPH 416.81.01.02', em um esquema dialélico desconsiderando-se os recíprocos. Foram obtidas cinco famílias, cada uma constituída por seis gerações: Genitor1, Genitor2, F1, F2 e os retrocruzamentos (RC1 e RC2). A família 'Ohio 8245 ' Hawaii 7998' apresentou menor média para severidade da doença, seguida por 'Hawaii 7998 ' CNPH 416.81.01.02' e 'Ohio 8245 ' CNPH 416.81.01.02', as quais, apresentaram maiores estimativas de herdabilidade e de predição de ganho por seleção. Em todas combinações, a herança da resistência genética à mancha-bacteriana foi do tipo quantitativa, com estimativa do número de genes variando de quatro a oito genes, conforme a família analisada. Foi observada segregação transgressiva nas famílias 'Ohio 8245 ' CNPH 401-08', 'Hawaii 7998 ' CNPH 401-08' e 'Hawaii 7998 ' CNPH 416.81.01.02'. Os efeitos gênicos foram do tipo aditivo para todas as famílias e os dados ajustados ao modelo aditivo-dominante, com o componente aditivo apresentando maior magnitude.The inheritance of resistance to bacterial spot (Xanthomonas campestris pv. vesicatoria, race T2) in tomato (Lycopersicon esculentum) was investigated in a field trial. The genotypes 'Ohio 8245' and 'Hawaii 7998' (resistant), 'CNPH 401-08' and 'CNPH 416.81.01.02' (susceptible) were crossed in a diallel scheme without reciprocals. Each cross was labeled as one family, represented by six different generations: Parent1, Parent2, F1, F2 and Backcrosses to parents (BC1 and BC2). The family 'Ohio 8245 ' Hawaii 7998' presented the lowest disease severity, followed by the family 'Hawaii 7998 ' CNPH 416.81.01.02' and by the family 'Ohio 8245 ' CNPH 416.81.01.02'. These last two families showed both higher broad and narrow sense inheritability estimates and the highest prediction of selection gain. The resistance was found to be quantitative, with four to eight genes involved, depending on the family. Transgressive segregation was observed in the 'Ohio 8245 ' CNPH 401-08', the 'Hawaii 7998 ' CNPH 401-08' and the 'Hawaii 7998 ' CNPH 416.81.01.02' families. The relevance of the additive effects was observed and for all the families the data fitted to additive-dominant model, with the additive component showing greater magnitude

Xanthomonas cynarae shares its host range with a closely related species, Xanthomonas gardneri

International audienceMultilocus sequence analysis for xanthomonads indicated a very close relationship between Xanthomonas gardneri, a tomato and pepper pathogen, and Xanthomonas cynarae, an artichoke pathogen. Whole-genome comparisons of representative strains from the two species revealed that the average nucleotide identity between the two species was above the threshold of 95-96%, and the two species could be merged into a single species. The type-III secretion systems of the two species were nearly identical, with minor differences in two genes. Furthermore, comparison of the type-III effector profiles showed high similarity. Given the close relationship between the species, we speculated that the two organisms might cross-infect. Inoculation of X. gardneri into artichoke resulted in a moderate disease reaction, although the disease on the bracts was very weak. Furthermore, following infiltration of leaves, X. cynarae reached significantly higher internal populations than X. gardneri. Infiltration of both species into pepper showed that the two species grew equally well and caused typical bacterial spot lesions. However, infiltration of X. cynarae at high concentration into tomato leaflets resulted in a hypersensitive reaction (HR). We have identified a unique gene associated with this HR and created a deletion mutant of this gene to determine whether this is the host-limiting factor. The mutant strain elicited an HR, indicating the presence of at least one additional factor in X. cynarae that limits its ability to colonize tomato

Molecular characterization of Xanthomonas strains responsible for bacterial spot of tomato in Ethiopia

Bacterial spot of tomato (BST) is a major constraint to tomato production in Ethiopia and many other countries leading to significant crop losses. In the present study, using pathogenicity tests, sensitivity to copper and streptomycin, and multilocus sequence analysis (MLSA), we identified a diverse group of Xanthomonas strains isolated from central Ethiopia. None of the strains were sensitive to copper or streptomycin. Multilocus sequence analysis was used to compare Ethiopian strains with representative Xanthomonas strains from a worldwide collection based on DNA sequences of six housekeeping genes (lacF, lepA, gyrB, fusA, gltA and gapA) and hrpB genes.Phylogenetic analysis of the concatenated sequences showed that X. gardneri, X. vesicatoria andX. perforans were associated with BST in Ethiopia, whereas Xanthomonas euvesicatoria was absent from the Ethiopian sample. There was no genetic diversity among the isolated strains belonging to X. gardneri and X. perforans. However, two X. vesicatoria haplotypes were identified indicating at least two different sources of introduction of X. vesicatoria to Ethiopia. All of the X. perforans strains were only pathogenic on tomato and were T3 strains with the exception of one identified as tomato race 4 (T4). The X. gardneri and X. vesicatoria strains were tomato race 2 (T2), but were variable in pepper race determinations indicating variation in effectors among strains

Herança da Resistência à mancha-bacteriana em tomateiro.

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