Caracterização de subamostras de tomateiro do BGH-UFV, quanto a resistência a begomovírus e análise da população viral em condições de campo

• Autor(a) principal: González Aguilera, Jorge
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/1337
• topic: Ty-2; Ty-3; Peruvianum; S. Lycopersicum; Estrutura genética; Geminivirose; Ty-2; Ty-3; Peruvianum; S. Lycopersicum; Genetic structure; Geminivirus; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA::MELHORAMENTO VEGETAL

The begomoviroses transmitted by whitefly (Bemisia tabaci) are among the main causes of losses in tomato in Brazil. To avoid damage and losses in tomato, it has been used resistant cultivars and hybrids, most of them carrying only the Ty-1 gene that provides tolerance to begomovirus in the country. In the world, the genes Ty-1, Ty-2 and Ty-3, and recently Ty-3a allele, and the genes Ty5 and Ty4 have been used in crop improvement programs. Ninety-four tomato accessions from the Vegetables Germplasm Bank of the Federal University of Viçosa (BGH-UFV) were evaluated under greenhouse and field conditions for resistance to bi segmented begomovirus present in Brazil, inoculated by biobalistic and via natural infection. Visual evaluations of symptoms (AVS) and confirmation of viral infection (IVC) by means of non-radioactive hybridization were performed at 15, 30 and 45 days after inoculation (DAI) under greenhouse conditions and 60 days after transplanting (DAT) under field conditions using a rating scale to quantify the AVS characteristic. Based on the percentage of infected plants at 45 DAI under greenhouse and at 60 DAT under field conditions, it was evaluated the incidence of the disease (ID). From the specific primers for genes Ty-2 and Ty-3, fragments were amplified by PCR to confirm the presence or absence of alleles of the genes evaluated in the accessions. The analysis of the complete sequence of nucleotides of the DNA-virus detected in the field indicated to be the Tomato severe rugose virus (a complex of species of begomovirus infecting tomato in Brazil). The sequences obtained were used for comparisons with previously described begomoviruses in phylogenetic and recombination analysis. The genetic structure and neutrality tests of ToSRV population showed genetic variability compared with other populations that had already been described in Brazil, showing negative values of neutrality which suggests the occurrence of negative selection (purifying) or a recent population expansion. As a result of the amplifications, it was identified the presence of markers related to allele Ty-2 gene in heterozygous in the accession BGH-6881 and the allele Ty-3 gene in three accessions (BGH-6878, BGH-6881 and BGH-6897). Based on the results of the ANOVA on the evaluations under greenhouse and field conditions, it was observed that the variables scores of visual symptoms was highly significant (P < 0.01) to differentiate all genotypes in both experimental conditions and at different intervals of evaluation. The accessions were divided into two groups by the Skott & Knot test. High Pearson correlations (&#961;) were found between visual data and viral infection (0.67 under greenhouse environment and 0.60 in the field). By the different behavior of the accessions in both experimental conditions, it was concluded that under greenhouse environment, the best results were found in the accessions BGH- 2144, BGH-2150, BGH 6878 and BGH-6881 and, under field conditions, in the accessions BGH-2080 and BGH-6881, all of them with low incidence and few geminivirus replication levels. The good performance of the accession BGH-6881 can be attributed to the presence of allele Ty-2 and Ty-3 genes, but compared to other accessions carrying the allele Ty-3 gene, it can be stated that the allele Ty-2 gene was responsible for the resistance to ToYSV obtained in greenhouse and to ToSRV in the field, or the combination of two genes that favor the response of the accession to begomoviruses. Considering the responses in both experimental conditions, the variables, the incidence of the disease and the presence of genes Ty-2 and Ty-3, it can be conclude that the accessions BGH-2080 and BGH-6881 are recommended as promising germplasm to be used in breeding programs because of their performance under greenhouse and field conditions, and can serve as basis for the production of crops better resistant to geminivirus in Brazil. The presence of ToSRV in the field and the confirmation of recombination events turn it possible to say that the constant monitoring of the evolution of the virus populations in the field will enable to design future strategies of control and epidemiology of begomoviruses in the main tomatoproducing regions in Brazil.