RESUMO
Disease-resistant potato cultivars with good tuber appearance and desirable agronomic traits are essential for meeting the demands of producers and the market. Attaining these cultivars is the focus of potato breeding programs whose aim is to benefit the productive chain. The purpose of this study was to estimate combining abilities and evaluate potato clones based on tuber appearance, yield, and resistance to the PVY and PVX viruses. Crosses between four commercial cultivars of potato with good tuber appearance were performed, using eight clones with proven resistance to PVY and PVX from the breeding program of UFLA. The clones obtained were evaluated for agronomic traits, tuber appearance, and the presence of both Ryadg and Rx1 alleles, which confer extreme resistance to the PVY and PVX viruses, respectively. The independent culling level method was used to select genotypes of commercial interest, as well as to estimate the combining abilities of the parents. We identified clones carrying the Ryadg and Rx1 alleles with agronomic traits suitable for the fresh market and for processing. The BRS Ana cultivar and CMA-399 and CMA-385 clones showed positive effects on general combining ability (GCA) for tuber yield, while the Monalisa cultivar showed positive effects on GCA for general tuber appearance.
Assuntos
Doenças das Plantas/genética , Potexvirus/genética , Potyvirus/genética , Solanum tuberosum/genética , Alelos , Cruzamento , Cruzamentos Genéticos , Resistência à Doença/genética , Genótipo , Imunidade Inata/genética , Fenótipo , Doenças das Plantas/virologia , Potexvirus/patogenicidade , Potyvirus/patogenicidade , Solanum tuberosum/virologiaRESUMO
Replication of Potato virus X (PVX) was reduced in transgenic protoplasts that accumulated wild-type coat protein (CPWT) of Tobacco mosaic virus (TMV) or a mutant CP, CP(T42W), that produced highly ordered states of aggregation, including pseudovirions. This reaction is referred to as heterologous CP-mediated resistance. However, protoplasts expressing a CP mutant that abolished aggregation and did not produce pseudovirions, CPT28W, did not reduce PVX replication. Similarly, in transgenic tobacco plants producing TMV CPWT or CP(T42W), there was a delay in local cell-to-cell spread of PVX infection that was not observed in CP(T28W) plants or in non-transgenic plants. The results suggest that the quaternary structure of the TMV CP regulates the mechanism(s) of heterologous CP-mediated resistance. Similarly, transgenic protoplasts that produced PVX CP conferred transient protection against infection by TMV RNA. Transgenic plants that accumulated PVX CP reduced the cell-to-cell spread of infection and resulted in a delay in systemic infection following inoculation with TMV or TMV RNA. Heterologous CP-mediated resistance was characterized by a brief delay in systemic infection, whilst homologous CP-mediated resistance conferred reduced or no systemic infection.
Assuntos
Proteínas do Capsídeo/metabolismo , Nicotiana/virologia , Doenças das Plantas/virologia , Plantas Geneticamente Modificadas , Potexvirus/patogenicidade , Vírus do Mosaico do Tabaco/patogenicidade , Proteínas do Capsídeo/genética , Linhagem Celular , Potexvirus/genética , Potexvirus/metabolismo , Nicotiana/genética , Vírus do Mosaico do Tabaco/genética , Vírus do Mosaico do Tabaco/metabolismo , Replicação ViralRESUMO
Tobacco plants were transformed with the open reading frame 3 gene from Potato virus X (PVX) coding for the p12 protein. Although the transgenic plants exhibited a normal morphological aspect, microscopic examination revealed extensive alterations in leaf tissue structure. After being challenged with PVX, the transgenic plants showed resistance to PVX infection and formation of specific leaf symptoms consisting of concentric rings encircled by necrotic borders. These novel symptoms were accompanied by biochemical changes normally associated with the hypersensitive response (HR) and were absent in noninfected transgenic plants or in PVX-infected nontransgenic plants. No equivalent virus resistance was observed after inoculation with Tobacco mosaic virus or Potato virus Y, suggesting the presence of a specific resistance mechanism. Despite development of HR-like symptoms, systemic acquired resistance was not induced in PVX-infected p12 transgenic plants. No evidence of an RNA-mediated resistance mechanism was found.
Assuntos
Proteínas do Capsídeo , Nicotiana/genética , Nicotiana/virologia , Potexvirus/genética , Potexvirus/patogenicidade , Capsídeo/genética , Capsídeo/metabolismo , Genes Virais , Fases de Leitura Aberta , Doenças das Plantas/genética , Doenças das Plantas/virologia , Folhas de Planta/metabolismo , Folhas de Planta/virologia , Plantas Geneticamente Modificadas , Nicotiana/metabolismoRESUMO
The PVX coat protein (CP) is involved in many aspects of plant-virus interaction (virion morphology, plant symptoms, viral pathogenesis and virulence, and genomic RNA accumulation). Different virus strains have been distinguished according to their compatibility with the host resistance genes Nx, Nb, and Rx. Substitution of the Thr 122 on the CP with a Lys in PVX strain HB has been shown to affect the response of potato cultivars with the Rx resistance gene. In PVX DX the avirulence determinant for the Nx gene has been localized in the Gln 78 of the coat. PVX strain MS, like PVX HB, is able to overcome the Rx, Nx, and Nb genes. Sequencing of the CP gene of PVX MS (EMBL accession number Z34261) shows that it has a Thr in codon 122 and a Gln in codon 78. These results suggest that, in addition to the coat protein gene, other regions of the viral genome are involved in the pathogenicity.