Defense-related candidate genes in Vitis species

Disease-resistant Vitis species defend themselves against pathogens by employing a variety of defense strategies, such as hypersensitive response and ontogenic resistance. Although the molecular events of defense pathways are still poorly understood in Vitis species, quantitative trait locus (QTL) and segregation analyses have demonstrated that resistance to some diseases is a monogenic trait, whereas resistance to others is a polygenic trait. Molecular marker-based mapping has located several QTLs for resistance to downy mildew, powdery mildew, and black rot in linkage groups. Numerous grapevine genes have been identified whose orthologues are known to play a role in disease resistance in other plants. Recently, resistance (R-) gene analogues sharing conserved domains with Pto, Xa21, and receptor-like kinases were identified in disease-resistant wild Vitis species. Several R-gene analogues were found to be tightly linked to a powdery mildew resistance locus in Muscadinia rotundifolia. Genes encoding defense-related transcription factors, proteins for the signal transduction, pathogenesis-related proteins, and enzymes in the synthesis of phytoalexin have also been isolated from Vitis species. These genes are promising candidates for improving disease resistance in susceptible grape cultivars. These discoveries corroborate the consensus that the sustainability of viticulture can be achieved by transferring genetic resources from disease-resistant Vitis species to V. vinifera-derived elite grape cultivars through the precision breeding and genetic engineering.