Genetic dissection of the natural dry-on-vine (NDOV) trait in grapevine

Abstract

The impact of mechanized raisin harvesting has been positive in terms of reducing crop losses due to the development of cultivars that exhibit the natural dry-on-vine (NDOV) trait in grape germplasm. However, while drying rates of specific genotypes are being determined and cultivars are being released, the genetic components influencing the NDOV trait are not yet known. A deeper understanding of genetic mechanisms influencing NDOV will enable scientists to develop tools for breeding applications, such as molecular markers for seedling selection, and allow the formulation of strategies for the further study of NDOV and its biochemical basis, which may provide insights for agricultural management practices. Previous genetic mapping attempts of the NDOV trait using distinct phenotypic data were unsuccessful. A study in tomato demonstrated that the gene Cpw1 affects fruit cuticle leading to fruit dehydration on the plant. Hence, Cpw1 was selected as a potential candidate underlying the NDOV phenotype in grapevine. By using the grapevine genome reference sequence, two loci were identified as having high homology to tomato Cpw1, one on chromosome 3 and another on chromosome 18, the latter having the higher homology and therefore being named VviCpw1. Sequences of these loci were retrieved from the genome sequences of ‘Thompson Seedless’, ‘Pinot Noir’, ‘Flame Seedless’, ‘Cabernet Sauvignon’ and Vitis cinerea B9 and used for multiple sequence alignments for homology quantification and identification of putative polymorphisms. The DNA sequence of VviCpw1 was cloned from the NDOV raisin cultivar ‘Sunpreme’ and introduced into tomato to verify function. In addition, screening for polymorphisms in raisin-related germplasm, with and without the NDOV trait, is underway using AmpSeq, while obtaining supporting phenotypic data from NDOV-segregating germplasm. Studies on cuticle features are also envisioned. Results from this study will enable the development of tools and a body of knowledge for the further understanding of the NDOV trait in grapevine.