ASHS 2024 Conference

Muscadine grapes (Muscadinia rotundifolia) are perennial vines grown commercially in the Southeast United States for the fresh market and as wine and juice grapes. Two highly sought-after traits in fresh market muscadine cultivars are stenospermocarpic seedlessness and perfect-flowered vines. However, the genetic disparity between Vitis and Muscadinia subgenera, coupled with differing chromosome numbers (Vitis=38 chromosomes, Muscadinia=40 chromosomes), presents challenges in introgression of stenospermocarpy from V. vinifera to M. rotundifolia. Although conventional breeding has introduced stenospermocarpy into M. rotundifolia, no molecular markers for this trait have been validated in muscadines. Recently, two Kompetitive Allele Specific PCR (KASP) markers targeting candidate genes for male sterility (VviINP1) and stenospermocarpy (VviAGL11) in V. vinifera have shown promise. Sequence comparisons with published V. rotundifolia genomes suggest that these markers might be effective across diverse Vitis, Muscadinia, and wide hybrid germplasm. In this study, we validated the predictive ability of KASP markers for flower sex and stenospermocarpy across thirteen Vitis x Muscadinia hybrid seedling populations and 191 diverse genotypes. In 2023, 891 seedlings were evaluated for seedlessness, with an additional 214 seedlings assessed for flower sex. Furthermore, 191 diverse accessions underwent evaluation for both flower sex and seedlessness. Of the 891 seedlings, 66 were seedless, 490 were seeded, and 335 could not be phenotyped due to fruit absence. Among the 214 seedlings assessed for flower sex, 88 were perfect, 106 were female, and 20 could not be phenotyped due to flower absence. The stenospermocarpy marker accurately predicted 771 of 783 seedlings and diverse material, while the flower sex marker matched 366 of 383 seedlings and diverse accessions. Discrepancies between marker predictions and observed phenotypes may be due to human error or pollen sterility. Notably, most fruitless seedlings were predicted to be stenospermocarpic, indicating potential issues with partial sterility or cold hardiness in seedless hybrids. We intend to reevaluate the populations for flower sex and seedlessness in summer 2024 to address discrepancies. Overall, the KASP markers developed in V. vinifera exhibited excellent predictive ability across diverse germplasm, offering valuable insights for muscadine breeding programs.