2019 ASHS Annual Conference

Gametophytic self-incompatibility (GSI) is a reproductive strategy that prevents self-pollination in many flowering plants, including rosaceous fruit trees. The GSI system in apple (Malus x domestica Borkh.) is regulated by a multi-allelic S locus, which consists of clusters of F-box genes (SFBB) that are expressed in the pollen and an S-RNase gene expressed in the pistil. In apple, the GSI system is prevalent, and most cultivars require cross-pollination to achieve desired levels of fruit set. To improve cross-pollination, growers plant pollinizer varieties into their orchard blocks on the basis of bloom phenology. However, in many cases, understanding of the degree of cross-compatibility between cultivar-pollinizer combinations is incomplete. To determine inter-cultivar compatibility, the S-RNase gene was used as a target for characterizing the S-genotypes of previously unreported apple cultivars and crabapples that could be potentially used as pollinizers. Additionally, some S-genotypes disputed in the literature were resolved in this project. The results of this work are intended to help apple growers identify cross-compatible pollen sources for optimizing orchard plantings and promoting consistent annual crop production.