2018 ASHS Annual Conference

Apple (Malus × domestica Borkh.) exhibits gametophytic self-incompatibility (GSI), which necessitates cross-pollination to achieve desired fruit and seed set in commercial orchards. The GSI mechanism is controlled by the multi-allelic S locus which harbors genes encoding pollen- and pistil-part determinants. In the pistil, S-RNases are expressed and are cytotoxic to incompatible pollen carrying S alleles identical to the seed parent, whereas pollen carrying S alleles differing from a seed parent are able to detoxify the S-RNases and inhibit degradation. Because the apple industry relies on consistent pollen viability it is imperative that pollinizer varieties produce cross-compatible pollen. In this study, the S-RNase gene was used as a target to determine the S-genotypes of over 30 crabapple varieties currently under evaluation for use as apple pollinizers. Polymerase chain reaction (PCR) methods using allele-specific primers in combination with consensus PCR and restriction fragment length polymorphism (RFLP) methods were used to determine S-haplotypes. Novel S-RNase sequences were characterized and submitted to the National Center for Biotechnology Information GenBank database, and molecular identification methods were developed. The results of this work serve to inform pollinizer-cultivar compatibility, and the methods developed aim to supplement future S-genotyping work.