Sex-linked molecular markers for two cold-hardy kiwifruit species, Actinidia arguta and A. Kolomikta

Abstract

Developing improved fruiting varieties of kiwiberry (Actinidia arguta) and other species of cold-hardy kiwifruit (e.g., A. kolomikta) is highly resource-inten-sive due to the dioecy, extended juvenile phase (3–5 years), and vegetative vigor of these woody, vining species. The ability to identify gynoecious plants at the seedling stage is therefore desired as a means of increasing the resource-use efficiency of breeding programs. In this study, sex-linked polymorphisms in both species were identified through reference-inde-pendent genotyping-by-sequencing (GBS) analysis; validated in independent populations; and converted into cost-effective, gel-based PCR markers appropriate for marker-assisted breeding programs. The marker for A. arguta, designed using male-allele-specific primers based on a SNP within a 157 bp GBS amplicon, exhibits perfect sex-linkage across a comprehensive set of kiwiberry germplasm currently available through the US nursery trade and the USDA’s National Plant Germplasm System (NPGS). By multiplexing conserved primers for a co-located internal 81 bp control amplicon, this male-specific marker was made effectively co-dominant, thereby enhancing scoring accuracy. Similarly, the 161 bp marker for A. kolomikta was designed with male-allele-specific primers based on a 3 bp indel within a 270 bp GBS fragment and exhibits perfect sex-linkage throughout the available A. kolomikta germplasm in North America. Both markers were validated in independent populations and are now being used for high-throughput sex-screening assays of seedling populations.