Towards improved markers for molecular characterization in kiwifruit

Actinidia, a genus of kiwifruit, has 54 species, with the commercially dominant species being one with two subspecies: Actinidia chinensis var. chinensis and A. chinensis var. deliciosa. The global kiwifruit industry has used a single variety for decades, but in the last 20 years, new varieties have been introduced, with breeders and propagation rights concerned about protecting them from fraudulent use. The genome of A. chinensis var. chinensis ‘Red5’ was searched for perfect microsatellites with repeat motifs of no less than two to ten bases. Out of 216,456 possible perfect microsatellite loci, 82 were chosen to be spread across all 29 chromosomes. Twenty microsatellite loci with repeat motifs over two have been developed for the varietal characterization of kiwifruit. The markers consist of repeating motifs of at least three bases that suffer less from problems in interpreting electrophoretic profiles due to stuttering. A single amplification protocol valid for all loci was developed. The markers were tested on a sample of 100 genotypes that included diploid, tetraploid, hexaploid, and octoploid individuals. The selected markers were able to clearly discriminate all genotypes except for two clonal mutations. This indicates that the microsatellite loci are highly effective in distinguishing between different kiwifruit varieties, regardless of their ploidy level. The ability to accurately characterize kiwifruit genotypes using these markers can greatly benefit breeding programs and conservation efforts for this important fruit crop.