GENETIC MARKERS: THEIR TRANSFERABILITY AND USEFULNESS ACROSS ACTINIDIA

Actinidia deliciosa ‘Hayward’ and Actinidia chinensis ‘Hort16A’ are both successful commercial crops and high genetic similarity between the two has been shown through molecular markers. The genus consists in more than 70 species, which form a polyploid series from diploid (2x = 58) to octaploid (8x = 232). Species have diverse fruit and vine characteristics that are of interest to breeders; and molecular markers that are transferable across species could therefore offer greater efficiency in trait transfer for fruit improvement in breeding programmes. Microsatellites or simple sequence repeats (SSRs) are tandem repeats of 2-5 nucleotide bases found throughout the genome. EST-derived microsatellite markers were sourced from A. deliciosa and A. chinensis cDNA libraries made from various tissues at different stages of development. The markers were used in the construction of a genetic map in a selected family of A. chinensis and were found to be highly polymorphic. We evaluated cross-species amplification of 20 markers which were fully informative in the A. chinensis mapping population across 21 Actinidia species available in New Zealand. Polymorphism information content (PIC) values were calculated to measure the allelic content for 17 markers amplifying in diploid taxa. All 20 markers showed some level of species amplification, indicating that primer sites were conserved across species. 95% of markers amplified in the taxa Stellatae, 90% in Leiocarpae and 83% in Maculatae. In Strigosae, only one taxon was available and although 95% of the markers amplified, it may not be representative of the section. Sequence homology was observed in the region of the EST from which the marker was derived. It is concluded that EST-derived microsatellite markers show cross-species amplification and are potentially useful in breeding programmes. However, markers of interest would need to be tested individually for confirmation of functional homology across species.