Introgression Breeding and Cultivar Improvement In Genus Actinidia

The recent development of research and industry of Actinidia in China are well recognized, but future sustainable development of the world kiwifruit industry will largely depend on China's rich genetic resources and breaking-through approach of Actinidia breeding. With recent advances in studies of plant gene-flow dynamics and evolutionary mechanisms, introgression selection and breeding has increasingly become fundamental important for kiwifruit breeders and germplasm curators to develop new breeding strategy and to use plant genetic resources and sustainably improve the cultivars. The continuous variation of diploid, tetraploid, hexaploid and octoploid and reticulated ploidy variations within and among Actinidia specie is phenomena in nature. Extensive investigation of inter-specific boundary of different ploidy, inter-specific gene flow occurred widely across China in past 10 years has greatly enhanced our understanding of intra- and inter-specific ploidy variation and phenotypic selection. Frequent intra- and inter-specific hybridization and continuous intra-specific ploidy variation found in species overlapped areas in natural range suggested existence of natural hybrid zones that underpin the reticulate evolutionary pattern in genus Actinidia. Recent field survey in China revealed a well structured natural hybrid zone of A. chinensis var. chinensis and A. chinensis var. deliciosa in Wuling Mountains, as well as a number of overlapping areas of different species and polyploidy races across south-central China, which provide us a ideal natural settings to study gene flow dynamics and discover useful genes and/or genotypes by unraveling pattern of gene introgression among the wild populations. Moreover, rapid development of molecular genetic technology should allow Actinidia breeders to identify individual genotypes within the hybrid zone through a comprehensive approach by examining interaction of ‘gene - genotype - phenotype - environmental gradient’. This new introgression breeding approach will greatly facilitate direct selection from natural gene pools effectively and enhance genetic improvement, and integrate genetic introgression research into kiwifruit breeding for rapid genetic improvement of current cultivars.