ACTINIDIA IN CHINA: NATURAL DIVERSITY, PHYLOGEOGRAPHICAL EVOLUTION, INTERSPECIFIC GENE FLOW AND KIWIFRUIT CULTIVAR IMPROVEMENT

The genus Actinidia has a remarkably wide geographic distribution in eastern Asia, with most taxa in south central and southwest China. Currently, 76 species and about 125 taxa are recognized within the genus. Natural genetic variation ranging from morphological traits to DNA level is briefly discussed: morphological variation of the most important fruit characteristics, nutritional value and flavour; gender variation of phenotype/genotypes; intra- and intertaxal ploidy variation; and heterozygosity as revealed by molecular markers. Infrageneric subdivision of Actinidia remains unresolved. Molecular approaches strongly suggest that the current subdivision of Actinidia is not natural and that substantial revision is needed. Although the Leiocarpae appears to be monophyletic, the other three traditional sections seem artificial. Molecular studies combined with fieldwork and analyses based on morphological characteristics indicate that relationships between the groups of Actinidia taxa are more easily understood if geographic distributions are also considered. Cluster analysis dendrograms and strict consensus trees based on morphological characters and DNA markers associated many Actinidia species into geographic groupings corresponding to north China, the Yangzi River Valley, southeastern China, southern China, and southwestern China. Probably, Actinidia should be divided into two sections Leiocarpae and Maculatae, the latter then being further divided into four series containing taxa from the Yangzi Valley and from the three southern parts of China. This may help resolve the delimitation of many species within Actinidia. Large-scale field sampling in areas of China with sympatric species (and, presumably, interspecific hybrids) has allowed investigation of interspecific gene flow among important taxa such as A. callosa var. henryi, A. chinensis, A. chrysantha, A. deliciosa, A. eriantha, A. fulvicoma var. lanata and A. latifolia. High interspecific gene flow was found between species and many common alleles occurred between species. It is likely that recurrent polyploidization combined with frequent hybridization amongst sympatric species has resulted in a reticulate evolutionary structure in the genus.