Pollen morphology of Actinidia and its systematic significance

There exist many taxonomic uncertainties in the genus Actinidia Lindl. as to the circumscription of sections and treatment of closely related species because of natural interspecific crossing. Little has been attempted to use micromorphological characters to address the problems. Pollen morphology of 21 species, 6 varieties and 4 interspecific hybrids (F-1) of the genus Actinidia was studied using SEM. A detailed description of the pollen grains was presented and a key to the species of the genus was given based on the pollen morphology observed. The results were summarized as follows: (1) The pollen grains are mainly prolate to subspheroidal in shape, and there were less distinct interspecific differences in the shape than those in size and ornamentation. (2) Most species introduced from the wild have three colporate apertures rather than three colporoid apertures as previously reported, the reason for which could be presumed that the pollen materials observed were harvested from specimens collected from different places with different habitats and that the plants might have undergone various crossings in the wild. (3) The pollen grains of interspecific hybrids were hollow and infertile, which may be due to the different ploidy levels between the parental species, a phenomenon common in the genus Actinidia. (4) The pollen of cultivated staminate varieties was compared with that of the wild types, and the ornamentation became finer than that of the later ones. This characteristic was presumed to be an important evolutionary trait beneficial to pollination in dioecious. plants, a phenomenon which is worthy of further study. (5) The pollen size of male plant individuals is found to be somewhat correlated with the fruit size, a phenomenon which may be helpful for early selection of hybrids.