Ploidy Variation and Their Effects on Leaf and Stoma Traits of Water Yam (Dioscorea alata L.) Collected in Myanmar

抄録

Water yam (Dioscorea alata L.) is a tuber crop widely cultivated in the tropics and sub-tropics in Africa as well as in Asia. It is clonally propagated by tubers in conventional cultivation due to the difficulty in sexual reproduction. However, a wide intra-specific variation is observed in various phenotypic traits and in somatic chromosome numbers ranging from 30 to 80. The authors investigated the intra-specific variation of ploidy and the effects on the phenotypic expression of a water yam collection from Myanmar. In the present report, the basic chromosome number of 20 (x=20) was adopted to determine the level of ploidy, according to the recent proposal by Arnau et al. (2009). Among 39 accessions, 24 (61.5%) consisted of diploids (2x=40), 11 of (28.2%) triploids (3x=60) and 4 of (10.3%) tetraploids (4x=80). Triploid accessions showed the largest leaves. The shape of the leaf became roundish and the SPAD value of leaf almost linearly increased along with the ploidy level. Size of stoma tended to enlarge as the ploidy level increased. In contrast, the stoma density decreased as the ploidy level went up. The intra-specific variation of phenotypic traits of the water yam collection from Myanmar is considered to be mainly due to ploidy variation. It is suggested that the information obtained in the present study could be not only useful to improve water yam but also significant for further investigation of genetic diversity within the species of water yam.