Abstract
Genetic improvement of major food yams is constrained by a number of factors, such as the scarcity of flowers and lack of synchronization between male and female flowering. Consequently, somaclonal variation including somatic polyploidization has been considered as a useful tool in yam breeding. Somatic polyploidization and its effect on phenotypic traits of Dioscorea species such as D. alata, D. japonica and D. zingiberensis has been reported; however, optimization of this method in two major yam species, D. rotundata and D. cayenensis, is yet to be achieved and the effect of polyploidization on phenotypic traits of this species yet to be elucidated. In the present study, a high rate of somaclonal polyploid variation was successfully achieved by in vitro colchicine treatment of D. rotundata and D. cayenensis. In most cases, except TDc 3704, the highest rate of polyploid induction appeared after 0.1% colchicine treatment. However, in triploid yellow yam accessions the induction rate was relatively low. Tetraploid variants of D. rotundata tended to display somewhat rounder leaves than their diploid parents. The size and shape of D. rotundata stoma were also affected by levels of ploidy, with tetraploid variants exhibiting larger stomata at a lower density compared to their diploid parents. The efficient method of in vitro polyploidy induction reported here is therefore a highly useful tool for obtaining polyploid variants for use as genetic resources in D. rotundata breeding. Key words: Leaf, nodal segment culture, ploidy level, somaclonal variation, stoma, white guinea yam, yellow Guinea yam.
Highlights
In terms of production, yams (Dioscorea spp.) are the fourth most important tuber crop in the world (FAOSTAT, 2014), serving as a staple for millions of people in tropical regions
The size and shape of D. rotundata stoma were affected by levels of ploidy, with tetraploid variants exhibiting larger stomata at a lower density compared to their diploid parents
In vitro seedlings of white yam accessions TDr 2720, TDr 1793, TDr 2351 and yellow yam accessions TDc 2790, TDc 2812 and TDc 3704 maintained in the Genetic Resource Unit (GRU) of the International Institute of Tropical Agriculture (IITA), Ibadan, Nigeria, were used
Summary
Yams (Dioscorea spp.) are the fourth most important tuber crop in the world (FAOSTAT, 2014), serving as a staple for millions of people in tropical regions. In a short period of 20 years from 1992 to 2012, the production quantity of yams in West Africa rapidly increased from about 27 to 54 million tons, largely through the use of landraces and rapid expansion of cultivated acreage from 2.4 to approximately 4.5 million hectares (FAOSTAT, 2014). To meet this growing demand, breeding of higher-yielding cultivars is becoming an important focus. Somaclonal variation including somatic polyploidization is being considered as a useful tool in yam breeding
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