The Development of New Genotypes of the White Yam by Mutation Induction Using Yam Mini-tubers

A method for the genetic improvement of the white yam, Dioscorea rotundata by mutation induction was investigated by irradiating mini-tubers of the yam with Gamma-rays. Batches of 150 mini-tubers of the well adopted local cultivar 'Obiaoturugo' were gamma irradiated at doses of 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90 Gray (Gy) using the 60Co gamma source at the Center for Energy Research and Development, Obafemi Awolowo Universitym, Ife-Ife in 2004. Each irradiated tuber including the control was divided into setts weighing 10-15g and planted in the field to establish the first mutated vegetative generation (MV1), separating setts from the head (H) and the tail (T) regions. In 2005, first generation tubers harvested from the MV1 generation were used to establish the MV2 populations. At the MV1 generation, increasing doses of Gamma-ray irradiation progressively inhibited sprouting of sets isolated from treated mini-tubers. These effects were more severe on sets from the tail (T) region than those from the head (H) region. Also, plant height, number of leaves, number of nodes and mean tuber yields per stand decreased with increased Gamma-ray doses. LD50 and GR50 were observed at 40Gy and 30Gy, respectively. At the MV2 generation, the observed differences among the treatments means disappeared (or were not significant). MV2 yam lines with modified vegetative characteristics were isolated. Distinct lines with bunchy and bushy vegetation and bushy with spreading vines were isolated. This is relevant, as one of the genetic improvement objectives apart from high tuber yields in yam, is for the development of lines that may be cropped without staking. (author)