Yukiko Kashihara, email@example.com
To contribute to reducing poverty and increasing food security, IITA is breeding new varieties of yam based on demand and value addition. This is usually done by crossing two parents of the same species (intraspecific breeding, e.g., Dioscorea rotundata clones, TDr Ehuru Ã— TDr Ehobia) or different species (interspecific hybridization, e.g., D. rotundata clone, TDr Ufenyi Ã— D. alata clone, TDa 85/00250) to transfer useful traits. However, intraspecific or interspecific yam breeding is still being constrained by poor flowering, low seed-setting, a low rate of seed germination, and differences in flowering periods as male and female parents flower at different times.
Interspecific hybridization is particularly useful to produce additional variations in Dioscorea species. For instance, interspecific hybridization of D. alata and D. rotundata can contribute to the transfer from D. rotundata to D. alata of genes conferring tolerance to anthracnose disease. However, interspecific hybridization is still a challenge. One example in Japan dealt with the hybridization between D. japonica and D. opposita produced with the aid of the embryo rescue technique (Araki et al. 1983). In addition to interspecific hybridization, the use of homozygous parents (having the same pairs of genes) could add efficiency to breeding. Anther culture can also produce homozygous plants through chromosome doubling of haploid plants. Establishing an anther culture system will further diversify breeding approaches. Therefore, current studies are focusing on (i) refining the embryo rescue technique to improve the efficiency of interspecific hybridization, and (ii) establishing a method for producing haploid yam which saves several generations in the breeding program.
Using ovule culture (excised ovules from the ovary and cultured on media), we obtained one plant which resulted from a cross in 2012. However, after flow cytometric analysis, we found that the plant was derived from an ovule parent. For anther culture, more investigation is needed to find out the optimum medium and conditions. The establishment of reliable tissue culture protocols and efficient working schemes is essential. The success of this will contribute to allowing wide hybridization and saving time and space for IITAâ€™s yam improvement program. Moreover, having haploids will be advantageous for yam research, especially in gene mapping, genomics, and other applications.
Araki, H. et al. 1983. Some Characteristics of Interspecific Hybrids between Dioscorea japonica Thunb. and Dioscorea opposite Thunb. Japanese Society for Horticultural Science 52:153-158.