Yam is a common name for plant species in the genus Dioscorea, including ‘nagaimo’ (Chinese yam, D. polystachya), ‘yamanoimo’ (Japanese yam, D. japonica) and ‘daijo’ (water yam, D. alata), which are cultivated in Japan. It is widely cultivated as a staple food in Africa, and especially in West Africa, about 54 million tons, equivalent to 95% of the world's total yam production, are produced annually. Among numerous yam species, Guinea yam (D. rotundata) is an important staple food crop and indispensable to the diet of the people in West Africa, with characteristics (color, taste and texture) that conform to food culture such as traditional cooking methods and processing techniques. On the other hand, since the production and consumption areas are concentrated in West Africa, research and technological development on breeding for productivity and quality improvement has hardly progressed.

At JIRCAS, we are focusing on Guinea yam and conducting research to improve productivity and quality through the utilization of diverse genetic resources. So far, we have provided advanced information and tools for yam research unlocking the use of wide genetic diversity of the crop, such as whole genome sequence, molecular markers for analysis of genetic diversity, a tool kit for variety identification, and various phenotyping tools including a non-destructive method to predict shoot biomass.

Recently, we reported the development of the D. rotundata Diversity Research Set (DrDRS), selected plant materials suitable for effective use of these advanced technologies in yam research, and it has been featured as a science news of the Crop Science Society of America (CSSA) with the expectation to play a role in future research and breeding of Guinea yam.

The DrDRS is a collection of 102 accessions of Guinea yam, selected using DNA markers to secure the genetic diversity of an original collection of 447 accessions maintained at the International Institute of Tropical Agriculture (IITA) in Nigeria. The inherent attributes of Guinea yam, such as long growth cycle, large plant size, and the underground tuber serves as both harvest and vegetative propagation material, makes researcher difficult searching for useful traits using a large number of genetic resources than other crops. This has also contributed to the delay in breeding and research on improvement of agronomic traits. However, DrDRS now provides researcher the possible option to carry out cultivation experiments to effectively evaluate various traits of Guinea yam on an appropriate scale. The DrDRS provides information on major agronomic traits, such as the number of stems per plant, growth period, number of tubers per plant, tuber weight and total yield per plant for all accessions, and the plant materials are available for distribution through IITA. We hope the resources that we have developed so far, including the genome information, DNA markers, evaluation methods, and DrDRS as research materials will be widely used for breeding and research of Guinea yam, and could lead to the development of improved varieties through the effective utilization of the wide range of genetic diversity of this crop in the future.

These studies have been carried out in collaboration with domestic and overseas institutions such as the Iwate Biotechnology Research Center (IBRC) and IITA. JIRCAS will continue to utilize the collaboration and achievements that have been accumulated so far to help in securing food supply to serve for the expected population growth in Africa and increasing the income of small-scale farmers through the development of improved varieties and cultivation techniques. 

References

Development of SSR markers for diversity studies on yam (Dioscorea) genetic resources
https://www.jircas.go.jp/en/publication/research_results/2015_b05

Whole genome sequence of Guinea yam (Dioscorea rotundata) and development of a DNA Marker for sex determination
https://www.jircas.go.jp/en/publication/research_results/2017_b02

Non-destructive shoot biomass evaluation for field grown yam (Dioscorea rotundata Poir)
https://www.jircas.go.jp/en/publication/research_results/2018_b01

SSR marker technology package for variety identification of white Guinea yam
https://www.jircas.go.jp/en/publication/research_results/2019_b03

Pachakkil B & Yamanaka S et al. (2021) Simple sequence repeat-based mini-core collection for white Guinea yam (Dioscorea rotundata) germplasm. Crop Science, https://doi.org/10.1002/csc2.20431

Contributors: YAMANAKA Shinsuke (Tropical Agriculture Research Front), MURANAKA Satoru (Crop, Livestock and Environment Division)