With West Africa accounting for 92% of the world’s annual yam production (67 million tons; FAO, 2018), yam plays a significant role in the region’s food security and income generation. While yam is a common name for the multiple crop species belonging to the genus Dioscorea, widely cultivated as a staple crop in tropical and subtropical regions, Dioscorea rotundata is the most cultivated species in this region, representing most yam production.
However, long growth cycles, inconsistent or no flowering, and dioecy—the possession of both male and female characteristics—continued to limit genetic research and breeding of D. rotundata. Other major limiting factors were nonsynchronous flowering of parental genotypes, the presence of multiple chromosomes (polyploidy), and persisting high levels of different forms of a particular gene (heterozygosity)..
Increasing yam productivity in West Africa through breeding requires efficient phenotyping and genotyping techniques. These techniques enable identifying materials with diverse target traits, such as high yield, early maturity, and optimal tuber size and shape. Even then, analysis and utilization of genetic resources with a wide variation range play a vital role in the genetic improvement of crop plants.
A group of researchers from seven international institutes, including IITA, carried out a study to develop a mini-core collection—which reduces the size of the core collection without losing the spectrum of diversity—from a core collection of 447 D. rotundata accessions maintained at the IITA Genetic Resources Center. The study evaluated the mini-core collection together with the existing yam reference materials—breeding lines and landraces.
According to the study, 90 SSR markers previously developed for yam diversity analysis from a microsatellite-enriched genomic library of yellow Guinea yam (D. cayenensis Lam.) were prescreened on 16 randomly selected D. rotundata core collection accessions to identify a set of polymorphic—several variants of DNA sequence—markers for further genotyping.
The researchers selected the base collection accessions based on the cluster’s diversity while ensuring that each cluster’s accessions were represented in the mini-core collection. They further validated the selected mini-core collection for its representation of the base collection based on the accessions’ geographical origins.
Although the selected mini-core collection does not cover the entire genetic diversity of D. rotundata in West Africa, it contains considerable diversity that can be studied further to dissect the genetic basis of key traits and the genetic improvement of yams. This is particularly the case for regionally important but under-researched local crops, such as yam in West and Central Africa.
The mini-core collection developed for D. rotundata in the study represents a small, easy-to-use resource that is invaluable to accelerate genetic and genomic studies, including improving this important crop for food security on the Continent.
This study was conducted under the project, “Use of genomic information and molecular tools for yam germplasm utilization and improvement for West Africa (EDITS-Yam; 2011–2015)” of the Japan International Research Center for Agricultural Sciences (JIRCAS), in collaboration with the Iwate Biotechnology Research Center, IITA, Tokyo University of Agriculture, Purdue University, La Trobe University, and the Kyoto University, with partial support from the Japan Society for the Promotion of Science.
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