Advanced Omic Technologies for Genetic Enhancement of Yam (Dioscorea spp.)

Yam (Dioscorea spp.) is a multi-species clonally propagated edible tuber in the tropical and sub-tropical regions of Africa, Asia, the Pacific and the Caribbean islands. The majoity of yam productioncomes from West Africa, which accounts for about 93% of the world's production of 63 million tons from 5.3 million hectares of area harvested. The crop is a dominant source of food and income for more than 60 million people in West Africa, contributing about 300 dietary calories per person each day. Most of the farmers grow traditional landraces of yams, several of which lack resistance to pests and diseases. Of these, nematodes (Scutellonema bradys, Meladoigyne spp),yam mosaic virus (YMV), and anthracnose (Colletotrichum gloeosporioides) are most devastating, reducing yield by 30-90%. The yam growing countries also face the challenges of declining soil fertility as well as increased exposure to irregular rainfall and long dry spells during the growing season, which contribute to lower tuber yields.

Dioscorea rotundata (white Guinea yam) andD. alata (water or greater yam) are the most important among the 10 cultivated Dioscorea spp. Genetic enhancement of these species is constrained by a number of challenges imposed by clonal nature of the crop, inadequate knowledge on genetic diversity, long breeding cycle, low propagation ratio, and limited tools and technologies to aid breeding and selection. An integrated approach, combining advanced technologies with conventional breeding, is essential to improve efficiency and accuracy in breeding for disease resistance, food quality, and other traits. The International Institute of TropicalAgriculture (IITA) has been leading efforts with different national and international partners for more than a decade to develop and apply advanced omics techniques for yam improvement. Next-generation sequencing techniques such as genotyping-by-sequencing (GBS) and whole genome genome sequencing and re-sequencing along with metabolomics are being utilized to understand the genetic structure and relationships within and betweeb different Dioscorea species. These will facilitate genomic studies such as linkage mapping, gene/QTL identification and association mapping for marjer-assisted selection. Additionally, researchers at IITA have established a highly efficient and simple Agrobacterium-mediated transformation system for D. rotundata. This protocol opens up an avenue for future genetic improvement of D. rotundata using candidate genes for diseases and pests resistance to attain sustainable production and also provide opportunities for functional genomic studies.