16 Past, Present, and Future of West African Sorghum Improvement: Building a Roa
16 Past, Present, and Future of West African Sorghum Improvement: Building a Roadmap for Climate-adaptive, Farmer-adopted Varieties
Abstract
Food security and sustainable economic prosperity are key goals for the countries of West Africa (WA). Sorghum (Sorghum bicolor) is among the most important staple crops in WA and has adapted to diverse environments and cultures over many years. However, the process of adaptation is not perfect, and the environment and stakeholder demand is changing, so further sorghum improvement is necessary. National and international sorghum breeding programs are working to improve yield, abiotic stress resilience, and biotic stress resilience. However, it has proved difficult to retain essential end-users’ traits, such as grain quality, and adoption of new varieties has remained low throughout the region. The natural genetic variation within locally adapted and preferred cultivars is key to rapidly develop new climate-adaptive varieties by continuously changing allele frequency and directly selecting outstanding lines through efficient genomics-assisted breeding. It is critical to understand the genetic architecture of adaptive traits, develop genomic tools for marker-assisted and genomic selections, and establish effective data management systems across the region. In this chapter, we describe the genetic diversity of the sorghum germplasm, as well as present an overview of sorghum improvement and perspectives for delivering rapidly and sustainably climate-adaptive breeding products in WA.
Keywords: sorghum, West Africa, breeding, adaptation, genetic diversity
The Sorghum Crop
Sorghum (Sorghum bicolor L. Moench), a C4 grass used mainly for grain and biomass production, is a staple crop for over 500 million people in Africa and Asia (National Research Council, 1996) and grown across various climates (Harlan & de Wet, 1972). Sorghum is a diploid species with 10 pairs of chromosomes and is a predominantly a self-pollinating crop, though it will readily cross-pollinate; gene flow is also commonly seen in sorghum (Barnaud et al., 2008b). The small size of the sorghum genome (about 730 Mbp) makes it a good model system among grass species (McCormick et al., 2018; Paterson et al., 2009) for genomic studies and genomics-assisted breeding.
Cultivated sorghums belong to Sorghum bicolor subspecies. bicolor, with their domestication estimated about 8,000 years ago in East Africa (around present-day Ethiopia and Sudan), followed by their diversification before diffusing south, east, and west (Harlan & de Wet, 1972; Wendorf et al., 1992). A second center of domestication was proposed in West Africa (WA) for guinea margaritiferum (Deu et al., 1994; Folkertsma et al., 2005). Five basic botanical types and ten intermediate types have been defined based on the spikelet and panicle morphology (Harlan & de Wet, 1972). These types—bicolor, durra, guinea, caudatum, and kafir—are originally distributed with respect to geographic regions acro