Development of marama bean, an orphan legume, as a crop

Abstract

Advances have been recently made in the breeding and characterization of three major legume crops of the semiarid tropics, chickpea, pigeon pea, and groundnut. However, other wild-growing legumes, called “orphan legumes,” with potential as crops, but are not yet cultivated would benefit from further attention. This review considers the domestication of one such plant, marama bean (Tylosema esculentum). Marama has long been recognized as a potential crop particularly for southern Africa, but coordinated, long-term research and development has been lacking. Marama is a perennial, outcrossing hexaploid, growing under extreme conditions in a restricted geographic range; only natural stands exist that are likely to be overexploited. Marama has two potential units of economic yield, seed and tuber. The seed is protein- and oil-rich, with potential in the pharmaceutical and cosmetic industries while the tuber is high in carbohydrates. In this review, the different aspects of bringing a wild plant into cultivation are considered, together with the additional socioeconomic benefits of developing a breeding program. An international collaboration is analyzing aspects of the plant structure and physiology, molecular biology, and its interactions with environment with a view to developing marama as a crop, with a role in food security, that could be harvested by local communities. Molecular topics considered include next-generation sequencing for developing molecular maps, genotyping by sequencing, identification of quantitative trait loci for important agronomic traits, protein quality, and incompatibility mechanisms. To achieve domestication requires seed gardens and fields, and the phenotyping of marama material from different locations. Community engagement will also ensure agronomic sustainability and farmer participation. This review describes an approach for a successful outcome of a breeding program to introduce improved marama and highlights the challenges in achieving this, which is a paradigm for the difficulties in the cultivation of “orphan species.”