College of Agriculture, Engineering
and Science (CAES)

Crop breeder, Dr Bruce Mutari.

Improving Zimbabwe’s Dry Beans for Processing, Nutrition and Drought-Resistance

Dr Bruce Mutari, a crop breeder at the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT) in Zimbabwe, achieved the title of doctor for his research into improving traits of dry (navy) beans for canning and nutritional quality and drought tolerance in Zimbabwe.

Mutari completed his undergraduate and honours degrees in crop science at the University of Zimbabwe, with his honours project focusing on the characterisation of finger millet accessions in Zimbabwe’s National Gene Bank. He then went on to master’s studies at South Africa’s University of Fort Hare where he investigated diversity studies and marker-assisted improvement for rust resistance in bread wheat.

Thanks to UKZN’s reputation for innovative advancements in plant breeding and for training eminent scientists throughout Africa as well as the presence of renowned academics such as Professor Julia Sibiya and Professor Hussein Shimelis, Mutari elected to do his PhD at the University to open doors to further opportunities.

Mutari’s focus on the Middle American gene pool of dry beans (Phaseolus vulgaris L.) was motivated by indications by processors in Zimbabwe that they wanted a variety of the navy bean that would be drought-tolerant with superior nutritional and canning qualities, while being suitable for the mandatory food fortification policy, the increased frequency of droughts and the considerable navy bean grain import bill. The biofortified variety processors were using poor canning quality resulting in negative consumer uptake.

‘The development of navy bean genotypes combining drought tolerance and micronutrient density is a sustainable and environmentally friendly approach to alleviate the effects of drought stress and micro-nutrient malnutrition in Zimbabwe,’ said Mutari.

Mutari has had six articles published in high-impact journals such as Field Crops ResearchCrop ImprovementEuphytica, and PLOS ONE. The articles included a literature review; interviews with navy bean farmers in Zimbabwe to identify their constraints and preferences; navy bean genotype evaluation to identify genotypes with high adaptability and stability; the impact of drought stress on various traits and qualities and identification of drought-tolerant genotypes; combining ability effects and mode of gene action of grain yield and yield attributing traits in navy beans under various conditions; and identification of drought-related putative candidate genes within the mapped genomic regions from a genome-wide association study.

Mutari, who noted that navy beans were strictly a business venture so culinary traits were not considered important for improvement, was able to identify farmer-preferred traits, marketing, and production constraints to be considered by the breeding programme in Zimbabwe. He identified stable high-yielding genotypes that are drought tolerant and possess desirable micronutrient density, superior canning, and nutritional quality. Drought stress apparently reduces zinc content, increasing iron content.

Mutari also identified trade-offs in improving grain yield with high-yielding genotypes demonstrating low concentrations of seed iron. He looked at the beans’ general combining ability (GCA), finding that some parent lines with poor GCA estimates produced superior cross-combinations. He also found molecular markers that could be used in breeding for drought tolerance, with most of the identified genes possessing known biological functions related to regulating drought stress response and growth and development under drought stress.

Challenges Mutari encountered during his studies included lengthy autoclave experiments owing to equipment limitations and the process of rigorous manuscript review which he said improved his competence and enhanced his scientific writing and data analysis skills that he has in turn used to assist other plant breeders.

Mutari received several awards recognising his outstanding contributions to the development and dissemination of dry bean cultivars for improved food, nutrition and income security, and to research in science and technology in Zimbabwe. These include the Young Scientist Award from the Regional Universities Forum for Capacity Building in Agriculture; selection as one of the most influential and successful plant breeders in Zimbabwe by the Zimbabwe Plant Breeders Association; and the Presidential multi-sectorial Robert Gabriel Mugabe Award for the bean breeding programme he led at Zimbabwe’s Crop Breeding Institute, which was awarded at the 12th Zimbabwe International Research Symposium.

Mutari joined ICRISAT in April 2020, where he is enjoying applying his knowledge, skills and experience to the Accelerated Crop Improvement programme for East and Southern Africa to develop climate-resilient and nutritious crop varieties for Africa to improve food, nutrition and income security.

Mutari thanked his supervisors Sibiya and Professor Edmore Gasura at the University of Zimbabwe for their guidance, constructive ideas and support; the Alliance for Bioversity International and International Center of Tropical Agriculture (ABC) for providing technical support and the germplasm used in the study; the Swiss Agency for Development and Cooperation (SDC) and the Government of Zimbabwe for financial support, and the Department of Research and Specialist Service for providing research space at its testing experiment stations.

Words: Christine Cuénod

Photograph: Abhi Indrarajan