As a child, Dr Nelia Nkhoma Phiri had intimate knowledge of cowpea, the crop she focused on for her doctoral research through UKZN.
She spent time living with her grandmother, a subsistence farmer in rural Zambia whose favourite crop was this indigenous legume.
‘We would eat the cowpea leaves throughout the year because we preserved some by drying them in the sun after boiling them a bit. As a young person, I got tired of eating the same things all year round. This inspired me to study plant breeding so that I could breed many different varieties and my grandmother could at least have variety,’ she said.
Phiri, the oldest of seven children whose parents died when she was 16, obtained a diploma in agriculture in 2004, a BSc in Agricultural Sciences in 2009 and an MSc in Plant Breeding and Seed Systems in 2014. Her degrees were from the University of Zambia and she started her PhD studies in Plant Breeding in 2017 at UKZN’s African Centre for Crop Improvement (ACCI) where her supervisors were Professor Hussein Shimelis and Professor Mark Laing.
‘For my doctoral project, I developed candidate cowpea breeding populations that are very high-yielding and resistant to diseases, drought and heat stress,’ said Phiri. ‘Farmers are using low-yielding cowpea varieties such as landraces and introduced varieties that are affected by many biotic and abiotic constraints prevalent in Zambia, and my objectives were to address these challenges.’
Cowpea is an important source of protein for millions of people in sub-Saharan Africa. It complements the nutrition provided by the dominant cereal crops in the region, supplying protein and amino acids essential for building and repairing the body. It is also drought-tolerant and used to feed both people and animals.
The first step of Phiri’s research was to identify cowpea farmers’ preferences and production constraints in Zambia to guide pre-breeding. Using participatory rural appraisal (PRA) research tools and focus group discussions, she interviewed 230 farmers in eastern, southern and northern Zambia, 93% of whom said they used landraces for production. Forty-five percent said low yields were a challenge, as were limited access to production inputs and insect pests and diseases. Farmers wanted high-yielding cowpea varieties that were disease-resistant and they indicated a willingness to adopt improved varieties.
‘My second step was to assess the genetic diversity among cowpea genotypes using phenotypic traits and single nucleotide polymorphism (SNP) markers, and to select distinct and complementary genotypes for developing improved cultivars,’ said Phiri.
A collection of 100 cowpea accessions from Zambia and Malawi were examined for different yield traits. Thereafter, 11 genotypes were selected as parents, based on genetic diversity as well as yield performance. The eleven genotypes were crossed using a half-diallel mating design that produced 55 F1 progenies.
The third step entailed determining combining ability and gene action controlling the yield and yield components among the crosses derived from 11 selected cowpea parents.
The progenies (F1s) and 11 parental lines were then evaluated to determine the combining ability effects, gene action controlling yield, and yield components among them. ‘Both progenies and parents exhibited significant (P<0.05) variation for the assessed yield and yield components,’ said Phiri.
In the fourth step, the F2 families were evaluated across four environments in Zambia and 30 families were selected with higher yield, yield-stability and adaptation. Analysis using additive main effects and multiplicative interaction (AMMI) indicated that the environment, genotype, and GEI effects were highly significant and the best families were identified for future breeding programmes.
Climate change-related stresses such as drought and heat are major challenges for sub-Saharan Africa and Phiri’s research was directly affected by this. ‘Zambia experienced a drought in the 2018/19 growing season which contributed to lower yields of some of the cowpea crosses that were evaluated in multiple environments. The annual rainfall decreased by 50% affecting rain-fed agriculture systems,’ said Phiri.
This hard reality is faced by smallholder farmers, as most cowpea growers in sub-Saharan Africa are dominated by rain-fed agriculture systems that are vulnerable to rainfall variability due to climate change.
Cowpea production is affected by all the main insect pests such as aphids (Aphis craccivora Koch), leafhoppers and diseases like cowpea aphid-borne mosaic virus (CABMV), cowpea mosaic virus (CMV) and cowpea mottle virus (CPMoV). ‘Breeding for disease and insect pest resistance becomes a major focus of cowpea improvement programmes in Zambia. However, there is limited cowpea germplasm with durable or horizontal pest and disease resistance, so evaluation of a diverse germplasm pool against several diseases and insect pests prevalent in the target environments is key to selecting breeding parents,’ said Phiri.
‘Overall, the study appraised the major preferences and perceived production constraints of cowpea growers for variety design and release. Also, new cowpea breeding populations were developed with enhanced yield and yield components for further genetic advancement and multi-location selection for variety release and deployment in Zambia,’ said Phiri.
Phiri hopes to release farmer-preferred cowpea varieties with market potential. ‘Future foods must consider high grain yield, drought tolerance and high nutritional and processing quality to help meet the desired level of food and nutrition security requirements, in the face of climate change,’ said Phiri, whose studies were supported by the Alliance for a Green Revolution in Africa (AGRA).
Phiri, who is employed by the Zambian Ministry of Agriculture under the Department of Seed Control and Certification Institute, will continue to work on the new cowpea breeding populations to advance and improve for yield gains and tolerance to field insect pests (eg aphids) and storage insect pests (eg weevils).
Words: Shelagh McLoughlin