Farmer knowledge identifies a competitive bean ideotype for maize–bean intercrop systems in Rwanda
Background: Plant genotypes are rarely developed for mixed cropping systems despite the potential of these systems to provide multiple ecosystem services. One of the most ubiquitously grown mixed cropping systems is a common bean (Phaseolus vulgaris L.) and maize (Zea mays L.) intercrop, but there is little consensus among researchers, and few known studies document farmer knowledge, about superior bean genotypes specifically for this intercrop system. Participatory plant breeding (PPB) is a well-accepted method of selecting varieties with farmers and could be a useful tool for identifying genotypes for intercrops. We used sole crop and intercrop PPB on-farm trials (n = 13) and interviews (n = 59) to document farmer knowledge about climbing bean genotypes and adaptation for intercrops in Rwanda, where smallholder farmers have traditionally grown beans and maize for generations. Results: Qualitative analysis demonstrated that farmers considered distinct attributes for different cropping systems. In intercrops, farmer evaluation prioritized five factors: universal traits and trait-based competitive ability, intrinsic competitive ability, environmental adaptation, and management. Farmers consider intrinsic competitive ability crucial, whereas most other studies have neglected this attribute in intercrop breeding strategies. Furthermore, farmers identified specific attributes that constitute an intercrop bean ideotype: adaptation, restricted height, columnar plant structure, even distribution of pods, fewer leaves, and earlier maturity. Farmers also had specific techniques for testing cropping system and environment interactions. Conclusions: PPB on-farm trial evaluations and interviews with farmers allowed us to combine traditional agroecological knowledge with plant breeding research to generate new knowledge that contributes to our understanding of intercrop breeding and bean traits for intercrops. Farmers demonstrated sophisticated understanding of methods to identify genotype adaptation, competitive ability, and specific traits that together create a bean ideotype for maize–bean cropping systems. Empowering farmers through on-farm testing of diverse genotypes, and even populations, could be a practical solution to expensive genotype by environment trials and improve the identification of highly adaptive and productive genotypes for diverse and resilient cropping systems.
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