ABSTRACT
Common bean (Phaseolus vulgaris L.) is the most widely grown and consumed pulse crop in the American and the sub-Saharan regions of the African continent (Akibode and Maredia, 2012). The crop is well adapted to a wide range of geoecological zones ranging from 200 m in temperate zones to 3000 m in tropical regions. Adaptation is associated with growth-habit differences where type IV climbing beans are grown at higher elevations and the three non-climbing habits are produced in shorter-season regions compromised by limited rainfall or frost-free dates. The non-climbing types are further separated into three growth habits: type I is a determinate bush; type II is an upright indeterminate short vine; and type III possesses a long prostrate vine (Singh, 1982). Breeding for higher yield has largely focused on the non-climbing types, as climbing beans, by nature, are more productive based on their higher node and pod numbers, and longer pod-filling periods assuming the inputs are adequate (Checa and Blair, 2012). Yields of climbing beans have been reported as high as 6 t ha−1 in Rwanda (Musoni et al., 2014) but yields are generally reduced in half when beans are grown in association with maize (Zea mays; Isaacs et al., 2016). One of the challenges for bean breeders has been to increase yield of short-season, bush beans, not just to enhance disease resistance, plant architecture or quality traits but to focus on actual yield improvement in the less favourable environments where beans are typically grown. Lower consumer demand compared to cereals fuelled
by government policies and higher commodity costs have forced bean production to marginal production areas where yields are compromised by shorter seasons, variable and limited rainfall patterns, poor soil fertility and marginal production systems. The need to provide a hungry world with a better balanced and nutritious diet makes it imperative to produce beans in a competitive and profitable manner, and one approach is to increase yield through breeding within the constraints imposed by the marketplace and production system (Beaver and Osorno, 2009).
