Abstract
Drought stress limits growth and yield of crops, particularly under smallholder production systems with minimal use of inputs and edaphic limitations such as nitrogen (N) deficiency. The development of genotypes adapted to these conditions through genetic improvement is an important strategy to address this limitation. The identification of morpho-physiological traits associated with drought resistance contributes to increasing the efficiency of breeding programs. A set of 36 bean genotypes belonging to the Middle American gene pool was evaluated. A greenhouse study using soil cylinders was conducted to determine root vigor traits (total root length and fine root production) under drought stress. Two field trials were conducted to determinate grain yield, symbiotic nitrogen fixation (SNF) ability and other shoot traits under drought stress. Field data on grain yield and other shoot traits measured under drought were related with the greenhouse data on root traits under drought conditions to test the relationships between shoot traits and root traits. Response of root vigor to drought stress appeared to be related with ideotypes of water use (water savers and water spenders). The water spender ideotypes presented deeper root system, while the water saver ideotypes showed a relatively shallower root system. Increase in SNF ability under drought stress was associated with greater values of mean root diameter while greater acquisition of N from soil was associated with finer root system. We identified seven common bean lines (SEA 15, NCB 280, SCR 16, SMC 141, BFS 29, BFS 67 and SER 119) that showed greater root vigor under drought stress in the greenhouse and higher values of grain yield under drought stress in the field. These lines could serve as parents for improving drought resistance in common bean.
Highlights
Drought stress is one of the major abiotic constraints limiting agricultural productivity, for smallholder systems
Based on genotypic differences in grain carbon isotope discrimination (CID-G), leaf stomatal conductance, canopy biomass, and grain yield under drought stress, the lines resistant to drought conditions were classified into two groups, water savers (G 40001, SER 16, ALB 60, ALB 6, BFS 10) and water spenders (NCB 280, NCB 226, SEN 56, SCR 16) (Polania et al 2016a)
Water spender lines were superior in their visual root growth rate under drought conditions and these were considered as genotypes with high root vigor (Table 1)
Summary
Drought stress is one of the major abiotic constraints limiting agricultural productivity, for smallholder systems. Drought is a major abiotic stress limitation for common bean (Phaseolus vulgaris) production, affecting around 60% of bean producing regions and generating losses in production from 10 to 100% (Polania et al 2016c). In order to respond to the increase in demand, common bean has to face challenges that include higher temperatures and the associated increase in evapotranspiration combinedwitherratic and lowerrainfall(Beebe et al 2013). Different climate models predict that many drought stressed areas in Eastern and Southern Africa will become drier over the decades (Jones and Thornton 2003; Williams et al 2007; Rippke et al 2016), exacerbating the limitations of bean production due to severe drought stress
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