Genotypic variation in water-use traits and drought response of Rwandan common bean cultivars

Water availability is the most limiting factor for global agricultural productivity. Rain-fed smallholder farming common to sub-Saharan Africa is particularly sensitive to unpredictable precipitation patterns and periods of drought - issues that are projected to be exacerbated by ongoing climate change. Common bean (Phaseolus vulgaris) is widely cultivated in East Africa and represents an important source of protein, carbohydrates, micronutrients and income for smallholder agriculture. Bean water-use traits and productivity responses to water limitation are thus of great importance. In this study we sought to investigate the genetic variation of water-use traits and responses to terminal drought among Rwandan landraces and improved cultivars of common bean.

Eighteen landraces and twelve improved cultivars were cultivated under realistic field conditions and evaluated for physiological traits related to water use, phenological properties, and effects of terminal drought treatment.

Considerable genetic variation was detected across landraces and improved cultivars for all investigated traits. There was a strong negative correlation between yield and intrinsic water-use efficiency. High yielding cultivars demonstrated low water-use efficiency. There was, however, also notable variation in this relationship, with some cultivars combining water-conserving properties and high productivity. Phenological data indicated a positive relationship between productivity and time to maturity. The lack of a consistent association between water-use traits and drought responses demonstrates that traits for drought avoidance and tolerance are genetically distinct and regulated separately.

Our results demonstrate a large degree of genetic variation and highlight the possibility of combining traits for water economy and drought tolerance while maintaining yield in common bean. The contrasting genotypes reported in this study could be used for genetic mapping of genomic regions and cultivars combining high grain yield with moderate water use and moderate tolerance to drought are suggested for future breeding efforts.