Assessing Water Deficit Stress Tolerance of Phaseolus vulgaris Parental Lines Using Carbon Isotope Discrimination.

Assessing water deficit stress tolerance of Phaseolus vulgarisparental lines using carbon isotope discrimination

Alvaro Sanz-Saez ^a*, Michael J.W. Maw^a, Jose Arnulfo Polania^b, Idupulapati M. Rao^b, Steven Beebe^b, and Felix B. Fritschi^a

^a University of Missouri, Division of Plant Sciences, 1-31 Agriculture Building, Columbia, MO 65211, USA.
^bCentro Internacional Agricultura Tropical (CIAT), Cali, Colombia.

Common bean (Phaseolus vulgaris L.) is a major food legume in Latin America and Africa. Bean yields are limited by drought stress during crop development due to stomatal closure and photosynthetic limitations. Phenotypic variation in drought tolerance could provide the potential to breed under terminal drought conditions. Natural isotopic carbon discrimination (CID) has been proposed as an indirect selection criterion for transpiration efficiency, grain yield, biomass and water status in several crop species. In addition, plant species showing low values of CID have been described as plants with high water use efficiency (WUE). The objective of this project was to study if there is genotypic variation in yield and yield component responses to drought among 14 parental genotypes used in CIAT’s common bean breeding program. In addition, this study also assessed if CID techniques are appropriate to predict common bean yield response in irrigated and rain fed plants. The genotypes were grown at the International Center for Tropical Agriculture (CIAT) in Colombia in 2012 and 2013 in both well-watered and rainfed conditions to examine their above ground biomass and  yieldto differences in water availability. At mid-pod filling growth stage, canopy biomass samples were collected, dried, ground, and CID was determined. Rain fed plants showed reduced above ground biomass, yield and CID in both years of the experiment in comparison with irrigated plants. Importantly, significant phenotypic variation in yield response to drought was found in both year. Among all genotypes, only BAT 477 and SEA 5, genotypes previously described as drought resistant, showed medium to high yield under irrigated conditions, and the highest yield under rainfed conditions. In general, yield was positively related with CID when irrigation and rainfed treatments were considered together, however when the correlation was analyzed by water treatment, irrigated plants showed a positive relationship between CID and yield, which concurs with previous reported studies, but under rainfed conditions, no correlation between yield and CID was found. This lack of correlation allowed BAT 477 to show high yield under rainfed conditions with relatively low values of CID. This findings reinforce the idea that further research is needed in order to understand more in depth the physiological mechanisms underlying common bean yield resistance to drought and how to introduce this findings in breeding programs.