Effective Use of Water and Increased Dry Matter Partitioned to Grain Contribute to Yield of Common Bean Improved for Drought Resistance

Abstract

Common bean (Phaseolus vulgaris L.) is the most important food legume in the diet of poor people in the tropics. Drought causes severe yield loss in this crop. Identification of traits associated with drought resistance contributes to improving the process of generating bean genotypes adapted to these conditions. Field studies were conducted at the International Center for Tropical Agriculture (CIAT), Palmira, Colombia, to determine the relationship between grain yield and different parameters such as effective use of water (EUW), canopy biomass, and dry partitioning indices (pod partitioning index, harvest index, and pod harvest index) in elite lines selected for drought resistance over the past decade. Carbon isotope discrimination (CID) was used for estimation of water use efficiency (WUE). The main objectives were: (i) to identify specific morpho-physiological traits that contribute to improved resistance to drought in lines developed over several cycles of breeding and that could be useful as selection criteria in breeding; and (ii) to identify genotypes with desirable traits that could serve as parents in the corresponding breeding programs. A set of 36 bean genotypes belonging to the Middle American gene pool were evaluated under field conditions with two levels of water supply (irrigated and drought) over two seasons. Eight bean lines (NCB 280, NCB 226, SEN 56, SCR 2, SCR 16, SMC 141, RCB 593, and BFS 67) were identified as resistant to drought stress. Resistance to terminal drought stress was positively associated with EUW combined with increased dry matter partitioned to pod and seed production and negatively associated with days to flowering and days to physiological maturity. Differences in genotypic response were observed between grain CID and grain yield under irrigated and drought stress. Based on phenotypic differences in CID, leaf stomatal conductance, canopy biomass, and grain yield under drought stress, the lines tested were classified into two groups, water savers and water spenders. Pod harvest index could be a useful selection criterion in breeding programs to select for drought resistance in common bean.

Root traits and their potential links to plant ideotypes to improve drought resistance in common bean

“…Bean lines with low grain yield under field conditions were characterized by poor root vigor, with a low rate of root growth and shallow root development under drought conditions. Genotypes with superior grain yield under drought stress under field conditions and classified as water spenders (Polania et al 2016a) showed higher root vigor with deeper rooting ability under drought stress in the greenhouse. Deep roots may develop from the basal roots that change their root angle to turn downward, or from lateral roots that develop from a tap root, or both (Bonser et al 1996;Ho et al 2005;Basu et al 2007;Lynch 2011;Miguel et al 2013;Beebe et al 2014;Burridge et al 2016).…”

“…diff. * * * * * * * Significant difference at 0.05 level as estimated from the MIXED procedure ** The genotypes were classified such as water saver, moderate water saver, water spender based on genotypic differences in grain carbon isotope discrimination (CID-G), leaf stomatal conductance, canopy biomass, and grain yield under drought stress (Polania et al 2016a) ( Fig. 3) with superior N uptake from the soil under drought stress ( Fig.…”

“…The irrigated control treatment received 5 irrigations in 2012 and 6 irrigations in 2013 to ensure adequate soil moisture for crop growth and development. Experimental units consisted of 4 rows with 3.72 m row length with a row-to-row distance of 0.6 m and plant-to-plant spacing of 7 cm (Polania et al 2016a).…”

“…under drought stress 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). Results obtained on root vigor under drought stress in the greenhouse are shown in Table 1.…”

“…However their contribution to superior grain yield depends on the type of drought (early, intermittent and terminal) and the agro-ecological conditions where the crop is grown (Rao et al 2017). According to agroecological zones and types of drought, breeding should target different plant ideotypes such as, the isohydric ('water saving') plant model and the anisohydric ('water spending') plant model (Polania et al 2016a). The water saving model might have an advantage in the harshest environments, whereas the water spending model will perform relatively better under more moderate drought conditions (Blum 2015).…”