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

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.

Using Carbon Isotope Discrimination to Assess Genotypic Differences in Drought Resistance of Parental Lines of Common Bean

“…When yield was compared with grain Δ 13 C, only SEA 5 and BAT 477 were consistently classified as water spenders, and SER 16 as a water saver. The classification of SEA 5 and BAT 477 as water spenders is consistent with previous studies that identified them as deep rooting genotypes that can access water deeper in the soil profile (White et al, 1990; Rao, 2014; Polania et al, 2017b). On the other hand, the water saver genotype, SER 16, likely was able to produce high yields under water‐limited conditions due to its capacity to remobilize previously fixed photosynthates to seed (Polania et al, 2016b).…”

“…This was in stark contrast with other genotypes such as BAT 881, CAL 143, and DOR 364, which had LAIs in the TDS environment that were only ?39% of those in the WW environment. Similar to BAT 477, G21212 and SEA 5 were among the genotypes with high LAI under TDS, which was probably related to greater soil exploration for water and nutrients associated with deeper roots, as previously reported for these genotypes (White et al, 1990;Polanía et al, 2009;Beebe et al, 2013;Polania et al, 2017b;Rao et al, 2017). However, since rooting depth was not measured in the present study, it is possible that mechanisms other than rooting depth (e.g., greater C remobilization) also played a role.…”

“…Reduced water availability has been linked with smaller leaf area and LAI in common bean (Kalaydjieva et al, 2015). However, lines that were able to maintain a greater LAI under drought conditions as a result of deeper roots exhibited greater biomass accumulation and yields (Beebe et al, 2014; Rao, 2014; Polania et al, 2017b). The sensitivity of leaf expansion was clear by the 1.7‐fold (average across both years) larger LAI in the WW than in the TDS environments.…”

“…2). Accumulation of greater shoot biomass in water-limited environments has been related with higher yields, probably as a result of larger pools of C for translocation to the pods and seeds, and/or because of enhanced ability of the genotypes to access more water with deeper roots (Assefa et al, 2013;Rao 2014;Polania et al, 2017aPolania et al, , 2017b.…”

“…According to Condon et al (2004), the selection of traits that increase any of these three factors under drought is paramount for breeding crops grown in water-limited conditions. Previous research on common bean has primarily focused on increasing WU by selecting varieties with deeper roots (Rao, 2014;Polania et al, 2017aPolania et al, , 2017b, and increasing HI by breeding for greater biomass accumulation during the vegetative stages and more efficient C remobilization from vegetative tissues to seeds (Rosales-Serna et al, 2004;Klaedtke et al, 2012;Rosales et al, 2012;Assefa et al, 2013). However, improvement of common bean WUE has received limited attention and usually is not a primary target in breeding programs, likely because it is difficult to quantify under field conditions (Araus et al, 2002;Easlon et al, 2014).…”