Reproductive fitness in common bean (Phaseolus vulgaris L.) under drought stress is associated with root length and volume

Abstract

Common bean (Phaseolus vulgaris L.) is an important grain legume crop, and drought stress during its reproductive stages affects flowering and pod-filling process. Mitigating drought stress requires the selection of resilient varieties that withstand drought stress. We hypothesized that drought affects the root system of common bean leading to decreased reproductive success, and a relationship exists between root traits and reproductive success. Objectives are to (1) quantify the effects of drought stress on root and shoot traits and pod set percentage in common bean, and (2) assess whether root traits had a relationship with reproductive success under drought. Seedling root traits were studied in solid agar medium. To understand the influence of drought on the root system of adult plants, the lines were grown in 150-cm columns for 48 days under full irrigation or withholding water for 41 days. Root angles ranged from 32.8° to 60.6°, with Pinto and Lariat having the narrowest (32.8°) and widest (60.6°) root angles, respectively. Drought stress decreased rooting depth (14%), root biomass (29%), total root length (35%), volume (41%), pod set percentage (53%), and pod weight (43%). However, the root: shoot ratio (70%) and Fo/Fm ratio were (13%) increased in response to drought stress compared to control. A positive relationship between root volume and total root length with pod set percentage (r2 ≥ 0.80) and pod weight plant−1 (r2 ≥ 0.35) was observed. The study identified the genotypes Topaz and Matterhorn as drought tolerant and susceptible, respectively. Topaz had a wider root angle, higher root biomass, root: shoot ratio, total root length, and volume along with higher pod set percentage and pod weight under drought compared to other genotypes. Hence, these traits can be included in the common bean drought stress breeding program.