Functional role and synergystic effect of root traits for phosphorus acquisition efficiency and their genetic basis in common bean (Phaseolus vulgaris L.)

The rapid increase of the global population, especially in the developing countries requires an increase in crop productivity to meet with current demands. However, in these countries several factors limit crop yields, especially low soil fertility and drought. In most of the countries in Latin America and Africa, more than half of the cultivated areas are affected by low phosphorus availability. Most of existing cultivars are not suitable for these unfavorable soils. The majority of the farmers in these regions cannot afford the application of chemical fertilizers to improve their soil fertility. Therefore, there is a need to identify root traits conferring phosphorus acquisition efficiency and to develop cultivars adapted to phosphorus stressed soils.;Root architectural phenes enhancing topsoil foraging are important for phosphorus acquisition. Here we describe the utility of a novel phene, basal root whorl number (BRWN), that has significant effects on topsoil foraging in common bean (Phaseolus vulgaris L.). Whorls are defined as distinct tiers of basal roots that emerge in a tetrarch fashion along the base of the hypocotyl. In this study, wild and cultivated bean taxa as well as a Recombinant Inbred Line (RIL) population were screened for BRWN and basal root number (BRN). Genotypes with three whorls had shallower root systems with a greater range of basal root growth angles (from 10 to 45 degrees from horizontal) than genotypes with two whorls (which ranged from 60 to 85 degrees from horizontal). Our results indicate that BRWN is associated with increased phosphorus acquisition and that this trait may have value for selection of genotypes with better performance in low phosphorus soils.;In addition, we performed a quantitative trait loci (QTL) analysis for BRWN using recombinant inbred lines (RILs) developed from two populations. Basal Root Whorl Number (BRWN) is a root architectural trait in common bean that plays an important role in soil exploration and resource acquisition. BRWN varies from one to five among bean genotypes, and is an important determinant of basal root number (BRN), with each whorl typically forming four basal roots. The objective of this study was to perform a quantitative trait loci (QTL) analysis for BRWN and BRN using two populations of recombinant inbred lines (RILs) developed from the crosses DOR364 x G19833 and G2333 x G19839. Phenotypic data on the number of basal root whorls and number of basal roots was measured on seedlings 3 days after imbibition. QTL analysis for basal root whorl number and total basal root number was performed using composite interval mapping in these two populations using four phenotypic datasets.;We also tested the hypothesis of the existence of synergetic effect between root characteristics responsible for nutrient acquisition efficiency in Common bean. Multiple root traits affect phosphorus acquisition, including root hair length and density (RHLD), and basal root growth angle (BRGA). We hypothesized that shallow BRGA and long root hairs are synergetic for phosphorus acquisition, meaning their combined effect is greater than the sum of their individual effects. The purpose of this study was to evaluate this hypothesis by quantifying the effect of root hairs and basal root growth angle alone and in combination among closely related genotypes. We established a set of field experiments with Recombinant Inbred Lines (RILs) of common bean (Phaseolus vulgaris L.) grouped in four distinct root phenotypes: long root hairs and shallow basal roots; long root hairs and deep basal roots; short root hairs and shallow basal roots; and short root hairs and deep basal roots. Results revealed substantial synergism between the two phenes. Long root hairs increased shoot biomass under phosphorus stress by 89.3% while shallow roots increased shoot biomass by 57.7%. Genotypes with both long root hairs and shallow roots had the greatest biomass accumulation, 298% greater than short-haired, deep-rooted phenotypes. Shoot biomass and phosphorus content of genotypes with long root hairs on deep roots and shoot biomass of genotypes with short root hairs on shallow roots did not differ, but were greater than those of genotypes with short root hairs on deep roots. We conclude that the morphological phene of longer root hairs and the architectural phene of shallower basal root growth are synergetic for phosphorus acquisition. (Abstract shortened by UMI.)...