FUNCTIONAL ROLE AND SYNERGYSTIC EFFECT OF ROOT TRAITS FOR PHOSPHORUS ACQUISITION EFFICIENCY AND THEIR GENETIC BASIS IN COMMON BEAN (PHASEOLUS VULGARIS L.)
Open Access
- Author:
- Miguel, Magalhaes Amade
- Graduate Program:
- Horticulture
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 13, 2010
- Committee Members:
- Jonathan Paul Lynch, Dissertation Advisor/Co-Advisor
Jonathan Paul Lynch, Committee Chair/Co-Chair
Kathleen Marie Brown, Committee Member
Barbara Jane Christ, Special Member - Keywords:
- basal root whorls
phosphorus
common bean
root architecture
QTL analysis
synergism. - Abstract:
- ABSTRACT FUNCTIONAL ROLE AND SYNERGYSTIC EFFECT OF ROOT TRAITS FOR PHOSPHORUS ACQUISITION EFFICIENCY AND THEIR GENETIC BASIS IN COMMON BEAN (PHASEOLUS VULGARIS L.) Magalhães A. Miguel Doctor of Philosophy, Horticulture Department, August 2012 The Pennsylvania State University Jonathan P. Lynch, Thesis Advisor 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). A set of 6 RILs contrasting for BRWN was evaluated for performance under low phosphorus availability in the greenhouse and in the field. In the greenhouse, plants were grown in a sand-soil media with low or high phosphorus availability. In the field, plants were grown in an Oxisol in Mozambique under low and moderate phosphorus availability. Wild bean accessions tended to have one or two BRWN whereas cultivated accessions had BRWN reaching 4 and sometimes 5. BRWN and BRN did not vary with phosphorus availability, i.e. BRWN was not a plastic trait in these genotypes. Greater BRWN was beneficial for phosphorus acquisition in low phosphorus soils. Genotypes with greater BRWN had almost twice the shoot biomass, greater root length (90 cm vs. 50 cm length), and greater leaf area (1.7 m2 vs. 0.89 m2) than related genotypes with less BRWN. In low phosphorus soil, shoot phosphorus content was strongly correlated with BRWN (r2= 0.64 in the greenhouse and r2=0.88 in the field). 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 found a total of 23 QTL associated with BRWN and BRN in the two populations. In the DOR364 x G19833 RIL population, we found 3 QTL in the first dataset with one QTL controlling 14.6% of the variation. For the fourth dataset, we found 7 QTL with one QTL controlling 23.8% of the variation in BRWN. For BRN, we detected 3 QTL in the 2005 dataset with one QTL controlling 13.7% of the variation. In the fouth dataset, we found 7 QTL on 5 linkage groups. One of the QTL on linkage group B7 controlled 25.9% of all the variation for BRN in that population. Variability in BRWN in the G2333 x G19839 RIL population was controlled by only one locus on linkage group B3. For basal root number in the DOR364 x G19833 RIL population, we detected 4 QTL on B3, B6 and B7 in the first trial, and two QTL on B2 in the second trial. No QTL was found in the third trial. For the fourth dataset we found one QTL in linkage group B3 controlling 19.3% of the variation in BRWN. This proportion of variation explained by relatively few loci suggests that the potential for genetic manipulation of these traits via these locus is very good. As we have observed in the results of QTL analysis of phenotypic data from four different data sets over the years, QTL were detected in different parts of the genome. It appears that there are several regions which contain QTL or genes that can contribute to the development of basal roots. 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). Shallow BRGA is an important trait for phosphorus acquisition efficiency by enhancing topsoil foraging, since in most soils, phosphorus is concentrated in the topsoil. Root hairs substantially increase phosphorus acquisition by expanding the soil volume subject to phosphorus depletion through diffusion. 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.