Genetic and Environmental Modulation of the Chickpea - Mesorhizobium Symbiosis
type: CreativeWork
description: Chickpea (Cicer arietinum) is a valuable crop grown worldwide. It fixes atmospheric nitrogen by establishing a symbiotic relationship with rhizobia and secretes organic acids from its roots and green tissues that play a role in interactions with beneficial microbes, insect herbivores, and pathogens. As chickpea is nodulated with diverse Mesorhizobium species, genetic factors related to both rhizobia and host plant, and environmental conditions are likely to influence plant growth and defence, and chickpea-Mesorhizobium symbiosis. The primary objective of this thesis is to investigate the effects of genetic and environmental factors, and their interactions, on plant traits related to growth, nitrogen fixation and responses to herbivory. A quantitative review was conducted using published data to investigate the effect of environmental factors, particularly drought, on legume growth, nitrogen fixation and its related traits in the light of a hierarchy of phenotypic plasticity. Drought reduced total nitrogen fixation and average nodule mass more severely than plant shoot mass and elicited a hierarchy of plasticities whereby number of nodules per plant varied substantially, and average nodule mass and nitrogen fixation per unit nodule mass were relatively conserved. Four experiments were carried out in a glasshouse, with specific objectives converging to the primary objective. The objective of experiment 1 was to investigate the interaction between plant variety, Mesorhizobium strain, and environment, and their effects on plant growth and nitrogen fixation and its related traits, from the perspective of phenotypic plasticity. Experiment 2 investigated the effects of rhizobia on the growth dynamic of chickpea varieties, nodulation and bacteroid morphology under different water regimes. Experiment 3 and 4 investigated the effects of drought and herbivory on chickpea growth and defence and explored the trade-offs between exudation of organic acids and growth. Experiment 1.…
abstract: Chickpea (Cicer arietinum) is a valuable crop grown worldwide. It fixes atmospheric nitrogen by establishing a symbiotic relationship with rhizobia and secretes organic acids from its roots and green tissues that play a role in interactions with beneficial microbes, insect herbivores, and pathogens. As chickpea is nodulated with diverse Mesorhizobium species, genetic factors related to both rhizobia and host plant, and environmental conditions are likely to influence plant growth and defence, and chickpea-Mesorhizobium symbiosis. The primary objective of this thesis is to investigate the effects of genetic and environmental factors, and their interactions, on plant traits related to growth, nitrogen fixation and responses to herbivory. A quantitative review was conducted using published data to investigate the effect of environmental factors, particularly drought, on legume growth, nitrogen fixation and its related traits in the light of a hierarchy of phenotypic plasticity. Drought reduced total nitrogen fixation and average nodule mass more severely than plant shoot mass and elicited a hierarchy of plasticities whereby number of nodules per plant varied substantially, and average nodule mass and nitrogen fixation per unit nodule mass were relatively conserved. Four experiments were carried out in a glasshouse, with specific objectives converging to the primary objective. The objective of experiment 1 was to investigate the interaction between plant variety, Mesorhizobium strain, and environment, and their effects on plant growth and nitrogen fixation and its related traits, from the perspective of phenotypic plasticity. Experiment 2 investigated the effects of rhizobia on the growth dynamic of chickpea varieties, nodulation and bacteroid morphology under different water regimes. Experiment 3 and 4 investigated the effects of drought and herbivory on chickpea growth and defence and explored the trade-offs between exudation of organic acids and growth. Experiment 1.…
author: Iqbal, Nasir
language: en
keywords: bacteroid, high-throughput phenotyping, leaf exudates, plasticity, reaction norm, trade-off
date published: 2023
date modified: 2026-07-24T00:50:39Z
provider: University of Adelaide
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Adelaide

PropertyValue
property ID: Handle
value: https://hdl.handle.net/2440/140197