BACTERIALLY MEDIATED WATER STRESS TOLERANCE IN WHEAT CONFERRED BY PHENAZINE-PRODUCING RHIZOBACTERIA

Abstract

The plant microbiome is the community of microorganisms living in association with plants and are considered to be a “second genome,” capable of directly modifying the plant’s biotic and abiotic environment. Predicted changes in the climate suggest that it is important to increase the plant’s ability to survive and recover from water stress. Plants recruit communities of plant growth promoting microorganisms (PGPMs) with functionalities that enhance their health. Previously, researchers showed that populations of phenazine-producing bacteria are higher in the rhizospheres of dryland wheat compared to irrigated wheat. My research investigates the selection by wheat of PGPMs with the functional capacity to produce phenazines. Phenazine-producing rhizobacteria are hypothesized to increase plant water stress recovery and root growth. I studied the interactions between drought tolerant winter wheat cultivars and the PGPM Pseudomonas chlororaphis 30-84.

In water-stress trials, the presence of the wild-type phenazine-producing bacteria almost doubled the survival rate of wheat seedlings and an enhanced phenazine-producer tripled the survival of wheat seedlings compared to seedlings treated with a phenazine-deficient mutant or the non-inoculated control plants. The presence of phenazine-producing bacteria improved root system architecture and seedling health following water stress. Seedlings colonized by phenazine-producing bacteria had 2 fold more root tips than the two controls. These results suggest that the presence of the phenazine-producing bacteria enabled plants to survive water stress and enhanced recovery, in part, via their influence on root system architecture.

I also investigated the composition of rhizosphere communities recruited by cultivars of winter wheat with different levels of drought tolerance. The role of soil legacy was investigated by collecting soils from adjacent fields with different long-term land use histories, e.g. dryland versus irrigated wheat production. The role of water stress on recruitment was examined by subjecting cultivars grown in soil with different land use histories to water stress. I showed that cultivars with higher drought tolerance had increased recruitment of phenazine-producing bacteria and did so more effectively from dryland soils. Given the potential for phenazine-producers to enhance plant adaptation to water stress, breeding for wheat cultivars that recruit indigenous soil phenazine-producing bacteria could increase water stress tolerance without need for application of microbial inoculum.