Specificity of root-bacterial interactions for drought stress tolerance in winter wheat

Plants cope with drought stress by a variety of mechanisms that occur above- and below-ground. Below the soil surface, root architecture and interactions with beneficial bacteria, including aminocyclopropane carboxylic acid deaminase-positive (ACC+) bacteria, may contribute to differences in drought tolerance. We hypothesized that drought tolerance of winter wheat can be improved when cultivars utilize root exudates to recruit and establish interactions with specific ACC+ bacteria and through root architecture that effectively taps soil water. Greenhouse studies were conducted to 1) identify variation in root exudate chemical profiles among winter wheat cultivars, and effects of ACC+ bacterial inoculation on root biomass, length, architecture and grain yield under water-stressed and non-stressed conditions, and 2) quantify the increase in drought tolerance of a non-responsive cultivar grown in the presence of the root exudates of an ACC+ bacterial-responsive, drought tolerant cultivar. ACC+ bacteria improved the drought tolerance of specific cultivars that possessed a unique root exudate profile and ability to sustain relatively large proportions of ACC+ bacteria in the rhizosphere. Furthermore, the productivity of a non-responsive cultivar was better protected under drought stress when grown in the presence of ACC+ bacteria and root exudates from an ACC+ bacterial-responsive cultivar. Thus, the ability of ACC+ bacteria to enhance drought tolerance was cultivar-specific, presumably due to the specificity of root exudate compounds that sustained ACC+ bacteria in the rhizosphere.