Abstract
With the increasing demand for alternative solutions to replace or optimize the use of synthetic fertilizers and pesticides, the inoculation of bacteria that can contribute to the growth and health of plants (PGPR) is essential. The properties classically sought in PGPR are the production of phytohormones and other growth-promoting molecules, and more rarely the production of exopolysaccharides. We compared the effect of two strains of exopolysaccharide-producing Rhizobium alamii on rapeseed grown in a calcareous silty-clay soil under water stress conditions or not. The effect of factors ‘water stress’ and ‘inoculation’ were evaluated on plant growth parameters and the diversity of microbiota associated to root and root-adhering soil compartments. Water stress resulted in a significant decrease in leaf area, shoot biomass and RAS/RT ratio (root-adhering soil/root tissues), as well as overall beta-diversity. Inoculation with R. alamii YAS34 and GBV030 under water-stress conditions produced the same shoot dry biomass compared to uninoculated treatment in absence of water stress, and both strains increased shoot biomass under water-stressed conditions (+7% and +15%, respectively). Only R. alamii GBV030 significantly increased shoot biomass under unstressed or water-stressed conditions compared to the non-inoculated control (+39% and +15%, respectively). Alpha-diversity of the root-associated microbiota after inoculation with R. alamii YAS34 was significantly reduced. Beta-diversity was significantly modified after inoculation with R. alamii GBV030 under unstressed conditions. LEfSe analysis identified characteristic bacterial families, Flavobacteriaceae and Comamonadaceae, in the RT and RAS compartments for the treatment inoculated by R. alamii GBV030 under unstressed conditions, as well as Halomonadaceae (RT) and several species belonging to Actinomycetales (RAS). We showed that R. alamii GBV030 had a PGPR effect on rapeseed growth, increasing its tolerance to water stress, probably involving its capacity to produce exopolysaccharides, and other plant growth-promoting (PGP) traits.
Highlights
Field crops are increasingly intensified to meet human food needs and renewable energy resources
We showed that R. alamii GBV030 had a Plant Growth Promoting Rhizobacteria” (PGPR) effect on rapeseed growth, increasing its tolerance to water stress, probably involving its capacity to produce exopolysaccharides, and other plant growth-promoting (PGP) traits
By comparing R. alamii YAS34 with R. alamii GBV030, the objective was to evaluate the level of specificity of bacterial inoculation in using two strains belonging to the same species (R. alamii) and producing the same type of EPS, but isolated from two different plant rhizospheres
Summary
Field crops are increasingly intensified to meet human food needs and renewable energy resources. Global warming may shorten crop cycles in cold regions, but has serious consequences for agriculture in arid and semiarid regions (Lotze-Campen, 2011). In these regions, drought is the main factor limiting the productivity of forests (Allen et al, 2010) and field crops (Simelton et al, 2012). The search for solutions to reduce the impact of drought on plants has led to focus on understanding the interactions between plants and microorganisms to find solutions to prevent future crop damages caused by climate change (Cavicchioli et al, 2019)
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