Abstract
This study reports the application of a novel bioprospecting procedure designed to screen plant growth-promoting rhizobacteria (PGPR) capable of rapidly colonizing the rhizosphere and mitigating drought stress in multiple hosts. Two PGPR strains were isolated by this bioprospecting screening assay and identified as Bacillus sp. (12D6) and Enterobacter sp. (16i). When inoculated into the rhizospheres of wheat (Triticum aestivum) and maize (Zea mays) seedlings, these PGPR resulted in delays in the onset of plant drought symptoms. The plant phenotype responding to drought stress was associated with alterations in root system architecture. In wheat, both PGPR isolates significantly increased root branching, and Bacillus sp. (12D6), in particular, increased root length, when compared to the control. In maize, both PGPR isolates significantly increased root length, root surface area and number of tips when compared to the control. Enterobacter sp. (16i) exhibited greater effects in root length, diameter and branching when compared to Bacillus sp. (12D6) or the control. In vitro phytohormone profiling of PGPR pellets and filtrates using LC/MS demonstrated that both PGPR strains produced and excreted indole-3-acetic acid (IAA) and salicylic acid (SA) when compared to other phytohormones. The positive effects of PGPR inoculation occurred concurrently with the onset of water deficit, demonstrating the potential of the PGPR identified from this bioprospecting pipeline for use in crop production systems under drought stress.
Highlights
Drought is a major abiotic stress threatening agricultural production worldwide
This study reports the development and use of a bioprospecting pipeline to effectively screen plant growth-promoting rhizobacteria (PGPR) for the ability to rapidly mitigate plant drought stress symptoms in multiple cereal hosts when applied to plants at the onset of water deficit conditions
By starting with samples of perennial grasses that appeared healthy under constant water deficit conditions in the semi-arid environment of El Paso, TX, we attempted to focus on rhizosphere microbiomes that may be selected for and adapted to mitigating drought tolerance to grasses under these conditions
Summary
Drought is a major abiotic stress threatening agricultural production worldwide. In the last 40 years, drought stress has reduced yields in cereals by as much as 10% (Lesk et al, 2016) and is forecasted to affect production on over 50% of the arable land by 2050 (Vinocur and Altman, 2005). PGPR readily colonize the root rhizosphere and establish both free-living and intimate associations with host plants Often, these interactions lead to enhancement of crop productivity and mitigation of biotic and abiotic stresses through a variety of mechanisms (Mayak et al, 2004; Berg, 2009; Dimkpa et al, 2009; Liu et al, 2013; Mendes et al, 2013; Vacheron et al, 2013; Porcel et al, 2014; Gontia-Mishra et al, 2016; Ngumbi and Kloepper, 2016; Vurukonda et al, 2016; Barnawal et al, 2017; Forni et al, 2017). Mechanisms associated with PGPR-derived drought tolerance include alterations in host root system architecture, osmoregulation, management of oxidative stress via the biosynthesis and metabolism of phytohormones or the production of antioxidants for scavenging reactive oxygen species (ROS), the production of large chain extracellular polysaccharide (EPS) that may serve as humectant, and transcriptional regulation of host stress response genes (Dimkpa et al, 2009; Liu et al, 2013; Vacheron et al, 2013; Osakabe et al, 2014; Timmusk et al, 2014; Gontia-Mishra et al, 2016; Ngumbi and Kloepper, 2016; Vurukonda et al, 2016; Barnawal et al, 2017; Forni et al, 2017)
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