Abstract
Vascular shrubs growing along the draw-down zones of saline lakes must develop adaptive mechanisms to cope with high salinity, erratic environmental conditions, and other biotic and abiotic stresses. Microbial endophytes from plants growing in these unique environments harbor diverse metabolic and genetic profiles that play an important role in plant growth, health, and survival under stressful conditions. A variety of bacterial endophytes have been isolated from salt tolerant plants but their potential applications in agriculture have not been fully explored. To further address this gap, the present study sought to isolate culturable bacterial endophytes from shrubs growing along the draw-down zone of Lake Bogoria, a saline alkaline lake, and examined their functional characteristics and potential in the biocontrol of the bean root rot pathogen, Fusarium solani. We collected shrubs growing within 5 m distance from the shoreline of Lake Bogoria and isolated 69 bacterial endophytes. The endophytic bacteria were affiliated to three different phyla (Firmicutes, Proteobacteria, and Actinobacteria) with a bias in the genera, Bacillus, and they showed no tissue or plant specificity. All selected isolates were positive for catalase enzyme grown in 1.5 M NaCl; three isolates (B23, B19, and B53) produced indole acetic acid (IAA) and only one isolate, B23 did not solubilize phosphate on Pikovskaya agar. Isolates, B19 and B53 exhibited more than 50% of mycelial inhibition in the dual culture assay and completely inhibited the germination of F. solani spores in co-culture assays while two isolates, B07 and B39 had delayed fungal spore germination after an overnight incubation. All isolates were able to establish endophytic association in the roots, stems, and leaves of been seedlings in both seed soaking and drenching methods. Colonization of bean seedlings by the bacterial endophytes, B19 and B53 resulted in the biocontrol of F. solani in planta, reduced disease severity and incidence, and significantly increased both root and shoot biomass compared to the control. Taxonomic identification using 16S rRNA revealed that the two isolates belong to Enterobacter hormaechei subsp., Xiangfangensis and Bacillus megaterium. Our results demonstrate the potential use of these two isolates in the biocontrol of the bean root rot pathogen, F. solani and plant growth promotion.
Highlights
Plants are sessile and have to acquire all their requirements for growth, development, and resistance to both biotic and abiotic stresses within the limited ecological unit
Experiments on two different Arabidopsis thaliana ecotypes grown under controlled environmental conditions on soils with different geochemistry by Bulgarelli et al (2012) concluded that the composition of root endophytes was influenced by soil type
The present study sought to explore the potential of bacterial endophytes from shrubs along the draw-down zone of Lake Bogoria for the biocontrol of bean root rot pathogen, F. solani
Summary
Plants are sessile and have to acquire all their requirements for growth, development, and resistance to both biotic and abiotic stresses within the limited ecological unit. Soil microorganisms play an important role in these plant interactions, establishing a symbiotic relationship with the plant thereby forming the plant microbiome. These plant–microbe interactions and their putative roles have been studied (Etesami et al, 2015; Potshangbam et al, 2017) and reviewed (Andreote et al, 2014; Berg et al, 2014; Etesami and Beattie, 2018; Hassani et al, 2018). Plants have been hypothesized to shape their microbial associations in the rhizosphere (Bulgarelli et al, 2012) This function is mediated by the release of root exudates which attract or repel microorganisms and the physical and chemical properties of soil which determine the soil microbial communities (Shakya et al, 2013). Zúñiga et al (2013) and Schikora et al (2016) reported that quorum sensing ability of bacteria using the auto-inducer, N-acyl homoserine lactone in gram negative bacteria plays a key role in bacterial endophytic colonization
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