Non-rhizobial nodule endophytes improve nodulation, change root exudation pattern and promote the growth of lentil, for prospective application in fallow soil

Abstract

Non-rhizobial endophytes (NREs) are active colonizers inhabiting the root nodules. Though their active role in the lentil agroecosystem is not well defined, here we observed that these NREs might promote the growth of lentils, modulate rhizospheric community structure and could be used as promising organisms for optimal use of rice fallow soil. NREs from root nodules of lentils were isolated and examined for plant growth-promoting traits, exopolysaccharide (EPS) and biofilm production, root metabolites, and the presence of nifH and nifK elements. The greenhouse experiment with the chosen NREs, i.e., Serratia plymuthica 33GS and Serratia sp. R6 significantly increased the germination rate, vigour index, development of nodules (in non-sterile soil) and fresh weight of nodules (33GS 94%, R6 61% growth) and length of the shoot (33GS 86%, R6 51.16%) as well as chlorophyll levels when compared to the uninoculated control. Scanning Electron Microscopy (SEM) revealed that both isolates could successfully colonize the roots and elicit root hair growth. The inoculation of the NREs resulted in specific changes in root exudation patterns. The plants with 33GS and R6 treatment significantly stimulated the exudation of triterpenes, fatty acids, and their methyl esters in comparison to the uninoculated plants, altering the rhizospheric microbial community structure. Proteobacteria dominated the rhizospheric microbiota in all the treatments. Treatment with 33GS or R6 also enhanced the relative abundance of other favourable microbes, including Rhizobium, Mesorhizobium, and Bradyrhizobium. The correlation network analysis of relative abundances resulted in numerous bacterial taxa, which were in cooperation with each other, having a possible role in plant growth promotion. The results indicate the significant role of NREs as plant growth promoters, which also includes their role in root exudation patterns, enhancement of soil nutrient status and modulation of rhizospheric microbiota, suggesting their prospects in sustainable, and bio-based agriculture.

Serratia spp. as plant growth-promoting bacteria alleviating salinity, drought, and nutrient imbalance stresses

“…As previously evidenced, phytohormone production, AHL, ACC deaminase, nitrogen fixation, P and Zn solubilization, and biofilm formation play crucial roles in stimulating plant growth under normal conditions through the activity of Serratia spp. strains ( Martínez et al, 2018 ; Hakim et al, 2021 ; Debnath et al, 2023 ).…”

Prevalence, diversity and applications potential of nodules endophytic bacteria: a systematic review

“…Moreover, studies at the field level have focused on leveraging nodule endophytes to enhance the growth and adaptation of legumes to degraded estuarine soils. They have demonstrated that non-rhizobial nodule endophytes exhibit a significant potential to improve nodulation, modulate root exudation patterns, and foster legume growth ( Dhole and Shelat, 2022 ; Debnath et al, 2023 ).…”

“…Studies have documented the nitrogen-fixing capabilities of Serratia sp., Herbaspirillum sp., Paenibacillus sp., Arthrobacter sp., Klebsiella sp., Pseudomonas sp., Bacillus sp., Bosea sp., and Enterobacter sp. strains isolated from legume nodules ( Valverde, 2003 ; Muresu et al, 2008 ; Selvakumar et al, 2008 ; Ibáñez et al, 2009 ; Knežević et al, 2021 ; Debnath et al, 2023 ).…”

“…Endophytes also influence osmotic processes, root morphology, and nitrogen metabolism in legumes ( Dudeja et al, 2012 ). Furthermore, non-rhizobial endophytes (NREs) have positively influenced lentil growth, modulating root exudates and rhizospheric community structure ( Debnath et al, 2023 ). Similarly, certain endophytes associated with peanut roots enhanced biomass production, demonstrating the broader impact of endophytes beyond nodulation ( Hossain et al, 2023 ).…”