Allelopathic potential of root endophytic bacterial metabolites on seeds germination of Casuarina equisetifolia

Abstract

We determined the role of endophytic bacteria of C. equietifolia, involved in synthesis of allelochemicals. The root endophytic bacteria were isolated and their biological activity was studied to determine their allelopathic potential in fermentation broth. Twenty one species of endophytic bacteria were isolated from the C. equisetifolia roots, of which Bacillus were the dominant genus, Acinetobacter and Staphylococcus were other dominant genera. These 21 endophytic bacteria inhibited the seeds germination of C. equisetifolia, among which Bacillus amyloliquefaciens was most inhibitory. Main allelopathic components of fermentation broth of 3-endophytic bacteria (Bacillus amyloliquefaciens, Bacillus aryabhattai and Paenibacillus glycanilyticus) with strongest allelopathic potential were rich in phenols, esters, organic acids, aldehydes, alcohols, ketones etc. Among them, two allelopathic substances [2,2'-methylenebis[6-(1,1-dimethylethyl)-4-methyl-Phenol and 1,2,3,4-Butanetetrol] were present in both endophytic bacteria fermentation broth and in root and soil extracts. These results confirmed that the secondary metabolites of C. equisetifolia root endophytic bacteria were allelopathic.

Root exudates and chemotactic strains mediate bacterial community assembly in the rhizosphere soil of Casuarina equisetifolia L

“…Studies on chemoattractants have typically focused on small-molecule organic acids and amino acids with a few reports related to phenols and fatty acids ( Li et al., 2017 ). In earlier work, we showed that 2,4-di-tert-butylphenol and methyl stearate could act as allelochemicals affecting the growth of C. equisetifolia trees and microorganisms, and we also found a high level of arginine in C. equisetifolia roots ( Li et al., 2016 ; Chen, 2021 ). 2, 4-di-tert-butylphenol was also shown to function as a bacteriostatic agent and a chemoattractant to attract beneficial strains to prevent soil-borne diseases ( Marchese et al., 2017 ).…”

“…Our previous studies have shown that Bacillus is present in the non-rhizosphere soils of C. equisetifolia , rhizosphere soils, and roots, with high abundance in the latter (Lin, unpublished). In addition, Bacillus can infect C. equisetifolia roots ( Chen, 2021 ). Therefore, we hypothesized that this bacterial genus underwent horizontal transmission and aggregated within the rhizosphere through chemotaxis, and then infected and proliferated in large numbers within the roots, subsequently protecting C. equisetifolia from soil pathogens.…”