Identification, Characterization, and Growth-Promoting Effects of Bacterial Endophytes Isolated from Okra (Abelmoschus esculentus L.)

Abstract

Microorganisms colonize plant roots and exhibit plant growth promotion properties, therefore functioning as biofertilizers. To effectively use plant growth-promoting rhizobacteria, understanding their colonizing behavior and ability to compete with co-existing bacteria is essential. In this study, 12 endophytic bacterial strains belonging to seven genera in four classes with 99–100% homology were isolated from the roots of okra plants (Abelmoschus esculentus L.). Four isolates (Okhm3, Okhm5-4, Okhm10, and Okhm11) were inoculated on okra seeds and their effects on plant growth and colonization with single and mixed inoculations were evaluated. Okra was cultivated using sterilized vermiculite, and the growth parameters and colonization were measured 30 d after seed inoculation. All strains exhibited plant growth promotion traits that could improve okra plant growth in pot culture experiments. Notably, Okhm5-4 and Okhm10 strains (belonging to the Ensifer and Pseudomonas genera) revealed the highest growth-promoting effects on okra plants. Both strains were detected in the endosphere and rhizosphere of okra plants. Okhm10 and Okhm5-4, with lower colonization than Okhm3, showed better growth than Okhm3. Therefore, the colonization potential does not determine the growth-promoting effects. While Okhm3 populations remained stable in both inoculation conditions, the population level of other strains decreased in the mixed inoculation. This study showed bacterial endophytes isolated from Okra can be exploited as bio-fertilizers for sustainable agriculture systems.