Indole 3-acetic acid producing bacteria from onion rhizosphere
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Date
2024-11-01
Authors
Fernando, G.R.
Abeysinghe, S.
Widana Gamage, S.M.K.
Rajapakse, R.G.S.C.
Journal Title
Journal ISSN
Volume Title
Publisher
Postgraduate Institute of Science (PGIS), University of Peradeniya, Sri Lanka
Abstract
Onion (Allium cepa L.) is an important crop in Sri Lanka. It is important as a condiment, a leafy vegetable, and an ingredient in indigenous medicine. A recent study showed that the growth and quality of onion bulbs can be improved by exogenous application of Indole 3-acetic acid (IAA). Some phytohormones are known to improve human health. The current study aimed at isolating and identifying IAA-producing bacteria from the onion rhizosphere and incorporating them into plant-growth-promoting-rhizobacterial (PGPR) consortia. Rhizobacteria were isolated from the roots of onions grown in three main onion-growing areas in Sri Lanka, viz., Jaffna, Dambulla, and Angunakolapelessa. Both free-living and endophytic bacteria were isolated in nutrient agar. Hundred and twenty-six morphologically distinct strains were isolated and screened for their ability to synthesize IAA, with and without induction, by the externally added tryptophan (0.2% [w/v]), which is a precursor of IAA. Accumulated IAA in the culture broth was estimated spectrophotometrically at 535 nm following Salkowski’s method. Twenty-one strains, including two endophytic bacterial strains, were found to be IAA producers. More efficient IAA production was obtained in tryptophan-induced cultures. Two strains, i.e., R1OJ2 and OD20 produced > 200 mg/L of IAA while ROJ10, ROJ7, ROD12, ROJ5, ROJ50, ROD16, ROD15, ROA10, and ROJ8 produced >100 mg/L when induced. None of these strains could produce > 100 mg/L without tryptophan but ROJ7, ROJ11, ROJ2, ROJ50, ROJ38, and ROD16 produced IAA around 50 mg/L. The endophytic strains, EOA7 and EOJ1, also showed high IAA production, 73.4 mg/L and 83.6 mg/L, respectively. According to a previous study, IAA at 50 mg/L promotes onion growth, while IAA at 200 mg/L increases phenol content, thus increasing its medicinal value. Hence, ROJ7, ROJ11, ROJ2, ROJ50, ROJ38, and ROD16 strains are good candidates for PGPR-consortium development, while ROJ2, ROD20, and ROA10 are good candidates for enhancing the medicinal value of onion.
Description
Keywords
Indole 3-Acetic acid , Onion , PGPR
Citation
Proceedings of the Postgraduate Institute of Science Research Congress -2024, University of Peradeniya, Sri Lanka, P. 101