The Potential of Plant Growth-Promoting Rhizobacteria (PGPR) as Biostimulants and Biodegradation Agents of Chlorpyrifos in Pesticide-Contaminated Shallot Fields

Abstract

HistoryShallots are a staple commodity in Indonesia, essential both as a culinary ingredient and as traditional medicine, resulting in consistently high demand.However, production is constrained by limited seed and fertilizer availability, while excessive use of synthetic fertilizers can harm the environment.Environmentally friendly alternatives, such as the use of rhizosphere microorganisms, are increasingly considered due to their role in improving soil fertility and promoting plant growth.This study aimed to explore and identify rhizosphere bacterial isolates from shallot plants in Anggeraja Subdistrict, Enrekang Regency, and evaluate their potential as plant growth-promoting rhizobacteria (PGPR), particularly in producing Indole-3-Acetic Acid (IAA) and solubilizing phosphate.Rhizosphere soil samples were collected from four villages Lakawan, Batunoni, Pekalobean, and Tampo-and isolated on nutrient agar.Isolates were characterized morphologically and physiologically, and their ability to produce IAA and solubilize phosphate was assessed using colorimetric and spectrophotometric methods.Among 60 isolates, 20 showed varying IAA production (0.02-3.92ppm) and phosphate solubilization (4.94-11.23ppm).Isolates BN14 and BN25 exhibited the highest IAA production, while BN02 showed the highest phosphate-solubilizing activity.Environmental factors such as soil C/N ratio and organic matter content likely influenced microbial activity.Greenhouse assays showed that several isolates enhanced shallot growth, with TP49 producing the most significant improvements in plant height (9.08cm), leaf number, root length (5.95cm), fresh weight (0.264g), and dry weight (0.0082g) compared to controls.Microscopic analysis confirmed biofilm formation on shallot roots, indicating successful bacterial colonization.Molecular identification using 16S rRNA gene sequencing revealed that selected high-performing isolates were closely related to Bacillus spp.These findings demonstrate the potential of indigenous rhizosphere bacteria as biofertilizers to enhance shallot productivity, support soil fertility, and promote sustainable agriculture in karst highland ecosystems of Enrekang.

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