Isolation and Morphological Characterization of Culturable Soil Microorganisms from Local Shallot Fields in Palu, Central Sulawesi, Exposed to Different Insecticide Intensities

Abstract

Soil microbial communities can be influenced by environmental factors such as insecticide exposure and the resulting chemical residues. The purpose of this study was to isolate and characterize rhizosphere microorganisms of local shallots from Palu from fields with different levels of insecticide exposure. The approach used was an isolation method using selective media for bacteria, actinomycetes, and fungi, followed by colony morphology characterization and Gram staining for bacteria and actinomycetes. A total of 26 isolates were obtained from this study, including 9 bacterial isolates, 4 actinomycete isolates, and 13 representative fungal isolates. Morphological characterization showed that actinomycete isolates had dry colonies, powdery/rough texture, and formed aerial mycelium, while fungal isolates were dominated by Aspergillus niger, Aspergillus flavus, and Trichoderma. Soil pH values ​​between locations were relatively uniform, while soil moisture showed variation and tended to be lower at high-intensity locations. The formation of rhizosphere microbial community structures from land with different insecticide exposures, so that these findings can be used as a basis for developing soil health bioindicators and local biological agent candidates to support sustainable shallot farming.