| Summary: | Observations have shown that seeds collected by harvester ants are less likely to mold. Based on evolutionary analysis and other research, it was hypothesized that harvester ants could apply actinomycetes to protect seeds, similar to the protection of mutualistic fungi by leafcutter ants. Two actinomycetes were successfully isolated from the harvester ant <i>Messor orientalis.</i> The taxonomic status of the actinomycetes was determined by 16S rRNA sequence analysis and biochemical experimental observations. Their inhibitory effects on plant pathogens were measured. One of the bacteria was identified as <i>Brachybacterium phenoliresistens</i> and denoted as <i>B. phenoliresistens MO</i>. The other belonged to the genus <i>Microbacterium</i>. It was named <i>Microbacterium</i> sp. Growth rate determination and coculture experiments were performed to explore the inhibitory effect of actinomycetes on indicator plant pathogens. The inhibition rates of the actinomycetes toward <i>Peronophythora litchii</i> and <i>Rhizoctonia solani</i> were 100% in media containing 30% or more fermentation broth, and they also showed an inhibitory effect on <i>Colletotrichum siamense</i>. The coculture experiment supported this result by showing that the growth of <i>P. litchii</i> and <i>R. solani</i> was inhibited in the presence of actinomycetes. Therefore, the results of this study show the agricultural application potential of these bacteria and may provide a reference for research on the symbiosis of harvester ants with actinomycetes.
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