Chiang Mai Journal of Science

     Endophytic actinobacteria are known for their beneficial effects on plant growth, including promoting growth, enhancing stress resistance, and improving nutrient uptake. However, research on the plant growth promotion (PGP) properties of endophytic actinobacteria isolated from mangroves is scarce. In this study, root samples from twelve mangrove species were collected from mangrove forests across five provinces in Thailand. A total of 54 endophytic actinobacteria strains were isolated, representing 7 families and 10 genera, including Streptomyces, Brevibacterium, Corynebacterium, Gordonia, Kocuria, Micrococcus, Micromonospora, Mycobacterium, Nonomuraea, and Rothia. One of these strains potentially represented a novel species within the genus Gordonia. Among the 54 isolates, 20 demonstrated phosphate solubilization, 9 showed potassium solubilization, 26 produced siderophores, and 22 produced indole compounds. Five strains that exhibited various PGP traits were selected for their ACC deaminase activity. Two isolates, Streptomyces sp. CBTP-06 and Brevibacterium sp. CBSO-02, tested positive for ACC deaminase activity. Notably, both strains significantly increased rice seedling growth, shoot length, root length, and root weight compared with those of the uninoculated control. These findings highlight mangrove-derived endophytic actinobacteria as promising bioinoculant candidates with the potential to improve plant growth and productivity in agricultural applications.