Actinobacteria From Bryophytes for Growth Promotion of Tropical Moss Species

Actinobacteria have shown significant potential in promoting the growth of various plant species, especially those that inhabit in association with plants. However, previous research has mainly focused on higher plant species. Bryophytes are a large group of non-vascular, non-flowering land plants without true vascular bundles, roots, stems, and leaves. Despite the extensive diversity of bryophytes in Thailand, research on the diversity of actinobacteria associated with bryophytes remains scarce. This study aimed to isolate actinobacteria from three bryophyte species in northern Thailand: Koponobryum papillosum Printarakul & Chantanaorr, Pseudotrismegistia undulata, and Sphagnum cuspidatulum C. Müll. A total of 52 isolates were identified, including 6 endophytic and 46 epiphytic isolates. These isolates were assigned to four genera: Brevibacterium (1 isolate), Microbacterium (1 isolate), Rhodococcus (6 isolates), and Streptomyces (44 isolates). All isolates were assessed for their plant-growth promoting abilities both in vitro and in planta. Most actinobacteria exhibited the in vitro ability to produce indole-3-acetic acid (IAA), siderophores, and solubilize tricalcium phosphate. Three isolates-Streptomyces brevispora RHP2, S. halstedii WS1, and Rhodococcus triatomae RHK22-were selected to evaluate their potential to enhance the growth of S. cuspidatulum C. Müll in soil. R. triatomae RHK22 was highly effective in promoting the regeneration of new shoots and significantly enhancing thallus height, fresh weight, dry weight, total chlorophyll content, and total carotenoid content (p < 0.05) of S. cuspidatulum C. Müll when applied as cell suspension and cell free supernatant.