LAUSR

We examined abundance, bioactivity, and endophytism of cultivable actinobacteria isolated from plant interiors of two Thai pigmented rice cultivars: Hom Nin (HN) rice and Luem Pua (LP) glutinous rice. Both rice cultivars housed the same amount of endophytic actinobacteria (33 isolates each). Microbispora (76%) and Streptomyces (73%) were the predominant endophytic actinobacteria of LP glutinous rice and HN rice, respectively. Sphaerisporangium (9%) was found only in LP glutinous rice. Twelve percent of endophytic actinobacteria was the possibility of discovering novel species from both rice cultivars. Most endophytic actinobacteria exhibited plant growth‐promoting potentials, including antimicrobial activity against test bacteria and phytopathogenic fungi, solubilization of phosphate, and production of biostimulants (i.e., ammonia, indole‐3‐acetic acid, and siderophore) and biocatalysts (i.e., amylase, cellulase, chitinase, lipase, and protease). Our findings revealed that seed phytochemicals of pigmented rice (e.g., anthocyanin, γ‐oryzanol, phytate, antioxidants, and content of amylose) were effectors, shaping the community structures and biofunctions of endophytic actinobacteria. We conclude that pigmented rice is yet a challenging source for discovery of bioactive and novel actinobacteria. This study also provides new insights into the plant‐endophyte interactions by which seed phytochemicals act as a primary checkpoint in the natural selection for establishing unique plant endophytomes.