Chiang Mai Journal of Science

Actinomycetes are well known as producers of biologically active compounds with high commercial value. They have been isolated from various sources including plant species.  In this study, the plant growth promoting traits of endophytic actinomycetes isolated from rice plants were evaluated, as well as their antagonistic activities against rice pathogenic fungi. Healthy rice plants were collected from nine provinces in Thailand. One hundred and ninety-one isolates were able to be recovered from the surface-sterilized roots and stems of the rice plants. Of these, 96 actinomycetes were classified as streptomycetes and 95 strains were non-streptomycetes species. Plant growth promotion assays showed that 79.6% and 30.9% of these isolates could produce siderophore and indole-3-acetic acid, respectively and 42.9% could solubilize phosphate. Potential strains which showed strongly antagonistic against rice pathogenic fungi, Fusarium oxysporum, Rhizoctonia solani and Helminthosporium oryzae, with plant growth promoting activities were selected to determine their effects on root system of rice seedlings in vitro. The results showed that the isolates R07-04, R07-06 and S03-26 could increase the number of adventitious roots, but led to shorter seminal roots. However, in the pot experiment, isolate R07-06 could promote rice growth better than the other isolates and significantly enhanced shoot length, root dry weight and shoot dry weight. An identification of the isolate R07-06 using the 16S rRNA gene showed that the strain was most closely 

related to Streptomyces lydicus DSM 40002T (100% similarity). These results demonstrate that endophytic Streptomyces R07-06 could be a promising strain to develop as an antifungal and plant growth promoting agent for rice plants.