With the aim of searching for potent diazotrophic bacteria that are free of public health concerns and optimize rice cultivation, the endophytic colonization and plant growth-promoting activities of some endophytic diazotrophic bacteria isolated from rice were evaluated. Among these bacteria, the emerging diazotrophic strains of the genus Novosphingobium effectively associated with rice plant interiors and consequently promoted the growth of rice, even with the lack of a nitrogen source. These results suggest that diazotrophic Novosphingobium is an alternative microbial resource for further development as a safe biological enhancer in the optimization of organic rice cultivation.

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White root disease causing by Rigidoporus sp. is a severe problem that decreases latex productivity and can even cause mortality of rubber trees. With the aim to control biologically this disease, antifungal actinobacteria were isolated from rhizospheric soils of some medicinal plants cultivated in Thailand. Among all isolated actinobacteria, an isolate TM32 exhibited distinctive antagonistic activity against the fungus. Cell-free culture broth of the isolate showed median effective dose (ED50) of 2.61 ml l −1 (equal to 1.19 g l −1 of metalaxyl). The isolate was also able to solubilize phosphate and to produce chitinase (enzyme activity = 0.093 ± 0.004 U ml −1), siderophore (average clear zone, 11.75 ± 0.96 mm) and indole-3-acetic acid (54.00 ± 1.00 μg ml −1). Application of biocontrol starters produced by this isolate in nursery stage of rubber trees farming showed greater suppression of the disease than direct use of its biocontrol agents. The biocontrol starters also enhanced growth of the rubber trees by increasing their heights. This might be due to the persistent growth of the isolate by using the organic substrate remaining in soil, which could later antagonize fungal pathogens through colonization at the rhizosphere and immunization of the rubber trees. The isolate revealed phylogenetically related to Streptomyces sioyaensis supported by 99 % similarity of 16S rRNA gene sequences. We concluded that application of the biocontrol starters produced by this Streptomyces isolate would be an alternative approach for sustainable control of soil-borne fungal invasion in long-term rubber tree farming. Keywords separated by '-' Hevea brasiliensis-Soil-borne fungal pathogen-Biocontrol-Actinobacteria-Antifungal activity Foot note information 2 4 Utilization of rhizospheric Streptomyces for biological control of Rigidoporus sp. causing white root disease in rubber tree 7

31Communities of bacterial endophytes within the rice landraces cultivated in the highlands of northern 32Thailand were studied using fingerprinting data of 16S rRNA and nifH genes profiling by PCR-DGGE. The

Nowadays, oil crops are very attractive both for human consumption and biodiesel production; however, little is known about their commensal rhizosphere microbes. In this study, rhizosphere samples were collected from physic nut and sacha inchi plants grown in several areas of Thailand. Rhizobacteria, cultivable in nitrogen-free media, and arbuscular mycorrhizal (AM) fungi were isolated and examined for abundance, diversity, and plant growth-promoting activities (indole-3-acetic acid (IAA) and siderophore production, nitrogen fixation, and phosphate solubilization). Results showed that only the AM spore amount was affected by plant species and soil features. Considering rhizobacterial diversity, two classes—Alphaproteobacteria (Ensifer sp. and Agrobacterium sp.) and Gammaproteobacteria (Raoultella sp. and Pseudomonas spp.)—were identified in physic nut rhizosphere, and three classes; Actinobacteria (Microbacterium sp.), Betaproteobacteria (Burkholderia sp.) and Gammaproteobacteria (Pantoea sp.) were identified in the sacha inchi rhizosphere. Considering AM fungal diversity, four genera were identified (Acaulospora, Claroideoglomus, Glomus, and Funneliformis) in sacha inchi rhizospheres and two genera (Acaulospora and Glomus) in physic nut rhizospheres. The rhizobacteria with the highest IAA production and AM spores with the highest root-colonizing ability were identified, and the best ones (Ensifer sp. CM1-RB003 and Acaulospora sp. CM2-AMA3 for physic nut, and Pantoea sp. CR1-RB056 and Funneliformis sp. CR2-AMF1 for sacha inchi) were evaluated in pot experiments alone and in a consortium in comparison with a non-inoculated control. The microbial treatments increased the length and the diameter of stems and the chlorophyll content in both the crops. CM1-RB003 and CR1-RB056 also increased the number of leaves in sacha inchi. Interestingly, in physic nut, the consortium increased AM fungal root colonization and the numbers of offspring AM spores in comparison with those observed in sacha inchi. Our findings proved that AM fungal abundance and diversity likely rely on plant species and soil features. In addition, pot experiments showed that rhizosphere microorganisms were the key players in the development and growth of physic nut and sacha inchi.