Enhancing Teak (Tectona grandis) Seedling Growth by Rhizosphere Microbes: A Sustainable Way to Optimize Agroforestry.

With its premium wood quality and resistance to pests, teak is a valuable tree species remarkably required for timber trading and agroforestry. The nursery stage of teak plantation needs critical care to warrant its long-term productivity. This study aimed to search for beneficial teak rhizosphere microbes and assess their teak-growth-promoting potentials during nursery stock preparation. Three teak rhizosphere/root-associated microbes, including two teak rhizobacteria (a nitrogen-fixing teak root endophyte-Agrobacterium sp. CGC-5 and a teak rhizosphere actinobacterium-Kitasatospora sp. TCM1-050) and an arbuscular mycorrhizal fungus (Claroideoglomus sp. PBT03), were isolated and used in this study. Both teak rhizobacteria could produce in vitro phytohormones (auxins) and catalase. With the pot-scale assessments, applying these rhizosphere microbes in the form of consortia offered better teak-growth-promoting activities than the individual applications, supported by significantly increased teak seedling biomass. Moreover, teak-growth-promoting roles of the arbuscular mycorrhizal fungus were highly dependent upon the support by other teak rhizobacteria. Based on our findings, establishing the synergistic interactions between beneficial rhizosphere microbes and teak roots was a promising sustainable strategy to enhance teak growth and development at the nursery stage and reduce chemical inputs in agroforestry.

Isolation, Characterization, and Efficacy of Actinobacteria Associated with Arbuscular Mycorrhizal Spores in Promoting Plant Growth of Chili (Capsicum flutescens L.).

Nowadays, microorganisms that display plant growth promoting properties are significantly interesting for their potential role in reducing the use of chemical fertilizers. This research study proposed the isolation of the actinobacteria associated with arbuscular mycorrhizal fungi (AMF) spores and the investigation of their plant growth promoting properties in the in vitro assay. Three actinobacterial strains were obtained and identified to the genus Streptomyces (GETU-1 and GIG-1) and Amycolatopsis (GLM-2). The results indicated that all actinobacterial strains produced indole-3-acetic acid (IAA) and were positive in terms of siderophore, endoglucanase, and ammonia productions. In the in vitro assay, all strains were grown in the presence of water activity within a range of 0.897 to 0.998, pH values within a range of 5-11, and in the presence of 2.5% NaCl for the investigation of drought, pH, and salt tolerances, respectively. Additionally, all strains were able to tolerate commercial insecticides (propargite and methomyl) and fungicides (captan) at the recommended dosages for field applications. Only, Amycolatopsis sp. GLM-2 showed tolerance to benomyl at the recommended dose. All the obtained actinobacteria were characterized as plant growth promoting strains by improving the growth of chili plants (Capsicum flutescens L.). Moreover, the co-inoculation treatment of the obtained actinobacteria and AMF (Claroideoglomus etunicatum) spores could significantly increase plant growth, contribute to the chlorophyll index, and enhance fruit production in chili plants. Additionally, the highest value of AMF spore production and the greatest percentage of root colonization were observed in the treatment that had been co-inoculated with Streptomyces sp. GETU-1.

Amycolatopsis eburnea sp. nov., an actinomycete associated with arbuscular mycorrhizal fungal spores.

A novel actinomycete, designated strain GLM-1T, was isolated from arbuscular mycorrhizal fungal spores from Funneliformis mosseae RYA08, collected from Aquilaria crassna Pierre ex Lec. rhizosphere soil in Klaeng, Rayong Province, Thailand. Morphological characteristics of this strain included long chains of rod-like cells and squarish elements. The cell-wall composition of this novel isolate contained meso-diaminopimelic acid. The whole-cell diagnostic sugars were arabinose and galactose. The predominant menaquinone was MK-9(H4). The major fatty acids were iso-C16 : 0 and iso-C15 : 0. Only phosphatidylethanolamine was detected as a polar lipid. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain GLM-1T was closely related to Amycolatopsis rhabdoformis SB026T (99.11 %) with a low DNA-DNA hybridization value of 22.6-34.7 %. Genome sequencing revealed a genome size of 10 Mbp. There were obvious distinctions in the average nucleotide identity values between stain GLM-1T and its closely related strains at around 86-93 % (ANIb) and 89-94 % (ANIm). The digital DNA-DNA hybridization values between strain GLM-1T and type strains of phylogenetically related species were 34-55 %. The G+C content of the genomic DNA was 71.8 mol%. Based on these data, strain GLM-1T is considered to represent a novel species of the genus Amycolatopsis, for which the name Amycolatopsiseburnea sp. nov. is proposed. The type strain is GLM-1T (=TBRC 9315T=NBRC 113658T).