Rhizobacteria and Arbuscular Mycorrhizal Fungi of Oil Crops (Physic Nut and Sacha Inchi): A Cultivable-Based Assessment for Abundance, Diversity, and Plant Growth-Promoting Potentials

Abstract

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.

Biosynthetic Gene Clusters from Swine Gut Microbiome

“…So far, few secondary metabolites from gut microbes have been well characterized. First, the majority of bacteria from nature are currently unculturable with traditional laboratory techniques [ 58 ]. Second, the expression of bioactive secondary metabolites may remain silent or at a relatively low level [ 59 ].…”

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

“…The bacterial colony presented on the agar medium was collected and sub-cultured on the same medium until becoming an axenic culture. The capability to fix atmospheric nitrogen of isolate CGC-5 was estimated following a modified acetylene reduction assay addressed by Wiriya et al [ 26 ], and its nitrogenase activity was 10.57 ± 0.26 nmol h −1 per mg cell protein. The isolate was preserved in 20% ( v / v ) glycerol at −20 °C before further investigation.…”

“…The auxin family consists of diverse molecular members such as IAA (the most abundant and basic auxin), indole-3-butyric acid, indole-3-propionic acid, etc. The capability to form auxins was estimated using a modified Salkowski’s colorimetric method, described in Wiriya et al [ 26 ]. Briefly, rhizobacteria were grown in 5 mL liquid media (Burk’s broth for isolate CGC-5 and ISP2 broth for isolate TCM1-050).…”

“…Plant root colonization by arbuscular mycorrhizal fungi is beneficial for ensuring a long-term synergistic interaction between host plants and their fungal partners. The capability of arbuscular mycorrhizal fungi to colonize teak roots was determined by the percentage of root colonization and the number of spores produced in the rhizosphere soil, described by Chaiyasen et al [ 28 ] and Wiriya et al [ 26 ]. At the end of pot experiments, planting materials and plant roots were collected from each pot.…”

Beta Diversity of Arbuscular Mycorrhizal Communities Increases in Time after Crop Establishment of Peruvian Sacha Inchi (Plukenetia volubilis)

“…At present, few studies have been done on the interaction of these fungi with Plukenetia volubilis species and their diversity. Previous studies under controlled conditions (greenhouse) have shown that AM fungi (genera: Paraglomus , Glomus , Acaulospora , Claroideoglomus , and Funneliformis ) stimulate growth and development and improve the drought tolerance of sacha inchi seedlings through alterations in the morphological, physiological, and biochemical characteristics of the roots [ 27 , 28 ]. Likewise, some AM fungal species have been reported in sacha inchi rhizospheric soils in the Peruvian rainforest and in Thailand [ 29 , 30 , 31 , 32 , 33 ].…”