Mass Production of Arbuscular Mycorrhizal Fungi on the Sorghum Plants Inoculated with Burkholderia arboris Using Soybean Mill Waste and Vermicompost-Amended Soil-Sand Substrate.

Arbuscular mycorrhizal (AM) fungi are being used as a new generation of biofertilizers to increase plant growth by improving plant nutrition and bio-protection. However, because of the obligatory nature of the plant host, large-scale multiplication of AM propagules is challenging, which limits its applicability. This study evaluates the ability of Burkholderia arboris to increase AM production in soybean mill waste and vermicompost amended by soil-sand mixture planted with sorghum as a host plant. The experiment was conducted in a nursery using a completely randomized design with four inoculation treatments (B. arboris, AM fungi, B. arboris + AM fungi, and control) under sterilized and unsterilized conditions. AM production was investigated microscopically (spore density and root colonization), and biochemically (AM-specific lipid biomarker, 16:1ω5cis derived from neutral lipid fatty acid (NLFA), and phospholipid fatty acid (PLFA) fractions from both soil and roots). Integrating B. arboris with AM fungi in organically amended pots was found to increase AM fungal production by 62.16 spores g-1 soil and root colonization by 80.85%. Biochemical parameters also increased with B. arboris inoculation: 5.49 nmol PLFA g-1 soil and 692.68 nmol PLFA g-1 root and 36.72 nmol NLFA g-1 soil and 3147.57 nmol NLFA g-1 root. Co-inoculation also increased glomalin-related soil protein and root biomass. Principal component analysis (PCA) further supported the higher contribution of B. arboris to AM fungi production under unsterilized conditions. In conclusion, inoculation of AM plant host seeds with B. arboris prior to sowing into organic potting mix could be a promising and cost-effective approach for increasing AM inoculum density for commercial production. Furthermore, efforts need to be made for up-scaling the AM production with different plant hosts and soil-substrate types.

Glycoproteins of arbuscular mycorrhiza for soil carbon sequestration: Review of mechanisms and controls.

Glycoproteins, e.g., glomalin related soil proteins (GRSP), are sticky organic substances produced by arbuscular mycorrhizal fungi (AMF). This review summarizes the information on i) the biochemical nature, physical state and origin of GRSP, ii) GRSP decomposition and residence time in soil, iii) GRSP functions, in particular the physical, chemical, and biochemical roles for soil aggregation and carbon (C) sequestration, and finally iv) how land use and agricultural management affect GRSP production and subsequently, organic C sequestration. GRSP augment soil quality by increasing water holding capacity, nutrient storage and availability, microbial and enzymatic activities, and microbial production of extracellular polysaccharides. After release into the soil, GRSP become prone to microbial decomposition due to stabilization with organic matter and sesquioxides, and thereby increasing the residence time between 6 and 42 years. Temperate soils contain 2-15 mg GRSP g-1, whereas arid and semiarid grasslands amount for 0.87-1.7 mg g-1, and GRSP are lower in desert soils. GRSP content is highest in acidic soils as compared to neutral and calcareous soils. Conservation tillage, organic fertilizers and AMF inhabiting crops (e.g. maize, sorghum, soybean, and wheat) increase GRSP production and transform C into stable forms, thereby sustaining soil health and reducing CO2 emissions. Crop rotations with non-mycorrhizal species (e.g. rapeseed) and fallow soils reduce AMF growth and consequently, the GRSP production. The GRSP production increases under nutrient and water deficiency, soil warming and elevated CO2. In the context of global climate change, increased C sequestration through GRSP induced aggregate formation and organic matter stabilization prolong the mean residence time of soil C. Protecting soils against degradation under intensive land use, stable aggregate formation, and prolonging the residence time of C calls for strategies that maximize GRSP production and functions based on reduced tillage, AMF-relevant crop rotations and organic farming.

Characterization and low-cost preservation of Chromobacterium violaceum strain TRFM-24 isolated from Tripura state, India.

BACKGROUND: Chromobacterium species, through their bioactive molecules, help in combating biotic and abiotic stresses in plants and humans. The present study was aimed to identify, characterize and preserve in natural gums the violet-pigmented bacterial isolate TRFM-24 recovered from the rhizosphere soil of rice collected from Tripura state. RESULTS: Based on morphological, biochemical and 16S rRNA gene sequencing, the isolate TFRM-24 was identified as Chromobacterium violaceum (NAIMCC-B-02276; MCC 4212). The bacterium is saprophytic, free living and Gram negative. The strain was found positive for production of IAA, cellulase, xylanase and protease, and showed tolerance to salt (2.5%) and drought (-1.2 MPa). However, it showed poor biocontrol activity against soil-borne phytopathogens and nutrient-solubilizing abilitiets. C. violaceum strain TRFM-24 did not survive on tryptic soya agar (TSA) beyond 12 days between 4 and 32 °C temperature hence a method of preservation of this bacterium was attempted using different natural gums namely Acacia nilotica (babul), Anogeissus latifolia (dhavda), Boswellia serrata (salai) and Butea monosperma (palash) under different temperature regime (6-32 °C). The bacterium survived in babul gum (gum acacia), dhavda and salai solution at room temperature beyond a year. CONCLUSION: Based on polyphasic approach, a violet-pigmented isolate TRFM-24 was identified as Chromobacterim violaceum which possessed some attributes of plant and human importance. Further, a simple and low-cost preservation method of strain TRFM-24 at room temperature was developed using natural gums such as babul, dhavda and salai gums which may be the first report to our knowledge.

Soybean Processing Mill Waste Plus Vermicompost Enhances Arbuscular Mycorrhizal Fungus Inoculum Production.

This study considered soybean processing mill waste (hulls) as an organic substrate for mass multiplication of indigenous arbuscular mycorrhizal (AM) fungi on sorghum and amaranthus as hosts. In the first experiment, from seven soybean processing mill wastes, three wastes were evaluated for their ability to multiply AM fungi on the two host plants. Among these wastes, hulls were found to be promising for the multiplication of AM fungi and were further examined in a second experiment in combination with vermicompost (VC), a mix of hulls plus vermicompost (SH + VC) amended with soil: sand mix (3:1 v/v) and a soil-sand mix used as a control (SS) in polybags containing the previous two host species. We found that SH blended with VC significantly improved AM fungus production in sorghum polybags assessed through microscopic (spore density in soil, colonization in roots) and biochemical parameters (AM signature lipids in soil: 16:1ω5cis neutral lipid fatty acid (NLFA); phospholipids fatty acid (PLFA) g-1 soil; 16:1ω5cis ester lipid fatty acid (ELFA) g-1 both in soil and roots; and glomalin content in soil. SH + VC contained significantly greater AM fungus populations than the other substrate combinations examined. Principal component analysis (PCA) also identified sorghum as a potential host supporting AM fungus populations particularly when grown under SH + VC conditions. Hence, the combination of soybean hulls and vermicompost was found to be a promising substrate for the mass production of AM fungi using sorghum as a host. These findings have important implications for developing AM fungus inoculum production strategies at the commercial scale.

Soil Biological Activity Contributing to Phosphorus Availability in Vertisols under Long-Term Organic and Conventional Agricultural Management.

Mobilization of unavailable phosphorus (P) to plant available P is a prerequisite to sustain crop productivity. Although most of the agricultural soils have sufficient amounts of phosphorus, low availability of native soil P remains a key limiting factor to increasing crop productivity. Solubilization and mineralization of applied and native P to plant available form is mediated through a number of biological and biochemical processes that are strongly influenced by soil carbon/organic matter, besides other biotic and abiotic factors. Soils rich in organic matter are expected to have higher P availability potentially due to higher biological activity. In conventional agricultural systems mineral fertilizers are used to supply P for plant growth, whereas organic systems largely rely on inputs of organic origin. The soils under organic management are supposed to be biologically more active and thus possess a higher capability to mobilize native or applied P. In this study we compared biological activity in soil of a long-term farming systems comparison field trial in vertisols under a subtropical (semi-arid) environment. Soil samples were collected from plots under 7 years of organic and conventional management at five different time points in soybean (Glycine max) -wheat (Triticum aestivum) crop sequence including the crop growth stages of reproductive significance. Upon analysis of various soil biological properties such as dehydrogenase, ß-glucosidase, acid and alkaline phosphatase activities, microbial respiration, substrate induced respiration, soil microbial biomass carbon, organically managed soils were found to be biologically more active particularly at R2 stage in soybean and panicle initiation stage in wheat. We also determined the synergies between these biological parameters by using the methodology of principle component analysis. At all sampling points, P availability in organic and conventional systems was comparable. Our findings clearly indicate that owing to higher biological activity, organic systems possess equal capabilities of supplying P for crop growth as are conventional systems with inputs of mineral P fertilizers.

Characterization of zinc-solubilizing Bacillus isolates and their potential to influence zinc assimilation in soybean seeds.

One hundred thirty-four putative Bacillus isolates were recovered from soybean rhizosphere soils of Nimar region to select effective zinc solubilizers for increased assimilation of zinc (Zn) in soybean seeds. These isolates were screened in vitro for zinc-solubilization ability on Tris-minimal agar medium supplemented separately with 0.1% zinc in the form of zinc oxide, zinc phosphate, and zinc carbonate. Of all, 9 isolates and a reference Bacillus cereus ATCC 13061 were characterized and identified as Bacillus species based on Gram-positive reaction, endospore-forming cells, and the presence of iso-C15:0 and anteiso-C15:0 as predominant fatty acids. On plate assay, two isolates KHBD-6 and KHBAR-1 showed a greater diameter of solubilization halo and colony diameter on all the three zinc compounds. The isolates KHBD-6, KHBAR-1, BDSD-2-2C, and KHTH-4-1 and the reference strain ATCC 13061 had higher soluble zinc concentration in liquid medium supplemented with zinc phosphate and zinc carbonate compounds as compared with the other isolates and uninoculated control. Evaluation under microcosm conditions showed that inoculation of isolates KHBD-6 (57.34 µg/g), KHBAR-1 (55.67 µg/g), and strain ATCC 13061 (53.10 µg/g) significantly increased the Zn concentration in soybean seeds as compared with the other isolates and uninoculated control (47.14 µg/g). This study suggests the occurrence of zinc-solubilizing Bacillus in soils of Nimar region and isolates KHBD-6 and KHBAR-1 were found to be promising zinc solubilizers for increased assimilation of Zn in soybean seeds.

Selection of plant growth-promoting Pseudomonas spp. that enhanced productivity of soybean-wheat cropping system in Central India.

The aim of this investigation was to select effective Pseudomonas sp. strains that can enhance the productivity of soybean-wheat cropping systems in Vertisols of Central India. Out of 13 strains of Pseudomonas species tested in vitro, only five strains displayed plant growth-promoting (PGP) properties. All the strains significantly increased soil enzyme activities, except acid phosphatase, total system productivity, and nutrient uptake in field evaluation; soil nutrient status was not significantly influenced. Available data indicated that six strains were better than the others. Principal component analysis (PCA) coupled cluster analysis of yield and nutrient data separated these strains into five distinct clusters with only two effective strains, GRP3 and HHRE81 in cluster IV. In spite of single cluster formation by strains GRP3 and HHRE81, they were diverse owing to greater intracluster distance (4.42) between each other. These results suggest that the GRP3 and HHRE81 strains may be used to increase the productivity efficiency of soybean-wheat cropping systems in Vertisols of Central India. Moreover, the PCA coupled cluster analysis tool may help in the selection of other such strains.