Characterization of functional activity in composted casing amendments used in cultivation of Agaricus bisporus (Lange) Imbach

97-109In cultivation of button mushroom [Agaricus bisporus (Lange) Imbach], casing layer that is nutritionally deficient to compost is believed to trigger the fruit body formation and this is conducted by the bacterial community residing in casing layer. The change in nutritional status of the casing is highly correlated with microbial flora. Therefore, an attempt was made to characterize the bacterial flora in casing layer, i.e., Farm Yard Manure and Spent Mushroom Substrate (FYM+SMS, 3:1) and Farm Yard Manure and Vermi Compost (FYM+VC, 3:1), employing phenetic approaches. Morphotypically different and functionally characterized bacterial isolates were identified by partial 16S rDNA gene fragment sequencing. Available data showed a significant variety of organisms that included Acinetobacter and Pseudomonas of the γ-proteobacteria, that were most frequently encountered genera. Amongst Gram-positive bacteria, Bacillus was the most highly represented genus that was derived from the agaric fruit bodies. In addition, FYM+SMS was found to be a high yielding casing mixture, which took minimum case run period together with superior fruit body quality as compared to FYM+VC

Diversity of phlD alleles in the rhizosphere of wheat cropped under annual rice–wheat rotation in fields of the Indo-Gangetic plains: influence of cultivation conditions

The antibiotic 2,4-diacetyphloroglucinol is a major determinant in the biocontrol of plant growth promoting rhizobacteria associated with crops of agronomic relevance. The phlD gene is a useful marker of genetic and phenotypic diversity of 2,4-DAPG-producing rhizobacteria. A two-step amplification procedure was developed in order to assess directly the presence of phlD in environmental DNA, avoiding the tedious procedure of phlD-positive strain screening and isolation. We found a predominance of one or two phlD alleles in wheat fields cultivated in rice–wheat rotations for twenty years, suggesting that continuous rice–wheat cropping would lead to an enrichment of particular phlD genotypes. We also recovered new sequences with no close relative among known phlD sequences, indicating that part of the phlD allelic diversity might have been missed using standard media culture conditions

Diversity of phlD alleles in the rhizosphere of wheat cropped under annual rice–wheat rotation in fields of the Indo-Gangetic plains: influence of cultivation conditions

The antibiotic 2,4-diacetyphloroglucinol is a major determinant in the biocontrol of plant growth promoting rhizobacteria associated with crops of agronomic relevance. The phlD gene is a useful marker of genetic and phenotypic diversity of 2,4-DAPG-producing rhizobacteria. A two-step amplification procedure was developed in order to assess directly the presence of phlD in environmental DNA, avoiding the tedious procedure of phlD-positive strain screening and isolation. We found a predominance of one or two phlD alleles in wheat fields cultivated in rice–wheat rotations for twenty years, suggesting that continuous rice–wheat cropping would lead to an enrichment of particular phlD genotypes. We also recovered new sequences with no close relative among known phlD sequences, indicating that part of the phlD allelic diversity might have been missed using standard media culture conditions

Inoculation of root microorganisms for sustainable wheat-rice and wheat-black gram rotations in India

The scarcity of non-renewable resources such as soils and fertilizers and the consequences of climate change can dramatically influence the food security of future generations. Mutualistic root microorganisms such as plant growth-promoting rhizobacteria (PGPR) and arbuscular mycorrhizal fungi (AMF) can improve plant fitness. We tested the growth response of wheat (Triticum aestivum [L.]), rice (Oriza sativa [L.]) and black gram (Vigna mungo [L.], Hepper) to an inoculation of AMF and PGPR alone or in combination over two years at seven locations in a region extending from the Himalayan foothills to the Indo-Gangetic plain. The AMF applied consisted of a consortium of different strains, the PGPR of two fluorescent Pseudomonas strains (Pseudomonas jessenii, R62; Pseudomonas synxantha, R81), derived from wheat rhizosphere from one test region. We found that dual inoculation of wheat with PGPR and AMF increased grain yield by 41% as compared to un-inoculated controls. Yield responses to the inoculants were highest at locations with previously low yields. AMF or PGPR alone augmented wheat grain yield by 29% and 31%, respectively. The bio-inoculants were effective both at Zero and at farmers’ practice fertilization level (70 kg N ha−1, 11 kg P ha−1 in mineral form to wheat crop). Also raw protein (nitrogen × 5.7) and mineral nutrient concentration of wheat grains (phosphorus, potassium, copper, iron, zinc, manganese) were higher after inoculation (+6% to +53%). Phosphorus use efficiency of wheat grains [kg P grain kg−1 P fertilizer] was increased by 95%. AMF and PGPR application also improved soil quality as indicated by increased soil enzyme activities of alkaline and acid phosphatase, urease and dehydrogenase. Effects on rice and black gram yields were far less pronounced over two cropping seasons, suggesting that AMF and PGPR isolated from the target crop were more efficient. We conclude that mutualistic root microorganisms have a high potential for contributing to food security and for improving nutrition status in southern countries, while safeguarding natural resources such as P stocks. (c) Elsevie

Impact of antifungals producing rhizobacteria on the performance of Vigna radiata in the presence of arbuscular mycorrhizal fungi

Plant growth-promoting rhizobacteria (PGPR) that produce antifungal metabolites are potential threats for the arbuscular mycorrhizal (AM) fungi known for their beneficial symbiosis with plants that is crucially important for low-input sustainable agriculture. To address this issue, we used a compartmented container system where test plants, Vigna radiata, could only reach a separate nutrient-rich compartment indirectly via the hyphae of AM fungi associated with their roots. In this system, where plants depended on nutrient uptake via AM symbiosis, we explored the impact of various PGPR. Plants were inoculated with or without a consortium of four species of AM fungi (Glomus coronatum, Glomus etunicatum, Glomus constrictum, and Glomus intraradices), and one or more of the following PGPR strains: phenazine producing (P+) and phenazine-less mutant (P-), diacetylphloroglucinol (DAPG) producing (G(+)) and DAPG-less mutant (G(-)) strains of Pseudomonas fluorescens, and an unknown antifungal metabolite-producing Alcaligenes faecalis strain, SLHRE425 (D). PGPR exerted only a small if any effect on the performance of AM symbiosis. G(+) enhanced AM root colonization and had positive effects on shoot growth and nitrogen content when added alone, but not in combination with P+. D negatively influenced AM root colonization, but did not affect nutrient acquisition. Principal component analysis of all treatments indicated correlation between root weight, shoot weight, and nutrient uptake by AM fungus. The results indicate that antifungal metabolites producing PGPR do not necessarily interfere with AM symbiosis and may even promote it thus carefully chosen combinations of such bioinoculants could lead to better plant growth