Fungal diseases result in significant losses of fruits and vegetables during handling, transportation and storage. At present, post-production fungal spoilage is predominantly controlled by using synthetic fungicides. Under the global climate change scenario and with the need for sustainable agriculture, biological control methods of fungal diseases, using antagonistic microorganisms, are emerging as ecofriendly alternatives to the use of fungicides. The potential of microbial antagonists, isolated from a diversity of natural habitats, for postharvest disease suppression has been investigated. Postharvest biocontrol systems involve tripartite interaction between microbial antagonists, the pathogen and the host, affected by environmental conditions. Several modes for fungistatic activities of microbial antagonists have been suggested, including competition for nutrients and space, mycoparasitism, secretion of antifungal antibiotics and volatile metabolites and induction of host resistance. Postharvest application of microbial antagonists is more successful for efficient disease control in comparison to pre-harvest application. Attempts have also been made to improve the overall efficacy of antagonists by combining them with different physical and chemical substances and methods. Globally, many microbe-based biocontrol products have been developed and registered for commercial use. The present review provides a brief overview on the use of microbial antagonists as postharvest biocontrol agents and summarises information on their isolation, mechanisms of action, application methods, efficacy enhancement, product formulation and commercialisation.

An investigation was undertaken to screen, select and evaluate a set of bacterial and cyanobacterial isolates from the wheat rhizosphere for their role as biofertilizers in wheat. From an initial set of 23 cyanobacterial strains and 110 bacterial isolates from wheat rhizospheric soil, 3 bacterial and 3 cyanobacterial strains were selected based on their plant growth promoting potential under laboratory and controlled greenhouse conditions. In vitro compatibility studies revealed positive interactions among the six strains. Pot experiments were conducted with wheat variety HD 2687, with a total of 51 treatments, along with recommended fertilizer controls. Various combinations of the selected set of three bacterial (PW1, PW5 and PW7) and three cyanobacterial isolates (CW1, CW2 and CW3) were used along with 1/3 N and full dose of P and K fertilizers. Significant enhancement in the soil microbiological (Dehydrogenase activity, FDA hydrolase, Alkaline phosphatase and microbial biomass) and plant growth/yield parameters were recorded. Observations revealed a two-fold increase in panicle weight in selected combinations (PW1+PW7+CW3; PW1+ CW1+CW2/CW1+CW3; CW2+CW3), as compared to control treatment involving full dose of chemical fertilizers. Such combinations, which also provided N savings of 40-80 kg N/ha are being further evaluated in field experiments. This study for the first time illustrated the positive and dynamic interactions among bacterial and cyanobacterial strains and their promise in integrated nutrient management of wheat crop.

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Biochar and arbuscular mycorrhizal fungi (AMF) can promote plant growth, improve soil properties, and maintain microbial activity. The effects of biochar and AMF on plant growth, root morphological traits, physiological properties, and soil enzymatic activities were studied in spinach (Spinacia oleracea L.). A pot experiment was conducted to evaluate the effect of biochar and AMF on the growth of spinach. Four treatments, a T1 control (soil without biochar), T2 biochar alone, T3 AMF alone, and T4 biochar and AMF together, were arranged in a randomized complete block design with five replications. The biochar alone had a positive effect on the growth of spinach, root morphological traits, physiological properties, and soil enzymatic activities. It significantly increased the plant growth parameters, such as the shoot length, leaf number, leaf length, leaf width, shoot fresh weight, and shoot dry weight. The root morphological traits, plant physiological attributes, and soil enzymatic activities were significantly enhanced with the biochar alone compared with the control. However, the combination of biochar and AMF had a greater impact on the increase in plant growth, root morphological traits, physiological properties, and soil enzymatic activities compared with the other treatments. The results suggested that the combined biochar and AMF led to the highest levels of spinach plant growth, microbial biomass, and soil enzymatic activity.

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In our endeavor to improve upon nitrogen fixation efficiency of a soil diazotroph that would be unaffected by synthetic nitrogenous fertilizers, we have deleted a part of the negative regulatory gene and constitutively expressed the positive regulatory gene in the chromosome of CBD15, a strain isolated from the local field soil. No antibiotic resistance gene or other foreign gene was there in the chromosome of the engineered strain. Wheat seeds inoculated with this engineered strain, which we have named HKD15, were tested for three years in pots and one year in the field. Yield of wheat was enhanced by ∼60% due to inoculation of seeds by HKD15 in the absence of any urea application. Ammonium only marginally affected acetylene reduction by the engineered strain. When urea was also applied, the same wheat yield could be sustained by using seeds inoculated with HKD15 and using ∼85kg less urea (∼40kg less nitrogen) than the usual ∼257 kg urea (∼120 kg nitrogen) per hectare. Wheat plants arising from the seeds inoculated with the engineered strain, exhibited far superior overall performance, had much higher dry weight and nitrogen content and assimilated molecular N much better. A nitrogen balance experiment also revealed much higher total nitrogen content. IAA production by the wild type and the engineered strain was about the same. Inoculation of the wheat seeds with HKD15 did not adversely affect the microbial population in the field rhizosphere soil.IMPORTANCE Application of synthetic nitrogenous fertilizers is a standard agricultural practice to augment crop yield. Plants, however, utilize only a fraction of the applied fertilizers, while the unutilized fertilizers cause grave environmental problems. Wild type soil diazotrophic microrganisms cannot replace synthetic nitrogenous fertilizers, as these reduce atmospheric nitrogen very inefficiently and almost none at all in presence of added nitrogenous fertilizers. If the nitrogen fixing ability of soil diazotrophs could be improved upon and sustained even in the presence of synthetic nitrogenous fertilizers, then a mixture of the bacterial and reduced quantity of chemical nitrogenous fertilizers could be employed to obtain the same grain yield, but at much reduced environmental cost. The engineered that we have reported here has considerably enhanced nitrogen fixation and excretion abilities and can replace ∼85 kg of urea per hectare, but sustain same wheat yield, if the seeds are inoculated with it before sowing.