Continuous decline of earth’s natural resources and increased use of hazardous chemical fertilizers pose a great concern for the future of agriculture. Biofertilizers are a promising alternative to hazardous chemical fertilizers and are gaining importance for attaining sustainable agriculture. Biofertilizers play a key role in increasing crop yield and maintaining long-term soil fertility, which is essential for meeting global food demand. Microbes can interact with the crop plants and enhance their immunity, growth, and development. Nitrogen, phosphorous, potassium, zinc, and silica are the essential nutrients required for the proper growth of crops, but these nutrients are naturally present in insolubilized or complex forms. Certain microorganisms render them soluble and make them available to the plants. The potential microbes, their mode of action, along with their effect on crops, are discussed in this review. Biofertilizers, being cost effective, non-toxic, and eco-friendly, serve as a good substitute for expensive and harmful chemical fertilizers. The knowledge gained from this review can help us to understand the importance of microbes in agriculture and the ways to formulate these microbes as biofertilizers for sustainable crop production.

Microbes as Biofertilizers, a Potential Approach for Sustainable Crop Production

For all living organisms, nitrogen is an essential element, while being the most limiting in ecosystems and for crop production. Despite the significant contribution of synthetic fertilizers, nitrogen requirements for food production increase from year to year, while the overuse of agrochemicals compromise soil health and agricultural sustainability. One alternative to overcome this problem is biological nitrogen fixation (BNF). Indeed, more than 60% of the fixed N on Earth results from BNF. Therefore, optimizing BNF in agriculture is more and more urgent to help meet the demand of the food production needs for the growing world population. This optimization will require a good knowledge of the diversity of nitrogen-fixing microorganisms, the mechanisms of fixation, and the selection and formulation of efficient N-fixing microorganisms as biofertilizers. Good understanding of BNF process may allow the transfer of this ability to other non-fixing microorganisms or to non-leguminous plants with high added value. This minireview covers a brief history on BNF, cycle and mechanisms of nitrogen fixation, biofertilizers market value, and use of biofertilizers in agriculture. The minireview focuses particularly on some of the most effective microbial products marketed to date, their efficiency, and success-limiting in agriculture. It also highlights opportunities and difficulties of transferring nitrogen fixation capacity in cereals.

Exploiting Biological Nitrogen Fixation: A Route Towards a Sustainable Agriculture

Global population growth poses a threat to food security in an era of increased ecosystem degradation, climate change, soil erosion and biodiversity loss. In this context, harnessing naturally-occurring processes such as those provided by soil and plant-associated microorganisms presents a promising strategy to reduce dependency on agrochemicals. Biofertilizers are living microbes that enhance plant nutrition by either by mobilizing or increasing nutrient availability in soils. Various microbial taxa including beneficial bacteria and fungi are currently used as biofertilizers, as they successfully colonize the rhizosphere, rhizoplane or root interior. Despite their great potential to improve soil fertility, biofertilizers have yet to replace conventional chemical fertilizers in commercial agriculture. In the last ten years, multi-omics studies have made a significant step forward in understanding the drivers, roles, processes and mechanisms in the plant microbiome. However, translating this knowledge on microbiome functions in order to capitalize on plant nutrition in agroecosystems still remains a challenge. Here, we address the key factors limiting successful field applications of biofertilizers and suggest potential solutions based on emerging strategies for product development. Finally, we discuss the importance of biosafety guidelines and propose new avenues of research for biofertilizer development.

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Rethinking Crop Nutrition in Times of Modern Microbiology: Innovative Biofertilizer Technologies

The world’s human population continues to increase, posing a significant challenge in ensuring food security, as soil nutrients and fertility are limited and decreasing with time. Thus, there is a need to increase agricultural productivity to meet the food demands of the growing population. A high level of dependence on chemical fertilizers as a means of increasing food production has damaged the ecological balance and human health and is becoming too expensive for many farmers to afford. The exploitation of beneficial soil microorganisms as a substitute for chemical fertilizers in the production of food is one potential solution to this conundrum. Microorganisms, such as plant growth-promoting rhizobacteria and mycorrhizal fungi, have demonstrated their ability in the formulation of biofertilizers in the agricultural sector, providing plants with nutrients required to enhance their growth, increase yield, manage abiotic and biotic stress, and prevent phytopathogens attack. Recently, beneficial soil microbes have been reported to produce some volatile organic compounds, which are beneficial to plants, and the amendment of these microbes with locally available organic materials and nanoparticles is currently used to formulate biofertilizers to increase plant productivity. This review focuses on the important role performed by beneficial soil microorganisms as a cost-effective, nontoxic, and eco-friendly approach in the management of the rhizosphere to promote plant growth and yield.

Agricultural Sustainability: Microbial Biofertilizers in Rhizosphere Management

Late wilt disease, caused by Cephalosporium maydis in maize plant, is one of the main economical diseases in Egypt. Therefore, to cope with this problem, we investigated the potentiality of plant growth promoting rhizobacteria in controlling this disease. Six strains (Bacillus subtilis, B. circulance, B. coagulanse, B. licheniformis, Pseudomonas fluroscence and P. koreensis) were screened for siderophore production, and using dual plate culture method and greenhouse experiment, antagonistic activity against C. maydis was studied. Using two superior strains, single and dual inoculation treatments in maize were applied in field experiment during the 2018 and 2019 seasons. Results indicated that B. subtilis and P. koreensis strains had shown the most qualitative and quantitative assays for siderophore production and antagonistic activities. In greenhouse, the most effective treatments on the pre- and post-emergence damping off as well as growth promotion of maize were T3 treatment (inoculated with B. subtilis), and T8 treatment (inoculated with P. koreensis). In field experiment, T5 treatment (inoculated with a mixture of B. subtilis and P. koreensis) showed significant increases in catalase (CAT), peroxidase (POX) and polyphenol oxidase (PPO) activities, as well as total chlorophyll and carotenoids than control treatments during the two growing seasons. In the same way, the highest effect in reducing infection and increasing the thickness of the sclerenchymatous sheath layer surrounding the vascular bundles in maize stem was observed and these results were a reflection of the increase in yield and yield parameters.

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Siderophore production by Bacillus subtilis MF497446 and Pseudomonas koreensis MG209738 and their efficacy in controlling Cephalosporium maydis in maize plant.

Microbial inoculants are gaining importance for attaining sustainable agricultural production systems. Nutrient supply capacity of soil is diminishing continuously owing to soil erosions, degradation, deposition of salts, undesirable elements and metals, water scarcity or excess and imbalanced nutrient supply system. Numerous complementary microbial inoculation combinations are contributing immensely in the management of plant nutrients by way of fixation, solubilization or transformation in soil. Thus, biological wastes and microbial inoculants are alternatives for nutrient demands to bridge future gaps in. A consortium of microorganisms provides enabling and congenial option to maintain their usable capacity for sufficient durations that heads to the positive impact on the microbial activity of soil for desired activities at the target sites. Increased application of agro-chemicals results in deleterious effect on biological system and dependence of future agriculture on these will lead to deterioration in soil health, threats of pollution of water bodies and cumulative effect of these is making production system highly vulnerable and unstable consequently leading to heavy load on the fiscal system. To ameliorate negative impacts, microorganisms are strongly emerging as alternatives for conserving productive capacity for sustainable productions and financial balance of economies. Microbial inoculants that have assumed definite and significant roles for their specificity and necessity and their use in various combinations have emerged as viable and sustainable options to maintain and even enrich the soil health. Since these microbial inoculants are used under varied farming situations and diverse climates with heterogeneous management skills, their efficacies under field conditions remain variable. Thus, it is never-ending process to identify solutions for constraints and application difficulties and further identify newer microbial inoculants for unexplored areas. Adequate timely and quality access of these inoculants to end users is equally important along with developing their skills to utilize these for witnessing desirable and visible impacts.

Microbial inoculants: potential tool for sustainability of agricultural production systems

Heat stress (HS) is one of the major abiotic stresses affecting the production and quality of wheat. Rising temperatures are particularly threatening to wheat production. A detailed overview of morpho-physio-biochemical responses of wheat to HS is critical to identify various tolerance mechanisms and their use in identifying strategies to safeguard wheat production under changing climates. The development of thermotolerant wheat cultivars using conventional or molecular breeding and transgenic approaches is promising. Over the last decade, different omics approaches have revolutionized the way plant breeders and biotechnologists investigate underlying stress tolerance mechanisms and cellular homeostasis. Therefore, developing genomics, transcriptomics, proteomics, and metabolomics data sets and a deeper understanding of HS tolerance mechanisms of different wheat cultivars are needed. The most reliable method to improve plant resilience to HS must include agronomic management strategies, such as the adoption of climate-smart cultivation practices and use of osmoprotectants and cultured soil microbes. However, looking at the complex nature of HS, the adoption of a holistic approach integrating outcomes of breeding, physiological, agronomical, and biotechnological options is required. Our review aims to provide insights concerning morpho-physiological and molecular impacts, tolerance mechanisms, and adaptation strategies of HS in wheat. This review will help scientific communities in the identification, development, and promotion of thermotolerant wheat cultivars and management strategies to minimize negative impacts of HS.

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Impacts, Tolerance, Adaptation, and Mitigation of Heat Stress on Wheat under Changing Climates

The agricultural sector is highly dependent on the availability and quality of seeds for a productive harvest. The response of all other inputs depends on quality of seeds to a large extent and estimated 15 – 20% contribution of quality seed alone to the total production which is depending upon the crop and it can be further raised up to 45% with efficient management of other inputs. Today, the Indian seed industry is the fifth largest seed market in the world and valued at more than Rs 2500 crores. The seed industry has grown steadily in the last four decades. A number of transformations have taken place in this sector over the past few decades like rising a penetration of the organised sector, growth in contract farming, agriculture becoming more mechanized, easy loan facilities, rise of exports, use of agrochemicals and high yielding seeds and an increasing role of the private sector in processing, branding and marketing, etc. Government took many progressive and reformative steps in last three decades for the growth of seed sector in the country. In terms of global trade, India is almost self-sufficient in flower, fruits and vegetables and field crops seeds. Research also have related to quality enhancement technologies such as cereals with higher proteins, minerals and vitamin contents like Golden rice, QPM and Fe and Zn enriched millets. A single-window clearance is recommended for faster release of useful transgenic crops along with its public awareness on benefits and possible risk issues in future.

https://www.chemijournal.com/archives/2019/vol7issue3/PartZ/7-2-504-920.pdf

A review: The Indian seed industry, its development, current status and future

Field experiment was conducted during rabi 2017-2018 at Instructional Agronomy Farm of Rajasthan College of Agriculture, MPUAT, Udaipur. The experiment consisted of twelve treatments (Pendimethalin 750 g ha-1 PE; Pendimethalin 1000 g ha-1 PE; Metribuzin 150 g ha-1 PE; Metribuzin 200 g ha-1 PE; Imazethapyr 50 g ha-1 PoE at 20 DAS; Imazethapyr 75 g ha-1 PoE at 20 DAS; Quizalofop- ethyl 40 g ha-1 PoE at 20 DAS; Quizalofop- ethyl 50 g ha-1 PoE at 20 DAS; Imazethpyr + Imazamox (RM) 15+15 g ha-1 PoE at 20 DAS; Imazethpyr + Imazamox (RM) 15+15 g ha-1 PoE at 20 DAS; Handweeding at 30 and 60 DAS; Weedy check). Pendimethalin and metribuzin were applied as pre-emergence while all other herbicides were applied as post-emergence at 20 days after sowing and handweeding at 30 and 60 DAS. The twelve treatments were replicated thrice in Randomize Block Design. The result showed that two hand weeding 30 and 60 DAS followed by pendimethalin 1000 g ha-1 PE and pendimethalin 750 g ha-1 PE significantly reduced weed density and dry weight, thereby attaining the highest seed yield. Net reurn and B C ratio was also the highest in pre-emergence application of pendimethalin 1000 g ha-1 PE and pendimethalin 750 g ha-1 PE.

https://www.chemijournal.com/archives/2020/vol8issue1/PartAG/8-1-389-455.pdf

Effect of chickpea ( Cicer arietinum L.) weed management practices on quality parameters, nutrient content and uptake by crop and weed

Sclerotinia stem rot is constantly appearing from moderate to severe form in major mustard growing tracts. Most of life S. sclerotiorum passes in form of sclerotia in the soil. Present study was carried out in order to determine effect of inoculum level on disease development and survival of S. sclerotiorum. Different inoculum levels were prepared from culture of S. sclerotiorum and 10 sclerotia/ pot were buried at various depths ranging from 1 to 20 cm for 60 days. The maximum disease incidence (93.67%) was observed with 10 per cent inoculum level; however disease incidence was least (6.34%) in 1 per cent inoculum level. Disease incidence increased with increasing in inoculum levels. In case of plant mortality, maximum plant mortality (43.00%) was recorded at 10 per cent inoculum level followed by 32.67 and 29.34 per cent @ 9 and 8 per cent, respectively. No plant mortality was noticed at 1 and 2 per cent inoculum level. Maximum amount of sclerotia germination (83.33%) was observed at 1 cm soil depth followed by 75.65, 73.34, 70.34 per cent germination @ 2, 3 and 4 cm depth of soil, respectively. It was observed that sclerotial germination decreased in tune with increase in soil depth. Lowest sclerotial germination (10%) was observed in 20 cm vertical soil depth. Findings of this study can be harnessed in varietal screening and formulation of disease management modules.

Tarun Kumar Jatwa

Papers

Microbial inoculants: potential tool for sustainability of agricultural production systems

Impacts, Tolerance, Adaptation, and Mitigation of Heat Stress on Wheat under Changing Climates

A review: The Indian seed industry, its development, current status and future

Effect of chickpea ( Cicer arietinum L.) weed management practices on quality parameters, nutrient content and uptake by crop and weed

Effect of Inoculum Levels on Disease Development and Survival Potential of Sclerotinia sclerotiorum Sclerotia