Asfa Rizvi

Growth stimulation and management of diseases of ornamental plants using phosphate solubilizing microorganisms: current perspective

Ornamental plants play an important role in human society since flowers are considered a vital component due to their beauty, texture, color, shape and fragrance. To produce high quality ornamentals, growers in general have intensified the use of agrochemicals without considering their deleterious impact on floral attributes. Also, the agrochemicals (including fertilizers and pesticides) used in floriculture are expensive and their excessive application results in emergence of pathogens resistant to such chemicals. It has, therefore, become imperative to develop renewable, inexpensive and eco-friendly fertilizers without producing any disturbing impact on quality of ornamentals. In this regard, phosphate solubilizing microorganisms (PSM) among plant growth promoting rhizobacteria have been identified as an efficient alternative to agrochemicals in floriculture. Even though, there are adequate reports on the effect of PSM on growth and development of numerous plants, information on the impact of PSM on production and quality of ornamental plants is, however, critically scarce. Considering these gaps and success of PSM application in floriculture achieved so far, efforts have been directed to highlight the impact of PSM on the production of ornamentals grown distinctively in different production systems. Also, the role of PSM in the management of ornamental diseases is discussed and considered. The review will conclude by identifying several PSM for future researches aiming to improve the health and quality of ornamentals grown in different production systems. Use of PSM is also likely to reduce the use of chemicals in floriculture.

Heavy metal induced oxidative damage and root morphology alterations of maize (Zea mays L.) plants and stress mitigation by metal tolerant nitrogen fixing Azotobacter chroococcum

Heavy metals are one of the major abiotic stresses that adversely affect the quantity and nutritive value of maize. Microbial management involving the use of plant growth promoting rhizobacteria (PGPR) is a promising inexpensive strategy for metal clean up from polluted soils. Considering these, metal tolerant plant growth promoting nitrogen fixing rhizobacterial strain CAZ3 identified by 16SrRNA gene sequence analysis as Azotobacter chroococcum was recovered from metal polluted chilli rhizosphere. When exposed to varying levels of metals, A. chroococcum survived up to 1400 and 2000 µg mL-1 of Cu and Pb, respectively and expressed numerous plant growth promoting activities even under metal stress. Strain CAZ3 secreted 65.5 and 60.8 µg mL-1 IAA at 400 µg mL-1 each of Cu and Pb, respectively and produced siderophores, ammonia and ACC deaminase under metal pressure. The melanin extracted from A. chroococcum revealed metal chelating ability under EDX. Following application, strain CAZ3 enhanced growth and yield of maize grown both in the presence of Cu and Pb. The dry biomass of roots of inoculated plants grown with 2007 mg Cu kg-1 and 585 mg Pb kg-1 was increased by 28% and 20%, respectively. At 585 mg Pb kg-1, the bioinoculant also increased the kernel attributes. At 2007 mg Cu kg-1 strain CAZ3 enhanced the number, yield and protein of kernels by 10%, 45% and 6%, respectively. Interestingly, strain CAZ3 significantly reduced the levels of proline, malondialdehyde and antioxidant enzymes in foliage. The roots of inoculated plants accumulated greatest amounts of metals compared to other organs. In kernels, the concentration of Pb was more as compared to Cu. The metal concentrations in roots, shoots and kernels, however, declined following CAZ3 inoculation. Copper and lead had substantial distortive impact on root and leaf morphology while cell death were visible under CLSM and SEM. Conclusively, A. chroococcum CAZ3 could be a most suitable and promising option to increase maize production in metal polluted soils despite the soils being contaminated with heavy metals.

Growth Stimulation, Nutrient Quality and Management of Vegetable Diseases Using Plant Growth-Promoting Rhizobacteria

Vegetables play an important role in human nutrition. And hence, to produce quality vegetables is a major challenge for growers. In order to optimize vegetable production, growers quite often use a heavy dose of agrochemicals without considering the deleterious impact of such chemicals on vegetables. Researchers have tried to minimize the use of agrochemicals in vegetable production vis-a-vis to develop resistant varieties, but all such approaches have been unsuccessful. The excessive use of agrochemicals can be replaced by “biofertilizers” especially plant growth-promoting rhizobacteria (PGPR) for producing safe and healthy vegetables without posing any threat to the environment. Moreover, as a biocontrol agent, PGPR will be useful in the management of vegetable diseases. In this chapter, some successful stories of PGPR applications in growth stimulation of popularly grown vegetables are described. Also, the disease suppressing ability of PGPR is considered and discussed. The strategy of incorporating low cost rhizotechnology in vegetable production system is likely to reduce dependence on chemicals applied by vegetable growers.

Perspectives of Plant Growth Promoting Rhizobacteria in Growth Enhancement and Sustainable Production of Tomato

Tomato is an important horticultural product with a high content of bioactive compounds such as folate, ascorbate, polyphenols, and carotenoids and many other essential nutrients. Due to these, tomatoes are considered extremely valuable to human health. To optimize tomato production, chemical fertilizers and pesticides are frequently used. These chemicals are however, destructive for both crops and soil ecosystems. A reduction of these detrimental practices is therefore urgently required to protect both tomato and environments from damaging effects of agrochemicals. In this context, microbial inoculation especially those consisting of plant growth-promoting rhizobacteria (PGPR) could be used to replace chemical fertilizers/pesticides. Also, PGPR can be integrated with such chemical practices to reduce their application in tomato cultivation. Plant growth-promoting rhizobacteria that naturally inhabit the rhizosphere stimulate the growth and development of tomato plants directly or indirectly via availability of many essential plant nutrients, phytohormones, or through suppression/destruction of plant diseases. A better understanding of the plant growth-promotion activity of these bacterial strains is likely to enhance the production of safe, fresh, and high-quality tomatoes while reducing chemical inputs in different agronomic setups.

Role of Nitrogen-Fixing Plant Growth-Promoting Rhizobacteria in Sustainable Production of Vegetables: Current Perspective

Vegetables due to high nutritional value comprising of carbohydrates, proteins, vitamins and several other essential elements are considered one of the important dietary constituents. In order to achieve optimum yields, agrochemicals are frequently used in vegetable cultivation. However, the excessive and inappropriate use of agrochemicals has been found deleterious for both soil fertility and vegetable production. The negative impact of agrochemicals in vegetable production practices can be avoided by the use of biofertilizers involving nitrogen-fixing plant growth-promoting rhizobacteria. The use of non-pathogenic nitrogen-fixing plant growth-promoting rhizobacteria to enhance vegetable production is, therefore, currently considered as a safe, viable and inexpensive alternative to chemical fertilization. Even though there are no direct connections between nitrogen-fixing organisms and vegetables, both symbiotic and asymbiotic/associative nitrogen-fixing bacteria have been used to facilitate the growth and yield of non-legume crops like vegetables through mechanisms other than nitrogen fixation. Indeed, there are numerous reports on the effect of plant growth-promoting rhizobacteria on vegetable production, but the information on nitrogen-fixing bacteria employed in vegetable production is scarce. Considering these gaps and success of nitrogen-fixing bacteria application in vegetable production achieved so far, efforts have been directed to highlight the impact of nitrogen fixers on the production of vegetables. Here, efforts will be made to identify most suitable nitrogen fixers which could be used to improve the health and quality of vegetables grown in different regions. The use of nitrogen fixers is also likely to reduce the use of chemicals in vegetable production.

Recent Advances in Management Strategies of Vegetable Diseases

Vegetables are one of the most important components of human foods since they provide proteins, vitamins, carbohydrates and some other essential macro- and micronutrients required by the human body. Phytopathogenic diseases, however, cause huge losses to vegetables during cultivation, transportation and storage. To protect vegetable losses, various strategies including chemicals and biological practices are used worldwide. Pesticides among agrochemicals have however been found expensive and disruptive. Due to the negative health effects of chemical fungicides via food chain, the recent trend is shifting towards safer and more eco-friendly biological alternatives for the control of vegetable diseases. Of the various biological approaches, the use of antagonistic microorganisms is becoming more popular throughout the world due to low cost and environment safety. Numerous phytopathogenic diseases can now be controlled by microbial antagonists which employ several mechanisms such as antibiosis, direct parasitism, induced resistance, production of cell wall-lysing/cell wall-degrading enzymes, and competition for nutrients and space. The most commonly used biological control agents belong to the genera, Bacillus, Pseudomonas, Flavobacterium, Enterobacter, Azotobacter, Azospirillum and Trichoderma, and some of the commercial biocontrol products developed and registered for the use against phytopathogens are Aspire, BioSave, Shemer etc. Here, an attempt is made to highlight the mechanistic basis of vegetable disease suppression by some commonly applied microbiota. This information is likely to help vegetable growers to reduce dependence on chemicals and to produce fresh and healthy vegetables in different production systems.

Growth Improvement and Management of Vegetable Diseases by Plant Growth-Promoting Rhizobacteria

Vegetables are an important part of human dietary systems. They contain several important nutrients including vitamins, antioxidants, etc. and affect immensely the human health. Vegetables are cultivated and consumed globally on a large scale and serve as the food of choice for millions of people across the globe. During cultivation, most of the vegetable crops are, however, often attacked by various insect pests and pathogenic microorganisms, thereby causing severe diseases, leading to huge yield losses. The agricultural practitioners depend heavily on chemical fertilizers to supply nutrients to vegetables while they apply pesticides to manage insect pests and to concurrently enhance vegetable production. The injudicious application of agrochemicals including pesticides into vegetable production practices adversely affects the soil fertility and consequently the plant health, thus making it unfit for human consumption. In order to protect the crops and to minimize yield losses due to phytopathogens, an alternate and inexpensive approach involving the use of plant growth-promoting rhizobacteria (PGPR) has been introduced into the vegetable production system. The application of PGPR formulations into the vegetable production strategies has been found to protect them from various diseases leading to improved yield and quality of the vegetables. The present chapter focuses on the disease incidence among some of the popularly grown vegetables and the role of PGPR in suppression of common vegetable diseases.

Metal Toxicity to Certain Vegetables and Bioremediation of Metal-Polluted Soils

The production of quality vegetables is a crucial issue worldwide due to consistently deteriorating soil health. Plants including vegetables absorb a number of metals from soil, some of which have no biological function, but some are toxic at low concentrations, while others are required at low concentration but are toxic at higher concentrations. As vegetables constitute a major source of nutrition and are an important dietary constituent, the heavy metal uptake and bioaccumulation in vegetables is important since it disrupts production and quality of vegetables and consequently affects human health via food chain. Considering the serious threat of metals to vegetables, an attempt in this chapter is made to highlight the effects of certain metals on vegetables grown in different agroclimatic regions of the world. Also, the bioremediation strategies adopted to clean up the metal-contaminated soil is discussed. The results of different studies conducted across the globe on metal toxicity and bioremediation strategies presented in this chapter are likely to help vegetable growers to produce fresh and contaminant-free vegetables.

Phosphate-Solubilizing Microorganisms in Sustainable Production of Wheat: Current Perspective

In terms of global production, wheat among cereals ranks third after rice and maize, contributing about 35% of the total food grain production. Wheat due to high nutritional value is considered one of the important dietary constituents and, hence, has become one of the better food choices around the world. For growth and development, wheat requires large amounts of major plant nutrients especially phosphorus (P). Application of sufficient amounts of P has many beneficial impacts on wheat including its role in growth, grain formation, and development, and in straw yield. Phosphorus deficiency, however, may adversely affect the growth and, therefore, hampers the physiological processes leading eventually to overall stunting of the plant. In order to circumvent the phosphorus problems and hence to achieve optimum yields, wheat growers usually apply excessive amounts of chemical phosphatic fertilizer which is both expensive and destructive to soil fertility. To overcome these problems, a physiologically versatile array of microorganisms especially belonging to phosphate-solubilizing group has been introduced into the agricultural system for improving wheat production. The P-solubilizing microorganisms (PSM) solubilize unavailable soil P and make it available for uptake by plants. The use of microbial phosphatic fertilizer (microphos) in wheat production system is considered an eco-friendly strategy without adversely affecting the soil health. Despite numerous informations available on the impact of P-solubilizing microorganisms on various plants, literature suggesting the use of PSM in wheat production is limited. Realizing the importance of PSM in enhancing the overall performance of wheat, attempt has been made to better understand as to how the PSM affects wheat production in variable agricultural practices. Also, efforts will be made to find PSM which could be applied to facilitate the growth and development of wheat grown in different agroecological niches. Constant and sustainable application of PSM is expected to decrease the use of fertilizers in wheat production strategies.

Metal-Legume-Microbe Interactions: Toxicity and Remediation

Heavy metals discharged from various sources accumulate within soils and disrupt ecosystems. The toxic metals are taken up by beneficial soil microbiota and growing plants and cause potential human risks via food chain. Also, heavy metals seriously affect the microbial compositions and their physiological functions. Among plant species, legumes play an important role in human dietary systems and supply nitrogen to legumes through symbiosis with rhizobia. Metals when present in legume habitat act as a devastating stress factor and restrict the growth of rhizobia, legumes, and legume-Rhizobium symbiosis. Several physical and chemical methods have been developed to remediate heavy metal-polluted soils, but these methods are unacceptable due to their high cost, and they are not environmentally friendly. Therefore, the use of metal-tolerant/metal-detoxifying microbes collectively called bioremediation offers a sustainable and low-cost option to clean up polluted soils. Besides remediation, the metal-tolerant microbes also promote plant growth by other direct or indirect means. Owing to the importance of legumes in maintaining soil fertility and human health, there is greater emphasis to identify the metal-resistant/metal-tolerant rhizobia and legume plants. The present chapter gives an in-depth insight into the impact of metals on rhizobia-legume symbiosis. Also, the role of metal-tolerant rhizobia in metal toxicity abatement is highlighted.