Md. Saghir Khan

Interactive effect of rhizotrophic microorganisms on yield and nutrient uptake of chickpea (Cicer arietinum L.)

Abstract The interactive effect of rhizotrophic microorganisms on the yield and nutrient uptake of chickpea plants and soil was determined in a sandy clay loam soil, deficient in available phosphorus (P). Plant yield and nutrient uptake were significantly enhanced as a result of inoculation with Rhizobium sp. and phosphate solubilising microorganisms (PSM), Pseudomonas striata or Penicillium variable . Plant yield and nutrient uptake were further augmented by the addition of AM fungus, Glomus fasciculatum in the combined inoculation treatment with Rhizobium sp.+ P . striata . However, a negative effect occurred on all the considered parameters when G. fasciculatum was added to the combination of Rhizobium sp. and P. variable . In addition, the available P status of the soil improved by the addition of P. striata with Rhizobium sp. and AM fungus. The nitrogen content of the soil did not show appreciable changes after the inoculation. The population of phosphate solubilising microorganism in combinations on root infections and spore density of the AM fungus in the soil showed increase between 45 and 90 days of plant growth.

Bioassociative Effect of Rhizospheric Microorganisms on Growth, Yield, and Nutrient Uptake of Greengram

Abstract The bioassociative effect of rhizospheric microorganisms on growth, yield, and nutrient uptake of greengram [Vigna radiata (L.) Wilczek] plant and available phosphorus (P) status of the soil was determined in a sandy clay loam soil, deficient in available P. Plant yield and nutrient [nitrogen (N) and P] uptake were significantly enhanced as a result of inoculation with Bradyrhizobium sp. (vigna) and phosphate solubilizing microorganisms (PSM), Pseudomonas striata or Penicillium variable. Plant yield and nutrient uptake were further augmented by the addition of AM fungus, Glomus fasciculatum in the combined inoculation treatment with Bradyrhizobium sp. (vigna) + P. striata. However, a negative effect occurred on all the considered parameters when G. fasciculatum was added to the combination of Bradyrhizobium sp. (vigna) and Penicillium variable. In addition, the available P status of the soil improved by the addition of P. striata with Bradyrhizobium sp. (vigna) and AM fungus. The nitrogen content of the soil did not show appreciable changes after the inoculation. The population of PSM in some treatments, percentage root infection and spore density of the AM fungus in the soil increased between 35 and 50 days of plant growth. These data suggest that if favorably interacting rhizospheric microorganisms are used as microbial inoculants, nodulation is improved as well as N and P uptake by greengram plant and hence also yield is increased. However, the applicability of this approach has to be tested in further field studies.

Impact of heavy metal toxicity on plant growth, symbiosis, seed yield and nitrogen and metal uptake in chickpea

Experiments were conducted to investigate the phytotoxic effects of heavy metals on chickpea, grown in unsterilised soils. Cadmium at 23 mg/kg soil, when used alone or in combination with other metals, was found to be the most toxic and significantly (P ≤ 0.05) reduced the plant growth, nodulation, chlorophyll content, and root and shoot N contents. Cadmium (23 mg/kg soil) and lead (390 mg/kg soil) reduced the number of nodules by 69.2 and 13.7%, respectively. Cadmium at 5.75 and 11.5 mg/kg soil decreased the seed yield by 14 and 19%, respectively, compared with the control. In contrast, lead at 97.5 and 195 mg/kg soil increased the seed yield by 12.3 and 8.8%, respectively, above the control. Generally, the chlorophyll content decreased with increasing rates of each metal. The root and shoot N content decreased by 33.3 and 30.7% at 23 mg/kg of cadmium, whereas lead at 390 mg/kg soil increased the root and shoot N content by 10 and 3%, respectively, above the control. The grain protein decreased gradually with increasing rates of each metal. An average maximum reduction (27%) in grain protein was observed with mixtures of 23 mg cadmium + 135 mg chromium + 580.2 mg nickel per kg soil. Flowering in chickpea plants was delayed following metal application. The degree of toxicity of heavy metals on the measured parameters decreased in the following order: cadmium, zinc, nickel, copper, chromium, then lead. Accumulation of heavy metals was higher in the roots relative to the shoots of chickpea and was significantly correlated with the concentration of the metals added to the soil.

Mechanism of Phosphate Solubilization and Physiological Functions of Phosphate-Solubilizing Microorganisms

Phosphorus (P) is the second important key plant nutrient after nitrogen. An adequate supply of P is therefore required for proper functioning and various metabolisms of plants. Majority of P in soils is fixed, and hence, plant available P is scarcely available despite the abundance of both inorganic and organic P forms in soils. A group of soil microorganisms capable of transforming insoluble P into soluble and plant accessible forms across different genera, collectively called phosphate-solubilizing microorganisms (PSM), have been found as best eco-friendly option for providing inexpensive P to plants. These organisms in addition to supplying soluble P to plants also facilitate the growth of plants by several other mechanisms, for instance, improving the uptake of nutrients and stimulating the production of some phytohormones. Even though several bacterial, fungal and actinomycetal strains have been identified as PSM, the mechanism by which they make P available to plants is poorly understood. This chapter focuses on the mechanism of P-solubilization and physiological functions of phosphate solubilizers in order to better understand the ecophysiology of PSM and consequently to gather knowledge for managing a sustainable environmental system. Conclusively, PSM are likely to serve as an efficient bio-fertilizer especially in areas deficient in P to increase the overall performance of crops.

Impact of zinc-tolerant plant growth-promoting rhizobacteria on lentil grown in zinc-amended soil

Though zinc is a plant nutrient at low levels, Zn ions can be highly phytotoxic at higher concentrations found in contaminated soils. Plant growth-promoting rhizobacteria can be used to decrease this toxicity. Indeed, in addition to their role in plant-growth promotion, rhizobacteria also reduce the toxicity of heavy metals. In turn, they can be effective for crops grown in metal-contaminated soils. Here, we isolated a zinc-tolerant plant growth-promoting rhizobacterium, Rhizobium species RL9, from a zinc-contaminated soil and assayed its plant growth-promoting activities in vitro. We found that the rhizobacterium strain RL9 tolerated zinc up to a concentration of 400 μg mL−1 on yeast extract mannitol agar medium. It produced 33 μg mL−1 of indole acetic acid in Luria Bertani broth at 100 μg mL−1 of tryptophan and was positive for siderophore, hydrogen cyanide and ammonia. Such phytohormones released by this strain could help in promoting the growth of legumes. We further tested the effect of rhizobacterium strain RL9 on lentils grown in zinc-amended soil. We found that when the rhizobacterium strain RL9 was added to soil contaminated with Zn at 4890 mg/kg, lentil dry matter increased by 150%, nodule numbers by 15%, nodule dry mass by 27%, leghaemogloblin by 30%, seed yield by 10% and grain protein by 8%, compared with uninoculated plants. We also found that the concentration of zinc was higher in uninoculated plant organs than in the inoculated counterpart. Our findings thus suggest that rhizobacterium strain RL9 could be exploited for bacteria-assisted reduction of zinc toxicity in zinc-contaminated soils due to its intrinsic abilities of expressing growth-promoting substances and reduction of the toxic effects of zinc.

Chromium Reducing and Plant Growth Promoting Potential of Mesorhizobium Species under Chromium Stress

ABSTRACT Chromium-reducing and plant growth–promoting potential, including production of siderophores by chromium(VI)-resistant Mesorhizobium species RC1 and RC4, isolated from chickpea nodules, was assessed both in the presence and absence of chromium(VI) under in vitro conditions. The Mesorhizobium strains displayed a high level of tolerance to chromium (400 μg ml− 1), and showed a varied sensitivity to antibacterial drugs, on yeast extract mannitol (YEM) agar plates. Mesorhizobium strains RC1 and RC4 reduced chromium(VI) by 84% and 83%, respectively at pH 7 in YEM broth after 120 h of incubation. Mesorhizobial strains RC1 and RC4 produced 27 and 35 μg ml− 1 of indole acetic acid (IAA), respectively, in Luria-Bertani broth with 100 μg ml− 1 of tryptophan. The IAA production by the mesorhizobial strains did not differ significantly (p ≤ .05) under chromium stress and showed a positive reaction for siderophore, HCN, and ammonia, both in the absence and presence of chromium(VI).The present observations suggest that the chromium reducing and plant growth promoting activities of the Mesorhizobium strains could be exploited for bioremediation of chromium(VI) and to enhance the legume productivity for chromium-contaminated soils.

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.

ACC deaminase producing Pseudomonas putida strain PSE3 and Rhizobium leguminosarum strain RP2 in synergism improves growth, nodulation and yield of pea grown in alluvial soils

Plant growth promoting rhizobacteria affects the overall performance of plants by one or combination of mechanisms. However, little information is available on how ACC deaminase secreting bacteria enhance crop production. The present study aimed at identifying ACC deaminase producing and phosphate solubilizing bacterial strains and to assess their plant growth promoting activities. Additionally, the effect of two ACC deaminase positive bacterial strains Pseudomonas putida and Rhizobium leguminosarum on pea plants was determined to find a novel and compatible bacterial pairing for developing efficient inoculants for enhancing legume production and reducing dependence on chemical fertilizers. The isolated bacterial cultures were characterized biochemically and by 16S rRNA sequence analysis. The plant growth promoting activities was determined using standard microbiological methods. The impact of P. putida and R. leguminosarum, on pea plants was determined both in pots and in field environments. Of the total 40 bacterial strains, strain PSE3 isolated from Mentha arvenss rhizosphere and RP2 strain from pea nodules produced ACC deaminase, solubilized insoluble phosphate, synthesized indole acetic acid, ammonia, cyanogenic compounds, exopolysaccharides and had antifungal activity. The dual inoculation of P. putida strain PSE3 and R. leguminosarum strain RP2 had largest positive effect and markedly increased the growth, symbiotic characteristics, nutrient pool and quantity and quality of pea seeds. The measured parameters were further augmented when inoculated pea plants were grown in soils treated with urea or DAP. A significant variation in the measured parameters of pea plants was observed under both pot and field trials following microbial inoculation but the bacterial cultures did not differ significantly in growth promoting activities. The results suggest that ACC deaminase positive bacterial cultures endowed with multiple potential can be targeted to develop mixed inoculants for enhancing pea production and hence, to reduce dependence on synthetic fertilizers.

Fungicidal Impact on Chickpea–Mesorhizobium Symbiosis

Abstract The effects of carbendazim, captan, thiram, and mancozeb, on plant vitality, chlorophyll content, N uptake, protein content, nodulation, and seed yield in chickpea (Cicer arietinum) were assessed in a controlled environment. Seeds treated with fungicides at 1 and 1.5 g. a.i./kg seed had no significant adverse effect on plant vigor, seed yield, and N and protein contents. In contrast, fungicides applied at 2 g. a.i./kg of captan, thiram and mancozeb, significantly reduced the measured parameters. In general, the toxicity of fungicides in terms of seed yield increased in the following order: Control = carbendazim > thiram > captan > mancozeb. Total chlorophyll content in foliage declined consistently with fungicides dose rates and application days. Seeds treated with lower rates of fungicides significantly increased nodulation (nodule number per plant and its dry mass) and were compatible with chickpea inoculum used in this study. Although carbendazim at 2 g a.i./kg seed had no phytotoxic effect assessed under greenhouse conditions, it significantly reduced the chlorophyll content, nodulation (60 d) and N content in shoots.

Role of Phosphate-Solubilizing Microbes in the Management of Plant Diseases

Soilborne phytopathogens are one of the major problems in sustainable crop production world over. To alleviate the damaging impact of pathogens on crop yields, huge quantities of toxic chemicals especially pesticides are used in modern agronomic practices, which, however, are extremely destructive to the environment. The non-desirability of applying huge quantities of pesticides to soil due in part to residue problems, emergence of resistance among soil phytopathogens, and lack of pathogen-resistant crop varieties has forced researchers to find solutions to the increasing pesticides problems. To this end, biological control measures consisting of microbial preparations are considered a promising option to the use of expensive and environment disruptive pesticides. Microorganisms including plant growth-promoting rhizobacteria (PGPR) in general have been found to synthesize a wide array of metabolites with significant fungicidal and bactericidal capabilities. The use of phosphate-solubilizing (PS) microorganisms among PGPR has produced both direct and indirect effects on growth and development of plants. The PS microbes endowed with biocontrol activity manage the pathogens by one or simultaneous mechanisms of antibiosis, lysis, competition, and myco-parasitism and prevent the yield losses. Even though the literature on the physiological role of PS microorganisms in crop enhancement via P supply is adequately available, the information on the ability of such organisms in the control of phytopathogens is scarce. Here, different mechanisms utilized by PS organisms for plant disease suppression are discussed. It is envisioned that the PS bacteria in the near future are expected to reduce, if not completely eliminate, the use of pesticides in insect-pests management strategies.