Mahaveer P. Sharma

Growth responses and dependence of Acacia nilotica var. cupriciformis on the indigenous arbuscular mycorrhizal consortium of a marginal wasteland soil

Abstract The responses of Acacia nilotica L. var. cupriciformis to phosphorus application and inoculation with the indigenous consortium of arbuscular mycorrhizal (AM) fungi were evaluated in a nursery experiment using soil from a marginal wasteland. A positive growth response to mycorrhizal inoculation was observed at an Olsen-P level of 20 ppm in the presence of the natural population of AM fungi. There was growth stimulation by either inoculation or additional P at the highest soil P of 40 ppm. Colonization was negatively correlated to soil P but P content of both shoot and root were positively correlated. Inoculation with the indigenous AM consortium significantly increased the uptake of P at all levels of applied P. Acacia is moderately dependent upon the AM symbiosis and exhibited a maximal mycorrhizal dependence (MD) of 18.25% at 20 ppm Olsen-P level under the conditions studied. A sharp and considerable reduction in MD and dry matter yield observed at 40 ppm P suggests that the external P requirement for maximal production of biomass was met at approximately 20 ppm Olsen-P.

Enhanced growth and productivity following inoculation with indigenous AM fungi in four varieties of onion (Allium cepa L.) in an alfisol.

ABSTRACT A field experiment was conducted to evaluate the benefit to growth of Allium cepa L. of inoculation with a mixed culture of indigenous arbuscular mycorrhizal (AM) fungi. Four locally adapted onion cvs., Pusa White Flat (PWF), Pusa White Round (PWR), Early Grano (EG) and Pusa Madhvi (PM) were grown at two phosphorus levels (25 and 50 kg P ha−1) in a P deficient alfisol. Inoculation significantly increased mycorrhiza formation over that caused by the level of native AM fungi present at the site. At harvest, all inoculated onion varieties showed higher values of bulb diameter, fresh weight, shoot dry matter, shoot p content and bulb yield than uninoculated plants. However, the magnitude of AM response for yield in a given onion variety was found to be different at different levels of P. This holds true in all the varieties tested. Inoculated plants tended to have greater bulb yield for varieties PM and PWR grown at 25 kg P ha−1. On the other hand, PWF and EG plants showed similar response at 50 kg P ha−1. The percent root length colonized by AM fungi between both the P levels of inoculated plants did not differ significantly. However, the extent of colonization varied among the varieties. The dependence of plants on mycorrhizal fungi for bulb production varied among the varieties grown at a particular P. EG and PWF plants showed maximum dependence on AM at 50 kg P ha where as PM and PWR plants exhibited a maximum MD at 25 kg P ha−1.

Mycorrhizal dependency and growth responses of Acacia nilotica and Albizzia lebbeck to inoculation by indigenous AM fungi as influenced by available soil P levels in a semi-arid Alfisol wasteland

A series of available phosphorus (Olsen) levels ranging from 10 to 40 ppm were achieved in a semi-arid soil. The influence of the levels of phosphorus on the symbiotic interaction between two subtropical tree species, Acacia nilotica and Albizzia lebbeck, and a mixed inoculum of indigenous arbuscular mycorrhizal (AM) fungi was evaluated in a greenhouse study. The extent to which the plant species depended on AM fungi for dry matter production decreased as the levels of soil P increased, but the degree of this decrease differed in the two species tested. Acacia nilotica colonized by AM fungi showed a significant increase in shoot P and dry matter at a soil P level of 10 ppm whereas in Albizzia lebbeck, such increase occurred at 20 ppm. Mycorrhizal inoculation response disappeared beyond soil P levels of 25 ppm in Acacia nilotica and 30 ppm in Albizzia lebbeck. Levels of soil P greater than 25 ppm suppressed AM fungus colonization in both species. Soil P levels of 30 and 40 ppm and 40 ppm caused negative mycorrhizal dependencies (MD) in Acacia nilotica and Albizzia lebbeck respectively. Values of MD for both species were negatively correlated with soil P levels. Based on the MD values, regression equations were developed to predict MD for given levels of available P.

Entomopathogenic nematodes, a potential microbial biopesticide: mass production and commercialisation status – a mini review

Parasitic nematodes have several important attributes that make them excellent candidates for biological control of soil insects. These nematodes can be produced by in vivo by baiting technique on insects and commercially by in vitro solid/liquid culturing. Numerous insect pests on many different crops are being controlled by these insect parasitic nematodes, including root weevils, flea beetles, mint root borer, colorado potato beetle, white grubs, caterpillars and plant parasitic root nematode, e.g. root-knot nematodes. Utilisation of entomopathogenic nematodes (EPN) has raised intense interest and has been a growing concern globally mainly because of its potential efficiency, exemption from registration and other impressive attributes for utilising against the control of soil dwelling pests. This review highlights the mass production, commercialisation and utilisation of EPN as microbial biopesticide in bio-intensive pest management programmes.

Dynamics of Plant Nutrients, Utilization and Uptake, and Soil Microbial Community in Crops Under Ambient and Elevated Carbon Dioxide

In natural settings such as under field conditions, the plant-available soil nutrients in conjunction with other environmental factors such as solar radiation, temperature, precipitation, and atmospheric carbon dioxide (CO2) concentration determine crop adaptation and productivity. Therefore, crop success depends on the intricate balance among these multiple environmental factors. Plant nutrients are the major constraint for crop productivity worldwide because it must be supplied externally to achieve maximum production. The depleting natural resources of mineral nutrients in addition to the global changes in climate caused by the emission of green house gases including CO2 are among the major concerns of crop production and food security. Moreover, crop demand for nutrients has been increased due to use of modern cultivars and improved irrigation facilities and is expected to be even higher under elevated CO2. Soil microorganisms including arbuscular mycorrhizal (AM) fungi partly enhance crop nutrient availability and acquisition in many soil types through symbiotic or non-symbiotic relationships. Atmospheric CO2 concentration is expected to be doubled from its current level of 400 μmol mol−1 at the end of this twenty-first century. Elevated CO2 increases growth and yield of many crops upon which humans depend for food and clothing. However, plant nutrient availability exerts major control on the degree of stimulation by elevated CO2 on crop growth and yield. One of the objectives of this chapter is to provide a summary of crop responses to plant nutrients mainly nitrogen, phosphorus, and potassium and underline in part the dynamics of soil microorganisms including AM fungi in the nutrient accessibility under current and elevated CO2 concentrations. Regardless of the CO2 levels, nutrient deficiencies negatively affect crop photosynthesis, growth and biomass production, yield, and yield quality. Elevated CO2 tends to compensate, at least partly, for the losses caused by nutrient deficiency especially by increasing plant growth due to improved efficiency of nutrient acquisition and utilization. However, crop species, deficiency of the specific nutrient, and its severity greatly influence the nutrient efficiency in crop plants. The critical tissue nutrient concentration required to achieve 90 % of maximum productivity of some plant nutrients is likely to be higher at elevated CO2. Another objective of this chapter is to discuss the influence of crop species, soil nutrient status, and elevated CO2 on the dynamics of nutrient uptake and utilization efficiency and resultant tissue nutrient concentration. Future research methods utilizing the combined effect of plant nutrient status and elevated CO2 on crops will improve our understanding of the complex relationships among various plant processes leading to efficient use of nutrient under field conditions.

Enhanced growth of micropropagated bulblets of Lilium sp. inoculated with arbuscular mycorrhizal fungi at different P fertility levels in an alfisol

Summary The effect of three arbuscular mycorrhizal (AM) inocula at four available levels of phosphorus (8.41, 12.53, 13.63 and 14.6 ppm) in non-disinfected soil was studied on the growth, flowering, P uptake and root colonization in micropropagated bulblets of Lilium sp. (Asiatic hybrid ‘Gran Paradiso’). The inoculated bulblets fared significantly better than the uninoculated ones in terms of all the growth variables, namely size, weight, shoot length, number of leaves and leaf area, and in P uptake. However, bulblets inoculated with different AM inocula had optimum growth at different P levels. Bulblets inoculated with indigenous mixed vesicular-arbuscular mycorrhiza species (VAM I) and Glomus intraradices isolate 2 (VAM III) showed the best growth and early flowering at available soil P of 13.6 ppm, whereas those inoculated with Glomus intraradices isolate 1 (VAM II) showed higher growth at 2.5 ppm available soil P. Amongst the three tested inocula, VAM I promoted maximum shoot length, bulblet size, and weight at 13.6 ppm P. The bulblets under this treatment also flowered earlier, nearly a month before the uninoculated control ones.

Response of Eucalyptus tereticornis to inoculation with indigenous AM fungi in a semiarid alfisol achieved with different concentrations of available soil P

Eucalyptus tereticornis was grown in a green house in a low phosphorus (0.67 ppm Olsens P) soil (Typic Haplustalf) inoculated with mixed indigenous arbuscular mycorrhizal (AM) fungi. Soil was amended to achieve P levels of 10, 20, 25, 30 and 40 ppm to evaluate the growth response and dependence of E. tereticornis to inoculation with AM fungi. A positive response to mycorrhizal inoculation was evident at the first two levels of soil P, i.e., at 0.67 and 10 ppm but not at the higher levels of soil P. Dry matter yield of inoculated plants beyond 20 ppm soil P was similar or even less compared to their uninoculated counterparts. Inoculated plants produced maximum dry matter (root and shoot) at 10 ppm soil P, whereas uninoculated plants did not produce until the level reached 20 ppm. The percentage root length colonized by AM fungi decreased from 31% to 3% as the concentration of P increased beyond 10 ppm soil P. Higher levels of soil P depressed the AM colonization significantly. Inoculated plants had higher shoot P and N contents compared to their uninoculated counterparts at all levels of soil P. However, at the first two lower levels of soil P, inoculated plants showed significantly higher shoot P and N contents over their respective uninoculated counterparts. The increasing shoot P accumulation beyond 10 ppm did not enhance dry matter yields. Inoculated plants had lower values of phosphorus utilization efficiency (PUE) and nitrogen utilization efficiency (NUE) at all levels of soil P except at the unamended level (0.67 ppm) where the inoculated plants showed higher values of NUE compared to uninoculated control plants. Taking dry matter yield into consideration, Eucalyptus plants were found to be highly dependent on 10 ppm of soil P for maximum dry matter production. Any further amendment of P to soil was not beneficial neither for AM symbiosis nor plant growth.

Improved photosynthetic efficacy of maize (Zea mays) plants with arbuscular mycorrhizal fungi (AMF) under high temperature stress

In this study, pot experiments were performed to investigate the effects of high temperature stress (44 °C) in maize plants colonized with and without arbuscular mycorrhizal fungi (AMF). Various parameters characterizing photosynthetic activity were measured in order to estimate the photosynthetic efficiency in maize plants. It was observed that density of active reaction centers of PSII, quantum efficiency of photosystem II (PSII), linear electron transport, excitation energy trapping, performance index, net photosynthesis rate increased in AMF (+) plants at 44 °C ± 0.2 °C. Efficiency of primary photochemical reaction (represented as Fv/Fo) increased in AMF (+) plants as compared to AMF (-) plants. AMF seems to have protected water splitting complex followed by enhanced primary photochemistry of PSII under high temperature. Basic morphological parameters like leaf width, plant height and cob number increased in AMF (+) plants as compared to AMF (-) plants. AMF (+) plants grew faster than AMF (-) plants due to larger root systems. Chl content increased in AMF (+) plants as compared to AMF (-) maize plants. AMF hyphae likely increased Mg uptake which in turn increased the total chlorophyll content in AMF (+) maize plants. This subsequently led to a higher production in photosynthate and biomass. Thus AMF (+) plants have shown better photosynthesis performance as compared to AMF (-) maize plants under high temperature stress.

Effect of Native Soybean Rhizobia and AM Fungi in the Improvement of Nodulation, Growth, Soil Enzymes and Physiological Status of Soybean Under Microcosm Conditions

The arbuscular mycorrhizal (AM) fungi-rhizobia synergism is a promising approach for improving the growth and nutrition of soybean. It is, therefore, imperative to evaluate potential soybean rhizobia and AM fungi singly to identify their stress protectant physiological traits, enhance growth and nodulation of soybean and improve soil health. The efficacy of five root nodulating soybean rhizobia and an indigenous AM fungus, Glomus intraradices, was evaluated on soybean (cv JS 93-05) under microcosm conditions. In general, all the inoculated plants showed higher fresh shoot and root weight, and nodule number as compared to uninoculated control plants. The plants inoculated with Bradyrhizobiumjaponicum (strain USDA 110), B. liaoningense 17c (MTCC 10753) and AM fungus showed higher growth and nodulation. However, the plants inoculated with rhizobia 12c (unidentified), B. japonicum DE2-5a (MTCC 10751) and USDA 205 did enhance nodulation but found at par with the other inoculated plants. Interestingly, these inoculated plants found to have comparatively higher nitrogen and phosphorus uptake. B. japonicum (strain USDA 110), native slow growing rhizobia isolate DE2-5a and AM fungi were also found to stimulate proline content in shoots, and trehalase and fluorescein diacetate activities in the rhizosphere soil. Considering the growth and physiological responses of AM fungi and rhizobial strains (DE2-5a and 17c) to soybean, there is a need for further testing the synergistic responses to evolve better survival candidates under drought-stress conditions.

Soil Biological Activity Contributing to Phosphorus Availability in Vertisols under Long-Term Organic and Conventional Agricultural Management

Mobilization of unavailable phosphorus (P) to plant available P is a prerequisite to sustain crop productivity. Although most of the agricultural soils have sufficient amounts of phosphorus, low availability of native soil P remains a key limiting factor to increasing crop productivity. Solubilization and mineralization of applied and native P to plant available form is mediated through a number of biological and biochemical processes that are strongly influenced by soil carbon/organic matter, besides other biotic and abiotic factors. Soils rich in organic matter are expected to have higher P availability potentially due to higher biological activity. In conventional agricultural systems mineral fertilizers are used to supply P for plant growth, whereas organic systems largely rely on inputs of organic origin. The soils under organic management are supposed to be biologically more active and thus possess a higher capability to mobilize native or applied P. In this study we compared biological activity in soil of a long-term farming systems comparison field trial in vertisols under a subtropical (semi-arid) environment. Soil samples were collected from plots under 7 years of organic and conventional management at five different time points in soybean (Glycine max) -wheat (Triticum aestivum) crop sequence including the crop growth stages of reproductive significance. Upon analysis of various soil biological properties such as dehydrogenase, β-glucosidase, acid and alkaline phosphatase activities, microbial respiration, substrate induced respiration, soil microbial biomass carbon, organically managed soils were found to be biologically more active particularly at R2 stage in soybean and panicle initiation stage in wheat. We also determined the synergies between these biological parameters by using the methodology of principle component analysis. At all sampling points, P availability in organic and conventional systems was comparable. Our findings clearly indicate that owing to higher biological activity, organic systems possess equal capabilities of supplying P for crop growth as are conventional systems with inputs of mineral P fertilizers.