Alok K. Srivastava

Growth promotion of tomato plants by rhizobacteria and imposition of energy stress on Rhizoctonia solani

Rhizobacteria isolated from the rhizosphere of tomato plants were used to inoculate seeds and roots in greenhouse assays. Three bacteria, Azospirillum sp., Azotobacter chroococcum and Pseudomonas fluorescens, provided a significant (P = 0.05) increase in seedling emergence rate. A. chroococcum was found most effective in increasing the total dry weight, root and shoot length of tomato plants, followed by P. fluorescens and Azospirillum sp. Variations in incubation temperature and soil moisture significantly (P = 0.01) influenced the total plant growth. Temperatures >30°C were not favourable for bacterial activity or plant growth. Inoculated seedlings at −5 kPa (25°C) showed maximum plant growth, whereas least response was observed at −15 kPa. Inoculated seedlings significantly (P = 0.05) reduced the disease incidence and severity of Rhizoctonia damping-off of tomato seedlings. Colonization of Rhizoctonia solani sclerotia by rhizobacteria was negatively correlated with germination of sclerotia in patato dextrose broth (r = −0.84) and in Pfeffers salts solution (r = 0.85). Bacteria were able to release 14C-labelled endogenous compounds from labelled sclerotia. Sclerotia exuded 37% (percentage of total label) 14C-labelled carbonaceous compounds in soil inoculated with P. fluorescens, 29% with A. chroococcum and 19% with Azospirillum sp. Loss of endogenous C compounds from sclerotia was correlated (r = −0.97) with repression of germination.

Myconanotechnology in agriculture: a perspective

Myconanotechnology is an emerging field, where fungi can be harnessed for the synthesis of nanomaterials or nanostructures with desirable shape and size. Though myconanotechnology is in its infancy, potential applications provide exciting waves of transformation in agriculture and fascinate microbiologists and other researchers to contribute in providing incremental solutions through green chemistry approaches for advancing food security. In this article, we provide a brief overview of the research efforts on the mycogenic synthesis of nanoparticles with particular emphasis on mechanisms and potential applications in agriculture and allied sectors.

Diversity and antagonistic potential of Bacillus spp. associated to the rhizosphere of tomato for the management of Rhizoctonia solani

Abstract Bacillus spp. has emerged as the most effective alternative to synthetic chemical fungicides. To get a better insight in the antagonistic potential of Bacillus strains, rhizospheric soil samples of healthy tomato plants from Indo-gangetic plain regions of India were analysed. A total of 108 Bacillus strains were obtained from preliminary screening. Potent strains identified on the basis of in vitro antagonistic and biochemical assays were subjected to diversity analysis using 16S-rDNA, BOX and ERIC-PCR. Furthermore, the four best performing antagonistic Bacillus strains under in vitro plant growth promotion and antagonistic assay were selected for pot experiment. In field study, Bacillus amyloliquefaciens MB101 and Bacillus subtilis MB14 showed drastic reduction in disease index by 55.7 and 41.74% with significant elevation in fruit yield up to 220 and 184 qha–1, respectively. The present study was successful in selecting effective Bacillus strains by performing phenotypic and genotypic characterisation of Bacillus strains that can be used as an integral component of integrated disease management of tomato root rot and damping-off.

An analytical study of nonlinear double-diffusive convection in a porous medium under temperature/gravity modulation

The article deals with nonlinear thermal instability problem of double-diffusive convection in a porous medium subjected to temperature/gravity modulation. Three types of imposed time-periodic boundary temperature (ITBT) are considered. The effect of imposed time-periodic gravity modulation (ITGM) is also studied in this problem. In the case of ITBT, the temperature gradient between the walls of the fluid layer consists of a steady part and a time-dependent periodic part. The temperature of both walls is modulated in this case. In the problem involving ITGM, the gravity field has two parts: a constant part and an externally imposed time-periodic part. Using power series expansion in terms of the amplitude of modulation, which is assumed to be small, the problem has been studied using the Ginzburg–Landau amplitude equation. The individual effects of temperature and gravity modulation on heat and mass transports have been investigated in terms of Nusselt number and Sherwood number, respectively. Further the effects of various parameters on heat and mass transports have been analyzed and depicted graphically.

Multifarious plant growth promoting characteristics of chickpea rhizosphere associated Bacilli help to suppress soil-borne pathogens

Wilt and root rot are the major constraints in chickpea production and very difficult to manage through agrochemicals. Hence, for an ecofriendly and biological management, 240 strains of Bacillus and Bacillus derived genera were isolated from chickpea rhizosphere, further narrowed down to 14 strains on the basis of in vitro production of indole acetic acid, siderophore, phosphate solubilization, hydrolytic enzymes and were evaluated for antagonism against chickpea pathogens (Fusarium oxysporum f. sp. ciceri race 1, F. solani and Macrophomina phaseolina). The strains were identified on the basis of physiological characters and 16S RNA gene sequencing. The genotypic comparisons of strains were determined by BOX-polymerase chain reaction profiles and amplified rDNA restriction analysis. These isolates were evaluated in greenhouse assay in which B. subtilis (B-CM191, B-CV235, B-CL-122) proved to be effective in reducing wilt incidence and significant enhancement in growth (root and shoot length) and dry matter of chickpea plants. PCR amplification of bacillomycin (bmyB) and β-glucanase genes suggests that amplified genes from the Bacillus could have a role to further define the diversity, ecology, and biocontrol activities in the suppression of soil-borne pathogens.

Isolation and characterization of siderophore producing antagonistic rhizobacteria against Rhizoctonia solani

Plant protection through siderophore producing rhizobacteria (SPR) has emerged as a sustainable approach for crop health management. In present study, 220 bacteria isolated from tomato rhizosphere were screened for in vitro antagonistic activity against Rhizoctonia solani AG‐4. Nine potent antagonistic strains viz., Alcaligenes sp. (MUN1, MB21, and MPF37), Enterobacter sp. (MPM1), Pseudomonas sp. (M10A and MB65), P. aeruginosa (MPF14 and MB123) and P. fluorescens (MPF47) were identified on the basis of physiological characters and 16S rDNA sequencing. These strains were able to produce hydrolytic enzymes, hydrogen cyanide, indole acetic acid, although, only few strains were able to solubilize phosphate. Two strains (MB123 and MPF47) showed significant disease reduction in glasshouse conditions were further evaluated under field conditions using three different application methods. Application of P. fluorescens (MPF47) in nursery as soil mix + seedling root treatments prior to transplantation resulted in significant disease reduction compared to control. Total chlorophyll and available iron were significantly higher in the MPF47 treated plants in contrast to infected control. In conclusion, siderophore producing bacteria MPF47 have strong biocontrol abilities and its application as soil mix + seedling root treatments provided strong shield to plant roots against R. solani and could be used for effective bio‐management of pathogen.

Deciphering Diversity of Salt-Tolerant Bacilli from Saline Soils of Eastern Indo-gangetic Plains of India

The intensive use of chemical fertilizers, monoculture and irrigation with surface saline water has resulted in the deterioration of soil health by enhancing the level of salinity in the Eastern Indo-Gangetic Plains of India. Therefore, diversity of halotolerant bacteria adapted to that environment and possessed the ability to produce plant growth hormones was explored, that could be used for salt stress amelioration. The 16S rRNA gene sequencing and fatty acid methyl ester (FAME) were used for diversity analysis of salt-tolerant bacilli. Among the 95 isolates, 55 strains showed plant growth promotion traits, production of industrially important enzymes (amylase, protease and cellulase) and tolerance to more than 4% NaCl. Using partial 16S rRNA sequences and FAME comparisons, 21 different species of Bacillus and Bacillus-derived genera were identified, viz. Bacillus megaterium, B. subtilis, B. licheniformis, B. firmus, B. horikoshii, B. pumilus, Bacillus sp., B. safensis, B. thuringiensis, B. simplex, B. agri, B. flexus, B. oceanisediminis, B. cereus, B. arsenicus, Paenibacillus dendritiformis, Lysinibacillus sp., L. sphaericus, B. marisflavi, Terribacillus sp., and B. mycoides. These isolates possess the ability to tolerate high salt, form endospores, withstand harsh environments, and also have the potential for plant growth promotion, which could be useful in formulation of new inoculants to enhance the availability of nutrients for crop growth under saline conditions.

Diversity of potential microbial parasites colonizing sclerotia of Macrophomina phaseolina in soil

The colonization of Macrophomina phaseolina sclerotia by microbial parasites was evaluated in unsterilized field soil at different levels of soil moisture (0,-5, and-10 kPa) and temperature (20, 30, and 40°C). The maximum colonization of sclerotia was recorded in soil held at-5 or-10 kPa at 30–40°C. Trichoderma harzianum isolate 25–92 and Pseudomonas fluorescens isolate 4–92 were recorded as potential sclerotial parasites, and they significantly (P=0.05) reduced the germination of sclerotia by 60–63%. Cells of P. fluorescens and buffer-washed conidia of T. harzianum were completely agglutinated at 28°C with crude agglutinin of M. phaseolina. The ability of different antagonists to parasitize the sclerotia were correlated with the agglutination ability of the antagonists.

EFFECT OF EXTERNAL ELECTRIC FIELD ON THE GROWTH OF NANOTUBULES

In the present investigation, we have studied the effect of electric field on the growth of carbon nanotubules. Different electric fields corresponding to 3, 6, 9, 15, and 21 V have been applied during the growth of the tubules. The estimate of the electric field corresponding to these voltages cannot be precisely evaluated in view of only approximately defined electrode dimensions. It has been observed that the application of electric field leads to the agglomerates (bundles) of nanotubules. The size, length, and alignment of these bundles varies with the strength of the applied electric field. The best results have been obtained with electric field corresponding to 6 V where the as-formed tubules are in parallel alignment and exist as bundles. As the electric field is increased, the alignment of tubules in the bundle becomes randomly oriented. The degree of randomness increases with increase of electric field after its optimum value corresponding to 6 V. The parallel alignment of the graphitic tubules i...

Characterization of antagonistic‐potential of two Bacillus strains and their biocontrol activity against Rhizoctonia solani in tomato

To investigate the biocontrol mechanism of two antagonistic Bacillus strains (Bacillus subtilis MB14 and Bacillus amyloliquefaciens MB101), three in vitro antagonism assays were screened and the results were concluded that both strains inhibited Rhizoctonia solani growth in a similar manner by dual culture assay, but the maximum percent of inhibition only resulted with MB101 by volatile and diffusible metabolite assays. Moreover, cell free supernatant (CFS) of MB101 also showed significant (p > 0.05) growth inhibition as compared to MB14, when 10 and 20% CFS mix with the growth medium of R. solani. After in vitro-validation, both strains were evaluated under greenhouse and the results concluded that strain MB101 had significant biocontrol potential as compared to MB14. Strain MB101 was enhanced the plant height, biomass and chlorophyll content of tomato plant through a higher degree of root colonization. In field trials, strain MB101 showed higher lessening in root rot symptoms with significant fruit yield as compare to strain MB14 and infected control. Next to the field study, the presence of four antibiotic genes (srfAA, fenD, ituC, and bmyB) also concluded the antifungal nature of both Bacillus strains. Phylogenetic analysis of protein sequences revealed a close relatedness of three genes (srfAA, fenD, and ituC) with earlier reported sequences of B. subtilis and B. amyloliquefaciens. However, bmyB showed heterogeneity in among both strains (MB14 and MB101) and it may be concluded that higher degree of antagonism, root colonization and different antibiotic producing genes may play an important role in biocontrol mechanism of strain MB101.