Santosh Babu

Cyanobacteria mediated plant growth promotion and bioprotection against Fusarium wilt in tomato

Cyanobacteria - phytopathogenic fungi - tomato plant interactions were evaluated for developing suitable biological options for combating biotic stress (Fusarium wilt) and enhancing plant vigour. Preliminary evaluation was undertaken on the fungicidal and hydrolytic enzyme activity of the cyanobacterial strains (Anabaena variabilis RPAN59, A. laxa RPAN8) under optimized environmental/nutritional conditions, followed by amendment in compost-vermiculite. Such formulations were tested against Fusarium wilt challenged tomato plants, and the Anabaena spp. (RPAN59/8) amended composts significantly reduced mortality in fungi challenged treatments, besides fungal load in soil. Cyanobacteria amended composts also led to an enhancement in soil organic C, nitrogen fixation, besides significant improvement in growth, yield, fruit quality parameters, N, P and Zn content. The tripartite interactions also enhanced the activity of defence and pathogenesis related enzymes in tomato plants. A positive correlation (r = 0.729 to 0.828) between P content and pathogenesis/defense enzyme activity revealed their role in enhancing the resistance of the plant through improved nutrient uptake. Light and scanning electron microscopy (SEM) revealed cyanobacterial colonization, which positively correlated with reduced fungal populations. The reduced disease severity coupled with improved plant growth/ yields, elicited by cyanobacterial treatments, illustrated the utility of such novel formulations in integrated pest and nutrient management strategies for Fusarium wilt challenged tomato crop.

Evaluating the efficacy of cyanobacterial formulations and biofilmed inoculants for leguminous crops

Our investigation was aimed towards evaluating the agronomic potential of biofilmed preparations (developed using Anabaena/Trichoderma as matrices with different agriculturally useful bacteria/fungi as partners) and selected cyanobacterial strains (Anabaena laxa (T7) RP8/Calothrix sp.). The formulations were prepared using paddy straw compost:vermiculite (1:1) as carrier and tested as inoculants in mungbean and soybean. The effects of the formulations were evaluated in terms of microbiological, nutrient availability, and plant biometric parameters. The Trichoderma viride–Bradyrhizobium biofilm exhibited 20–45% enhancement in fresh/dry weight of plants over other microbial treatments, while the T. viride–Azotobacter biofilm exhibited highest dehydrogenase activity in the soil and nitrogen fixation. T7 RP8 recorded statistically at par yield values with the T. viride–Bradyrhizobium (T5) biofilm treatment in mungbean. In soybean, among all the treatments, the T5 biofilm recorded the highest fresh weight of plants and available N in soil at harvest. The Anabaena–T. viride biofilmed formulations proved to be the most promising for soybean, recording 12–25% enhanced yield and microbial activity (measured as dehydrogenase activity). This study highlights the promise of cyanobacterial inoculants and biofilmed biofertilizers as promising inputs for integrated nutrient management strategies in agriculture.

EVALUATING THE ESTABLISHMENT AND AGRONOMIC PROFICIENCY OF CYANOBACTERIAL CONSORTIA AS ORGANIC OPTIONS IN WHEAT–RICE CROPPING SEQUENCE

Cyanobacteria represent promising organic inputs in rice–wheat cropping system, as they contribute towards accretion of N and C, besides secreting growth-promoting substances which influence plant productivity and soil fertility. The present study focused towards using a combinatorial approach for evaluating field-level colonization of cyanobacteria in soil and their effect on soil microbiological and plant parameters, employing agronomic and molecular tools. A consortium of cyanobacterial strains (BF1, Anabaena sp., BF2, Nostoc sp., BF3, Nostoc sp. and BF4, Anabaena sp.) was employed in different three-and four-member combinations along with 75% N + Full dose of P and K fertilizers. A significant enhancement in microbial activity and plant growth/yields and savings of 25% N in the wheat–rice cropping sequence were recorded, especially in treatments involving 75% N + Full dose of PK+BF1+BF2+BF4 and T5, i.e. 75% N + Full dose of PK+BF1+BF2+BF3. Such treatments were significantly higher or statistically at par with fertilizer controls – 75% N + Full dose of PK fertilizers. The use of DNA-based markers further helped to establish the colonization of the inoculated cyanobacteria, especially BF2 and BF3 strains. Our study clearly illustrated the establishment of inoculated cyanobacterial strains and their role in enhancing the crop productivity and soil health of the rice–wheat cropping system.

Exploring nutritional modes of cultivation for enhancing lipid accumulation in microalgae

The objective of this study was to identify the most promising nutritional mode of growth for enhanced biomass and lipid productivity in a set of twenty microalgal strains, grown under photoautotrophic and mixotrophic/heterotrophic conditions using 2% glucose as carbon source. These included four cyanobacterial strains (Cyanosarcina, Phormidium, Nostoc and Anabaena) and sixteen green algae belonging to six genera (five strains each of Chlorella and Chlorococcum, two of Scenedesmus and one each of Chlamydomonas, Kirchneria, Bracteacoccus and Ulothrix). Lipid productivity ranged from 2–13% under photoautotrophic conditions, 1.7–32% under mixotrophic conditions and 0.9–20% under heterotrophic conditions. MIC‐G5 Chlorella sp. followed by MIC‐G11 Chlorella sp. exhibited the highest cellular lipid content (355 and 271 μg/ml) and lipid productivity of 32% and 28% respectively in mixotrophic condition. In the glucose supplemented conditions (heterotrophic), a significant reduction in PUFA from 25.1 to 9.4, 29.2 to 12.4 and 44.7 to 10.2 was observed in MIC‐G4, MIC‐G5 and MIC‐G11, respectively. A remarkable enhancement of 33–70% in SFA was recorded under mixotrophic conditions. As the quality of biodiesel is based on high SFA and low PUFA, our results illustrate the significance of glucose supplemented condition as a promising strategy for generating high value biodiesel from algae.

PROSPECTING CYANOBACTERIA-FORTIFIED COMPOSTS AS PLANT GROWTH PROMOTING AND BIOCONTROL AGENTS IN COTTON

The potential of cyanobacteria-based compost formulations was evaluated in cotton crop at two agro-ecological locations (Nagpur and Sirsa) as plant growth promoting (PGP) and biocontrol agents. Compost-based formulations fortified with Calothrix sp. or Anabaena sp. enhanced germination and fresh weight of plants, and microbiological activity by 10–15%, besides increased available nitrogen (by 20–50%) in soil at Nagpur. In the fungi-infected fields at Sirsa, Anabaena – T. viride biofilmed formulation performed the best, recording 11.1% lower plant mortality than commercial Trichoderma formulation. Scanning electron microscopy confirmed the colonisation of inoculated cyanobacteria/biofilms on roots. Significant correlation between mortality, increased activity of hydrolytic enzymes and fresh weight of plant roots were recorded. Calothrix sp. and Anabaena sp. proved promising as both PGP and biocontrol agents, while biofilmed formulations substantially reduced mortality of cotton plants in sick plots. This study illustrates the promise of cyanobacteria as viable inoculation option for integrated nutrient and pest management strategies of cotton.

Deciphering the biochemical spectrum of novel cyanobacterium-based biofilms for use as inoculants

An investigation was done using cyanobacterium Anabaena torulosa as a matrix for developing novel biofilms, with anti-grazer traits against microfauna/pathogenic fungi, through co-inoculation of agriculturally important bacteria and fungi. The biofilms generated were evaluated after 4, 6 and 9 weeks of incubation for the activity of hydrolytic enzymes and fungicidal activity against phytopathogenic fungi. The activity of β-1,3-glucanase, in general, showed a gradual increasing trend up to 9 weeks, while endoglucanase activity was highest after 6 weeks of incubation, and a 40–50% reduction in chitosanase activity was recorded by the end of 9 weeks of incubation. Observations revealed that the fungus–cyanobacterium biofilms, especially Anabaena–Aspergillus awamori, exhibited the highest activity of β-1,3-glucanase and ranked second in terms of chitosanase activity. Fungicidal activity was recorded up to 9 weeks in most of the biofilms, and the highest values were recorded in cyanobacterium–Bacillus and cyanobacterium–fungus biofilms. Such biofilms were also tested against selected nematodes in microcosm experiments, which revealed no significant deleterious effects. The biocontrol activity of such biofilmed preparations against phytopathogenic fungi, but not towards selected nematodes, illustrates their promise in agriculture as potential inoculants that can effectively establish in soil.

Micronutrient enrichment mediated by plant-microbe interactions and rice cultivation practices

ABSTRACT A field experiment was conducted to evaluate the effect of different plant growth promoting microorganisms (PGPM) on micronutrient enrichment of rice crops grown under conventional (flooded) and SRI (System of Rice Intensification) practices. Significant differences were recorded among treatments and cultivation practices in terms of soil microbial activity reflected in enhanced nutrient uptake, enzyme activity, and yield. The Anabaena-based biofilm inoculants were particularly superior under both methods of cultivation, leading to 13–46% enhancement of iron and 15-41% enhancement of zinc in rice grains over uninoculated controls. SRI was found to be superior in terms of enhancing the concentration of zinc, copper, iron, and manganese (Zn, Cu, Fe and Mn), particularly in grains, and significant in increasing the activity of defense- and pathogenesis- related enzymes and yield parameters. This study illustrates the utility of cyanobacteria-based inoculants for both methods of rice cultivation and their significant interactions with the plant, leading to micronutrient enrichment of rice grains. Such formulations can complement the current biofortification strategies and help in combating the problems of malnutrition globally.

Cyanobacterial inoculation elicits plant defense response and enhanced Zn mobilization in maize hybrids

Abstract The present investigation evaluated the effect of inoculating different cyanobacterial formulations on a set of hybrids of maize, in terms of plant defense enzyme activity, soil health parameters, Zn concentration, and yields. Microbial inoculation showed significant effects on accumulation of Zn in flag leaf, with A4 (Anabaena–Azotobacter biofilm) recording the highest values. Analysis of variance (ANOVA) indicated that both the hybrids and cyanobacterial treatments brought about significant variation in terms of glomalin-related soil proteins and polysaccharides in soil and the activity of defense enzymes in roots and shoots of the plants. Cyanobacterial inoculants—A4 (Anabaena–Azotobacter biofilm) and A1 (Anabaena sp.–Providencia sp., CW1 + PW5) enhanced the activity of peroxidase, PAL and PPO in roots, which also showed a positive correlation with Zn concentration in the flag leaf. Grain yield ranged from 7.0 to 7.29 t/ha among the different inoculants. Comparative analyses of treatments showed that A3 (Anabaena–Trichoderma-biofilmed formulation) and hybrid B8 (Bio-9681) were superior in terms of parameters investigated. This represents the first report on the genotypic responses of maize hybrids to cyanobacteria-based inoculants. Future research should focus on dissecting the role of root exudates and cyanobacteria-mediated Zn mobilization pathway in maize.

Enhancement of plant growth and yields in Chickpea (Cicer arietinum L.) through novel cyanobacterial and biofilmed inoculants.

The use of Rhizobium inoculants in chickpea is well established; however, meagre efforts have been directed towards the use of other microbial supplements for improving nutrient uptake and yields. A set of novel cyanobacterial and biofilmed inoculants were evaluated in chickpea under field conditions. A significant two-fold enhancement in leghaemoglobin content of nodules and plant biomass was recorded with Anabaena laxa treatment. The inoculants - Anabaena laxa and Anabaena - Rhizobium biofilmed formulation proved to be the top-ranking treatments. Soil chlorophyll, nitrogen-fixation and available N possessed high positive direct effects on grain yield through positive - correlations and - high direct effects and also had high positive indirect effects through other component traits. The cumulative effect of improved plant growth and nutrient uptake exhibited a positive correlation with microbiological activity, especially nitrogen fixation, soil chlorophyll and soil available nitrogen. This may account for the significantly higher yield parameters in the A. laxa treatment, which recorded 50% higher grain yield (1724kgha(-1)) as compared to control (847kgha(-1)).

Deciphering the factors associated with the colonization of rice plants by cyanobacteria

Cyanobacteria‐rice plant interactions were analyzed using a hydroponics experiment. The activity of plant defense and pathogenesis‐related enzymes, scanning electron microscopy, growth, nitrogen fixation (measured as ARA), and DNA fingerprinting assays proved useful in illustrating the nature of associations of cyanobacteria with rice plants. Microscopic analyses revealed the presence of short filaments and coiled masses of filaments of cyanobacteria near the epidermis and cortex of roots and shoot tissues. Among the six cyanobacterial strains employed, Calothrix sp. (RPC1), Anabaena laxa (RPAN8), and Anabaena azollae (C16) were the best performing strains, in terms of colonization in roots and stem. These strains also enhanced nitrogen fixation and stimulated the activity of plant defense/cell wall‐degrading enzymes. A significantly high correlation was also recorded between the elicited plant enzymes, growth, and ARA. DNA fingerprinting using highly iterated palindromic sequences (HIP‐TG) further helped in proving the establishment of inoculated organisms in the roots/shoots of rice plants. This study illustrated that the colonization of cyanobacteria in the plant tissues is facilitated by increased elicitation of plant enzymes, leading to improved plant growth, nutrient mobilization, and enhanced plant fitness. Such strains can be promising candidates for developing “cyanobacteria colonized‐nitrogen‐fixing rice plants” in the future.