Rajendran Vijayabharathi

Evaluation of Streptomyces strains isolated from herbal vermicompost for their plant growth-promotion traits in rice.

Six actinomycetes, CAI-13, CAI-85, CAI-93, CAI-140, CAI-155 and KAI-180, isolated from six different herbal vermi-composts were characterized for in vitro plant growth-promoting (PGP) properties and further evaluated in the field for PGP activity in rice. Of the six actinomycetes, CAI-13, CAI-85, CAI-93, CAI-140 and CAI-155 produced siderophores; CAI-13, CAI-93, CAI-155 and KAI-180 produced chitinase; CAI-13, CAI-140, CAI-155 and KAI-180 produced lipase; CAI-13, CAI-93, CAI-155 and KAI-180 produced protease; and CAI-13, CAI-85, CAI-140 and CAI-155 produced ß-1-3-glucanase whereas all the six actinomycetes produced cellulase, hydrocyanic acid and indole acetic acid (IAA). The actinomycetes were able to grow in NaCl concentrations of up to 8%, at pH values between 7 and 11, temperatures between 20 and 40 °C and compatible with fungicide bavistin at field application levels. In the rice field, the actinomycetes significantly enhanced tiller numbers, panicle numbers, filled grain numbers and weight, stover yield, grain yield, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere, the actinomycetes also significantly enhanced total nitrogen, available phosphorous, % organic carbon, microbial biomass carbon and nitrogen and dehydrogenase activity over the un-inoculated control. Sequences of 16S rDNA gene of the actinomycetes matched with different Streptomyces species in BLAST analysis. Of the six actinomycetes, CAI-85 and CAI-93 were found superior over other actinomycetes in terms of PGP properties, root development and crop productivity. qRT-PCR analysis on selected plant growth promoting genes of actinomycetes revealed the up-regulation of IAA genes only in CAI-85 and CAI-93.

Plant growth promoting rhizobia: challenges and opportunities

Modern agriculture faces challenges, such as loss of soil fertility, fluctuating climatic factors and increasing pathogen and pest attacks. Sustainability and environmental safety of agricultural production relies on eco-friendly approaches like biofertilizers, biopesticides and crop residue return. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters (PGP), emphasizes the need for further strengthening the research and their use in modern agriculture. PGP inhabit the rhizosphere for nutrients from plant root exudates. By reaction, they help in (1) increased plant growth through soil nutrient enrichment by nitrogen fixation, phosphate solubilization, siderophore production and phytohormones production (2) increased plant protection by influencing cellulase, protease, lipase and β-1,3 glucanase productions and enhance plant defense by triggering induced systemic resistance through lipopolysaccharides, flagella, homoserine lactones, acetoin and butanediol against pests and pathogens. In addition, the PGP microbes contain useful variation for tolerating abiotic stresses like extremes of temperature, pH, salinity and drought; heavy metal and pesticide pollution. Seeking such tolerant PGP microbes is expected to offer enhanced plant growth and yield even under a combination of stresses. This review summarizes the PGP related research and its benefits, and highlights the benefits of PGP rhizobia belonging to the family Rhizobiaceae, Phyllobacteriaceae and Bradyrhizobiaceae.

Plant growth-promoting traits of biocontrol potential bacteria isolated from rice rhizosphere

Seven isolates of bacteria (SRI-156, SRI-158, SRI-178, SRI-211, SRI-229, SRI-305 and SRI-360) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum and plant growth promotion (PGP) of the plant. In the present study, the seven isolates were characterized for their physiological traits (tolerance to salinity, pH, temperature and resistance to antibiotics and fungicides) and further evaluated in the field for their PGP of rice. All the seven isolates were able to grow at pH values between 5 and 13, in NaCl concentrations of up to 8% (except SRI-156 and SRI-360), temperatures between 20 and 40°C and were resistant to ampicillin (>100 ppm; except SRI-158 and SRI-178) but sensitive (<10 ppm) to chloramphenicol, kanamycin, nalidixic acid, streptomycin (except SRI-156 and SRI-211) and tetracycline. They were tolerant to fungicides benlate and captan, except SRI-158 and SRI-178, bavistin and sensitive to thiram (except SRI-156 and SRI-211) at field application level. In the field, four of the seven isolates (SRI-158, SRI-211, SRI-229 and SRI-360) significantly enhanced the tiller numbers, stover and grain yields, total dry matter, root length, volume and dry weight over the un-inoculated control. In the rhizosphere soil at harvest, all the isolates significantly enhanced microbial biomass carbon (except SRI-156), microbial biomass nitrogen and dehydrogenase activity (up to 33%, 36% and 39%, respectively) and total N, available P and% organic carbon (up to 10%, 38% and 10%, respectively) compared to the control. This investigation further confirms that the SRI isolates have PGP properties.

Evaluation of Streptomyces spp. for their plant-growth-promotion traits in rice

Five strains of Streptomyces (CAI-17, CAI-68, CAI-78, KAI-26, and KAI-27) were previously reported to have potential for charcoal rot control and plant growth promotion (PGP) in sorghum. In this study, those 5 Streptomyces strains were characterized for their enzymatic activities and evaluated for their PGP capabilities on rice. All the Streptomyces strains were able to produce lipase and β-1,3-glucanase; grew in NaCl (up to 8%), at pH 5-13, and at temperatures 20-40 °C; and were resistant to ampicillin, sensitive to nalidixic acid, and highly sensitive to chloramphenicol, kanamycin, streptomycin, and tetracycline. They were highly tolerant to the fungicide bavistin but were highly sensitive to benlate, benomyl, and radonil. When evaluated on rice in the field, Streptomyces significantly enhanced tiller and panicle numbers, stover and grain yields, dry matter, root length, volume and dry weight, compared with the control. In the rhizosphere at harvest, microbial biomass carbon and nitrogen, dehydrogenase activity, total nitrogen, available phosphorus, and % organic carbon were also found significantly higher in Streptomyces-treated plots than in the control plots. This study further confirms that the selected Streptomyces have PGP activities.

Plant growth-promoting traits of Streptomyces with biocontrol potential isolated from herbal vermicompost

Abstract Three strains of Streptomyces (CAI-21, CAI-26 and MMA-32) were earlier reported by us as having potential for biocontrol of charcoal rot of sorghum, caused by Macrophomina phaseolina (Tassi) Goid., and plant growth promotion (PGP) of the plant. In the present investigation, the three Streptomyces were characterised for their physiological traits (tolerance of salinity, temperature, pH and resistance to antibiotics) and further evaluated in the field for their PGP of rice, grown by a system of rice intensification methods. All three Streptomyces were able to grow in NaCl concentrations of up to 12% (except MMA-32), at pH values between 5 and 13 and temperatures between 20 and 40°C. They were highly resistant to ampicillin and trimethoprim (>800 ppm), sensitive to chloramphenicol, kanamycin and nalidixic acid (50–100 ppm) and highly sensitive to streptomycin and tetracycline (5–25 ppm). When evaluated for their PGP activity on seedlings of rice, % germination and shoot and root lengths were significantly enhanced over the control. In the field, the Streptomyces strains significantly enhanced the panicle length, filled grain numbers and weight, panicle weight, 1000 seed weight, tiller numbers, total dry matter, root length (39–65%), root volume (13–30%), root dry weight (16–24%), grain yield (9–11%) and stover yield (11–22%) over the control. In the rhizosphere soil (0–15 cm from root) at harvest, the population of actinomycetes was significantly enhanced as was microbial biomass carbon (27–83%) and nitrogen (24–43%), dehydrogenase activity (34–152%), available P (13–34%) and N (30–53%) and % organic carbon (26–28%). This study further confirms that the selected Streptomyces have PGP properties.

Biological activity of entomopathogenic actinomycetes against lepidopteran insects (Noctuidae: Lepidoptera)

Vijayabharathi, R., Kumari, B. R., Sathya, A., Srinivas, V., Abhishek, R., Sharma, H. C. and Gopalakrishnan, S. 2014. Biological activity of entomopathogenic actinomycetes against lepidopteran insects (Noctuidae: Lepidoptera). Can. J. Plant Sci. 94: 759-769. The aim of the present study was to identify an efficient broad-spectrum bio-pesticide for the control of lepidopteran insects from microbes in various ecological niches. A total of 111 microbes isolated from various herbal vermi-composts and organically cultivated fields were evaluated for their intracellular metabolites (ICM), extracellular metabolites (ECM) and whole culture (WC) against early instars of lepidopteran insects. Fifteen actinomycete isolates which showed insecticidal activity against 2nd instar Helicoverpa armigera were selected and further screened against Spodoptera litura and Chilo partellus. A significant broad spectrum insecticidal activity was found in the order ECM>ICM>WC against all the insects under laboratory conditions. All these actinomycete isolates also registered significant activity under greenhouse conditions on 2nd instar H. armigera. The actinomycete isolates were identified by 16S rDNA sequencing and matched with Streptomyces species using BLAST search. Among all the 15 isolates, SAI-25 (S. griseoplanus), CAI-155 (S. bacillaris) and BCA-698 (S. albolongus) showed consistent entomopathogenic activity against all the three insects suggesting their potential as broad-spectrum biocontrol agents against other lepidopterans.

A Renaissance in Plant Growth-Promoting and Biocontrol Agents by Endophytes

Endophytes are the microorganisms which colonize the internal tissue of host plants without causing any damage to the colonized plant. The beneficial role of endophytic organisms has dramatically documented worldwide in recent years. Endophytes promote plant growth and yield, remove contaminants from soil, and provide soil nutrients via phosphate solubilization/nitrogen fixation. The capacity of endophytes on abundant production of bioactive compounds against array of phytopathogens makes them a suitable platform for biocontrol explorations. Endophytes have unique interaction with their host plants and play an important role in induced systemic resistance or biological control of phytopathogens. This trait also benefits in promoting plant growth either directly or indirectly. Plant growth promotion and biocontrol are the two sturdy areas for sustainable agriculture where endophytes are the key players with their broad range of beneficial activities. The coexistence of endophytes and plants has been exploited recently in both of these arenas which are explored in this chapter.

Microbes as interesting source of novel insecticides: A review

Microbes are ubiquitous, survive in all sorts of environments and have a profound influence on the earth. In the present day plant protection scenario, development of resistance to chemical pesticides is the major hurdle in insect pest management. In recent years, several microbes with potential insecticidal properties have come to light. Viruses, bacteria, fungi and protozoa that are known to produce an array of metabolites or toxins, form the basis for microbial insecticides. Since these versatile organisms are amenable for genetic engineering, strains with good insecticidal properties can be identified, evaluated and utilized for pest control. This paper reviews the insecticidal properties of microbes and their potential utility in pest management. Keywords: Microbes, insecticides, metabolites, pest management. African Journal of Biotechnology , Vol 13(26) 2582-2592

Plant growth-promoting actinobacteria: a new strategy for enhancing sustainable production and protection of grain legumes

Grain legumes are a cost-effective alternative for the animal protein in improving the diets of the poor in South-East Asia and Africa. Legumes, through symbiotic nitrogen fixation, meet a major part of their own N demand and partially benefit the following crops of the system by enriching soil. In realization of this sustainability advantage and to promote pulse production, United Nations had declared 2016 as the “International Year of pulses”. Grain legumes are frequently subjected to both abiotic and biotic stresses resulting in severe yield losses. Global yields of legumes have been stagnant for the past five decades in spite of adopting various conventional and molecular breeding approaches. Furthermore, the increasing costs and negative effects of pesticides and fertilizers for crop production necessitate the use of biological options of crop production and protection. The use of plant growth-promoting (PGP) bacteria for improving soil and plant health has become one of the attractive strategies for developing sustainable agricultural systems due to their eco-friendliness, low production cost and minimizing consumption of non-renewable resources. This review emphasizes on how the PGP actinobacteria and their metabolites can be used effectively in enhancing the yield and controlling the pests and pathogens of grain legumes.

Soil Microbes: The Invisible Managers of Soil Fertility

Soil health is represented by its continuous capacity to function as a vital living system. Since soil health is the major driving factor for sustainable agriculture, it has to be preserved. Microorganisms are an essential and integral part of living soil influencing various biogeochemical cycles on major nutrients such as carbon, nitrogen, sulphur, phosphorous and other minerals and play superior role in maintaining soil health than other biological component of soil. They also have the capacity to suppress soil borne pathogens and indirectly help in agricultural productivity. Besides contribution of specific microbes to soil health by participating on nutrient cycles, certain other microbes directly/indirectly promote plant growth through the production of phytohormones, enzymes and by suppressing phytopathogens and insects. The vast functional and genetic diversity of microbial groups including bacteria, fungi and actinomycetes supports in all the above ways for soil health. This book chapter gives an outline of such microbes and their contribution in promoting soil health and its role as soil health indicators.