Rakshapal Singh

Biodiversity acts as insurance of productivity of bacterial communities under abiotic perturbations

Anthropogenic disturbances are detrimental to the functioning and stability of natural ecosystems. Critical ecosystem processes driven by microbial communities are subjected to these disturbances. Here, we examine the stabilizing role of bacterial diversity on community biomass in the presence of abiotic perturbations such as addition of heavy metals, NaCl and warming. Bacterial communities with a diversity gradient of 1–12 species were subjected to the different treatments, and community biomass (OD600) was measured after 24 h. We found that initial species richness and phylogenetic structure impact the biomass of communities. Under abiotic perturbations, the presence of tolerant species in community largely contributed in community biomass production. Bacterial diversity stabilized the biomass across the treatments, and differential response of bacterial species to different perturbations was the key reason behind these effects. The results suggest that biodiversity is crucial for maintaining the stability of ecosystem functioning and acts as ecological insurance under abiotic perturbations. Biodiversity in natural ecosystems may also uphold the ecosystem functioning under anthropogenic disturbance.

Synergy between Glomus fasciculatum and a beneficial Pseudomonas in reducing root diseases and improving yield and forskolin content in Coleus forskohlii Briq. under organic field conditions

Root rot and wilt, caused by a complex involving Fusarium chlamydosporum (Frag. and Cif.) and Ralstonia solanacearum (Smith), are serious diseases affecting the cultivation of Coleus forskohlii, a crop with economic potential as a source of the medicinal compound forskolin. The present 2-year field experiments were conducted with two bioinoculants (a native Pseudomonas monteilii strain and the exotic arbuscular mycorrhizal (AM) fungus Glomus fasciculatum) alone and in combination under organic field conditions in order to evaluate their potential in controlling root rot and wilt. Combined inoculation of P. monteilii with G. fasciculatum significantly increased plant height, plant spread, and number of branches; reduced disease incidence; and increased tuber dry mass of C. forskohlii, compared to vermicompost controls not receiving any bioinoculants. Increase in tuber yields was accompanied by an increase in plant N, P, and K uptake. Co-inoculation of P. monteilii with G. fasciculatum significantly improved the percent AM root colonization and spore numbers retrieved from soil. This suggests P. monteilii to be a mycorrhiza helper bacterium which could be useful in organic agriculture. The forskolin content of tubers was significantly increased by the inoculation treatments of P. monteilii, G. fasciculatum, and P. monteilii + G. fasciculatum.

Effect of arbuscular mycorrhizal fungi and Pseudomonas fluorescens on root-rot and wilt, growth and yield of Coleus forskohlii

Abstract Root-rot and wilt caused by Fusarium chlamydosporum affects the cultivation of Coleus forskohlii, a medicinal plant grown for its roots, which contain a pharmaceutically important compound called forskolin. In this study, management of this disease under low and high inoculum levels was assessed with four arbuscular mycorrhizal (AM) fungi and a strain of Pseudomonas fluorescens. The AM fungus Glomus fasciculatum and P. fluorescens were the most effective treatments that reduced the severity of root-rot and wilt of C. forskohlii by 56–65% and 61–66%, respectively, under lower and higher levels of pathogen F. chlamydosporum. G. fasciculatum increased the dry shoot and root weight by 108–241% and 92–204%, respectively, while in plants treated with P. fluorescens, an increase of 97–223% and 97–172% in dry shoot and root weight, respectively, was observed. Although P. fluorescens was effective, it gave higher root yields only under lower inoculum level of the pathogen. G. fasciculatum performed equally well under both lower and higher inoculum levels. Increase in yields with both the biocontrol agents was accompanied by increase in P uptake (230–303%) and in K uptake (270–335%). The forskolin content of the roots was significantly increased (14–21%) by G. fasciculatum, P. fluorescens or G. mosseae under lower inoculum level of pathogen.

A Cr(VI)-reducing Microbacterium sp. strain SUCR140 enhances growth and yield of Zea mays in Cr(VI) amended soil through reduced chromium toxicity and improves colonization of arbuscular mycorrhizal fungi

Pot culture experiments were conducted in a glasshouse to evaluate the effects of four efficient Cr(VI)-reducing bacterial strains (SUCR44, SUCR140, SUCR186, and SUCR188) isolated from rhizospheric soil, and four arbuscular mycorrhizal fungi (AMF—Glomus mosseae, G. aggregatum, G. fasciculatum, and G. intraradices) alone or in combination, on Zea mays in artificially Cr(VI)-amended soil. Presence of a strain of Microbacterium sp. SUCR140 reduced the chromate toxicity resulting in improved growth and yields of plants compared to control. The bioavailability of Cr(VI) in soil and its uptake by the plant reduced significantly in SUCR140-treated plants; the effects of AMF, however, either alone or in presence of SUCR140 were not significant. On the other hand, presence of AMF significantly restricted the transport of chromium from root to the aerial parts of plants. The populations of AMF chlamydospores in soil and its root colonization improved in presence of SUCR140. This study demonstrates the usefulness of an efficient Cr(VI)-reducing bacterial strain SUCR140 in improving yields probably through reducing toxicity to plants by lowering bioavailability and uptake of Cr(VI) and improving nutrient availability through increased mycorrhizal colonization which also restricted the transport of chromium to the aerial parts.

Complementarity among plant growth promoting traits in rhizospheric bacterial communities promotes plant growth.

An assessment of roles of rhizospheric microbial diversity in plant growth is helpful in understanding plant-microbe interactions. Using random combinations of rhizospheric bacterial species at different richness levels, we analysed the contribution of species richness, compositions, interactions and identity on soil microbial respiration and plant biomass. We showed that bacterial inoculation in plant rhizosphere enhanced microbial respiration and plant biomass with complementary relationships among bacterial species. Plant growth was found to increase linearly with inoculation of rhizospheric bacterial communities with increasing levels of species or plant growth promoting trait diversity. However, inoculation of diverse bacterial communities having single plant growth promoting trait, i.e., nitrogen fixation could not enhance plant growth over inoculation of single bacteria. Our results indicate that bacterial diversity in rhizosphere affect ecosystem functioning through complementary relationship among plant growth promoting traits and may play significant roles in delivering microbial services to plants.

Influence of Nitrogen and Potassium Fertilization on Yield and Quality of Rosemary in Relation to Harvest Number

Rosemary is an important aromatic and spice plant. Its cultivation for production of its essential oil has gained importance in recent years. An experiment was conducted in a red sandy loam (Kandiustalf) soil to study the impact of cultivation of this multiharvest crop at different nitrogen (N) and potassium (K) application regimes on soil fertility and crop yield at the farm of the Central Institute of Medicinal and Aromatic Plants, Resource Center, Bangalore, during 2003–2005. The treatments consisted of all combinations of N levels (0, 150, and 300 kg per hectare per year) and K levels (0, 50, and 100 kg per hectare per year). Five harvests were taken at about 5‐month intervals. The results showed that initially the soil alone was able to meet the crop requirements for K, but with the progress of time, addition of K to the soil in the form of fertilizer became necessary for obtaining optimum yields. At the end of five harvests, exchangeable K in soil was significantly lower as application of K decreased from 100 to 50 and 0 kg per hectare per year. Soil fertility could be maintained and oil yields of rosemary from four harvests could be increased from 146.6 L to 344.7 L per hectare by application of 150 kg N and 100 kg K.

Contribution and assessment of recycled menthol mint vermicompost on productivity and soil quality in mint and mint-rice-wheat rotation: A case study

Trials in farmers’ field(s) were conducted to study the usefulness of vermicompost (VC) produced from distillation waste of menthol mint (Mentha arvensis L. cv. Kushal) using earthworms (Eisenia foetida) in reducing the inputs of chemical fertilizers and improving soil health in menthol mint-based cropping systems. Results of the first trial conducted on menthol mint (sole crop) in the fields of 45 farmers clearly indicated that 75% of the chemical fertilizer inputs can be reduced by supplementing the fields with 5tha �1 of menthol mint VC leading to higher levels of profits to the farmers by significantly improving herb and oil yield (6.7 and 8.4%, respectively) compared to the full recommended dose of chemical fertilizers (NPK 75:60:60kgha �1 ). The second trial was conducted in the fields of six farmers adopting a menthol mint cropping system (mint–rice–wheat–mint) where significantly higher yields were recorded in plots supplemented with 5tha �1 of menthol mint VC+25% of the recommended dose of chemical fertilizers; an increase of 5.6–7.2% in mint oil and 6.6% in wheat yield over the plots receiving the full recommended dose of chemical fertilizers (NPK 75:60:60kgha �1 ). However, in the case of rice, the highest grain yield was observed within plots receiving the full recommended dose of chemical fertilizers. Dataobtained on soil properties clearlyshowedthat apart from enhancing the yields of crops,the integration of VC with chemicalfertilizersconsiderably improvedthe soil fertility/sustainabilitystatus in terms of organic carbon, available N, P and K.

Assessment of Organic and Inorganic Fertilizers for Growth, Yield and Essential Oil Quality of Industrially Important Plant Patchouli (Pogostemon cablin) (Blanco) Benth.

Abstract The present study was conducted to evaluate the right proportion of organic and inorganic fertilizers for growth, oil yield and nutrient uptake pattern of patchouli. The results indicated that significantly higher oil yield was recorded in 75 % VC+25 % NPK (256 %) followed by100 % NPK (249 %) as compared to control. An increase of 6 % in essential oil content was achieved in treatment with 75 % VC+25 % NPK and 25 % VC+75 % NPK but the effect was non-significant. Also, the quality of essential oil, which is basically measured by patchouli alcohol, was not affected by any treatments. Enhancement in vermicompost doses significantly improved the bulk density (0.61- 13.94 %), total organic carbon (3.3-34.4 %) and soil microbial biomass (3-149 %). Availability of N, P and K was significantly higher in 75 % VC+25 % NPK (20 %, 103 % and 64 %, respectively) over control. Maximum nutrient (N, P and K) uptake was found in treatment with 100 % NPK (78 %, 67 % and 54 %, respectively) followed by 75 % VC+25 % NPK (76 %, 63 % and 51 %, respectively). The present study clearly indicated that 75 % chemical fertilizer could be saved by integrating 75 % vermicompost with 25 % chemical fertilizer resulted similar oil yield and improved soil health.

Evaluation of influence of planting date on growth, artemisinin yield and seed yield of Artemisia annua under Bangalore agro-climatic conditions

Artemisia annua is an important crop grown for producing the anti-malarial drug artemisinin. It has been recently introduced to Bangalores agro-climatic conditions of South India. A field experiment was carried out at the Central Institute of Medicinal and Aromatic Plants (CIMAP), Bangalore, from November 2004 to July 2007 to optimize the planting date for maximum herb, artemisinin and seed yield under the semi-arid tropical conditions of Bangalore. The study revealed that it was best to transplant seedlings of A. annua in the later part of October to get optimum herb, artemisinin and seed yield under Bangalores agro-climatic conditions.

Effect of N and K doseson biomassand diterpenoid lactones production of Kalmegh (Andrographi spaniculata Nees.) in a semi-arid tropical climate

Kalmegh (Andrographis paniculata Nees.) is widely used as a medicinal herb in India and South-East Asian countries for treatment of liver disorder, bowel complaints, malaria, hypertension etc. Field experiments were conducted at CSIR-CIMAP, Research Centre, Bangalore, India to study the effect of doses of nitrogen (N) (0, 50, 100 and 150 kg ha−1) and potash (K) (0, 41 and 82 kg ha−1) on growth, biomass yield, nutrient uptake and diterpenoid lactones production. The results clearly revealed that application of 100 kg N ha−1 and 82 kg K ha−1 produced significantly higher herbage/biomass yield (6.1 t ha−1) as compared to control (1.42 t ha−1). The similar trends were observed in N and K uptake pattern. The application of 100 kg N ha−1 and 82 kg K ha−1 significantly increased the production of andrographolide (33.24 kg ha−1) and neo-andrographolide (12.31 kg ha−1) yield over control (16.02 and 4.06 kg ha−1, respectively).