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2016 - 201912020 - 20211
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Subject: Microbiology × Author: Manpreet Kaur × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    Isolation and screening of pesticide-tolerant phosphate-solublizing bacteria from potato rhizosphere
    (Punjab Agricultural University, Ludhiana, 2021) Manpreet Kaur; Vyas, Pratibha
    The present study was carried out with the aim to develop pesticide-tolerant phosphatesolubilizing bacterial inoculants for improving the growth and phosphorus uptake in potato. A total of 37 phosphate-solubilizing bacteria were isolated from the rhizosphere of potato growing at different locations of Punjab and Himachal Pradesh. The bacterial isolates showed phosphate solubilization index ranging from 1.3 to 6.7 mm on modified Pikovskaya agar and phosphate solubilization in liquid medium varying from 115.4 – 919 µg ml-1 with significant difference among the isolates. The isolates were further tested for their tolerance against two commonly used pesticides in potato on minimal salt agar medium amended with three concentrations 1.25, 2.5 and 7.5 μl ml-1 (lower, recommended and higher dosages) of chlorpyrifos and 0.187, 0.375 and 0.75 g ml-1 (lower, recommended and higher dosages) of carbofuran. Out of 37 PSB isolates, only 7 showed pesticide tolerance. The phosphate solubilising ability of the isolates was found to decrease significantly with increased concentrations of pesticides. Seven pesticide-tolerant PSB were identified as Arthrobacter oxydans (PR2PSB2), Bacillus licheniformis (PR3PSB9, PR3PSB10, PR3PSB12 and PR3PSB13), Bacillus subtilis (PR3PSB11) and Bacillus flexus (PR4PSB1) based on phenotypic features, biochemical tests and Matrix-Assisted Laser Desorption/Ionization time of Flight Mass Spectroscopy (MALDI-TOF-MS) analysis. Four pesticide-tolerant and phosphate-solubilizing bacterial isolates belonging to different species were tested for their ability to promote growth and phosphorus uptake in potato in pesticide amended soils under greenhouse conditions in pots. A significant difference was observed in the growth parameters, P content in shoots and soil P with the use of pesticide-tolerant PSB strains over the uninoculated control. The plant growth promotion and phosphorus content decreased with an increase in pesticide concentrations. The bacterial strains also differed significantly in their ability to promote the potato growth and phosphorus uptake. The highest growth promotion and P uptake was observed with consortium 1 containing Bacillus licheniformis, Bacillus flexus and Bacillus subtilis (PR3PSB10, PR4PSB1 and PR3PSB11). The study has led to the selection of pesticidetolerant phosphate-solubilizing bacterial consortium for improved growth and phosphorus uptake in potato.
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    ThesisItemOpen Access
    Synthesis and characterization of nanosilica particles from rice husk and its effect on soil microbes and vegetative growth in tomato
    (Punjab Agricultural University, Ludhiana, 2016) Manpreet Kaur; Kalia, Anu
    Rice husk, a waste by-product of rice sheller industry, has serious disposal problems. Turning this waste into nanosilica particles (SiNPs) is an ecologically as well as economical prudent technology. The SiNPs were synthesized from rice husks of 3 basmati and 6 parmal rice varieties by giving the acid pre-treatment using conventional heating and microwave irradiation techniques prior to charring in muffle furnace at 7000 C. The particle size ranged from 20 to 80 nm of individual and 150 to 200 nm of the agglomerated particles for the tested varieties. The synthesized SiNPs along with other micro silica sources (i.e. Rice Husk Ash (RHA), Kaolinite and Sodium Silicate) were applied to soil at six different concentrations to assess their effect on soil properties, total microbial population, soil enzymatic activities and vegetative growth of tomato. The SiNPs and RHA application caused decrease in pH, OC and EC while enhanced the soil available Nitrogen (N). The SiNPs significantly enhanced the soil microbial population, soil dehydrogenase, acid and alkaline phosphatase activities while significantly decreased the urease activity. A numerical increase in shoot and root length, number of laterals and total chlorophyll content of tomato cv. Chhuhara and a significant increase in rhizospheric microbial populations occurred by foliar application of SiNPs. The applied SiNPs remained on leaf surface as aggregates and were observed to be internalized through stomata as confirmed by Scanning EM and SEM-EDS studies. The tomato root-endophytic fungal interactions remained unaffected which further accentuates the beneficial effects of SiNP application in tomato.