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Phosphorous (P) is an essential macronutrient and most soils contain high levels of P. However, its availability to plant is limited by rapid immobilization of phosphorous compounds to insoluble forms and hence plant available forms of P in soils are found in low amounts. Phosphate solubilizing bacteria provide an eco-friendly alternative to convert insoluble phosphates into plant available forms. In the present study, three phosphate solubilizing bacterial isolates (PB-1, PB-4 and VC-01) with visually significant phosphate solubilizing abilities were isolated from tomato rhizosphere soil. In-vitro study in pikovskaya’s agar revealed that isolate PB-1 had the highest phosphate solubilizing ability with a phosphate solubilizing index of 2.08±0.07 followed by isolate VC-01 (1.31±0.09) and PB-4 (1.24±0.08). Isolates were used as bacterial inoculum to assess their ability to promote tomato (Lycopersicon esculentum var. Srijana) seedling and plant growth in in-vitro and greenhouse experiment respectively. Isolate PB-4 showed best growth promotion in seedling assay whereas isolate PB-1 and VC-01 also promoted seedling growth compared to control. In greenhouse experiment however, isolates VC-01 and PB-1 significantly enhanced all parameters (shoot length, root length, shoot and root dry weight) compared to uninoculated control whereas isolate PB-4 had a positive effect on all parameters except root length.Kathmandu University Journal of Science, Engineering and TechnologyVol. 13, No. 2, 2017, page: 61-70

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Microbial isolates from plant associated habitats are being considered as valid alternatives to synthetic pesticides. The aim of the study was to select beneficial fungi belonging to Trichoderma genus, to be added as soil inoculants, in order to develop an innovative, economic and suitable alternative to synthetic fertilizers for growth promotion of plants. The isolated Trichoderma were characterized and identified by morphological and microscopic analysis. The antagonistic effects of these Trichoderma isolates were tested against three pathogenic fungi; Sclerotinia minor, Fusarium oxysporum and Fusarium solani. Dual culture technique was employed and percentage of inhibition (I %) on mycelial growth of pathogenic fungi was calculated. Isolates BC and KB, showed the highest antagonistic effect against S. minor by 100%. Isolate DH and TH showed partial suppression of F. solani y 64.74% and 70.94% respectively. Isolates HA and Y restrain F. oxysporum by 85.12% and 85.90% respectively. Hence, BC, KB, DH, TH, HA, and Y could be a potential bio-control agent, BCA. In vitro and in vivogrowth promotion study was carried out by seed treatment method.Isolate EO revealed highest growth promotion activity in all parameters. In vitro studies of seedling assay indicated that isolate EO exhibited best effect on almost all the parameters; root length, shoot length, plant wet weight, plant dry weight, germination percentage and seedling vigour index in in vitro condition. However, greenhouse studies indicated that GS showed highest shoot length, TH promoted highest root length and HA showed maximum number of leaves. Significant difference was observed inroot length in greenhouse experiment and plant wet weight in seedling assay at p≤0.05. The results presented in this study further reinforce the concept of biological control and plant growth promotion by Trichoderma as an alternative disease control strategy.