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Subject: Agricultural Microbiology × Author: Fathima, Shaheena K M × End date: 2016 × Start date: 2011 ×
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    ThesisItemOpen Access
    Utilization of free living diazotrophic bacteria from Wayanad as a biofertilizer
    (College of Horticulture, Vellanikkara, 2015) Fathima, Shaheena K M; KAU; Girija, D
    Agriculture is heavily dependent on the use of chemical fertilizers. However, excessive and unbalanced use of these inputs may lead to environmentalpollution and health hazards. Biofertilizers are biological fertilizers which play a key role in maintaining productivityand sustainability of soil, thereby protecting the environment. Hence, a study was undertaken to isolate, screen and evaluate free living diazotrophic bacteria to develop an efficient biofertilizer. Rhizosphere soils and plant samples were collected from ten healthy black pepper gardens of different locations of Wayanad district. A total of 43 free living diazotrophic bacteria were isolated on three different N-free media (Jensen’s agar, Beijerinckia agar and Ashby’s agar). Maximum population of nitrogen fixers was obtained on Jensen’s agar. Twenty predominant isolates were selected, including eleven isolates from rhizosphere soil and nine isolates from phylloplane, based on their growth characteristics on N-free media for further evaluation. Twenty selected isolates were screened under in vitro condition for growth, nitrogen fixation and acid tolerance. As pH was lowered from 7.0 to 5.0, a reduction in growth and nitrogen fixation was observed. However, among the isolates, two from the rhizosphere (NKdS and NPS-1) and two from phylloplane (NKPV-2 and NPPV) performed better. Twenty selected isolates were screened in vitro for plant growth promoting activities like production of IAA, HCN, siderophore and ammonia.The antagonistic activity of all the twenty isolates was tested against three soil borne plant pathogens Fusarium oxysporum, Rhizoctonia solaniand Ralstonia solanacearum. Isolates NkdS, NPPV and NKS-1 were found to exhibit antagonistic activityagainst Rhizoctonia solani.Six isolatesinhibited the growth ofRalstonia solanacearum. None of the isolatesrecorded antagonistic activity against Fusarium oxysporum. Four most promising diazotrophs including, two rhizosphere isolates (NKdS and NPS-1) and two phylloplane isolates (NPPV and NKPV-2) were selectedfor in xxx planta evaluation, based on nitrogen fixation ability, tolerance to acidic pHand PGPR activities. 16S rDNA sequence analysis was carried out and promising isolates were identified asMicrobacterium sp. (NKdS and NPPV); Cellulosimicrobium sp. (NPS-1) and Brevundimonas sp. (NKPV-2). In planta evaluation was carried out with tomato as the test crop. These isolates were applied alone, in combination with 75% N and with 75% N + 50% FYM. Diazotrophs were inoculated as seed treatment, seedling dip and soil/foliar application. Seeds treated withKAU Azotobacter formulation triggered faster germination compared to all other treatments. However, after 7 days of sowing, maximum number of seedling emergence (90.24%) was recorded in seeds treated with Cellulosimicrobium sp. Plant height, number of leaves, fresh weight and volume of root, fresh weight and dry weight of plants,yield per plant, average fruit weight and number of fruits were observed to be maximum in treatment T12 (Microbacterium sp.+ 75% N + 50% FYM). T11 (Cellulosimicrobium sp. +75% N + 50% FYM) recorded maximum girth of stem, leaf area and minimum days to flowering. Total nitrogen content of index leaf and plant was maximum in T12 (Microbacterium sp. + 75% N + 50% FYM). The same treatment recorded maximum nitrogen content in soil at 60DAS. At harvest, T11 (Cellulosimicrobium sp. + 75% N + 50% FYM) recorded highest nitrogen content in soil. Population build up of bioinoculants in soil was higher in presence of FYM.Endophytic colonization was higher in root, in case of soil application of bioinoculants and higher in leaves, in case of foliar spray. The study revealed that novel, free living diazotrophic bacteria like Microbacterium and Cellulosimicrobium could be exploited as biofertilizer formeeting 25% of the nitrogen requirement. Results also indicated the importance of application of organic manure along with the isolates, for their best performance