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Theses

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2016 - 20173
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Subject: Plant Pathology × End date: 2017 × Start date: 2016 × Type: Thesis ×
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    ThesisItemOpen Access
    REACTION OF AROMATIC AND GLUTINOUS RICE GENOTYPES AGAINST SHEATH ROT (Sarocladium oryzae) DISEASE AND ITS MANAGEMENT WITH IDM MODULE
    (AAU, Jorhat, 2017-07) Singh, Manjay; Das, B. C.
    Sheath rot of rice caused by Sarocladium oryzae (Sawada) Gams and Hawksworth, has gained the status of major disease of rice, and yield losses varies from 9.6 to 85%. The present investigation was under taken to identify the resistant genotypes/cultivars as a donor gene for the development of HYV and to evaluate the efficacy of different IDM Modules for management of sheath rot of rice. The sheath rot disease sample was collected from the rice field of Regional Agriculture Research Station, Titabar. The isolates were cultured, purified and mass culture was prepared in half boiled rice grain, and single grain insertion method was followed for inoculation in aromatic and glutinous rice genotypes/ cultivars. Among the genotypes/ cultivars that were screened, eight entries showed resistant reaction from aromatic rice and five entries showed resistant reaction from glutinous rice genotypes/ cultivars. The physiological parameters were evaluated in both resistant and susceptible genotypes/ cultivars of both aromatic and glutinous rice. The resistant entries possess a higher concentration of phenol, protein and lower concentration of starch and sugar as compared to the susceptible one. The total phenol concentration was increased in, Resistant (R), Moderately resistant (MR), Moderately susceptible (MS) and decreased in susceptible genotypes/ cultivars after infection. Similarly, protein, starch, and TSS were found to be decreased in all the categories of genotypes/ cultivars (R, MR, MS, S). However, maximum reduction was observed in susceptible genotypes/ cultivars after infection. The interaction among the stem attacking fungal pathogens showed that Sarocladium oryzae suppresses the growth of Rhizoctonia solani and Sclerotium oryzae. in both in vitro and in vivo, while Sclerotium oryzae was more sensitive against Sarocladium oryzae as compared to Rhizoctonia solani. Among the modules that were evaluated for management of sheath rot disease of aromatic and glutinous rice. PDI and PDS were significantly reduced and increase of growth parameters and yield, in the entire module as compared to the inoculated control. However, the maximum reduction of PDI, PDS and increase of growth parameters and yield were recorded in Module- 2, where seeds were treated with carbendazim @ 2g/ kg of seed, soil application of Pseudomonas fluorescence @ 2.5kg/ha (2.5kg +50kg FYM) and 50% of potash of recommended dose at tillering stage along with Foliar spray with Carbendazim @ 0.2% after 30 days of transplanting and Foliar spray with Bioveer @ 2% at booting stage.
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    ThesisItemOpen Access
    Bioremediation and management of bacterial blight of rice with compatible consortia of arsenic degrading bacteria and plant growth promoting microbes
    (AAU, Jorhat, 2017) Talukdar, Kuldeep; Bora, L. C.
    Microorganisms influence the fate of heavy metals in the environment. Increasing anthropogenic and irrigation activities had escalated the risk of arsenic pollution in crop fields and this has added new thoughts for research workers to explore microbial transformation as a tactic to achieve arsenic bioremediation. Present study was made to exploit the potential of arsenic absorbing bacteria (AAB) and develop consortial formulation with plant growth promoting Pseudomonas fluorescens Pf-1 for bioremediation of arsenic and management of bacterial blight (BB) of rice in Assam. Out of six Bacilli bacteria isolated from arsenic contaminated soils of Assam, two Bacilli showing phylogenetic similarity with Paenibacillus sp. and Bacillus cereus had potential for arsenic bioremediation. The two Bacilli strains could tolerate 1000ppm of arsenic with 98.30 and 97.68 per cent absorption ability, respectively. Talc based consortial bioformulations were prepared using these arsenic absorbing microbes along with P. fluorescens Pf-1 and field evaluated for management of bacterial blight of rice along with arsenic bioremediation. Significantly highest reduction of bacterial blight severity (41.11%) and highest reduction of arsenic (17.56ppm) was recorded with the treatment comprising consortial formulation of Paenibacillus sp. and Pseudomonas fluorescens Pf-1. Population dynamics of the bioagents in different bioformulations were assayed upto 90 days for their compatibility assessment in sterilized and unsterilized soil conditions. Significantly higher population count of Paenibacillus sp., Bacillus cereus and P. fluorescens Pf-1 was recorded upto 90 days of soil inoculation in both sterilized and unsterilized soil depicting positive compatibility of the microbes in varied soil micro-environmental conditions. The consortial formulation of Paenibacillus sp. and Pseudomonas fluorescens Pf-1 also significantly enhanced yield of rice (24.67g/plant) as well as other yield attributing characters of rice plant. Enzymatic assay experiment tested the activity of glutaredoxin-dependent arsenate reductase (glutaredoxin 2 from E. coli), with NADPH/arsenate being the electron donor/acceptor. Compared to the control without protein extracts or glutaredoxin, arsenate reduction by E. coli glutaredoxin 2 was observed, with absorption decreasing at a rate of 0.0012 ABS/min.
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    ThesisItemOpen Access
    Development of RNA based vaccine against Cucumber mosaic virus infecting Bhut Jolokia (Capsicum chinense Jacq.) crop and Citrus tristeza virus infecting citrus plantations of Assam
    (AAU, 2016) Borah, Munmi; Nath, P. D.
    “Development of RNA based vaccine against Cucumber mosaic virus infecting Bhut Jolokia (Capsicum chinense Jacq.) crop and Citrus tristeza virus infecting citrus plantations of Assam” were carried out at and Department of Plant Pathology, Assam Agricultural University, Assam, India and Laboratory of Plant Breeding and Biometry, Department of Crop Science, AUA, Athens, Greece. Utilizing virus genome properties enabled the design of novel, safe, and efficacious vaccines against different viral diseases infecting plants. In this study, it was shown that, dsRNA derived from viral sequences could interfere with cognate virus infection in a sequence-specific manner by delivering dsRNA to plant cells. In dsRNA-mediated protection, a dsRNA homolog of a viral silencing suppressor gene expressed in plants, which interferes with or prevents various stages of the viral life cycle, resulting in attenuated disease symptoms or resistance. It was aimed to produce CMV specific RNA vaccine to manage CMV infecting Bhut Jolokia crop of Assam. Application of these RNA based vaccines at the seedling stage could effectively reduce CMV infection at the later stage of the crop. These virus-free seedlings of Bhut Jolokia crop could give rise to a healthy crop growth. Taking it as a model system, it was further aimed to produce CTV specific RNA vaccine and to carry out a proof-of-concept to substantiate the same concept further in management of CTV infecting citrus plantations of North East India. A protocol for the synthesis of dsRNA using T7 RNA polymerase was utilized to produce RNA based vaccine against Cucumber mosaic virus infecting Bhut Jolokia (Capsicum chinense Jacq.) crop and Citrus tristeza virus infecting citrus plantations of Assam. CMV-encoded 2b gene based dsRNA was produced and tested against CMV infecting Bhut Jolokia (Capsicum chinense Jacq.) plants of Assam. The infection of CMV in Bhut Jolokia pepper plants was successfully interfered, demonstrating the applicability of RNA-based vaccination. In this study, double-stranded RNA derived from CMV-2b silencing suppressor gene sequence in Escherichia coli, could interfere with cognate virus infection. When dsRNA CMV-2b exogenously applied, along with CMV strain, onto Bhut Jolokia plants resulted in suppressing CMV infection. DAS-ELISA was used to identify the presence of CMV in the inoculated plants. Bhut Jolokia Pepper plants infected with CMV became severely stunted, nonproductive with dull light green foliage having a leathery appearance. In contrast, plants that received dsRNA of CMV-2b were less symptomatic and remained healthy as compared to those infected by CMV. Four experiments were conducted where; disease incidence was 15%, 5%, 29.5% and 0% when dsRNA of CMV-2b molecules were co-applied with CMV, as compared to 55%, 55%, 92% and 70% when only CMV was infected. As a result of dsRNA mediated resistance crop canopy increased, which is necessary for improved yields of the crop. This study constitutes a non transgenic approach of protection of Bhut Jolokia pepper plants against CMV. With the success of CMV specific RNA vaccine, the investigation further aimed towards production of a dsRNA construct coding for the three silencing suppressors of CTV to generate RNA-based resistance and to conduct a proof-of-concept of specific protection against viral infection. It was aimed to get more insight on the role of the CP, p20 and p23 genes as silencing suppressors of CTV in pathogenesis through topical application of these dsRNA molecules. The CP, p20 and p23 gene sequences of the North East India strain of Citrus tristeza virus was folded into a double-stranded (ds) RNA structure. dsRNA of sufficient quantities (several micrograms) obtained using in vitro transcription protocols for CP, p20 and p23 genes of the virus. The proof-concept experiment on application of these dsRNA against CTV infected citrus plants revealed that, while applied topically over leaf surface against the cognate virus, all three dsRNA constructs (CTV-CP, CTV-p23 and CTV-p20), could suppress the virus replication. This results successfully interpreted the proof -of -concept about the suppression of viral titre locally up to 10 days of topical application, through RNAi based method in citrus crop infected with CTV-North East India strain. The results support the view that a dsRNA intermediate in virus replication acts as efficient initiator of post transcriptional gene silencing in natural virus infections, triggering the viral RNA for degradation. A dsRNA construct encoding silencing suppressors could be significantly suppressed the replication of viruses and confer potential resistance against the virus.