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20201
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Subject: Plant Pathology × End date: 2020 × Start date: 2020 × Thesis Type: M.Sc ×
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    ThesisItemOpen Access
    MOLECULAR SCREENING OF CITRUS GERMPLASM FOR SIMULTANEOUS DETECTION OF Candidatus Liberibacter species ASSOCIATED WITH CITRUS GREENING DISEASE
    (AAU, Jorhat, 2020-08) Paul, Amitha; Nath, P.D.
    An effort was made to screen the Citrus germplasm maintained at the Citrus Research station (CRS), Tinsukia, Assam to identify the prevalence of Ca. Liberibacter species associated with citrus greening disease (CGD) and to understand the differential reaction of various varieties to CGD. Overall, 32 germplasm were screened comprising 16 species, 1 hybrid and 1 unidentified cultivar. The severity of CGD based on symptomatology showed that; major parts of the germplasm were infected with CGD. The conventional PCR assay with two pairs of primers of these varieties showed that, only three (3) varieties namely; Khasi Papeda, Trifoliate Orange and Citrange are free from CGD infection. The presence of Citrus Psyllid insects in symptomatic trees, further amplification of its DNA with the specific primer confirmed the probability of vector mediated the spread of CGD in the field. Further differentiations of Asian and African strains by PCR and RFLP assays confirmed the absence of African strains. Similarly, comparative quantification of infected (10 samples) and suspected healthy (3 varieties) were done by Real time PCR to differentiate the known Ca. Liberibacter species in a singleplex reaction. The assay confirmed that the suspected healthy accessions were resistant and the others were infected with only Ca. Liberibacter asiaticus. The sequence similarity and evolutionary divergence analysis of the CGD isolates under current study showed sequence similarity with the „Ca. L. asiaticus‟ isolates (Asian-common isolates) from Southeast Asia, rather than the other diverse atypical Indian isolates present in the rest part of the country.