Prevalence of Citrus tristeza virus in Mandarin of Sikkim Himalayan Region

The assessment of Citrus tristeza virus incidence in mandarin of Sikkim, involving sampling techniques, was estimated by DAS-ELISA. Mandarin orchards had high CTV incidence (46.32%), however, differential prevalence with regard to age of plant and location was observed. The CTV prevalence was relatively high in older orchards (51.01%) than that of younger ones (40.80%). Under all the plant age groups, south district had the highest CTV incidence (52.50%) and east district had the lowest (37.71%). The spatial distribution of CTV in plants indicates high concentration in twig followed by leaf tissue, however, stem had relatively less concentration. High aphid infestation was observed in all mandarin growing groves with the maximum in south district and minimum in east district. Taxoptera citricida was the predominating aphid species followed by T. aurantii, however, Aphis spp population was significantly less. Aphid infestation and CTV prevalence were positively and significantly correlated.