Infection of Citrus tristeza virus (CTV) in Assam was detected by double antibody sandwich-enzyme-linked immuno-sorbent assay (DAS-ELISA). Field surveys were carried out in 8 citrus growing districts of Assam (Tinsukia, Lakhimpur, Jorhat, Kokrajhar, North Cachar Hills, Karbi Anglong, Golaghat and Kamrup). Altogether, 411 samples were collected from three different citrus species, viz., Assam lemon (Citrus limon), Gul nemu (Citrus jambhiri) and Khasi mandarin (Citrus reticulata) to test against CTV. Results of biological indexing showed Kagzi lime (Citrus aurantifolia) to be the better indicator plant (symptom expression 60%) than Assam lemon (symptom expression 30%). The symptom expression on the indicator host was observed from 5th to 9th week after inoculation. The inoculated plants again tested after 9th week using DAS-ELISA assay. The results revealed that percentage of positive plants were 90% in Kagzi lime followed by Assam lemon (80%). This indicated that even the symptomless plants after inoculation give the positive reactions in DAS- ELISA assay. 261 samples were found to be infected using ELISA with polyclonal antisera to CTV. The species Assam lemon (C. limon) were found to be susceptible to CTV with estimated disease incidence up to 76.47% followed by Khasi mandarin (C. reticulata; 61.18%) and Gul nemu (C. jambhiri; 52.03%). Different age groups (<10, 10 to 15 and >15 years) of the citrus trees indicated that prevalence of CTV was more in older plants.
Key words: ELISA, Citrus tristeza virus (CTV), Assam lemon, Khasi mandarin, Gul nemu.
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