Distribution of Citrus tristeza virus in the Darjeeling hills and their biological symptoms in mandarin orchards

Mandarin (Citrus reticulata Blanco), a traditional fruit crop growing at altitude from 500 to 1500 m in the Darjeeling hills of Northeastern Himalayan region, plays an pivotal role in the economy of the poor farmers of the region. Citrus tristeza virus (CTV), member of a phloem limited Closterovirus and transmitted by brown citrus aphid, is one of the important virus causing losses in mandarin orchards in the Darjeeling hills. A survey was conducted in mandarin orchards at 30 locations covering all the Taluks/blocks during April-July, 2011 and biological symptoms, incidence and distribution of CTV were studied. A general decline symptom along with chlorosis, poor as well as growth stunting was observed in majority of the mandarin orchards. ELISA showed that mandarin samples of 29 locations were CTV positive showing considerable virus titer (OD value) of 3–10 fold compared to healthy control. The ELISA positive samples were further confirmed by RT-PCR. The present study concluded that CTV is widely distributed in all the mandarin growing areas in the Darjeeling hills and CTV isolates occurring in this region are decline inducing isolates.