Citrus, a collective generic term, comprising a number of species and varieties of fruits, popular at global level for their characteristics flavor and attractive range of colours, citrus fruits are good source of vitamin-C. It is originated from southern slopes of Himalayas, entire north-eastern region of India and adjacent China. Citrus consists of number of species but 8 species are generally cultivated for edible purpose. Citrus is spread throughout the tropics and subtropics, roughly 40°N and 40°S latitudes. The major region subtropical latitude of northern hemisphere is North America, Mediterranean, East Asia including India and southern hemisphere is South America, South Africa, Australia. The total global area on citrus accounts to 9.68 million hectares producing 135.76 million tonnes. India covers 953.4 thousand ha and producing 11655 thousand tonnes of citrus. Northeastern states are accounting 147 thousand hectares citrus groves producing 868 (‘000 tonnes). Assam covers 29 thousand hectares citrus area and producing 309 thousand tonnes. India has 4th position at global level in citrus production. It is 3rd most important fruit crop in India. Citrus growing regions of the world are threatened by a complex problem causing the decline of citrus orchards, citrus decline is serious setback in all over the world. Citrus decline (complex problem) gradually decline of production, productivity of orchards, finally orchards become unproductive. Major causes of citrus decline – Abiotic and biotic, such as Abiotic causes consist- soil and nutrient related problems, moisture content, physiological disorders. Biotic causes are rootstock, phanerogamic parasites, intercrops, insects-pest, nematodes and diseases (fungal, bacterial and viral). Major causes of citrus decline in Northeastern India: 1. Citrus trunk borer; 2. Occurrence of greening disease exists in north eastern citrus growing region (Ghosh et al., 1982). Greening and tristeza are present in Khasi mandarin, tristeza is also present in Kagzi lime and Assam lemon in the NE of India by Bhagabati et al., (1989). Das et al., (2007) also reported greening disease in NE states of India through PCR technique. This is the main cause of citrus decline in NE states; 3. High Incidence of CTV (Singh et al., 2017) in NE states of India; 4. Phytophthora rot and 5. Overall neglect of grove.

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