Incidence of Citrus Greening Disease in the Punjab

Of 626 trees sampled in representative citrus plantations in Punjab, Rajasthan, Himachal Pradesh, and Uttar Pradesh, and analysed by the Schwarz chromatographic method, 69 per cent were found infected by the greening pathogen. All major varieties were found more or less infected with incidences ranging from 29 per cent for Kinnow to 100 per cent for Musambi and Jaffa sweet oranges. Singularly a 16-year-old block of 23 varieties imported from the United States showed low rates of infaction under circumstances where adjacent blocks of commercial trees manifested 89 per cent infection. This suggests that spread of the virus by psyllids is slow and that it may be possible to live with the virus in the Punjab provided plantations are started with virus-free nursery stock and that trees are sprayed to slow down the spread of psyllids. Twenty-five per cent of plants tested in nurseries were found infected. Movement of such plants accounts for some spread of the disease.

Though greening disease is widespread in the Punjab Plain, it is misleading to suggest that it alone is responsible for the serious decline of citrus in the area. There are many other factors involved in the poor growth of trees, including high soil pH values, salinity, inadequate drainage, pernicious intercropping, poor pest control, and miscellaneous diseases, among them tristeza and a combination eruptive budunion crease-inverse, fovea like pitting destructive to the predominantly grown varieties Musambi and Blood Red sweet oranges when budded on rough lemon or jatti khatti Fraser and Singh, (4). A review of all factors involved in the citrus decline problem-including culture, irrigation, drainage, soils, nutritional deficiencies, insects, and diseases has recently been published by Chadha et al., (1).