PJB-2005-53
OCCURRENCE AND DISTRIBUTION OF VIRUS AND VIRUS-LIKE DISEASES OF CITRUS IN NORTH-WEST FRONTIER PROVINCE OF PAKISTAN
MUHAMMAD ARIF, ATTIQUE AHMAD, MUHAMMAD IBRAHIM AND SHER HASSAN
Abstract
In order to assess the occurrence and distribution of citrus virus and virus-like diseases, extensive surveys were conducted in citrus growing area of NWFP during 2001-03. Based on characteristic symptoms expression and serological indexing, the major virus, viroid and prokaryotic diseases commonly observed in citrus orchards and nurseries were citrus tristeza, citrus variegation, citrus exocortis, citrus cachexia (-xyloprosis), citrus greening and stubborn. Average incidence of citrus tristeza closterovirus (CTV) was 27%, citrus variegation ilarvirus (CVV) 31%, citrus exocortis viroid (CEVd) 16%, citrus cachexia viroid (CCVd) 4%, citrus greening (Liberobacter sp) 4% and stubborn (Spiroplasma citri) 2%, respectively. High incidence of these devastating pathogens has caused the severe citrus decline syndrome and drastic yield and quality losses in citrus fruits in the region. The field isolates of CTV and CVV were reproduced on diagnostic hosts through graft and mechnical transmission. CTV produced vein clearing and chlorosis on young leaves of Citrus aurantium, C. lemon cv. Eureka, C. sinensis. Field isolates of CVV was readily sap transmitted on young seedlings of C. sinensis, C. aurantium and C. lemon cv. Eureka and produced severe variegation and crinkling symptoms on C. sinensis and leaf cupping, variegation and crinkling symptoms on C. aurantium. CVV also produced local chlorotic lesions on Vigna ungiculata and V. sinensis and systemic chlorosis, mottling, vein banding and distortion on Phaseolus vulgaris cv. Red Kidney and Bountiful. The virus produced leaf thickening, vein banding and mottling in Nicotiana tabacum cv. White Burley and Samson NN and Petunia hybrida. The status of virus and viruslike diseases have been reported in 10 major citrus growing districts of NWFP. Futhermore, recommendations have been made to manage the citrus fruits through integrated disease management approaches.
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