The extensive replacement of the sour orange rootstock, susceptible to citrus tristeza disease, with the tolerant Volkamer lemon rootstock, in citrus-growingthe citrus growing areas of North Africa and the Near East triggered the emergence of a new serious citrus disease. The disease is characterized by the typical stem pitting on the wood with gum deposits in the bark of V lemon rootstock, similar to the symptoms of cachexia on mandarin and the gummy bark on sweet orange. Citrus viroids have therefore been indicated as presumed causal agents of the gummy bark complex on V. lemon. Currently, the disease is devastating many citrus groves in the new reclaimed land of Egypt, where the V. lemon is largely used for its adaptability to arid zones. Molecular investigations carried out in this study on symptomatic and asymptomatic trees have confirmed the presence of different citrus viroids. Hop stunt viroid (HSVd) and Citruscitrus bark cracking (CBCVd) were prevalent viroids in symptomatic trees, mainly as mixed infections. The severity of symptoms in biological indexing (stem pitting and cracking), induced by both agents indicated that the disease could be a result of a synergic action of HSVd and CBCVd.
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