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Exocortis (citrus exocortis viroid)

This pathogen causes bark-shelling and stunting of trees on trifoliate orange, trifoliate hybrids, and Rangpur lime rootstocks [Picture]. Sour orange rootstock is tolerant. In the early stages of the disease, gum exudes from pustules at the base of the trunk and may extend from below the soil line to the bud union. New bark forms beneath the pustules, and the outer bark sloughs off forming the characteristic bark-shelling [Picture]. The tree eventually declines. The pathogen is spread via grafts and also via pruning tools. The pathogen can be detected following grafting on Etrog citron. Symptoms on this indicator plant include stunting and leaf deformation [Picture] and necrosis of the leaf midrib [Picture].