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a viral disease of citrus trees grafted on the root-stocks of the sour orange and lime. Tristeza is common in tropical and subtropical regions. It does not occur in the USSR, where it is the object of external quarantine. The disease is characterized by the dying of conducting tissues at the site where the scion unites with the rootstock. Mild infection causes chlorosis. The leaf blades curl, and then the leaves dry out and fall off. Severe infection kills individual branches and entire trees. In diseased plants, shoot formation is weak and the roots rot. The trees flower earlier and more abundantly, but the fruits are small and fall off prematurely. The virus is transmitted from the stock and grafts by the black citrus and melon aphids and by the dodder Cuscuta subinclusa.
Control measures include observing imported material in introduction-quarantine nurseries for three years, using tristeza-resistant rootstocks of trifoliate orange and rangpur lime, and controlling insects that transmit the disease.
I. T. ABRAMOVA [26–661–t]