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20231025 111942
August / September 2024

Citrus biosecurity threats

SA Fruit Journal: August / September 2024

This is the third instalment in our citrus biosecurity threats series. By CRI Biosecurity Division

Citrus Leprosis Symptoms of Citrus Leprosis (CL) Round to elliptical local lesions appear on leaves, twigs and fruit. Leaf lesions, both on the upper and lower sides, are usually not raised. They’re round to elliptical and pale green to yellow with a dark-brown central spot about 2–3 mm in diameter, surrounded by a chlorotic halo, in which 1–3 brownish rings frequently appear, surrounding the central spot. Larger lesions may form by the fusion of two or more adjacent lesions. Severe infections lead to premature leaf fall. On fruit, lesions are flat to slightly depressed necrotic spots, 5–15 mm in diameter, with a yellow halo and are distributed over the whole fruit rind. Gum exudation may be seen on the lesions. On green fruit, the lesions are initially chlorotic and darken to brown or black and become slightly depressed. A yellow halo can be observed around the lesions as they mature. In severe infections, fruit drop occurs, mainly in cases where the lesions are close to the peduncle. On twigs, lesions are cortical, grey or brown or sometimes dark reddish, later turning into crusty scabs.
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