Wilt and Dieback of Mexican Lime Caused byFusarium oxysporum

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Abstract
Serious wilt and dieback of greenhouse-grown C. aurantifolia seedlings has occurred in Florida [USA] for several years. Early symptoms are reticulate chlorosis and epinasty of the young leaves followed by wilting, leaf abscission, shoot dieback and gum exudation. Initially, symptoms are sectorial then the dieback progresses rapidly, and plants seldom survive more than 4-6 wk. F. oxysporum was isolated consistently from the xylem of the main stem and from twigs of affected plants. The disease syndrome was reproduced in nearly 100% of the plants by dipping wounded and nonwounded root systems of Mexican lime seedlings in a suspension of spores and mycelial fragments of this fungus. The 1st symptoms appeared 4 wk after inoculation and all plants died within the following 2 wk. F. oxysporum was reisolated from the main stem of all root-inoculated lime seedlings. Seedlings of C. excelsa inoculated by the root-dip method developed symptoms similar to those on Mexican lime. Rangpur lime (C. limonia) seedlings exhibited chlorosis, mild wilt and stunting but did not die when inoculated with F. oxysporum. Inoculated plants of 9 other Citrus spp. and relatives showed no symptoms and the fungus could not be reisolated from stem tissue. The pathogen was designated as F. oxysporum emend. Snyd. et Hans. f. sp. citri form. nov. Most naturally infected Mexican limes with mild or moderate symptoms recovered following biweekly drench applications of benomyl at 1.3 g (a.i. [active ingredient])/l. Drench application of benomyl 2, 14 and 28 days after inoculation of plants with high spore concentrations delayed symptom expression, but all of the seedlings eventually died.

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