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Etiology

Wilt and Dieback of Mexican Lime Caused by Fusarium oxysporum. L. W. Timmer, Associate professor, Texas A&I University Citrus Center, Welaco 78596, Present address of senior author: University of Florida, IFAS, Agricultural Research and Education Center, Lake Alfred, 33850; S. M. Garnsey(2), G. R. Grimm(3), N. E. El-Gholl(4), and C. L. Schoulties(5). (2)(3)Research plant pathologists, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, Orlando, Fl 32803; (4)(5)Biologist and plant pathologist, respectively, Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Gainesville, 32602. Phytopathology 69:730-734. Accepted for publication 2 February 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-730.

Serious wilt and dieback of greenhouse-grown Mexican lime (Citrus aurantifolia) seedlings has occurred in Florida 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. Fusarium 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 first symptoms appeared 4 wk after inoculation and all plants died within the following 2 wk. Fusarium 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 nine 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.)/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.