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Physiology and Biochemistry

Host-Selective Toxins from Alternaria citri. K. Kohmoto, Visiting researcher, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824, Present address of senior author: Laboratory of Plant Pathology, Tottori University, Tottori City, Japan; R. P. Scheffer(2), and J. O. Whiteside(3). (2)Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, MI 48824; (3)Plant pathologist, University of Florida Agricultural Research and Education Center, Lake Alfred, FL 33850. Phytopathology 69:667-671. Accepted for publication 15 January 1979. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-667.

Filtrates from cultures of Alternaria citri are selectively toxic to rough lemon or tangerine leaves. Two related toxic compounds were isolated from the A. citri cultures that are selectively pathogenic to rough lemon. Both compounds affected susceptible rough lemon when 50 μl of solution (0.1 μg toxin per ml) was applied to leaves; tangerine and other nonhost plants were not visibly affected at 1,000 μg/ml. A rough lemon selection that is tolerant to the rough lemon-infecting isolates was affected by the toxins, but symptom development was delayed. Isolates pathogenic to Dancy tangerine yielded a toxin that visibly affected the host species when applied (50 μl, 1.0 μg/ml) to leaves. The tangerine-specific toxin at 1,000 μg/ml did not affect rough lemon or other nonhost species. Several conditions favoring toxin production in culture were determined; especially notable was the stimulatory effect of ZnSO₄ in the medium. Procedures are described for purification of toxins, based on solvent extractions and chromatography. Each of the toxins caused leakage of electrolytes from susceptible, but not from resistant, tissue.