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Isolation, Pathogenicity, and Partial Host Range of Alternaria limicola, Causal Agent of Mancha Foliar de los Citricos in Mexico. MARY E. PALM, USDA-ARS, BARC-West, Beltsville, MD 20705-2350 USDA-APHIS. EDWIN L. CIVEROLO, USDA-ARS, BARC-West, Beltsville, MD 20705-2350. Plant Dis. 78:879-883. Accepted for publication 13 May 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/PD-78-0879.

Alternaria limicola is confirmed as the cause of mancha foliar de los citricos (citrus leaf spot), a leaf and twig disease of citrus in Mexico, formerly called “citrus bacteriosis.” The fungus was isolated from 15 of 16 samples of symptomatic leaves of six species of Citrus collected during 1989 and 1990 in the Pacific coast state of Colima and from symptomatic leaves of an additional species of Citrus collected during 1990 in Guerrero, Mexico. Xanlhomonas campestris was not isolated from any of the leaf lesions. Greenhouse-grown Mexican lime (C. aurantiifolia) and Duncan grapefruit (C. x parodist) seedlings were inoculated by spraying young, actively growing, terminal foliage with aqueous suspensions containing 200-400 conidia per milliliter of either A. limicola or A. citri. Lesions similar to those observed on naturally infected plants developed only on those plants inoculated with A. limicola. The fungus was reisolated from all inoculated plants. This work confirms previous reports that the primary cause of mancha foliar de los citricos is a species of Alternaria and extends previous studies by fulfilling Koch's postulates for A. limicola. Additionally, it was determined that isolates of A. limicola from six other species of Citrus were identical in morphology to isolates from Mexican lime. Koch's postulates for isolates from these six additional host species were fulfilled. Lesion age and part of the lesion excised affected the isolation frequency of A. limicola. The highest isolation frequencies were from the part of the maturing lesions that included a high percentage of the necrotic area and from old lesions.