The four described Alternaria diseases of citrus include: (i) Alternaria Mancha foliar de los citricos is caused by A. limicola Simmons & Palm. Isolation, Pathogenicity, and Partial Host Range of Alternaria limicola, Causal Agent of Mancha Foliar de los Citricos in Mexico. MARY E. PALM, USDA-ARS. Alternaria Rot Worldwide, Alternaria species can cause four distinct diseases of citrus: Alternaria leaf spot of Rough Lemon, mancha foliar de los citricos, and.
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During the packing process, the tops of alternaria lesions may be lopped off, making visual identification difficult. Alternaria is spread by airborne spores. Even the leaf contributes to the inoculum.
Early fruit drop is common, especially if infection has occurred shortly after petal fall. Some alteranria come from fruit lesions but they are not a major inoculum source. The disease is likely found in other countries that produce susceptible cultivars. The fruit rind responds to infection by forming a barrier of corky tissue that erupts from the surface.
Although the spores are airborne and carried by winds, alternaria brown spot is often spread among groves on nursery stock transported by humans. Citrus Diseases March, idtools.
Alternaria is extremely common on certain cultivars of tangerines while citrus canker is uncommon on tangerine cultivars. In the later stages of the disease, the corky tissue can fall out, forming craters or pockmarks on the surface of the fruit.
Spores are produced on older lesions formed on wilted twigs and mature leaves. Fruit – young fruit lesions occur on immature fruit for 4 months post petal fall and cause slightly sunken dark spots with yellow halos. Lesions are flat and visible on both sides on the leaf.
Leaf – initial foliar lesions occur on young tissue as small brown to black spots that develop prominent yellow halos. Alternaria fruit lesions can crack around the outer edge, giving a moat-like appearance. Rain events or sudden changes in relative humidity also favor spore alternagia. A fungal toxin is produced that can cause necrosis and chlorosis along the veins extending from lesions.
Fact Sheet: Alternaria | Citrus Diseases
On more mature fruit, lesions can vary from small specks to large pockmarks. Older lesions have a brittle paper-like texture in the middle of the lesions.
Grapefruit and lemons may also be affected. Lesions expand into irregular or circular necrotic areas which can involve large portions of the leaf, altdrnaria on highly susceptible cultivars like ‘Minneola’. Dancy tangerine hybrids [‘Minneola’ tangelo ‘Honeybell”Orlando’ tangelo, ‘Sunburst’, ‘Nova,’ and ‘Lee’] and ‘Murcott’ ‘Honey’ tangerine frequently have fruit infections of alternaria brown spot.
This tool is part of the Citrus Resource. Alternaria brown spot fruit lesions are easily confused with citrus canker.