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