Alternaria brassicae

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  Symptoms of Alternaria brassicae on cabbage

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  Alternaria brassicae

Alternaria brassicae

Alternaria brassicae is a fungal pathogen that primarily affects plants in the Brassicaceae family, which includes economically important crops such as cabbage, broccoli, cauliflower, and canola. This pathogen is responsible for causing the disease known as Alternaria leaf spot, which can lead to significant yield losses in affected crops.

Taxonomy

Alternaria brassicae belongs to the genus Alternaria, which is part of the family Pleosporaceae. The genus is known for its wide range of plant pathogenic species that affect various crops worldwide. Alternaria species are characterized by their production of darkly pigmented spores, which are often produced in chains.

Morphology

Alternaria brassicae produces conidia that are typically oblong to ellipsoid in shape, with transverse and longitudinal septa. These conidia are borne on conidiophores that emerge from the surface of infected plant tissues. The spores are darkly pigmented, which helps them survive in adverse environmental conditions.

Life Cycle

The life cycle of Alternaria brassicae involves both asexual and sexual reproduction, although the asexual stage is more commonly observed. The fungus overwinters as mycelium or conidia on plant debris or in the soil. In the presence of favorable conditions, such as high humidity and moderate temperatures, the conidia germinate and infect host plants.

Infection typically occurs through natural openings or wounds in the plant tissue. Once inside the host, the fungus colonizes the tissue, leading to the development of characteristic leaf spots. These spots can coalesce, causing large areas of necrosis and defoliation.

Symptoms

The primary symptom of Alternaria brassicae infection is the appearance of circular, dark brown to black spots on the leaves, stems, and pods of infected plants. These spots often have concentric rings, giving them a target-like appearance. As the disease progresses, the spots may enlarge and merge, leading to extensive tissue damage and premature leaf drop.

Epidemiology

Alternaria brassicae is favored by warm, humid conditions, which promote the germination of conidia and the spread of the disease. The pathogen can be disseminated by wind, rain splash, and contaminated equipment. Dense plant canopies and poor air circulation can exacerbate the spread of the disease.

Management

Management of Alternaria brassicae involves a combination of cultural, chemical, and biological control strategies. Cultural practices include crop rotation, removal of plant debris, and ensuring adequate plant spacing to improve air circulation. Fungicides can be used to protect plants, especially during periods of high disease pressure. Biological control agents, such as antagonistic fungi and bacteria, are also being explored as potential management options.

Related Pages

• Alternaria
• Brassicaceae
• Plant pathology
• Fungal diseases of plants

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