Dark leaf and pod spot

Alternaria brassicae

Alternaria brassicae is a fungal pathogen that commonly affects cruciferous vegetables, including crops like cabbage, cauliflower, broccoli, and other Brassica species. The disease caused by this fungus is known as Alternaria leaf spot or black spot of crucifers. Here is an overview of Alternaria brassicae:

Symptoms:

  1. Leaf Lesions: The characteristic symptom is the development of dark, round to irregularly shaped lesions on the leaves of affected plants.
  2. Lesion Appearance: Lesions typically have a dark brown to black color with a concentric ring pattern, giving them a distinctive appearance.
  3. Leaf Yellowing: As the disease progresses, the areas surrounding the lesions may turn yellow, leading to a general yellowing of the affected leaves.
  4. Defoliation: In severe cases, the infected leaves may wither and die, leading to defoliation.

Disease Cycle:

  1. Survival: The fungus can survive on infected plant debris in the soil, contributing to the disease's persistence.
  2. Spore Production: Alternaria species, including Alternaria brassicae, produce conidia (asexual spores) on infected plant material.
  3. Spread: Conidia are dispersed by wind, rain, or other means to healthy plants, initiating new infections.
  4. Infection: The conidia can germinate and penetrate plant tissues, causing new infections on leaves and other plant parts.

Management:

  1. Resistant Varieties: Planting resistant varieties is an effective strategy to reduce the impact of Alternaria leaf spot.
  2. Crop Rotation: Practicing crop rotation helps break the disease cycle and reduces the availability of inoculum in the soil.
  3. Sanitation: Removing and destroying infected plant debris helps minimize the source of inoculum.
  4. Fungicide Applications: In cases of severe infections, fungicides may be used for disease management. Application timing and choice of fungicides should align with local recommendations and disease severity.

Importance:

  • Alternaria leaf spot can lead to reduced yields and quality of cruciferous vegetables.
  • The disease is favored by warm and humid conditions, making it more prevalent in certain regions and during specific times of the growing season.