Alternaria porri

Fungal Disease

Alternaria porri

Fungal Disease

Alternaria porri

Fungal Disease

Alternaria porri

Fungal Disease

Purple blotch of garlic, caused by the fungus Alternaria porri, is a significant disease that primarily affects leaves, seed stalks, and bulbs. The initial symptoms appear as small white lesions on the leaves or seed stalks, which, under humid conditions, expand into elliptical purplish blotches surrounded by a yellow border. These lesions can grow several centimeters long and show dark and light concentric rings due to fungal sporulation. As the disease progresses, the lesions may coalesce, causing the affected leaf to wilt and die, starting from the tips. Within 3-4 weeks, severely affected leaves turn yellow and collapse.

In less favorable conditions, lesions may remain as small white flecks without much expansion. Purple blotch can also affect seed stalks and floral parts, and in severe cases, it can girdle the seed stalks, destroying them before seed maturity. Bulbs may be attacked, particularly around the neck, leading to yellow to reddish watery rot. Over time, the infected bulb scales become desiccated and dark, though only the outer scales are usually affected.

Managing purple blotch involves monitoring humidity levels, as humid conditions favor disease development, and implementing appropriate fungicidal treatments when necessary to prevent its spread and minimize crop loss.