Black rot

Black rot is a severe bacterial disease caused by Xanthomonas campestris. It primarily affects the vascular system of plants, leading to impaired transport of nutrients and water, which results in wilting, chlorosis, and eventual tissue necrosis.

This pathogen has a wide host range, specifically targeting members of the Brassicaceae family. Crops significantly impacted by the disease include rapeseed (canola), Indian mustard, turnip, and various types of cabbage, radish, and kale.

The primary symptom is the appearance of V-shaped yellow (chlorotic) lesions that start at the leaf margins and progress inwards. As the infection spreads, the leaf veins turn black, creating a characteristic network of dark lines. In advanced stages, the vascular bundles in stems and stalks become darkened and necrotic.

The disease thrives in warm, humid conditions with temperatures ranging from 20°C to 30°C. Spread occurs primarily through water splashing (rain or overhead irrigation), contaminated seeds, and insect vectors. The bacteria can persist in soil debris, weeds, and volunteer crops throughout the winter season.

Preventative management is critical because there are no effective curative chemical treatments once the bacteria enter the vascular system. Integrated pest management strategies include using certified disease-free seeds, implementing a multi-year crop rotation, controlling cruciferous weeds, and applying protective measures to minimize mechanical damage to the crops.