Late blight

Phytophthora infestans is a destructive oomycete pathogen responsible for the disease known as late blight. It belongs to the class Oomycetes and is notoriously famous for causing devastating epidemics in solanaceous crops, primarily potatoes and tomatoes. Due to its rapid reproduction and high virulence, it remains one of the most studied and feared organisms in plant pathology.

Symptoms of the disease typically appear as water-soaked lesions on leaves and stems, which rapidly turn dark brown or black. In humid conditions, a characteristic white, velvety fungal growth develops on the underside of infected leaves. The tubers of potatoes exhibit reddish-brown, dry, granular rot, which can quickly turn into a mushy decay if opportunistic bacteria invade the damaged tissue.

The life cycle of the pathogen is highly adapted to environmental conditions. Under favorable moisture levels, P. infestans produces sporangia, which can act directly as spores or release motile zoospores. These spores are disseminated primarily by wind and splashing rainwater. Upon landing on a suitable host surface, the spore germinates and penetrates the plant epidermis, establishing an infection that quickly colonizes plant tissues.

Environmental requirements for an epidemic include cool, moist weather. Relative humidity levels exceeding 90% and moderate temperatures ranging from 15°C to 20°C are optimal for the pathogen to thrive. Under these conditions, the incubation period is significantly shortened, allowing the fungus to spread rapidly across fields, leading to total foliage destruction within a short timeframe.

• Utilizing disease-resistant potato and tomato varieties.
• Implementing strict crop rotation practices to break the infection cycle.
• Maintaining field hygiene by destroying infected plant debris.
• Executing a scheduled fungicide spray program based on weather forecasts.
• Monitoring fields regularly to detect early signs of initial infection.