Late blight is a devastating disease that affects potatoes and other plants in the Solanaceae family. The first recorded outbreak of late blight in potatoes occurred in the early 1840s in Europe, and it quickly spread to other parts of the world. The disease was responsible for the ‘Irish Potato Famine’ in the mid-19th century, which caused widespread starvation and death.
CAUSES OF LATE BLIGHT
Late blight in potatoes is caused by a water mold called Phytophthora infestans. The pathogen can survive in infected plant debris and soil, allowing it to persist and re-infect new crops in subsequent seasons. The spread of late blight in potatoes is facilitated by factors such as the movement of infected plant material, favorable environmental conditions, and the development of new strains of the pathogen with increased virulence and fungicide resistance.
SYMPTOMS OF LATE BLIGHT
Late blight will first appear as water-soaked spots, usually at the tips or edges of lower leaves where water or dew tends to collect. Under moist, cool conditions, water-soaked spots rapidly enlarge and a broad yellow hollow may be seen surrounding the lesions.
Tuber lesions first appear as irregular, dark blotches. When cut open, affected tissue is water-soaked, reddish brown and extends with an irregular margin into the tuber flesh. Lesions may start as a superficial decay that continues to develop after tubers are harvested and placed into storage.
CYCLE OF LATE BLIGHT
- Sporangia may be developed on diseased tubers or potato stems if they are left behind during harvest or thrown at the field boundaries.
- The potato stem or tuber represent a source of primary inoculum if cultivated in the following agricultural season.
- The pathogen colonize several of the emerging sprouts and sporulates producing the sporangia under high humidity. These sporangia help transmit the disease.
- It usually takes 3-7 days for the disease to begin to display evident symptoms. One such symptom is on the underside of the leaves, the fungus develops white sporulation that is easily visible.
- The cycle of infection by sporangia repeats every 4-10 days, depending on the temperature and humidity levels in the area.
- Sporangia infect tubers in the soil when it is washed away by rain or brought by irrigation water. Tubers that have been partially exposed can readily become infected.
- The principal source of inoculum for the next crop batch is these diseased tubers.
HOW IT IS SPREAD
It can spread rapidly from one potato field to nearby fields if environmental conditions are favorable. The pathogen can be spread through water, wind, and insects. The spread of the disease can also be facilitated by infected seed potatoes or contaminated farm equipment.
EFFECT OF POTATO BLIGHT IN POTATOES
It is a serious threat to potato production worldwide and can cause significant economic losses to farmers. According to the Food and Agriculture Organization (FAO), late blight can cause losses of up to 50-100% in potato production in susceptible varieties under favorable environmental conditions.
EFFECTS OF POTATO BLIGHT IN KENYA
In Kenya, late blight is a major problem to potato farmers and can cause significant yield losses. According to a report by the International Potato Center (CIP), late blight can cause yield losses of up to 80% in Kenya. This can have a significant impact on the livelihoods of small-holder farmers who depend on potato production for income and food security
Some important techniques for management of late blight in potato;
- Planting certified seed potato or Selection of disease-free tubers for planting.
- The potato tubers must be stored under cold temperature.
- Use of optimal fungicide.
- Sanitation in the storage area.
- Potato tubers must be treated with 1:1000 mercuric chloride solution for 90 minutes prior to storage. This helps in inhibiting the growth of mycelium.