E Lireni Kikon and Dr. Phool Kumari
KVK Dimapur
Introduction:
Potato (Solanum tuberosum L.) an annual plant belonging to family solanaceae is an important starchy tuber. It is the fourth most commonly grown food crop in the world after maize, wheat and rice. It grows best in cooler climates, particularly in elevated tropical areas. Temperature is a critical environmental factor affecting seed sprout development and tuber formation. Sprouting is minimal at 6°C, increases at 9°C and peaks at 18°C. Optimal initiation and formation of tubers occur within 16–22°C. Soil temperatures above 20°C hinder tuber formation and when they rise beyond 30°C, physiological growth is almost completely arrested.
Potato crop is affected by approximately 160 diseases and disorders of which 50 are caused by fungi, 10 by bacteria, 40 by viruses and others by non-parasitic or due to unknown causes. Fungal diseases are late blight, early blight, black scurf, fusarial wilt/dry rot, wart, powdery scab, charcoal rot etc. Among these, Early blight caused by Alternaria solani and late blight caused by Phytophthora infestans are considered the most destructive diseases affecting potato production globally. These diseases significantly reduce yield, productivity and profitability in potato farming.
Early blight: In India the pathogen Alternaria solani was reported for the first time from Farukhabad district of Uttar Pradesh. This pathogen causes leaf and stem diseases in tomato as well as in potato. When severe, the disease is thought to be one of the most prevalent and destructive potato diseases, resulting in a 40% reducing in yield especially in India’s plains. In general, the disease gets worse when there is high humidity or frequent rain, especially if it's followed by warm and dry weather.
Symptoms of Early blight:
The disease usually appears first on older leaves as small, dark brown to black spots. As the infection progresses, these spots enlarge and develop distinct concentric rings, giving them a characteristic target-like appearance. The tissue surrounding the lesions often turns yellow and severely affected leaves may dry up and fall off prematurely.
In advanced stages, the disease may also affect the stems, where dark, elongated lesions with concentric markings can be seen. Severe infection leads to early defoliation of the plant, resulting in reduced vigor and poor tuber development. In some cases, the fungus may infect the tubers, producing dark, sunken, dry lesions with corky tissue beneath the skin.
Condition that favors the spread of the disease
• Warm temperatures (24–30°C).
• High humidity and leaf wetness.
• Dry periods alternating with moisture. Stress from drought followed by humidity strongly favors the disease development.
Late blight: The late blight disease of potato has the famous history of causing the great Irish famine during 1840-1845. Late blight disease of potato is still one of the most devastating diseases in potato-producing regions around the world causing huge economic losses. Global production of potato is approximately reduced by 15 per cent due to the disease. The late blight disease was recorded in India for the first time between 1870 and 1880 in the Nilgiri hills and subsequently appears in most of the potato growing regions in varying degrees causing yield losses to the extent of 90 per cent.
Symptoms of Late blight:
The pathogen produces water-soaked lesions with chlorotic borders that are small at first but expand rapidly under humid conditions, blighting the entire plant in only a few days with subsequent rotting of the developing tubers. Symptoms of the disease appear near the leaf tips as water-soaked irregular pale green lesions, which rapidly grow into large brown to black necrotic spots on the upper surface of infected leaves. On the stem it appears as a brown lesion eventually leading to collapse. In severe cases the disease can affect the entire crop in a week and transform it into a dark blighted crop. The disease also affects tubers, making them hard, dry and rigid, resulting in rotting in the field and in storage. The main distinguishing feature of late blight disease under favourable weather condition is the appearance of white fluffy fungal growth on the underside of the leaf.
Condition that favors the spread of the disease are
• Cool temperatures (10–20 °C) especially cool nights.
• High humidity (RH >90%.
• Prolonged leaf wetness (10–12 hours or more).
Managementof Early and Late blight of potato:
• Use healthy, certified and disease-free seed tubers
• Follow crop rotation with non-host crops
• Grow resistant or tolerant potato varieties if available
• Maintain proper plant spacing for good air circulation
• Ensure balanced fertilization, especially adequate nitrogen and potassium
• Avoid water stress and prolonged leaf wetness
• Remove and destroy infected plant debris
• Monitor fields regularly, especially during cool and humid weather
• Apply recommended fungicides (e.g., mancozeb, chlorothalonil) at regular intervals when symptoms appear or when the conditions are favourable
• Apply preventive fungicides such asMancozeb, Chlorothalonil, Copper-based fungicides etc. before disease onset
• Use systemic fungicides, Ridomil MZ @ 2.5g/litre of water at an interval of 7–10 days or as per disease pressure and weather conditions. Apply at the first appearance of disease or when conditions favor late blight (cool, humid, cloudy weather)
• While spraying, ensure thorough coverage of foliage and stems at early stages of infection
Conclusion:
The fungal diseases in potato can be managed by planting healthy seed tubers, practicing crop rotation, and ensuring good field hygiene. Timely spraying of protective and systemic fungicides, along with using resistant varieties, helps keep the crop healthy and productive. Integrated management combining these methods offers the most effective protection against these fungal threats.
