Groundnut, or peanut, is a vital oilseed crop grown worldwide, valued for its economic and nutritional benefits. However, it is often affected by foliar diseases, which harm the leaves and above-ground parts, reducing crop health and yield. A major foliar disease is Tikka disease, caused by two fungal pathogens Cercospora arachidicola and Cercosporidium personatum (or Cercospora personata). Tikka disease creates dark spots on leaves, leading to premature leaf drop and significant yield losses. Tikka disease is a global concern for groundnut farmers, requiring effective management to protect crops.
Types of Tikka disease in groundnut:
Early and late leaf spot are the two main types of Tikka disease in groundnut. Early leaf spot is caused by Cercospora arachidicola, while late leaf spot is caused by Phaeoisariopsis personata. Both fungi produce characteristic leaf spots, leading to defoliation and reduced yield, making them collectively known as Tikka disease.
Early Leaf Spot (ELS):
- Causal Pathogen: Caused by the fungus Cercospora arachidicola.
- Symptoms: Appears earlier (10–18 days after emergence) with pale areas on the upper leaf surface that develop into yellow spots with necrosis. Spots are circular to irregular, 1–10 mm in diameter, with a yellow halo. At maturity, spots are reddish-brown to black on the upper surface and orange on the lower surface. Sporulation occurs on the upper leaf surface.
Late Leaf Spot (LLS):
- Causal Pathogen: Caused by the fungus Phaeoisariopsis personata (also known as Cercosporidium personatum).
- Symptoms: Appears later (28–35 days after emergence or near harvest) with small necrotic flecks that enlarge into dark brown to black spots. Spots are round, 1.5–6.00 mm in diameter, and lack a prominent yellow halo. Sporulation occurs primarily on the lower leaf surface.
Comparison of Early Leaf Spot (ELS) vs Late Leaf Spot (LLS)
| Aspect | Early Leaf Spot (ELS) | Late Leaf Spot (LLS) |
|---|---|---|
| Pathogen | Cercospora arachidicola | Cercosporidium personata |
| Spots | Brown spots with yellow halos | Dark brown to black spots with ring patterns and dense spores |
| Sporulation | Occurs on the upper surface of leaves | Occurs on the lower surface of leaves |
| Timing | Early stage (10–18 days after emergence) | Late stage (28–35 days after emergence or near harvest) |
Symptoms of Tikka Disease in groundnut
The main symptoms of Tikka disease include:
- Small, circular, dark brown or black spots on leaves.
- Yellow halos around the spots in early leaf spot.
- Spots merging to form larger patches, causing leaves to turn yellow and fall off.
- Black lesions on stems and pods in severe cases.
- Premature leaf drop, leading to reduced photosynthesis and lower yields.
Pathogen of Tikka Disease
Tikka disease is caused by two fungal pathogens:
- Cercospora arachidicola: Causes early leaf spot and produces spores on the upper leaf surface.
- Cercosporidium personatum: Causes late leaf spot and produces spores on the lower leaf surface.
Both fungi survive in plant debris and soil, spreading through wind and rain.
Disease Cycle of Tikka Disease
The disease cycle of Tikka disease involves the following steps:
- The fungi survive in infected plant debris and soil.
- Spores are spread by wind and rain to healthy plants.
- High humidity and warm temperatures (25-30°C) favor fungal growth.
- The disease spreads rapidly during flowering and pod formation, causing severe damage.
How does tikka disease affect the yield and quality of groundnut crops?
Effects on Yield:
- Reduced Photosynthesis:
- The presence of leaf spots and defoliation reduces the leaf area available for photosynthesis, leading to lower energy production for the plant. This can result in stunted growth and reduced pod formation.
- Yield Loss:
- In severe cases, yield losses can range from 15% to over 50%, depending on the timing of infection and the effectiveness of management practices. Early infections are particularly damaging as they can lead to significant defoliation before the plants reach maturity.
- Pod Development:
- The disease can also affect pod development, leading to fewer pods per plant and smaller pod sizes. This directly translates to lower overall yield.
Effects on Quality:
- Seed Quality:
- Infected plants may produce seeds that are smaller and of lower quality. The presence of lesions on pods can also lead to increased susceptibility to other pathogens, further degrading seed quality.
- Market Value:
- The quality of groundnuts is crucial for market acceptance. Seeds from infected plants may have reduced oil content and inferior taste, making them less desirable for consumers and processors.
- Increased Aflatoxin Risk:
- Tikka disease can predispose groundnuts to aflatoxin contamination, a toxic compound produced by certain molds. Aflatoxins are harmful to human and animal health and can lead to significant economic losses due to strict food safety regulations.
Tikka Disease Management Strategies:
- Crop Rotation: Rotating groundnuts with non-host crops can help break the disease cycle.
- Resistant Varieties: Planting disease-resistant groundnut varieties can significantly reduce the incidence of tikka disease.
- Fungicide Application: Timely application of fungicides can help control the spread of the disease.
- Cultural Practices: Implementing good agricultural practices, such as proper spacing and sanitation, can reduce disease pressure.