TIKKA LEAF SPOT ON GROUNDNUT LEAF
TIKKA
LEAF SPOT ON GROUNDNUT LEAF
[FUNGAL DISEASE]
(Source:https://www.plantsdiseases.com/p/diseases-of-groundnut.html)
CAUSING
ORGANISM:
1. Cercospora
arachidicola
2. Cercospora
personata
GENERAL
CHARACTERS:
ü Shape: Cylindrical or elliptical.
ü Size: Small (20-60 µm long).
ü Color: Hyaline (transparent) to grayish.
ü Septation: Typically multi-septate.
BIOCHEMICAL
TEST:
Both species have same biochemical characters.
ü Catalase Test: Positive
ü Oxidase Test: Negative
ü Protease Production: Positive
ü Cellulase Production: Positive
ü Amylase Production: Positive
ü Lipase Production: Positive
ü Pectinase Production: Positive
ü Melanin Production: Positive (dark pigment production
on culture media)
ü Enzyme Activity for Lignin Degradation: Positive
SYMPTOMES:
1. Cercospora
arachidicola
ü Leaf Spots: Small, circular to irregularly
shaped spots that start as light brown or grayish with darker borders.
ü Lesions: The spots may become larger and
merge, leading to large, irregular patches of necrotic tissue.
ü Sporulation: In humid conditions, the spots may
have a grayish or olive-green fungal growth (conidia) visible on the underside
of the leaves.
ü Defoliation: Severe infections can lead to
premature leaf drop, reducing photosynthesis and impacting plant yield.
2. Cercospora
personata
ü Leaf Spots: Initially, the lesions are small,
circular, and brown, with a dark brown to black margin.
ü Lesions: As the disease progresses, the
spots can become larger, often with a reddish or purple-brown center and a
distinct dark margin.
ü Sporulation: The spots may have a grayish or
olive-green appearance due to fungal conidia on the underside of the leaf.
ü Defoliation: Similar to Cercospora
arachidicola, severe infections can lead to significant leaf drop and
reduced plant vigor.
PATHOGENESIS:
1.
Cercospora arachidicola
·
Taxonomy:
ü Genus: Cercospora
ü Family: Cercosporaceae
·
Pathogen
Characteristics:
ü Conidia (spores) are typically
elliptical to cylindrical and are produced in the lesions on the underside of
the leaves.
ü The fungus thrives in warm, humid
environments.
2.
Cercospora personata
- Taxonomy:
ü Genus: Cercospora
ü Family: Cercosporaceae
- Pathogen Characteristics:
ü Conidia are usually cylindrical to
slightly curved and are also produced in the lesions on the underside of the
leaves.
ü This species also prefers warm and
humid conditions for optimal growth and sporulation.
LIFE
CYCLE:
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Cercospora arachidicola and Cercospora personata share similar disease cycles:
1. Inoculum Source: Both pathogens primarily survive in infected plant debris or soil, where they produce conidia that serve as inoculum for the next cropping season.
2. Dissemination: Conidia are dispersed by wind, rain splash, and irrigation, allowing the pathogen to spread to new plants.
3. Infection: Under favorable conditions (high humidity and temperatures), conidia germinate on the leaf surface, penetrate through stomata or directly through the cuticle, and start to colonize the leaf tissue.
4. Colonization and Symptom Development: Inside the leaf, the fungi produce necrotic lesions, which expand and can eventually lead to significant leaf drop. New conidia are produced in these lesions, continuing the cycle of infection.
5. Overwintering and Survival: The pathogens overwinter in plant debris or soil, providing a source of inoculum for subsequent growing seasons.
TREATMENT
AND CONTROLE MESURNENT:
Effective treatment and control measures for
managing Cercospora leaf spot in groundnuts (peanuts) involve a
combination of cultural practices, resistant varieties, and chemical controls.
1.
Cultural Practices:
a. Crop Rotation:
ü Rotate with non-host crops such as
cereals or legumes that are not susceptible to Cercospora spp.
This helps reduce the inoculum load in the soil.
b. Field Sanitation:
ü Remove and destroy infected plant
debris and weeds that can harbor the pathogens. This reduces the sources of
inoculum for future infections.
c. Planting Practices:
ü Avoid planting groundnuts in fields
with a history of severe Cercospora infections. Choose
well-drained fields to minimize prolonged leaf wetness.
ü Space plants adequately to improve
air circulation and reduce humidity around the plants, which can help reduce
fungal growth.
d. Irrigation Management:
ü Use drip irrigation instead of
overhead irrigation to reduce leaf wetness, which can favor fungal development.
ü Avoid watering late in the day to
allow leaves to dry before nightfall.
2.
Resistant Varieties:
ü Variety Selection: Select and plant groundnut
varieties that are resistant or tolerant to Cercospora leaf spot. These varieties can significantly
reduce the incidence and severity of the disease.
ü Local Recommendations: Consult local agricultural
extension services or seed suppliers for recommendations on resistant varieties
suited to your region.
3.
Chemical Control:
a. Fungicide Application:
ü Preventive Application: Apply fungicides preventively,
especially during periods of high humidity and when conditions are favorable
for disease development.
ü Curative Application: If symptoms are detected,
fungicides can be used to manage the disease. However, fungicides are more
effective when applied early in the disease cycle.
b. Fungicide Types:
ü Protective Fungicides: Include systemic fungicides that
protect the plant from infection. Commonly used fungicides include:
Ø Chlorothalonil (e.g., Bravo)
Ø Copper-based fungicides
Ø Mancozeb
ü Systemic Fungicides: These can move within the plant
and provide longer-lasting protection. Examples include:
Ø Propiconazole (e.g., Tilt)
Ø Tebuconazole (e.g., Folicur)
c. Application Timing:
ü Apply fungicides according to the
manufacturer's recommendations and local guidelines. This often involves
multiple applications throughout the growing season, starting before symptoms
appear.
4.
Integrated Pest Management (IPM):
a. Monitoring:
ü Regularly inspect plants for early
signs of infection and assess disease severity to determine the need for
interventions.
b. Thresholds:
ü Use economic thresholds to decide
when to apply fungicides. This involves monitoring the level of disease and
comparing it to acceptable damage levels.
c. Combining Methods:
ü Combine cultural practices, resistant
varieties, and chemical treatments to manage the disease more effectively and
sustainably.
CONCLUSION:
Cercospora arachidicola and Cercospora personata are two
distinct fungal pathogens responsible for early and late leaf spot diseases in
peanuts, respectively. Though they share similarities in their enzyme
activities and biochemical properties, such as positive catalase and cellulase
production, they differ in disease presentation, spore morphology, melanin
production, and optimal growth conditions. Understanding these differences is
crucial for accurate diagnosis, timely intervention, and effective management
strategies to control leaf spot diseases in peanut crops.
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