This disease is common whenever potato is grown under favorable conditions may causes serious damage to the crop. In those areas where both late and early blight of potato disease occur, it is the early blight that comes in the season earlier than the late blight.
While late blight epidemics are in cooler areas, the early blight is free from inhibition caused by weather condition and occur in cooler as well as warm area. The disease also interacts in tomato, chillies, eggplant, and related wild hosts. Among the fungal disease, early blight is the most destructive.
Symptoms of early blight
The disease first becomes visible as small, isolated, scattered, pale brown spots on the leaflets. Those spots become covered with a deep growth of the fungus. The lower leaf attacked first and disease progressed upward.
In the necrotic spot, concentric rings appear on the older leaves and darkened areas on the stem. This give a target board like effect. There is usually a narrow chlorotic zone around the spots which fades into normal green and increases with a increase in size of the spots.
There may be a few spots or a large no. of them may appear, occupying major portions of the leaf. When the leaf lesions involve larger veins, chlorosis commonly extends well beyond the necrotic spots.
Why is doing?
This is due to the toxin alternaric acid produced by fungus and translocated through the veins. In dry weather, the spot became harder and the leaves curl. The affected area in humid weather, is the increase and larger rotting patches may appear. In several stacks, leaves shrivel and fall down. In several infection all the aerial portion of the plant have a blighted appearance.
The causal organism for the early blight of potato is Alternaria solani. The mycelium consists of septate, branched, light brown hyphae which become darker with age. The hyphae are at first intercellular, later penetrating into the cells of the invaded tissues. Conidiophores emerge through the stomata from the dead center of the spots. These are 50-90x 9µm, dark colored and borne singly. There are both transverse and longitudinal septa in the mature conidia. Alternaria solani produces a non-specific toxin known as alternaric acid. The role of acid in disease is doubtful.
The pathogen is mainly soil -borne. The primary infection may be through tubers. The mycelium of the fungus dormant in dry infected leaves for a year or more. Conidia have been foundto retain viability for 17 months at room temperature. Mycelium and conidia thus survive in the soil in diseased plant debris to cause primary infection in the next year ‘crop collateral hosts such as tomato play an important role in the perpetuation and dissemination of the pathogen. The climate and soil exert a considerable influence on the development of the disease.
It becomes serious when the season begins with abundant moisture followed by low temperature. Bhatia et al.1972 studied the phenolic content of resistant and susceptible varieties of tomato in relation to early blight disease.
- Always avoid the affected tubers.
- Remove the affected plants from the field.
- Field should be free from the plant debris and the others.
- Use of fungicide like Mancozeb and Chlorothalonil as on market availability.
- Avoid the water logging condition.