In this article we will discuss about the symptoms of the diseases phytophthora on potato and colocasia.
i. Symptoms of Phytophthora on Potato:
1. “Late-blight of potato” (Solanum tuberosum) appears in the fields only after blossoming period.
2. First symptom is the appearance of many small, black or purplish-black areas (Fig. 63) on the leaves.
3. These black patches then increase in size covering the entire leaf and turn into brown-coloured.
4. The fungal sporangia appear clearly on the undersurface of the leaf as powdery bloom with a distinct border, thus producing blight.
5. After leaf, the stem is attacked and ultimately the whole plant is shrivelled.
6. After shrivelling of the whole plant, the tubers are affected showing the symptom of brownish or purplish colouration of their skin.
7. The infection spreads inwards and the whole tuber turns brown.
ii. Symptoms of Phytophthora on Colocasia:
Leaves and flowers of Colocasia antiquorum (Arvi) are attacked by Phytophthora colocasiae, and the characteristic symptom of the late-blight of Colocasia is the presence of many large concentric rings (Fig. 64 A, B).