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Symptoms and signs

Symptoms of early blight occur on fruit, stem and foliage of tomatoes and stem, foliage and tubers of potatoes. Initial symptoms on leaves appear as small 1-2 mm black or brown lesions. Under conducive environmental conditions, the lesions enlarge and are often surrounded by a yellow halo (Figures 2 and 3). Lesions greater than 10 mm in diameter often have dark pigmented concentric rings. This so-called "bullseye" type lesion is highly characteristic of early blight (Figure 4). As lesions expand and new lesions develop, entire leaves may turn chlorotic and dehisce, leading to significant defoliation. Lesions on stems are often sunken and lens-shaped with a light center and have the typical concentric rings (Figure 5). On young tomato seedlings, lesions may completely girdle the stem, a phase of the disease known as "collar rot," which may lead to reduced plant vigor or death.


Figure 2	Figure 3

Figure 4	Figure 5

Infection of both green and ripe tomato fruit normally occurs through the calyx with lesions sometimes reaching a considerable size (Figure 6). The lesions appear leathery and may have the characteristic concentric rings. Infected fruit will frequently drop prematurely. Symptoms on potato tubers are characterized by sunken, irregular lesions (Figure 7), which are often surrounded by a raised purple border. Beneath the lesion surface, the tuber tissue is leathery or corky with a brown discoloration. Early blight lesions on tubers tend to be dry and are less prone to invasion by secondary organisms compared to lesions of other tuber rots. After prolonged storage, severely diseased tubers may become shriveled.


Figure 6	Figure 7

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