Early Blight is a plant disease that affects tomato and potato crops, causing significant damage and reducing yield. Alternaria solani is the fungus that causes this disease. It is prevalent in many regions, including Minnesota, where it occurs in nearly every growing season. Early Blight infects the plant’s leaves, stems, and fruits, leading to severe defoliation and damage to the fruit.
The fruit can become sunburned in tomatoes due to the loss of leaves. This disease can be devastating for farmers as it can significantly impact their yields, especially when susceptible cultivars are used and weather conditions are favorable for the disease to spread.
Early Blight Management in Tomato
The Disease Cycle of Early Blight
The life cycle of early Blight of tomato, caused by the fungus Alternaria solani, can be divided into the following stages:
- Spore Production: The fungus produces spores on infected leaves and flowers, which release spores into the air and spread the disease to healthy plants.
- Germination: The spores come into contact with a suitable host, typically tomato leaves, and germinate in the presence of moisture.
- Penetration: The fungal hyphae penetrate the tomato plant through wounds or stomata, the tiny pores in leaves through which they exchange gases.
- Establishment of Infection: Once inside the plant, the fungus begins to colonize the tissues, causing the plant to weaken and produce the characteristic dark, circular leaf lesions.
- Sporulation: The fungus continues to grow, producing more spores and spreading the infection to other parts of the plant and other plants nearby.
- Repeat Cycle: The cycle of infection, sporulation, and spread continues, potentially leading to significant damage to the tomato crop and reducing yield.
The Causal Organism of Early Blight
- The causal organism of Early Blight is Alternaria solani and Alternaria tomatophila. These two species are closely related and are capable of causing early Blight in tomato plants.
- They can overwinter in infected plant debris and soil and survive on tomato seed or be introduced to tomato transplants, which can help them spread from one location to another.
Damage Symptoms of Early Blight in Tomato Field
- Leaf damage: The first signs of the disease appear as small black or brown lesions on the leaves, which can enlarge to 10 mm or more in diameter with characteristic concentric rings. As the disease progresses, the entire leaves may turn yellow and fall off, resulting in significant defoliation.
- Stem damage: Lesions on the stems are often lens-shaped with a light center and the same concentric rings seen on the leaves. On young seedlings, the stem lesions may completely girdle the stem, causing reduced plant vigor or death.
- Fruit damage: The fruit can also be affected by Early Blight, with black or brown spots or scabs on the skin. Sunburn can occur on exposed fruit due to the loss of leaves, further reducing the marketability of the fruit.
- Reduced plant vigor: Early Blight can cause significant defoliation, reducing the plant’s ability to photosynthesize and reducing plant vigor. This, in turn, can negatively impact yield and fruit quality.