Alternaria leaf spot disease is a common fungal disease that affects many vegetable crops, such as eggplants, tomatoes, and carrots. Alternaria leaf spots can cause significant yield losses if not managed properly. The disease is caused by two species of Alternaria fungi, which produce characteristic leaf spots with concentric rings on the infected plants.
Alternaria Rot Management in Eggplant
The Causal Organism of Alternaria Leaf Spot Disease
The causal organism of Alternaria leaf spot disease is a fungus called Alternaria melongenae, A. solani. It is a common pathogen that affects many crops, including eggplant, and can cause significant yield losses if not managed properly.
The Disease Cycle of Alternaria Leaf Spot Disease
- Survival: The pathogen survives in infected plant debris left on the soil surface or buried in the soil and on or in the seed.
- Infection: Under favorable conditions in the spring, the fungi produce spores carried by wind and splashing rain. When these spores come into contact with susceptible host tissue, they germinate and penetrate the plant surface, causing infection.
- Disease development: Once the pathogen has infected the plant tissue, it grows and reproduces, causing characteristic leaf spots with concentric rings. The spots may coalesce to cover large areas of the leaf blade, and severely affected leaves may drop off. In the case of A. melongenae, the fungus may also infect the fruits, causing large deep-seated spots that turn yellow and drop off prematurely.
- Spore production: As the disease progresses, the fungus produces new spores, which can be carried by wind and rain to infect other plants, leading to secondary disease cycles.
- Disease cycle continuation: Secondary disease cycles can occur if the weather remains favorable for spore production and infection. In some cases, the pathogen may also overwinter on infected plant debris or in seed, leading to new infections in subsequent growing seasons.
Causes/Conditions Favorable for Alternaria Leaf Spot Disease Spread in the Field.
- Environmental factors: Heavy dews, rainy conditions, and temperatures between 66 and 73 F favor spore production and secondary infections.
- High humidity levels can also contribute to disease development, as the moisture on the leaf surface provides an ideal environment for the pathogen to grow and reproduce.
Symptoms of Alternaria Leaf Spot Disease
- Irregular spots on the leaves: The disease causes irregular spots on the leaves, typically 4-8 mm in diameter. These spots have a dark brown or black center and a yellow halo around the edges.
- Concentric rings: The spots may have concentric rings, a characteristic feature of Alternaria infections.
- Coalescing of spots: The spots may coalesce and cover large areas of the leaf blade, leading to the death of the affected tissue.
- Leaf drop: Severely affected leaves may drop off prematurely, leading to defoliation and reduced plant vigor.