Alternaria leaf spot

Alternaria solani is a fungal pathogen that produces a disease in tomato and potato plants called early blight. The pathogen produces distinctive "bullseye" patterned leaf spots and can also cause stem lesions and fruit rot on tomato and tuber blight on potato.

Causal organism : Alternaria solani Ell. Mart

Damage symptoms:

• This is a common disease of chilli occurring on the foliage at any stage of the growth.


• The fungus attacks the foliage causing characteristic leaf spots and blight. Early blight is first observed on the plants as small, black lesions mostly on the older foliage.


• Spots enlarge, and by the time they are one-fourth inch in diameter or larger, concentric rings in a bull's eye pattern can be seen in the center of the diseased area.


• Tissue surrounding the spots may turn yellow. If high temperature and humidity occur at this time, much of the foliage is killed.


• Lesions on the stems are similar to those on leaves, sometimes girdling the plant if they occur near the soil line.


• Transplants showing infection by the late blight fungus often die when set in the field. The fungus also infects the fruit, generally through the calyx or stem attachment.


• Lesions attain considerable size, usually involving nearly the entire fruit; concentric rings are also present on the fruit.

Survival and spread:

• Primary : The fungus spends the winter in infected plant debris in or on the soil where it can survive at least one and perhaps several years. It can also be seed borne.


• Secondary: The spores are transported by water, wind, insects, other animals including man, and machinery. Once the initial infections have occurred, they become the most important source of new spore production and are responsible for rapid disease spread.

Favourable conditions:

• Warm, rainy and wet weather