P. ChowdappaIndian Institute of Horticultrual ResearchBangalore, Karnataka, IndiaEmail: pallem22@gmail.com
Host: Lycopersicon esculentum Mill. (tomato)Disease name: Early blightPathogen name: Alternaria solani Sorauer
Early blight infection, caused by Alternaria solani, on a tomato stem. Small, dark, slightly sunken areas develop and enlarge to form circular, elongated, or lens-shaped spots with light-colored centers. The lesions typically exhibit concentric rings.
Early blight, caused by Alternaria solani, is a major production constraint in tomato wherever this crop is grown. In one study, yield losses were 78% at 72% disease intensity, and each 1% increase in intensity reduced tomato yield by 1.36%. Early blight produces symptoms on tomato foliage, stems, and fruit. Symptoms usually appear on the older leaves as small, irregular, dark brown to black spots. The spots enlarge into circular lesions consisting of concentric rings, often surrounded by yellow halos, resulting in a characteristic “target-spot,” a diagnostic symptom of early blight. A. solani can be identified by the long-beaked conidia, each of which contains 9–11 transverse septa as well as vertical septa. The conidia are borne singly or in chains of two on distinct conidiophores. The pathogen can survive from season to season on volunteer tomato seedlings or plant debris on the soil. Warm (28–30°C) and humid (>85% relative humidity) environmental conditions are conducive to infection.
Several preventive fungicides are available that can be applied at 7- to 10-day intervals, alternating one fungicide after another, for effective disease management. Other cultural practices, such as the use of disease-free seed or transplants and removal of infected plant debris from the field, can help reduce inoculum.
Photographer: S. P. Mohan Kumar
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