Host: The Disease primarily affects Solanaceae, namely Tomatoes and Potatoes. Potatoes and
Tomatoes are planted across the world as a food source.
The Pathogen: The cause of Early Blight of Tomato is the fungus Alternaria Solani
(Ascomycota, Dothideomycetes).
Epidemiology: Alternaria Solani primarily overwinters thanks to infected crop debris. The
mycelium of the pathogen can survive for several years, as its dark pigmentation increases its
resistance to lysis. In mild climates the pathogen survives on weedy solanaceous hosts, such as
Potatoes and Tomatoes but also Horsenettle. Humid temperatures of 24-29C are favorable for
infection and germination of spores, with an optimum of 28-30C. When these temperatures are
reached Condia germinates and begins infection.
Symptoms: Initial symptoms are small 1-2 mm black or brown lesions. Under favorable
conditions these lesions will enlarge and often be surrounded by a yellow outline. Larger lesions
have dark pigmented rings present, and this “Bullseye” pattern is characteristic of early blight.
The expansion of Lesions can lead to the leaves turning chlorotic and can result in extreme
defoliation. Infection of tomatoes normally occurs through the Calyx, and infected fruit will
frequently drop prematurely.
Control: Sanitary practices such as removal of Infected soil and crop debris as well as
controlling the presence of weeds that serve as alternative hosts to the disease are beneficial in
controlling Alternaria Solani. Ensuring new crops are pathogen free and rotating fields to non
susceptible host crops helps control the level of inoculum in the soil. The most important control
is ensuring optimal tuber maturity as immature tubers are susceptible to wounding and infection,
as well as handling harvests carefully to prevent wounding of crops and avoiding harvesting
during wet conditions if possible.
References
Kemmitt, G. 2002. Early blight of potato and tomato. The Plant Health Instructor
https://www.apsnet.org/edcenter/disandpath/fungalasco/pdlessons/Pages/PotatoTomato.aspx
Roy, Chapol K., et al. “Control of Early Blight of Tomato Caused by Alternaria Solani and
Screening of Tomato Varieties against the Pathogen.” The Open Microbiology Journal, vol. 13,
no. 1, 2019, pp. 41–50.
https://openmicrobiologyjournal.com/VOLUME/13/PAGE/41/
Gulzar, Naveed, et al. “Tomato Early Blight (Alternaria Solani), Pathogen, Disease Development
and Defense Response Phytohormone Signaling.” International Research Journal of Plant
Science, vol. 12, Aug. 2021, pp. 01–10., https://doi.org/http:/dx.doi.org/10.14303/irjps.2021.25.
https://www.interesjournals.org/articles/tomato-early-blight-alternaria-solani-pathogen-disease-d
evelopment-and-defense-response-phytohormone-signaling.pdf