Anthracnose of Tomatoes

Symptoms. The most characteristic symptom develops on ripe fruit. The fruit may be infected when green and small, but symptoms do not appear until it begins to ripen. Symptoms first become visible on ripe fruit as small, circular, indented spots in the skin. A lesion may enlarge to ½ inch in diameter and become more sunken (Figure 3). As the spots expand, they develop dark centers or concentric rings of dark specks, which are the spore-producing bodies (acervuli) of the fungus. The flesh beneath a lesion may have a lighter color than the surrounding tissue and granular in texture. The center of a lesion is usually tan, and as the lesion matures it becomes dotted with small black specks (microsclerotia). The surface of a mature lesion generally remains smooth and intact.
Disease Cycle. Colletotrichum coccodes survives from year to year as microsclerotia, often in association with plant debris. Under wet and warm conditions, the microsclerotia germinate and produce hyphae and conidia in acervuli. Microsclerotia can survive for long periods in the soil under adverse weather conditions. The fungus may infect fruit resting on the soil surface. Microsclerotia andconidia may also be splashed onto foliage and fruit. Once in contact with the fruit, conidia germinate and infect fruit. The fungus also causes latent infections in immature tomato fruit. Latent infections are activated after exposure of the fruit to low temperatures or after fruit maturation and plant senescence. Once latent infections are activated, symptoms develop rapidly. Ripe or overripe tomatoes are highly susceptible, and symptoms progress rapidly on them. Conditions that favor plant infection are temperatures from 50 to 86°F (10 to 30°C) [with an optimum of 68-75°F (20-24°C)], together with free moisture. Spread of microsclerotia and conidia is favored by splashing rain and overhead irrigation.