Survey Instruction Details:
Visual symptoms of Hemileia vastatrix infection are well described (Ferreira and Boley, 1991; Arneson, 2005).
Masses of orange urediniospores appear on the undersurface of leaves with spots on the upper leaf surface.
The fungus sporulates through the stomata rather than breaking through the epidermis as most rusts do, so it does not form the pustules typical of many rusts. The powdery lesions on the undersides of the leaves can be orange-yellow to red-orange in color, and there is considerable variation from one region to another.
In old lesions, often a white cottony growth can be found, caused by the hyperparasite Lecanicillium lecanii .
Infections occur on the coffee leaves. The first observable symptoms are small, pale yellow spots on the upper surfaces of the leaves. The spots continue to increase in diameter.
While the lesions can develop anywhere on the leaf, they tend to be concentrated around the margins, where dew and rain droplets collect. The centers of the spots eventually dry and turn brown, while the margins of the lesions continue to expand and produce urediniospores. Early in the season, the first lesions usually appear on the lowermost leaves, and the infection slowly progresses upward in the tree. The infected leaves drop prematurely, leaving long expanses of twigs devoid of leaves.
Significant reduction in photosynthetic rate can radically affect plant functions such as floral initiation and root and shoot growth. This can be followed by death of branches or even of the whole plant. Thus, yield loss is usually indirectly related to the severity of the disease. This reduced photosynthetic capacity and the heavy carbohydrate sink created by fruits limits the amount the growth of woody tissue that gives rise to the next season"s crop. Therefore, the following season"s crop is reduced.
All Coffea (coffee) genotypes are susceptible to H. vastatrix to some degree, though cultivars such as Timor and Icatu exhibit a high resistance.