Basic Information | Advanced Information | Diagnostic Information
Passalora fulva primarily causes foliar symptoms. The fungus first appears as an olive-green to gray velvety mycelia on the undersides of older leaves. Within the mycelia are many one- to three-celled conidia. As the disease progresses, pale green lesions coalesce into larger yellowish-brown lesions with poorly defined margins. The leaves then become very chlorotic and curl and begin to prematurely drop. Defoliation continues to younger leaves until the entire plant has died.
In rare cases leaf mold can spread to the stems, petioles, blossoms, and both immature and mature fruit. Symptoms on fruit may begin as brown diffuse lesions at the stem end. As the disease progresses on the fruit, a bronze leathery rot forms with irregular margins.
The clear sign of fungal growth is the olive-green to grey mycelia on the undersides of leaves. One- to three-celled conidia can also be observed under a microscope. Late in the season, sclerotia may be found in the soil or on dead plant debris.
Drawing of leaf mold conidiophores (left) and conidia (right) by A. Chin.
Often Confused With
- Botrytis grey mold: Dark grey mycelia form with visible conidia on foliage and other plant parts that resemble the mycelia of Passalora fulva.
- Late blight: Large yellowish-brown lesions with irregular margins for on the foliage of tomato plants. Coppery-colored lesions on fruit are similar to fruit symptoms caused by P. fulva.
- Powdery mildew: Yellow, irregular lesions form on the upper surfaces of leaves; whitish- grey mycelium develops on the both sides of the leaves. These leaves eventually drop prematurely; fruit rarely develop symptoms.
- Acid Potato Dextrose Agar is a general fungal medium that inhibits the growth of bacteria.
- V8 Agar is used for general isolation of fungi and oomycetes.
Rapid Diagnostic Tests
- Real-Time Polymerase Chain Reaction (PCR) Assay: Yan et al. 2008. J. Applied Microbiology (pdf).