Brazil, a new location for powdery mildew on parsley and fenchel plants

Parsley (Petroselinum sativum) is an herbaceous plant used in gastronomy and for extraction of anetol, a phenyl propanol derivative. Fenchel (Foeniculum vulgare) is also an herbaceous plant, used as a condiment and for medicinal purposes. Both plants belong to the family of Apiaceae. Plants collected in the area of the Department of Plant Production (College of Agronomic Sciences - UNESP/FC) showed typical symptoms of powdery mildew on the leaves (Figure 1 A, B and C).

For species identification, mycelium, conidiophores and conidia on the leaves were collected with the aid of a fine needle. The mycelium had superficial hyphae which were hyaline, flexuous, ramose and measured 4.8 µm in diameter. The conidia (38.7 - 49.2 x 12.8 - 15.2 µm) were cylindrical and produced singly (Figure 1D). Conidiophores were straight; foot cells (21-45 x 5 -11 μm) were cylindrical, followed by a longer cell and one or two shorter cells. Germ tubes were produced apically terminating in lobed appressoria (Polygoni type). Fibrosin bodies and chasmothecia were not observed. On the basis of the morphological characteristics, the powdery mildew conformed to Oidium subgenera Pseudoidium (Cook et al., 1997; Braun, 1987). The fungus closely matched the description of Erysiphe heraclei DC., a pathogen previously reported as attacking many species of the Apiaceae family in the American continent (Koiko & Saenz, 1994).

To confirm the pathogenicity, healthy plant parsley leaves were inoculated with conidia from infected plants using an eyelash brush and then kept in a germination chamber (BOD type - Biological Oxygen Demand) at 22°C with a photoperiod of 14 hours. After 7 days, powdery mildew symptoms appeared on the inoculated leaves of the plants, but not on the control plants (non-inoculated). The morphological characteristics of the reisolated pathogen were the same to those observed on the naturally infected plants.

E. heraclei is recorded on many species of the Apiaceae family, such as carrot (Daucus carota), coriander (Coriandrum sativum), celery (Apium graveolens), and zizia (Zizia aurea) in countries such as the United States, France, Iraq, Chile and Italy (Koiko & Saenz, 1994, Koiko & Saenz, 2004). The disease is thought to be introduced through contaminated seeds. This is the first report of powdery mildew on parsley and fenchel plants in Brazil.