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Powdery Mildew of Dill (Anethum graveolens): A New Disease Caused by Erysiphe heraclei Detected in Spain

Powdery mildew was observed for the first time on dill (Anethum graveolens L.) in several commercial greenhouses in Almería (southern Spain) during the spring and summer of 2002. Fungal growth appeared as typical white, dense, persistent powdery mildew colonies on leaves, inflorescences, and stems. Hyphae were 6 to 10 μm wide (mean = 6.88, standard deviation [SD] = 1.22, and n = 50). Conidia were produced singly on unbranched three-celled conidiophores, were cylindrical to ovate, and ranged in length from 26 to 42 μm (mean = 33.7, SD = 4.33, n = 55) and width from 12 to 18 μm (mean = 14.4, SD = 1.46). No fibrosin bodies were observed. Germ tubes were formed from the ends of conidia. Appressoria from mycelia were lobed. Conidiophores were 64 to 154 μm long (mean = 110, SD = 19.86, n = 30) with straight foot cells 24 to 42 μm long (mean = 33.8, SD = 6.17) and 6 to 10 μm wide (mean = 8.4, SD = 1). No cleistothecia were found so an accurate identification of the species was not possible. However, on the basis of morphological characteristics of the imperfect state, this powdery mildew corresponds with Erysiphe heraclei, the powdery mildew of umbelliferous crops (1) that was previously reported on dill from France and Portugal (2) and recently from Turkey (3). In Spain, the disease has been previously reported in other umbelliferous plants, such as carrot and celery (2), which are common crops in southern Spain. When infected with E. heraclei, these plants can serve as potential sources of inoculum.

References: (1) U. Braun. Page 216 in: A Monograph of Erysiphales (Powdery Mildew). Nova Hedwigia. J. Cramer Berlin-Stuttgart, 1987. (2) U. Braun. Pages 116--117 in: The Powdery Mildew (Erysiphales) of Europe. Gustav Fischer-Verlag, Jena, Germany, 1995. (3) E. M. Soylu and S. Soylu. Plant Pathol. 52:423, 2003.