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First Report of Powdery Mildew on Asclepias curassavica in Italy

Asclepias curassavica is grown in Italy for landscape use in parks and gardens. In 2001, severe outbreaks of a previously unknown powdery mildew were observed in commercial farms located in Albenga (northern Italy). Powdery mildew developed on the lower surface of leaves of container grown plants. The upper surface of infected leaves turned reddish and sometimes yellow. Infected tissues wilted, and leaves dropped prematurely. Conidiophores emerged through the stomata. Conidia were hyaline and had variable shape, mitrate when located at the apex of the conidiophore, and subcylindric when borne in the middle of a chain. Conidia measured 46 to 74 × 12 to 24 μm. Cleistothecia were not observed. The causal agent was identified as Oidiopsis sp. Pathogenicity was confirmed by gently pressing diseased leaves on leaves of healthy A. curassavica plants. Plants were maintained in a growth chamber at 20 to 24°C after inoculation. After 12 to 14 days, powdery mildew signs developed. Leveillula taurica has been reported as causal agent of powdery mildew on A. carassavica in India and on Asclepias sp. in Morocco (1). Also in our case, L. taurica should be the causal agent, since the genus Leveillula has as anamorph the genus Oidiopsis (2). In Switzerland, Phyllactinia suffulta has been described as incitant of a similar powdery mildew on A. syriaca.

References: (1) G. Bergen. Ann. Epiphyt. Nuove Serie, IV, 1:21, 1938. (2) J. Palti. The Bot. Rev. 54:423, 1988.