Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Sawadaea powdery mildew of box elder (Acer negundo) in Wisconsin.

Abstract

Box elder (Acer negundo) leaves affected by powdery mildew were collected from a single tree in an urban yard in the autumn of 2006 in Madison, Wisconsin, USA. Leaf blades were pale green-to-tan and necrotic. Very sparse white mycelium was observed on the lower surface of the leaves using a dissecting microscope. Chasmothecia were present singly or in groups of a few on the lower surface of the leaves. Based on morphological analysis, the pathogen was identified as belonging to the genus Sawadaea. However, DNA was extracted from the chasmothecia and analysis of a 542-bp sequence of nuclear rDNA ITS (GenBank Accession No. EF122238) revealed a 100% match with the respective sequence obtained from GenBank for Sawadaea bicornis (Accession No. AB193380).