First Report of Powdery Mildew Caused by Golovinomyces cichoracearum on Coreopsis leavenworthii

Coreopsis leavenworthii Torr. & Gary, commonly referred to as Leavenworth’s tickseed, is a native wildflower species distributed throughout Florida. The plant is grown commercially primarily for seed. In May 2005, powdery mildew was observed on greenhouse-grown C. leavenworthii. Abundant conidiophores with conidial chains covered leaves and stems giving the white powdery appearance typical for powdery mildew (Fig. 1). Infection was severe and resulted in the death of some plants. Conidia were hyaline, primarily ellipsoid-ovoid, averaged 33 by 18 μm, and lacked fibrosin bodies (Fig. 2). Appressoria were nipple-shaped. No ascomata were observed. Based on morphological characteristics, the pathogen was identified as Golovinomyces sp. (1). In order to determine the species of the pathogen, the ribosomal internal transcribed spacers 1 and 2, and the 5.8s rRNA gene were sequenced from two isolates obtained from different greenhouses and compared to sequences in the National Center for Biotechnology Information (NCBI) database. The sequences obtained from the two isolates were identical to each other (Accession No. DQ871605) and to six sequences from G. cichoracearum from various hosts in the Asteraceae. G. cichoracearum has been reported to infect several Coreopsis spp. in the USA, Canada, Europe, Japan, and New Zealand (2,3,4), but this is the first report of G. cichoracearum infecting C. leavenworthii and the first report of it infecting any Coreopsis spp. in Florida.