First Report of Pepper Powdery Mildew Caused by Leveillula taurica in Oklahoma.

Abstract

During April 1999, bell peppers (Capsicum annuum L.) from a commercial hydroponics greenhouse in Oklahoma County, OK, were severely affected by powdery mildew caused by Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica (Lév.) Salmon). Defoliation levels (50 to 75%) were similar for cvs. Valencia, Lavender Islander, Sweet Chocolate, Aladdin, Purple Beauty, Golden Summer, Chocolate Beauty, Early Sunsation, Fat N'Sassy, Lilac, Sweet Rainbow Mix, and Ivory. Fruit from infected plants were small and unmarketable. Newly infected leaves exhibited light powdery colonies that were visible on abaxial leaf surfaces. On older leaves, abaxial leaf surfaces were completely covered by powdery mildew. Severely infected leaves developed chlorotic and necrotic patches on adaxial leaf surfaces prior to leaf drop. L. taurica was identified by the presence of endophytic mycelia, often-branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 50 measurements of each type, pyriform conidia averaged 67.8 ± 5.3 × 17.9 ± 2.2 μm and cylindrical conidia averaged 62.7 ± 6.2 × 15.7 ± 2.0 μm. Although conidia were slightly longer and narrower than those reported for isolates of L. taurica from pepper in California (2), dimensions were within the range reported for the species (1). The teleomorph of this powdery mildew pathogen was not observed. Peppers were grown from seed on the site. The source of L. taurica for the outbreak and the potential impact of powdery mildew on field production of peppers are unknown. Tomatoes in another hydroponics greenhouse within 100 m were not affected. This is the first report of L. taurica in Oklahoma.