Occurrence of powdery mildew caused by Golovinomyces orontii on Lactuca sativa var. ramosa (lettuce) in China

Lettuce (Lactuca sativa L. var. ramosa Hort.) is one of the most popular leafy vegetables in China, which contains abundant vitamin C and moderate iron. In August and October 2017, two different lettuce cultivars, heading type with green leaves (iceberg lettuce) and looseleaf type with red leaves, infected by powdery mildews were collected in Jilin Agricultural University (43.81°N; 125.41°E), Changchun, China. The disease incidence was approximately 60-70%. This disease initially formed small, amphigenous and indistinct white colonies, finally covering whole leaf surfaces, which caused leaf yellowing and withering and severely influences on yield and quality. Conidia were formed in short chains (catenescent) without fibrosin bodies. Chasmothecia were not observed on the collected samples. Based on the morphological characteristics of the fungus on lettuces, internal transcribed spacer (ITS) and 28S rDNA sequences and pathogenicity, the pathogen was identified as Golovinomyces orontii. It is the first report of G. orontii infections on lettuce in China. The information may be helpful for disease monitoring to lettuce growers and breeders.