X. Xu, and
Y. Feng, Key Laboratory of Plant-Microbe Interaction, Department of Life Science, Shangqiu Normal University, Shangqiu 476000, China; and
C. Li, Key Laboratory of Plant-Microbe Interaction, Department of Life Science, Shangqiu Normal University, Shangqiu 476000, China, and Key Laboratory of Plant Genetics and Molecular Breeding, Department of Life Science, Zhoukou Normal University, Zhoukou 466001, China
Sonchus asper is an exotic annual herb belonging to the Asteraceae family. Crude extracts of S. asper leaves have antiphlogistic and antibacterial properties. In May 2011, severe infection of powdery mildew was observed on S. asper in Henan Province, a central area of China. Symptoms began as small, nearly circular white spots that later enlarged and coalesced. As the disease progressed, white mycelia covered the entire plant, including the inflorescence. The voucher specimens are kept at the Key Laboratory of Plant-Microbe Interaction, Shangqiu Normal University. Conidiophores were erect, 108 to 220 × 10 to 12 μm, and composed of a cylindrical foot cell followed by two to three short cells. Nipple-shaped appressoria were formed on ectophytic mycelia. Conidia were hyaline and cylindrical, without distinct fibrosin bodies, and ranging from 29 to 42 × 19 to 24 μm. Long, unbranched germ tubes were formed from the ends of the conidia. These morphological characteristics suggested that the powdery mildew fungus is the anamorph of Golovinomyces cichoracearum (1,2). Chasmothecia were not observed in the collected samples. To confirm the identification, the internal transcribed spacer (ITS) region of the rDNA was amplified with ITS1 and ITS4 primers (4) and sequenced. The ITS sequence obtained was assigned Accession No. JQ010848 in GenBank, and had 99% similarity to two ITS sequences from different G. cichoracearum accessions (HM449077 and AY739111). The ITS sequence analysis further verified that the causal agent of the powdery mildew on S. asper was G. cichoracearum. Pathogenicity was confirmed by inoculating five healthy plants of S. asper with a conidial suspension (105 conidia/ml) from the infected plants, with five noninoculated plants serving as control. Inoculated plants developed the original powdery mildew symptoms after 10 days, whereas control plants remained healthy. G. cichoracearum (synonym Erysiphe cichoracearum) is a cosmopolitan powdery mildew fungus, parasitic on numerous plant species in the Asteraceae family. It was reported to be infecting S. asper in Bulgaria (3). To our knowledge, this is the first report of G. cichoracearum infections on S. asper in China. S. asper is one of the most important Chinese herbal medicines. The sudden appearance of powdery mildew caused by G. cichoracearum on this plant could result in substantial production loss of S. asper unless fungicide applications are employed.
References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) R. T. A. Cook and U. Braun. Mycol. Res. 113:616, 2009. (3) G. Negrean and C. M. Denchev. Mycologia Balcanica, 2004, 1:63. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.