First report in Korea of powdery mildew of Matricaria chamomilla caused by Golovinomyces cichoracearum

German chamomile (Matricaria chamomilla) is an exotic medicinal herb with many cultivars. Since November 2006, severe infections of a powdery mildew have been found on this plant in herb gardens in Taean and Pyeongchang, Korea. Initial symptoms were the spotted growth of a white, superficial mycelium. As the disease progressed, white mycelial growth completely covered the whole plant including the inflorescence (Fig. 1a). Chasmothecia were formed mainly on stems and lower surface of the leaves (Fig. 1b). The voucher specimens are kept at Korea University (KUS-F14027, 22492, 22504).

Conidiophores were 90−165(−220) µm long and producing 2−6 immature conidia in chains with sinuate edge-line (Fig. 2a). Conidia were ellipsoid or doliform, 30−42 x 16−24 µm,and without distinct fibrosin bodies (Fig. 2b).Chasmothecia were dark brown, spherical, 95−135 µm in diameter and contained 10−18 asci (Fig. 2c). Appendages were mycelioid, 12−28 per chasmothecium, 0.5−2.5 times as long as the chasmothecial diameter, 1−5-septate.Asciwere shortly stalked, 50−75 x 32−45 µm and two-spored. Ascospores were ellipsoid-ovoid and 22−28 x 15−18 µm. Based on these characteristics, this fungus was identified asGolovinomyces cichoracearum (Braun, 1987). To confirm the identification, the ITS rDNA was amplified and sequenced, and the sequence of the region was deposited in GenBank (Accession No. GU048822). Comparison with the sequences available in the GenBank database revealed that the ITS sequence shares 100% similarity with the sequence of Golovinomyces cichoracearum on Achillea millefolium (AB077685). Therefore, the sequence analysis verified the pathogen to be G. cichoracearum.

Two powdery mildew species have been reported to infect M. chamomilla (Braun, 1987). Podosphaera fusca (syn. Sphaerotheca fusca, S. fuliginea) has been recorded in Canada, Egypt, Germany, Switzerland, USSR (Farr & Rossman, 2009) and recently in Japan (Tanda, 1998). Golovinomyces cichoracearum (syn. Erysiphe cichoracearum) is a rather common powdery mildew species infecting German chamomile in Europe (Farr & Rossman, 2009) and Japan (Tanda, 1998). To our knowledge, this is the first report of G. cichoracearum infections of German chamomile in Korea. As German chamomile is becoming widely cultivated in commercial farms for industrial purpose in Korea, powdery mildew infections pose a serious threat to safe production of this herb.