First Report of Chaetomella raphigera Causing Leaf Spot on Rosa chinensis in China
Authors: Zhang M. , Li J. J. , Wu H. Y. , Geng Y. H. , Han W. L. 
Published: March 2014

China rose, Rosa chinensis Jacq., is extensively cultivated as an ornamental plant in China (1). During the course of a disease survey of China rose in Henan Province, a leaf spot was observed on about 20 China roses, cultivated in a garden in Zhengzhou, Henan Province, in early October 2012. The early symptom appeared as small round, pale brown lesions on the leaves. Lesions expanded into 5 to 15-mm-diameter spots that were near round or irregular and brown. Both sporodochial and pycnidial conidiomata developed in necrotic areas of diseased leaves when placed in moist chambers. Pycnidia were elongated, reniform, with a single raphe over the top, pale to dark brown, and 260 to 350 × 150 to 210 μm. Sporodochia were pale luteous and 100 to 280 × 80 to 180 μm. Setae, conidiophores, conidiogenous cells, and conidia were the same between two types of conidioma. Setae were pale to dark brown, 0 to 2 septate, straight with rounded end, clavate to curved at apex, and 22 to 60 × 2 to 5 μm. Conidiophores were up to 120 × 1 to 2 μm, filiform, cylindric, and branched. Conidiogenous cells were enteroblastic, collar and channel minute. Conidia were nonseptate, hyaline, ellipsoid or cymbiform, smooth, guttulate, and 4 to 6.5 × 1.5 to 2.5 μm. Two pure cultures (zm12276-1 and zm12276-2) were obtained by picking spores from independent conidiomata on one leaf and then subsequently grown on potato dextrose agar (PDA), producing the same two kinds of conidiomata. The characteristics of conidial size and distinctly different conidiomata with setae are diagnostic of Chaetomella raphigera M.E. Swift (3,4). The identity of our fungus (zm12276-1) was confirmed to be C. raphigera by DNA sequencing of the ITS1-5.8S-ITS2 region. The DNA sequence was 99% identical to those of the other C. raphigera isolates (AY487076 and AY487085) (2). The ITS sequence from zm12276-1 was deposited in GenBank (KF483474). Pathogenicity was tested by inoculating 10 leaves of R. chinensis with mycelia plug from colony of zm12276-1 (0.5 cm in diameter). An equal number of fresh leaves inoculated with the plugs of non-colonized PDA medium served as the control. All leaves were incubated in clear plastic box with a dish of sterile distilled water at 25°C under ambient light. After 7 days, 90% of the inoculated leaves showed symptoms identical to those observed on R. chinensis leaves affected in the field. From each of the symptomatic leaves, C. raphigera was recovered, whereas controls remained symptom-free and no fungus was isolated from the control leaves. Koch's postulates were repeated three times with the same results using the pure culture of zm12276-1. C. raphigera has been previously reported on Rosa sp. in the United States (4). To our knowledge, this is the first report of C. raphigera infecting R. chinensis in China. The disease cycle and the control strategies in the regions are being further studied.

References: (1) C. Z. Gu and K. R. Robertson. Pages 339-381 in: Flora of China, vol. 9. Science Press, Beijing and Missouri Botanical Garden, 2003. (2) A. Y. Rossman et al. Mycol. Progr. 3:275, 2004. (3) B. C. Sutton. The Coelomycetes. CAB International Publishing, New York, 1980. (4) M. E. Swift. Mycologia 22:165, 1930.