Authors
A. Garibaldi,
D. Bertetti, and
M. L. Gullino, Centre of Competence for the Innovation in the Agro-Environmental Sector (AGROINNOVA), University of Torino, Via Leonardo da Vinci, 44, 10095 Grugliasco, Italy
Spider flower (Cleome hassleriana L. [synonym = C. spinosa]) is used as a tall border in parks and gardens worldwide. During July 2008, severe outbreaks of a powdery mildew were observed in a public park in Torino (northern Italy). Leaves were covered with dense, white hyphae and conidia, especially on the adaxial surface. Hyphae were also present on petioles and fruits, but not on petals and stems. As the disease progressed, infected leaves turned chlorotic, curled, and wilted. Conidia were hyaline, cylindrical, single, and measured 31.1 to 48.2 × 12.9 to 17.6 μm (average 37.1 × 15.6 μm). Germ tubes terminating in a moderately lobed appressorium were produced terminally. The cylindrical foot cells of the erect condiophores were 19.2 to 27.8 × 6.5 to 8.6 μm (average 23.3 × 7.7 μm). Fibrosin bodies were absent. Chasmothecia were observed mostly on the lower surfaces of leaves. At maturity, they were dark amber and spherical with a diameter of 92.9 to 151.0 μm (average 121.4 μm). Each chasmothecium contained six stalked asci (average size 63.7 × 35.9 μm). Each ascus contained four ellipsoid ascospores that measured 17.3 to 26.4 × 10.9 to 15.6 μm (average 23.3 × 12.8 μm). The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced (1). The 602-bp sequence was deposited in GenBank under the Accession No. GQ149478 and was 99% similar to that of Erysiphe cruciferarum (Accession No. EU140958). As proof of pathogenicity, diseased leaves of C. hassleriana were pressed against leaves of three healthy 4-month-old potted plants of the same species for 10 min. Three noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a greenhouse at 22 to 25°C in isolation. After 11 days, typical powdery mildew colonies developed on inoculated plants. Noninoculated plants did not develop symptoms. The pathogenicity test was repeated once. Powdery mildew on C. hassleriana caused by E. cruciferarum was reported in Italy (2) but the pathogen was not characterized. Herbarium specimens are deposited at AGROINNOVA Collection, University of Torino, Italy.
References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena, Germany, 1995.
