© 2003 Plant Management Network.
First Report of Powdery Mildew of Convolvulus arvensis (Field Bindweed) Caused by Erysiphe convolvuli var. convolvuli in North America
Dean A. Glawe and Gwenyth E. Windom, Puyallup Research and Extension Center, Washington State University, 7612 Pioneer Way East, Puyallup 98371-4998; Gary G. Grove and Jennifer S. Falacy, Irrigated Agriculture Research and Extension Center, Washington State University, Prosser 99350-8694
Corresponding author: Dean A. Glawe. firstname.lastname@example.org
Glawe, D. A., Windom, G. E., Grove, G. G., and Falacy, J. S. 2003. First report of powdery mildew of Convolvulus arvensis (field bindweed) caused by Erysiphe convolvuli var. convolvuli in North America. Online. Plant Health Progress doi:10.1094/PHP-2003-1021-01-HN.
Field bindweed (Convolvulus arvensis L.) is widespread in the Pacific Northwest where it is considered a noxious weed (4). Farr et al. (3) do not include any powdery mildews on this host species in their list of fungi on plants in the United States. Two powdery mildew fungi occur on this plant. Erysiphe convolvuli DC var. convolvuli is reported on this host in Europe, Asia, North Africa, and South America (1,2). Leveillula taurica (Lév.) Arnaud also is reported on this host (1), but not in the United States (3). Features used to distinguish these fungi include conidial shape and size, number of ascospores per ascus, and ascospore size (1,2). Braun (1,2) further differentiated three varieties of E. convolvuli. Erysiphe convolvuli var. convolvuli and E. convolvuli var. calystegiae U. Braun both exhibit unbranched, hyphoid ascocarp appendages but the former occurs on Convolvulus and exhibits 3 to 4 ascospores per ascus, and the latter occurs on Calystegia and exhibits 5 to 6 ascospores per ascus. Erysiphe convolvuli var. dichotoma Zheng and Chen is distinguished from both other varieties by branched ascocarp appendages.
During 2002, collections of a powdery mildew fungus attacking C. arvensis were made from Pierce, Spokane, Whitman, and Yakima counties, WA. Powdery mildew also has been found on this host in Oregon (Melodie Putnam, personal communication). Signs of the disease include white patches of dense mycelium on infected leaves. The fungus formed superficial hyphae with lobed appressoria (Fig. 1); ascocarps (Fig. 2) (76-) 79-110 (-120) µm, with mycelioid appendages, short-stipitate asci (Fig. 3) (62.5-) 63-73.5 (-82) × (34.5-) 39-43 (-50) µm, each with 3 to 6 ellipsoid to subpyriform ascospores (15.5-) 18.5-27 (-28) × (8-) 8.5-13 (-16) µm; conidiophores exhibited cylindric foot cells; conidia (Fig. 4) were cylindrical to ellipsoid-cylindric, with finely striate to reticulate surfaces, (18.5-) 22-33 (-36.5) × (7-) 9-12 (-13.5) µm. A voucher specimen collected near Mabton, Yakima County, WA was deposited with the Mycological Herbarium in the Department of Plant Pathology, Washington State University.
Based on morphological features we determined the fungus to be E. convolvuli. The host genus and the number of ascospores per ascus clearly fit Braun’s (1,2) conception of E. convolvuli var. convoluli. He (1,2) noted that in this variety asci usually are 3-to-4-spored, but occasionally are 2- or 6-spored. In material that we examined some immature ascospores appeared abortive, suggesting that ascospore number can vary if some spores fail to develop to maturity.
It is uncertain whether powdery mildew caused significant damage to field bindweed. By late summer, plants infected with the powdery mildew fungus showed dramatic signs of the disease. Given the economic significance of this weed, further work would appear warranted to determine whether the seemingly poor condition of the plants at the time of collecting was caused by the powdery mildew infection, natural senescence, or some other factor.
1. Braun, U. 1987. A monograph of the Erysiphales (powdery mildews). Beih. Nova Hedwigia 89:1-700.
2. Braun, U. 1995. The Powdery Mildews of Europe. Gustav Fischer Verlag, Jena.
3. Farr, D. F., Bills, G. F., Chamuris, G. P., and Rossman, A. Y. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.
4. William, R. D., Ball, D., Miller, T. L., Parker, R., Yenish, J. P., Miller, T. W., Morishita, D. W., and Hutchinson, P. J. S. 2002. Pacific Northwest Weed Management Handbook. Oregon State University, Corvallis.