Edmunds J I, Miller D J, Stuteville D L
Pioneer Hi-Bred International, Inc., W8131 State Hwy 60, Arlington, WI 53911.
Department of Plant Pathology, Throckmorton Hall, Kansas State University, Manhattan 66506.
Plant Dis. 1998 Jul;82(7):832. doi: 10.1094/PDIS.1998.82.7.832A.
In July 1996 and August 1997, dense amphigenous mycelia bearing Oidium conidia infected the lower stems and leaves of alfalfa (Medicago sativa L.) plants in research nurseries in south-central Wisconsin, causing the defoliation of the affected leaves. In the greenhouse, the disease spread rapidly from transplanted field plants to adjacent flats of alfalfa seedlings. A teleomorphic state of the fungus was not observed. Morphological characteristics of the oidia were similar to those of Erysiphe pisi (1). Conidia were ellipsoid-cylindrical and closely resembled those shown from Pisum sativum L. (2). Dry (2) conidia averaged 14.6 × 41.4 μm (range: 13.0 to 15.6 × 39 to 46.8 μm). Conidia shaken from mildewed alfalfa plants onto plants of garden pea (Pisum sativum) cv. Early Perfection and red clover (Trifolium pratense L.) cv. Lakeland infected both hosts. However, powdery mildew developed sooner and was much more severe in pea than in red clover. Noninoculated control plants remained free of powdery mildew. This is the first report of powdery mildew in alfalfa in Wisconsin fields. In extensive pathogenicity studies in greenhouses in Wisconsin (2), conidia from at least one isolate from red clover infected Medicago falcata L. and M. sativa L. var. glutinosa Urban, but not alfalfa cv. Vernal. References: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980. (2) J. R. Stavely and E. W. Hanson. Phytopathology 56:309, 1966.
1996年7月和1997年8月，威斯康星州中南部研究苗圃中，带有粉孢分生孢子的密集叶生菌丝体感染了紫花苜蓿（Medicago sativa L.）植株的下部茎和叶，导致受影响叶片落叶。在温室中，病害从移栽的田间植株迅速传播到相邻的紫花苜蓿幼苗苗床。未观察到该真菌的有性态。粉孢子的形态特征与豌豆白粉菌（Erysiphe pisi）相似（1）。分生孢子为椭圆形至圆柱形，与豌豆（Pisum sativum L.）上的分生孢子极为相似（2）。干燥（2）分生孢子平均大小为14.6×41.4μm（范围：13.0至15.6×39至46.8μm）。从染病紫花苜蓿植株上抖落的分生孢子接种到豌豆（Pisum sativum）品种Early Perfection和红三叶（Trifolium pratense L.）品种Lakeland植株上，两种寄主均被感染。然而，豌豆上白粉病发病更早且比红三叶严重得多。未接种的对照植株未感染白粉病。这是威斯康星州田间紫花苜蓿白粉病的首次报道。在威斯康星州温室进行的广泛致病性研究中（2），来自红三叶至少一个分离株的分生孢子感染了黄花苜蓿（Medicago falcata L.）和紫花苜蓿（Medicago sativa L.）变种glutinosa Urban，但未感染紫花苜蓿品种Vernal。参考文献：（1）H. J. Boesewinkel. Bot. Rev. 46:167, 1980.（2）J. R. Stavely和E. W. Hanson. Phytopathology 56:309, 1966.
