Mottle Leaf, a Virus Disease of Cherries '

A graft-transmissible disease of cherry trees herein referred to as mottle leaf is known to have existed in different sections of the Pacific Northwest for the last several years. In 1917 D. F. Fisher photographed ^ cherry leaf specimens collected near Monitor, Wash., which exhibited symptoms similar to mottle leaf. Zeller (8) * reported having observed the disease in 1920 on Napoleon (Royal Ann) cherry trees growing in Oregon. Leaf specimens exhibiting typical mottle leaf symptoms were observed in the collection of Dr. C. W. Hungerford, University of Idaho, from Bing cherry trees growing in the Lewiston (Idaho) district, and collected September 1, 1922. Cherry leaves collected by B. F. Dana near Kennewick, Wash., during the summer of 1924 and deposited in the collections of the Department of Plant Pathology, State College of Washington, have also been examined, and these apparently represent typical mottle leaf. Several orchardists near Wenatchee, Wash., have given interesting accounts of the early appearance of peculiar malformed leaves on their cherry trees, and it is considered probable that as early as 1910 a few cherry trees growing in the north central part of Washington were affected by mottle leaf. At the present time sweet cherry trees growing in Washington, Oregon, Idaho, and British Columbia have been found to be affected by the disorder. In California, one Waterhouse cherry tree was observed that exhibited symptoms considered typical of mottle leaf. Preliminary investigations reported in 1935 by McLarty^ and by Reeves (6) demonstrated that mottle leaf was a graft-transmissible disease of sweet cherries. Previously, the disorder had been vaguely attributed to various factors such as unfavorable soil conditions, severe spring frosts, rosette or little leaf, poor root systems, chlorosis, and crown gall. Subsequent observations and transmission tests have definitely indicated that the disease is of virus origin and also have revealed that variations of symptom expression occur on different varieties of both sweet and sour cherries. Mottle leaf has been observed occurring naturally under field conditions on the sweet cherry (Prunus avium L.) and the wild cherry (P. emarginata (Dougl.) Walp.), but it has been transmitted to other species of Prunus, The