Disease Note.

Occurrence of Sphaerotheca fuliginea Race 3 on Cucurbits in Israel. R. Cohen, Department of Vegetable Crops, ARO, Newe Ya'ar Research Center, PO Box 90000. N. Katzir, S. Schreiber, and R. Greenberg, Department of Vegetable Crops, ARO, Newe Ya'ar Research Center, PO Box 90000, Haifa 31-900 Israel; and O. Yarden, Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76100, Israel. Plant Dis. 80:344. Accepted for publication 22 January 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0344D.

Powdery mildew caused by Sphaerotheca fuliginea is a devastating disease of cucurbits with a wide geographic distribution. Three races of S. fuliginea have been differentiated (2), but in Israel only races 1 and 2 have been reported (1). Race 3 of S. fuliginea was first observed in Israel in autumn 1988 on the new melon (Cucumis melo L.) hybrid Petra, which was found to be resistant to races 1 and 2 under laboratory and greenhouse conditions. The response of Petra to powdery mildew differed in two field experiments. In the first, conducted in October 1988 at Gilgal in the Jordan Valley, plants of Petra were heavily infected, whereas in the other experiment, conducted 1 month later at 'En Tamar in the Arava Valley, the plants were free of the disease. In both experiments plants of melon hybrid Galia, resistant to race 1 of S. fuliginea but susceptible to race 2, were severely diseased. To confirm this finding and for further investigation of the distribution of this race in Israel, 23 cucurbit powdery mildew isolates were collected during 1994 to 1995 from various regions in Israel. Detached leaves of the melon cvs. Ananas Yoqne'am (susceptible), PMR 45 and Noy Yizre'el (resistant to race 1 and susceptible to race 2), and PMR 6 and Dulce (resistant to races 1 and 2) (2), were placed on benzimidazole-amended water agar and used as differentials for race identification. PMR45 and PMR6 are the cultivars suggested by Thomas (2) for race identification. Isolates that were capable of infecting PMR 6 and Dulce were identified as race 3. Of the 23 isolates, seven were identified as race 1, 11 as race 2, and five as race 3. The five isolates of race 3 were found on Oriental pickling melon at 'En Tamar, in spring 1994, on a Galia-type breeding line, Misgav Western Galilee, in autumn on cv. Revigal, Yair experiment station, central Arava Valley, in winter 1995, on cv. Revigal at Hammat Gader, Golan Heights, in winter and on a Galia-type breeding line, at Newe Ya'ar, Yizre'el Valley, in autumn 1995.