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Sudden Wilt of Melons in Southern Israel: Fungal Agents and Relationship with Plant Development

November 1997 , Volume 81 , Number  11
Pages  1,264 - 1,268

S. Pivonia , Arava Research and Development, Sapir Center 86825, Israel ; R. Cohen , Department of Vegetable Crops, Agricultural Research Organization, Newe Ya'ar Research Center, P.O. Box 1021, Ramat Yishay 30095, Israel ; U. Kafkafi , Department of Field Crops, The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Sciences, Rehovot 76100, Israel ; I. S. Ben Ze'ev , Ministry of Agriculture and Rural Development, Plant Protection and Inspection Services, P.O. Box 78, Bet Dagan 50250, Israel ; and J. Katan , Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Sciences, Rehovot 76100, Israel



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Accepted for publication 24 July 1997.
ABSTRACT

Fungi belonging to five genera, Monosporascus sp., Pythium aphanidermatum, Rhizoctonia solani, Olpidium sp., Fusarium solani, and F. proliferatum, were the species most frequently isolated from the root systems of wilted melon. Diseased plants were collected from 24 fields in the northern and central Arava region of southern Israel during the fall seasons of 1994 and 1995. In pathogenicity tests conducted under field conditions, in artificially inoculated microplots, the first wilt symptoms were observed at various stages of fruit maturation. High mortality levels (73 to 97%) were recorded for inoculation combinations in which Monosporascus sp. was involved. Inoculations with the other fungi listed resulted in lower incidences of wilt. The combination of F. solani and P. aphanidermatum resulted in higher mortality than that caused by each pathogen alone. Monosporascus sp. seems to be the primary pathogen, although other fungi could also induce wilt. The dry weight of plants grown in naturally infested soil ceased to accumulate 33 days after transplanting, in contrast to plants grown in methyl bromide-treated soil. At this stage, the first wilt symptoms were observed. Fruit load affected wilt incidence. At the end of the growing season, 98% mortality was recorded for plants having the normal fruit load (2.5 fruits per plant) compared with 75 and 12% for plants that had their fruits thinned to one or zero per plant, respectively.



© 1997 The American Phytopathological Society