Lisker, N., Department of Seed Research, Institute of Field and Garden Crops, ARO, Bet Dagan, 50250, Israel

One of the causes of poor stands in wheat fields in Israel is a complex interaction of environmental conditions which weaken the seeds and lead to subsequent infection by weakly parasitic seed-borne and/or soil-borne fungi. Wheat seeds of six cultivars (Bet Hashita, Bet Lehem, Dariel, Deganit, Lakhish and Shafir) were treated with the following fungicides: thiram, oxine-copper, CQ 864, CO 1054, TCMTB, a mixture of diniconazole + imazalil, terbuconazole, guazatine or Panoctine Super 301000. Only treatments with thiram, oxine-copper and Panoctine Super did not have a phytotoxic effect on germination and on seedling development. The most prevalent fungi in wheat seeds were Alternaria spp. (>95%). Rhizopus and Aspergillus niger were also isolated. Seed treatments with the above fungicides considerably reduced fungal growth. These fungicides were also used to treat artificially weakened seeds. Seeds were weakened by immersion in hot water (45°C) for different periods of time until the percentage of emerging seedlings decreased to <50% in a natural clay loam soil. When weakened seeds were sown in soils collected at Bet Dagan, Kibbutz Shuval or Kibbutz Nir Oz, thiram, oxine-copper and Panoctine Super significantly increased the percentage seedling emergence. TCMTB, guazatine and diniconazole + imazalil also occasionally significantly increased the percentage seedling emergence. When weakened seeds, either treated or not with fungicides, were sown in sterile sand, seedling emergence was high (≈80%) and no significant differences were observed among treatments. These results indicate that in some natural soils, weakly parasitic fungi may attack weakened seeds and reduce seedling emegence. Fungicides can effectively protect the weakened seeds against weak parasites. © 1990.