Toxin Production By Isolates of Ceratocystis ulmi

Cuttings of two elm species, Ulmus pumila and U. hollandica \u27Belgica\u27, were used to assay toxin production by nine isolates of Ceratocystis ulmi representing collections from Asia, Europe, and North America. After 17 days of fungus growth in liquid culture, filtrates were collected and bioassayed by visual symptom expression over an approximate 10-hour period. A variation in toxin production was evident. One of the isolates from the Netherlands produced a low toxin titer. The other isolate from the Netherlands and the one from Asia produced highly significant symptoms on the resistant Siberian elm shoots and an Iowa isolate\u27s filtrate reaction was significant on this elm species