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Viability of Ceratocystis ulmi in Young Seedlings of American Elm and the Effects of Extracts from their Tissues on Conidial Germination. Lawrence R. Schreiber, Research Plant Pathologist, Crops Research Division, ARS, USDA, P.O. Box 365, Delaware, Ohio 43015. Phytopathology 60:31-35. Accepted for publication 6 July 1969. DOI: 10.1094/Phyto-60-31.

Roots of 1- to 5-month-old American elm seedlings were inoculated with a spore suspension of Ceratocystis ulmi, and periodic isolations were made for 22 weeks. The fungus was recovered initially from 60 to 80% of the plants, but percentage recovery decreased in succeeding isolations. After 16 to 22 weeks, the fungus could not be recovered. Water extracts from leaves and stems of 1- to 5-month-old plants were fungistatic. Leaf extracts were fungicidal when their concentration was increased. No inhibition occurred with extracts from stems of plants 6 to 7 months old, stem and leaf extracts from plants 10 to 12 months old, or any root extracts. The inhibitor was dialyzable and heat stable at 98 C for 30 min. Survival of C. ulmi was also studied in rooted sprouts from inoculated 3- to 4-year-old American elms. The fungus was isolated from 95% of the sprouts immediately after sampling, from 62% 4 months later, and from 43% after 10 months. The more rapid loss in viability of the fungus appears to be associated with seedlings rather than with juvenile tissue in general. Unlike those from 1- to 5-month-old seedlings, extracts from sprout leaves and stems did not inhibit conidial germination. Foliar wilt and dieback did not occur in inoculated seedlings or sprouts.