Abstract

We examined growth of the Dutch elm disease fungus, Ophiostoma ulmi, on callus derived from a susceptible American elm (Ulmus amencana, selection A), an American elm of intermediate resistance (U. americana, selection 8630), and a resistant Siberian elm (Ulmus pumlia) at 16, 22, and 28°C (61,72, and 83°F) and inoculation concentrations of 15 × 10⁶, 2 × 10⁶, or 0.3 × 10⁶ conidia/ml. After 72 hours, the rates of fungal growth for all treatments were most rapid on calli from the American 8630 selection followed by the American A and Sibenan selections. While fungal growth was more rapid over American 8630, it was more dense on American A. Most rapid fungal growth occurred at 22°C (72°F) and was directly proportional to the inoculum concentration. A significant interaction was noted between callus source and temperature.