280 Botryosphaeria dothidea Causes Premature Breaking of Endodormancy and Reduces Cold Hardiness in Cercis canadensis

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  • 1 The Morton Arboretum, 4100 Illinois Route 53, Lisle, IL 60532

Near-lethal abiotic stresses, e.g., low or high temperatures, chemicals, etc., can break endodormancy prematurely and reduce cold hardiness in woody plants. It is not well-ducumented whether biotic stresses can cause the same effect. Botryosphaeria dothidea causes canker in redbud (Cercis canadensis) and many other woody plants and is one of the most limiting factors growing redbud in the landscape. Two-year-old seedlings were planted in a nursery in May 1998 at The Morton Arboretum. Trees were inoculated (n = 10/treatment) with the fungus in Sept. 1998 using the stem slit method (a slit was cut about 5 cm above the base of the trunk and the wound was covered with parafilm after treatment). The treatments were T1 = control (PDA, Potato Dextrose Agar),T2 = 1-mm mycelium plug, T3 = low spore suspension (25 μL), T4 = high spore suspension (25 μL). Stem cold hardiness was evaluated by artificial freezing tests in Nov. 1998. The mean LT50 (the temperature at which 50% of the tissues is killed) from ion leakage were T1 (Control) = -29.3 °C, T2 (mycelium): -24.05 °C, T3 (low spore) = -18.75 °C, and T4 (high) = -16.4 °C. T3 and T4, the low- and high-spore inoculation, significantly reduced cold hardiness in redbud stem tissues. The LST (lowest survival temperature) based on visual observation of the samples after 7 days indicated all Botryosphaeria dothidea-treated plants had lower cold hardiness compared to control. Endodormancy was broken in B. dothidea-treated plants after placing plants under 16 h of light and 23 /18 °C day/night temperature for 1 month after the treatment. The highest percent budbrealk was for T4 (high spore), followed by T3 (Low Spore) and T2 (Mycelium).

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