XVI International Botanical Congess

Field-grown Cucurbita texana was used in a study to determine if stress ethylene from damaged leaves promotes changes in sex expression. The timing and magnitude of Diabrotica beetle damage to leaves was mimicked using a hole puncher (15% removed from all leaves). Endogenous ethylene concentrations were measured directly by inserting a needle into the hollow chamber of branch internodes. Over six weeks, ethylene concentrations were measured from the internode adjacent to the growing tip of the main branch and two internodes basal to the tip. Continuously damaged plants had significantly greater ethylene levels than undamaged plants one day after damage (weeks 2 and 3) and two days after damage (weeks 4 and 5). By week 6, no significant differences were evident. Ethylene levels also climbed following natural insect feeding. Damaged plants produced significantly fewer pistillate buds than undamaged plants, indicating that stress ethylene does not induce femaleness. A second messenger suppressing pistillate bud production may be produced when damaged.