Interactions between ethylene-bis-nitrourethane and Gibberellic acid during the germination of lettuce seed

Exposing lettuce seed (variety Grand Rapids) to temperatures from 30°-42° C inhibits subsequent germination at 25° C. This inhibition can be overcome by the addition of gibberellic acid (GA) either during or after the heat treatment. Ethylene-bis-nitrourethane (EBNU) and ethylene dinitramine (EDNA), although without effect when applied alone, have been shown to increase the activity of GA when present in admixture during the heat treatment. The compounds act synergistically only when the seeds are kept at 30° and 35° C for 72 hours or longer.EBNU and EDNA do not increase the effectiveness of GA in breaking natural or heat induced dormancy in lettuce seeds.