Ethylene, 2-Chloroethylphosphonic Acid, and Witchweed Germination

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Abstract
In laboratory studies, ethylene and an ethylene-releasing agent, 2-chloroethylphosphonic acid (hereinafter referred to as CEPA), stimulated germination of aged, pretreated but still dormant witchweed (Striga lutea Lour.) seed. Ethylene gas at 10−1 μl/L produced maximal (89 to 98%) seed germination. Witchweed seed also germinated when incubated directly in Eustis loamy sand treated with CEPA. A half-maximal response was obtained with 10 mg of CEPA per kg of soil. Vapors produced by apple (Pyrus malus L. Mill) slices, by an alkaline solution of CEPA, and by soil treated with CEPA also stimulated germination. Vapors from soil contained an inhibitor of the ethylene-induced seed germination. Exposure of the soil vapors to 20% potassium hydroxide removed the inhibitor. Germination studies with 10% carbon dioxide, carbon dioxide-free air, and ethylene indicated that carbon dioxide inhibited the ethylene-induced germination of witchweed seed.