Smoke chemicals and coumarin promote the germination of the parasitic weed Orobanche aegyptiaca

The stimulation of the germination of Orobanche aegyptiaca by smoke derived from burning cellulose is described. The smoke, dissolved in distilled water, was as effective in stimulating germination as the strigol analogue GR24. High concentrations of the smoke dissolved in water were inhibitory. The putative active compound present in smoke contains an unsaturated lactone ring, as does the strigol analogue GR24 and strigol itself. Coumarin, an unsaturated lactone, generally regarded as a germination inhibitor, is also able to stimulate germination, although radicle elongation was inhibited. When exposure was short and the concentration 10(-5)M, a high rate of germination and radicles appearing to be normal were obtained. Derivatives of coumarin were less active than the parent compound. The developing radicle of the Orobanche seed, treated with GR24 or smoke water, contains starch grains along its entire length, which may be an indication of its ability to form an haustorium. Phenolics are also present along the radicle, but tend to concentrate at the radicle apex in germinating seeds whose elongation is inhibited.