Factors affecting the activity of GR7 in stimulating germination of Striga hermonthica (Del.) Benth.

Experiments with the alkaline heavy clays of the Sudan Gezira showed that when the strigol analogue GR7 was applied to moist soil prior to subjecting Striga hermonthica seeds to moist conditions (‘conditioning’) for 7–14 days, there was no significant increase in germination. Conditioning of seeds in soils treated with GR7 had an adverse effect on the responsiveness of seeds when GR7 was added again after conditioning. Under ideal conditions, when GR7 was applied to conditioned seeds in moist soil, up to 75% germination could be induced by 2.0 kg/ha incorporated to 2–3 cm depth. Residual activity of GR7 persisted in air-dry soil, but at 50% moisture there was complete loss within 1 day. However, when conditioned seeds were put into the soil immediately after GR7 application its activity increased with increasing soil moisture.