BROOMRAPE (OROBANCHE CERNUA) CONTROL BEFORE ATTACHMENT TO HOST THROUGH CHEMICALLY OR BIOLOGICALLY MANIPULATING SEED-GERMINATION

The germination phase of Orobanche cernua Loefl. is a critical period in the life cycle of this parasitic weed. By stimulating the germinati on through chemicals in the absence of hosts or through natural stimul ants by exposing seeds to trap crops the seed bank can be reduced. Sev en series of laboratory and glasshouse experiments were conducted to i nvestigate different methods of testing and to study the effect of sev eral chemicals, root exudates of germinating crop seeds, and their int eractions on O. cernua. Compared to experiments in the incubator bette r results were obtained when germination was tested in the presence of seedlings of host plants under glasshouse conditions. GR24 at 0.1 and 1.0 mg/kg was found most effective in stimulating the germination of the seeds followed by gibberellic acid at 10 and 20 mg/kg. Without add ition of chemicals, trap crops strongly increased germination. Especia lly greengram (Vigna radiata) and sunhemp (Crotalaria juncea) were eff ective. The effects of (concentrations of) chemicals and trap crops in teracted. The positive effect of trap crops was observed even when the re was already a strong stimulation by GR24 at 1.0 mg/kg, but under th ese conditions trap crops were less effective at 0.1 mg/kg GR24. Withi n one host plant species, no differences between cultivars in their ef fect on Orobanche germination could be detected.