Dose-response of seeds of the parasitic weeds Striga and Orobanche toward the synthetic germination stimulants GR 24 and Nijmegen 1

Striga and Orobanche seeds germinate in response to a host-derived germinat ion stimulant. Dose-response curves of the synthetic strigolactone analogue s GR 24 and Nijmegen 1 were determined, and their activities were compared to that of the naturally occurring stimulant sorgolactone. Typical sigmoida l curves were obtained. ED50 values for GR 24 were in the order of 10(-9)-1 0(-8) mol/L; for Nijmegen 1 these values were 3 orders of magnitude higher. Both synthetic stimulants are appreciably active at low concentrations and merit investigation as agents for the suicidal germination approach (i.e., treatment of the soil with stimulant in the absence of a host).