Regulation of Witchweed (Striga asiatica) Conditioning and Germination by dl-Strigol

Abstract

The conditioning and germination processes of witchweed [Striga asiatica (L.) Kuntze] seeds were regulated by synthetic dl-strigol (ST) or natural stimulants (STM) present in a corn (Zea mays L.) root-exudate solution. Seeds conditioned in water for 7 and 14 days required 10−10 and 10−12M ST, respectively, to induce maximum germination (ca. 80%). Surprisingly, conditioning seeds in ST or STM had an adverse effect on the responsiveness of the seeds to the same compounds after conditioning. Compared to seeds conditioned in water, these ST- or STM-conditioned seeds required not only higher concentrations of ST or STM to induce maximum germination, but also longer immersion time to become conditioned. ST or STM inhibits conditioning and thus the regulation of germination by ST or STM depends mainly on the stage of conditioning of seeds when they are exposed to ST or STM. ST or STM stimulates germination only after a pre-germination threshold is reached during conditioning. Exposure of seeds to ST or STM before this critical level is reached apparently inhibits conditioning.