Witchweed [Striga asiatica (L.) Kuntze] seeds conditioned for 3 weeks in either water or 0.01% (w/v) sodium hypochlorite (NaOCl) had 83 to 95% germination after being treated with dl-strigol, kinetin, zeatin, or natural stimulants from corn (Zea mays L.) root exudates. None of these compounds, however, induced germination of seeds conditioned in 0.025 or 0.050% (w/v) NaOCl. Seeds conditioned in 0.075, 0.1, or 0.15% (w/v) NaOCl had 8, 56, and 76% germination, respectively, during the first week of conditioning and 10, 100, and 100% germination after 2 weeks of conditioning. Germination in these concentrations of NaOCl was termed “atypical”.

Annual application of AC-94377 at 3.4 kg ha−1 in the field reduced survival of shallowly buried (1.25 cm deep), undisturbed wild mustard seed compared to untreated check seed in two 4-yr-long trials. By the second fall, greater than twofold more untreated check seed survived as did AC-94377-treated seed. Moreover, no AC-94377-treated seed survived beyond year three following treatment in fall alone or fall plus spring in each of 3 yr. In contrast, 25% of untreated check seed survived into the fall of year four. AC-94377 applied in spring alone, fall alone, or both spring and fall for each of 4 yr progressively reduced seed survival. Seed survival expressed as a percent of the initial number of seed buried was best modeled as a negative exponential function of time in years. In the greenhouse, more wild mustard seed on the soil surface established after AC-94377 treatment at 3.4 kg ha−1 when enclosed in large seed packets (5 by 12 cm), like those used in the field, than when in small seed packets (5 by 6.25 cm), whether or not the packets contained soil. When soil was added to either sized seed packet, fewer seed survived compared to seed not in seed packets or seed in packets without soil. Thus, it is likely that the field seed survival study underestimated effectiveness of AC-94377 to reduce wild mustard seed survival.

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.