In the present study, strigone (1) was isolated as a natural SL.
Although 1 has the molecular formula same to those of putative
didehydro-orobanchol (strigol) isomers, 1 appeared to be different
from those detected in tobacco, red clover, and tomato by LC–MS/
MS and GC–MS analyses (data not shown). The observation that
highly potent germination stimulation activity of 1 on S. hermonthica
while it is a rather weak stimulant on O. minor implies that different
root parasitic plants may respond to an SL with different
sensitivities. Therefore, it would be expected to find species-specific
SLs (or specific mixtures of SLs) for root parasites with very
narrow host ranges such as O. hederae which parasitizes only ivy