Alectrol and orobanchol, germination stimulants for Orobanche minor, from its host red clover

Three seed germination stimulants for a parasitic weed, clover broomrape (Orobanche minor), were isolated from the root exudate of its host, red clover (Trifolium pratense) and structures of the two of the stimulants were determined. One was identified as alectrol and the other was a novel strigol-related compound which was named orobanchol. Orobanchol was tentatively proposed to be a strigol isomer based on its MS and NMR spectral data. This is the first report on germination stimulants of Orobanche spp. from genuine host plants. GC-MS techniques to analyze strigolactones are also described.