Germination Stimulants of Witchweed (<i>Striga asiatica</i>) from Hydrophobic Root Exudate of Sorghum (<i>Sorghum bicolor</i>)

Abstract

Hydrophobic exudate from roots of sorghum [ Sorghum bicolor (L.) Moench. # 3 SORVU ‘IS 8768’] contain four p -benzoquinones which in the dihydroquinone form are active as germination stimulants of witchweed [ Striga asiatica (L.) Kuntz. # STRLU]. The three minor p -benzoquinones were partially characterized and found to be structurally similar to sorgoleone, the major p -benzoquinone of this exudate. Herbicidal activity of the hydrophobic exudate was due to concentration- and pH-dependent inhibition of root elongation in some but not all weeds tested. Witchweed has apparently adapted these “defense” compounds of sorghum as host-specific germination stimulants.