Germination Stimulants of Witchweed (Striga asiatica) from Hydrophobic Root Exudate of Sorghum (Sorghum bicolor)

Abstract

Hydrophobic exudate from roots of sorghum [Sorghum bicolor(L.) Moench. #3SORVU ‘IS 8768’] contain fourp-benzoquinones which in the dihydroquinone form are active as germination stimulants of witchweed [Striga asiatica(L.) Kuntz. # STRLU]. The three minorp-benzoquinones were partially characterized and found to be structurally similar to sorgoleone, the majorp-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.