Sunflower sesquiterpene lactone models induce Orobanche cumana seed germination

Six sunflower sesquiterpene lactone models which share structural features of the lactone rings of strigol and its synthetic analogues, the GR family, with different conformational flexibilities were tested as Orobanche cuman a germination stimulants. Among them, parthenolide and 3,5-dihydroxydehydro costus-lactone significantly increased O. cumana germination, presenting hi gher activity than GR-24, used as a standard in the germination bioassay. T he effect of these two compounds is species-specific, showing no germinatio n stimulant activity on other Orobanche spp. tested (O. crenata, O. ramosa and O. aegyptiaca). Data presented are discussed in terms of a structure-ac tivity relationship. (C) 2000 Elsevier Science Ltd. All rights reserved.