| Abstract
| - Studies of the structure−activity relationship (SAR) directed to evaluate the effect of severalsesquiterpene lactones (SL) as germination stimulants of three Orobanche spp. (O. cumana, O.crenata, and O. ramosa) have been achieved. Results are compared with those obtained in the samebioassay with an internal standard, the synthetic analogue of strigol GR-24. A high specificity in thegermination activity of SL on the sunflower parasite O. cumana has been observed, and a relationshipbetween such activity and the high sunflower SL content is postulated. Molecular properties of thenatural and synthetic germination stimulants (GR-24, GR-7, and Nijmegen-1) and SL have beenstudied using MMX and PM3 calculations. Consequently, comparative studies among all of themand their activities have been made. SL tested present similarities in molecular properties such asthe volume of the molecule and the spatial disposition of the carbon backbone to the naturalgermination stimulant orobanchol. These properties could be related to their biological activity. Keywords: Sesquiterpene lactones; guaianolides; germacranolides; eudesmanolides; SAR studies;germination stimulants; allelopathy; parasitic weeds; Orobanche cumana; Orobanchaceae
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