Plant growth inhibitory activities by secondary metabolites isolated from Latin American flora

This chapter studies phytochemicals that are biodirected, to find botanical-origin biopesticides targeted against weeds. It describes the identification of some monoterpenes, diterpenes, sesquiterpene lactones, limonoids, triterpenes, coumarins, and flavonoids, including their chemical derivatives from plants belonging to the families Asteraceae, Celastraceae, Gomortegaceae, Lauraceae, Meliaceae, Monimiaceae, Poaceae, and Winteraceae. The findings show that some natural compounds or their derivatives possess plant growth regulatory (PGR)or herbicidal activities. Compounds with acetylated and a-ß-unsaturated carbonyl derivatives showed mainly PGR activity. It seems that an a-methylene-?-lactone and a group a,ß-unsaturated carbonyl are important for structural activity requirements. Allelopathic activities were assayed with Triticum aestivum, T. vulgare, Trifolium pratense, T. alexandrinum, T. angustifolium, Lolium multiflorum, Lactuca sativa, Physalis ixocarpa, and Raphanus sativus as weed seeds models. All of them are weedy pests in wheat, oat, potatoes, corn, bean, and other important crops of Latin America. Very little is known about the inhibitory activity of these natural compounds and their derivatives. Natural compounds that we have isolated represent a valuable resource for the study toward noxious weedy species of the allelopathic activities of these plants and their control. Progress in biochemical and allelopathic characterization of this pathway is outlined.