Interspecifi c variation in the allelopathic potential of the family Myrtaceae

Allelopathy is a type of biotic interference wherein a plant releases bioactive metabolites into an environment, thereby aff ecting the adjacent biota. Stressful environments stimulate the production of these metabolites. Th e present study tests the novel weapons hypothesis, which postulates that species belonging to the same genus and from the same environment have similar allelopathic eff ects. Th e aim of this study was to assess the allelopathic eff ects that the aqueous leaf extracts of 15 species belonging to fi ve genera of the Myrtaceae family have on the seed germination and initial seedling growth of lettuce (Lactuca sativa L.), tomato (Solanum lycopersicum L.) and onion (Allium cepa L.). Germination rates, average germination times, informational entropy of germination and allelopathic eff ects, as quantifi ed with a response index, were calculated. A taxonomic distance matrix based on Gower dissimilarity and a Euclidean distance matrix were constructed. Th e results revealed that all extracts from donor species signifi cantly increased average germination time or reduced the germination rate of eudicotyledonous plant species. Th e only extracts that showed no eff ect on monocotyledonous seeds were those of Campomanesia pubescens O. Berg and Psidium cinereum Mart. We conclude that eudicotyledonous and monocotyledonous plants were both signifi cantly aff ected by the presence of all extracts tested. Our results make it clear that each species behaves distinctly in relation to allelopathic activity, with no apparent grouping by genus or subtribe. Th erefore, the hypothesis was rejected, because plants from the same environment and with taxonomic proximity do not necessarily display similar production of secondary metabolites.