Date Published: January 13, 2017
Publisher: Public Library of Science
Author(s): Fabrizio Araniti, Antonio Lupini, Francesco Sunseri, Maria Rosa Abenavoli, Manuel Joaquín Reigosa.
Dittrichia viscosa (L.) W. Greuter is a pioneer species belonging to the Compositae family. It is widespread in the Mediterranean basin, where it is considered invasive. It is a source of secondary metabolites, playing an important ecological role. D. viscosa plant extracts showed a phytotoxic activity on several physiological processes of different species. In the current study, the allelopathic potential of D. viscosa VOCs, released by its foliage, was evaluated on seed germination and root growth of lettuce. The VOCs effect was also studied on lettuce adult plants in microcosm systems, which better mimicked the open field conditions. D. viscosa VOCs inhibited both seed germination and root growth of lettuce. The VOCs composition revealed a large presence of terpenoids, responsible of the effects observed. Moreover, D. viscosa VOCs caused an alteration on plant water status accompanied by oxidative damages and photoinhibition on lettuce adult plants.
Dittrichia viscosa (L.) W. Greuter (syn. Inula viscosa (L.) Aiton., Cupularia viscosa G. et G.) is an evergreen perennial shrubby-weed belonging to the family Compositae. It is native to the Mediterranean region and it is considered a ruderal species due to its abundance in anthropic altered areas , and in particular, in metal-polluted sites . D. viscosa has a remarkable pioneer nature since it colonizes different habitats in the Mediterranean basin where it often creates large monospecific communities . In Australian and some European countries, this species is considered an important environmental weed for its high seed production and spreading, and for its resistance/adaptation to adverse conditions [3, 4]. D. viscosa is characterized by a quite substantial root apparatus and the ratio between below- and above-ground biomass is 0.24 . The canopy is very dense reaching 150 cm of height and total leaf area per plant comprises 200 cm2 . Glandular hairs, which produce a sticky resin from which derives “viscosa” name, cover the entire plant conferring its strong typical fragrance .
Consistent with previous results , the allelopathic potential of D. viscosa was confirmed through a bioassay that imitated natural environmental conditions of allelochemical VOCs release. For this reason, lettuce seeds, seedlings and adult plants were placed in open containers included in a ventilated growth chamber, and exposed to D. viscosa VOCs, directly released by plant parts. In particular, the effects of D. viscosa VOCs were demonstrated on lettuce seed germination and root growth, physiological processes largely employed to establish the secondary metabolites phytotoxicity  and the allelopathic potential of species .
The results gave the first evidence of the allelopathic potential of D. viscosa through a bioassay that mimed natural environmental conditions of VOCs release. The effects of VOCs on plant-plant interaction and communication were studied through a physiological and metabolomic approach, for the first time.