Physical and Cultural Weed Control Working Group of - European ...

9 th EWRS Workshop on Physical and Cultural Weed Control 22
Samsun, Turkey, 28 – 30 March 2011
biological importance: it is known for its antibacterial and antifungal activities, antispasmodic
effects, acetylcholine esterace inhibition, lipid peroxidase inhibition, radical scavenging effect,
white blood cell macrophage stimulant and cardiac depressant activity (Kirimer et al., 1995). High
carvacrol concentrations are observed in arid and semiarid environments (D'Antuono et al., 2000;
Lawrence, 1984).
The sustainability of agriculture relies on the development of strategies that lower the need for
costly external inputs and minimize detrimental effects on the environment, which often involve
either inappropriate or excessive use of agrochemical inputs. Sustainable agriculture integrated with
allelopathy could reduce the heavy dependence on synthetic herbicides and other agrochemicals,
and therefore ease problems such as environmental contamination, use of unsafe agricultural
products and effects on human health (Khanh et al., 2007). Indeed, in aromatic plants, allelopathy
has been investigated as an interactive mechanism to explain competition between species (Muller
et al., 1964; Angelini et al., 2003; Economou et al., 2007). Essential oils have been extracted from
many aromatic plants (including Origanum sp.) and evaluated for allelopathic properties. The
germination of several plant species was strongly inhibited by essential oils. Therefore, the possible
use of essential oils as herbicides is widely discussed (Katz et al., 1987; Dudai et al., 1999).
Several experimental strategies for assessing potential phytotoxical targets of A/M plants are
outlined in this study. The main strategies involve the phytotoxicity of “oregano” plant extracts on
Sorghum halepense, Cyperus rotundus and Solanun eleagnifolium, in terms of (i) inhibitory effects
by in vitro and in vivo assays, and (ii) effects on weed growth in field experiment using “oregano”
as cover crop in maize.
Materials and methods
Laboratory experiments
Plant tissues (leaves, inflorescences and shoots) from Origanum hirtum collected from Ikaria, an
island of east Aegean Sea, were evaluated for their inhibitory action on the studied weeds and on
the bioindicators Avena sativa and Vicia faba. Avena sativa was included in this study, because (a)
it is extensively used in allelopathy research as the receiver plant to test compounds released by
donor plant (2), (b) its seeds germinate evenly, resulting in uniform and rapid plant growth to
quantify the biological response and (c) oat biotest is considered as sensitive method (Rice, 1984).
In vitro experiments were conducted in Petri dishes, where the weed seeds were subjected to a dose
response bioassays with “oregano” extract. The seed germination and the radical length were
measured to evaluate the phytotoxicity of oregano extract. Therefore, 20 oat seeds (or 5 faba bean
seeds) were placed onto two layers of filter paper in Petri plates (9 cm in diameter) treated with 3 ml
of test solution as per treatment, covered and incubated at 25 o C in the dark. The tissues were
physically dried, extracted according to the methodology at room temperature and aqueous dilutions
of 5 and 10% v/v were tested on the growth of the aforementioned plants. Pot experiments were
curried out in growth champers. The 10-cm diameter pots were filled with 500 g of soil mixture
(soil/peat/perlite, 2:1:1 v/v) and irrigated with 100 mL full-strength Hoagland nutrient solution
(Hoagland and Arnon, 1950) twice weekly and with tap water when needed. The pots were sown
with 10 seeds of oat (or 5 seeds of faba bean) and aqueous extracts were also added. The inhibitory
action was evaluated by determining the shoot and root dry weight of the studied plants. The
experiments were conducted in a Complete Randomized Design (CRD), treatments were replicated
4 times and only deionised water was used in control.
Field experiments
Two field experiments were conducted during 2009 and 2010 in the Vonitsa region of western
Greece. Site was located at 38 o 53′36.44″ N, 20 o 53′54.91″ E. The soil was a clay loam, whose
physicochemical characteristics (0- to 15-cm depth increment) were clay 283 g kg -1 , silt 320 g kg -1 ,