Allelopatic effect of different caster bean organs (Ricinus communis L.) on reducing germination and growth of dodder (Cuscuta campestris Yuncker)

Dodder (Cascuta campestris Yuncker) is an annual parasitic plant from the Convolvulaceae family (Mishra et al.، 2007). It wraps around many adjacent dicot and a few monocot plants، penetrates in their vascular tissue and exploits photosynthates، nutrients and water (Lanini & Kogan، 2005). Consequently، the growth، vigor and production of the host plant will be severely reduced (Nadler-Hasasr & Rubin، 2003). Dodder is not able to complete its cycle، if it is not attached to a host. Therefore، it is entirely dependent on its host for supplying water، assimilates and minerals (Mishra et al.، 2007). Considering the nature of dodder habit، it is rarely possible to completely control dodder by using different chemical herbicides (Lanini & Kogan، 2005). In addition، because of increasing the environmental concerns caused by applying synthetic herbicides، there is considerable attention to alternative strategies for weeds management (Batish et al.، 2002; Bowmik & Inderjit، 2003). In recent years، allelopathic plants، an alternative strategy for weed management، have received massive attention (Narwal، 2010; Jamil et al.، 2009). Due to the importance of dodder as a parasitic weed، this research was conducted with the purpose of studying the allelopathic effects of aqueous extracts and decay durations of caster bean (Ricinus communis L.) organs on germination and emergence of dodder.

The current study was conducted based on three separate experiments using a completely randomized design (CRD) with factorial arrangement with three replications. The first experiment was conducted in petri dishes and consisted of caster bean organs at four levels (root، stem، leaf and total plant without inflorescence) and their aqueous extract concentrations at 11 levels (0، 1، 2، 3، 4، 5، 6، 7، 8، 9 and 10%). The second experiment was conducted in pots and factors were caster bean organs at 4 levels (root، stem، leaf and total plant without inflorescence) and their aqueous extract concentrations in 5 levels (0، 2. 5، 5، 7. 5 and 10%). The third experiment was conducted with caster bean organs at 4 levels (root، stem، leaf and total plant without inflorescence) and decay durations at 8 levels (0، 15، 30، 45، 60، 75 and 90 days of decay and control). All experimental data were analyzed by ANOVA and the means were separated by Duncan''s multiple range test at 5% probability level.

The results of the first and the second experiment showed that aqueous extract of caster bean organs has a significant effect on dry weight، length of seedling and germination of dodder. From the third experiment، decay duration had a significant effect on the mentioned traits. Leaf aqueous extract in comparison with other organs had the most effect on the studied traits. The complete suppression of emergence was observed in 0، 15، 30 and 45 days of decay by using caster bean leaves. In conclusion، caster bean residues showed great potential for reducing germination and growth of dodder. Therefore، allelopatic potential of caster bean can be considered as a sustainable approach in integrated dodder management systems. In the future، the effective concentrations of aqueous extracts of caster bean organs may be useful as sources for producing biological herbicides.