evaluation of allelopathic effects of eucalyptus (eucalyptus globules labill.) on germination, morphological and biochemical criteria of barley (hordeum vulgare l.) and flixweed (descurainia sophia l.)

in order to examine the allelochemic effects of seed and leaf aqueous extracts of eucalyptus (eucalyptus globules labill.) on germination, growth, morphological and biochemical criteria of barley (hordeum vulgare l.) and flixweed (descurainia sophia l.), a series of experiments with five levels of seed and leaf aqueous extract of eucalyptus, including concentrations of 30, 50, 70, 90 and 100 percents by weight–volume, separately for seed and leaf with control treatment (distilled water) in a completely random design with three replications were conducted. all experiments conducted in laboratory of biology, faculty of sciences, ferdowsi university of mashhad during 2010. the results showed that the seeds and leaves aqueous extracts of eucalyptus at all concentrations had inhibitory effects on final germination percentage and germination rate of both species. the inhibitory effects enhanced as the extract concentration increased. the shoot and root lengths and fresh and dry weights were greatly reduced in flixweed than in barley. similarly, chlorophyll a and b and total chlorophyll contents were decreased in leaf of barley and flixweed in both species, accumulation of proline and soluble sugars amounts increased, it seems that this is an adjustment mechanism for ameliorate of stress tolerance. the results of this study also showed that the seeds aqueous extract of eucalyptus was more effective in morphological and biochemical characteristics of two species than to leaves; it was also observed that allelopathic impacts of eucalyptus seeds was more for dicotyledon species (flixweed) than to monocot (barley). finally, it seems that the allelopathic chemicals of seeds and leaves aqueous extracts of eucalyptus may have the potential as biological herbicide or new formulation of herbicide.