Allelopathic effects of aqueous extracts of rape residues on winter wheat seed germination and early growth

Abstract

The optical density of 1:10 concentration of aqueous extract of all rape residues was by 4.0–12.4 times higher compared to optical density measured at lower concentrations. The optical density of aqueous extracts of rape residues correlated with the amount of germinated winter wheat (r = 0.45, P<0.01) and length of roots (r = 0.64, P<0.05) of winter wheat. Allelopathic effect of Brassicaceae plants on crop and weed is an important factor in agriculture. Laboratory experiments were conducted in 2011 to evaluate the allelopathic effects of aqueous extracts of winter and spring oilseed rape residues (threshing remains, stubble and roots) on winter wheat germination and early growth. Oilseed rape residues were extracted and evaluated for toxicity. Treatments included: 1) threshing remains of winter oilseed rape, 2) stubble of winter oilseed rape, 3) roots of winter oilseed rape, 4) threshing remains of spring oilseed rape, 5) stubble of spring oilseed rape, and 6) roots of spring oilseed rape. In addition, various concentrations of aqueous extracts were evaluated for phytotoxicity. Impacts of extracts upon winter wheat grown in Petri dishes on filter paper moistened with prepared aqueous extracts were determined in controlled growth chamber experiments. Germination of winter wheat was stimulated by extracts of threshing remains of winter rape and also extracts of stubble of spring rape. Aqueous extracts of roots of winter oilseed rape and threshing remains and stubble of spring rape also stimulated winter wheat hypocotyl and radical elongation. The lowest (1:6250) concentration of aqueous extract of oilseed rape residues, compared to distilled water, had no significant effect on winter wheat germination. Higher concentrations (1:1250, 1:250, 1:50 and 1:10) of aqueous extracts of rape residues, compared to distilled water, inhibited germination of winter wheat from 6.5 to 19.8% percentage points. The growth of shoots and roots of winter wheat was stimulated accordingly from 20.2 to 27.6% and from 7.5 to 9.9% at lower concentrations (1:6250, 1:1250 and 1:250) of rape residue aqueous extracts. The highest optical density readings were obtained with aqueous extracts of winter oilseed rape threshing remains, and lowest readings with extracts of spring oilseed rape roots.