Varietal variation in allelopathic activity in wheat and barley and possibilities for use in plant breeding

Most breeding traits are the same in conventional and organic cereal breeding. However, a trait that is very important in organic and low-input fan-ning, but until now been neglected in breeding, is weed competitive ability. Morphological and physiological characters, mainly influencing either the biomass growth or the uptake of nutrients and water, are used as potential breeding traits. However, the significance of allelopathy, i.e. root exudates inhibiting weed growth, is more and more envisaged. In both barley (Hordeum vulgare L.) and wheat (Triticum aestivum L.), there is a large variation in potential allelopathic activity, measured as the root growth inhibition of ryegrass (Lolium perenne L.). Landraces and old cultivars of barley are in general more allelopathic than new bred cultivars, but there are exceptions that could be used in breeding. In wheat, there is an opposite trend as Swedish landraces and old cultivars are less allelopathic than new ones. Swedish cultivars are also in general less allelopathic than cultivars from western and central Europe and North America. In a screening of 813 spring wheat cultivars and lines two cultivars were found to be as allelopathic as the most allelopathic barley and are now used in a conventional breeding programme to improve the allelopathic proprieties of the Swedish spring wheat.