The influence of winter oilseed rape (Brassica napusssp.oleiferavar.biennis) cultivar and grass genotype on the competitive balance between crop and grass weeds

Abstract

SUMMARYThree experiments conducted over two years (2002–04) at the Crops Research Unit, University of Reading, investigated competition between autumn sown oilseed rape cultivars (Brassica napusL. ssp.oleiferavar.biennis(DC.) Metzg.) andLolium multiflorumLam.,L.×boucheanumKunth andAlopecurus myosuroidesHuds., sown as indicative grass weeds.Rape cultivar (cv.) had a substantial effect on grass weed seed return. Over the six cultivars tested,L. multiflorumspikelet production ranged from just under 400 spikelets/m2in the presence of cv. Winner to nearly 5800 in competition with cv. Lutin. Cultivar competitiveness was associated with high biomass, large dense floral layers and early stem extension. There was some evidence of differential competitive tolerance between rape cultivars.The results suggested that rape cultivars could be screened for competitiveness by measuring floral layer interception of photosynthetic active radiation.L.×boucheanumcultivars varied in ability to compete with rape. In the absence of inter-specific competition, spikelet density was similar for Aberecho and Polly (circa31 000 spikelets/m2) but when grown with rape Polly outyielded Aberecho (i.e. 12 090 and 7990 spikelets/m2respectively).