Effect of water stress on the agressiveness of oilsseed rape (Brassica napus L.) and two mustards (Sinapis alba L. and S. arvensis L.).

Oilseed rape (Brassica napus L.), a winter sown crop, may compete for water especially with Brassicaceae weeds. Investigating plant competition under water stress conditions is necessary for achieving a good yield in a Mediterranean climate characterized by a scarse water availability. This experiment was carried out to study the competiveness of oilseed rape (Brassica napus L.) with two brassicaceae weeds (Sinapis alba L. and S. arvensis L.). Species were grown at a density of two plants per bucket either in monoculture or as a binary mixture under water stress conditions in a greenhouse. Results of monoculture showed that B. napus had the highest shoot dry matter. Shoot dry matter of B. napus was more reduced by intraspecific competition than by interspecific competition due to S. arvensis. Shoot dry matter of S. alba in monoculture was higher than in mixture with S. arvensis, but more reduced in mixture with B. napus. In case of S. arvensis, shoot dry matter was more reduced by interspecific competition than by intraspecific competition. Agressivity based on grain yield showed, that B. napus was the most agressive species followed by S. alba. This agressivity did not change by the imposed water stress.