Effect of plant density on competitiveness of Brassica napus, Sinapis alba and S. arvensis under water stress conditions.

Under Mediterranean climate, oilseed rape is subjected especially to the competition of weeds with respect to water. Herbicides registered for this crop do not effectively control species of the same family, in particular Sinapis alba and Sinapis arvensis. Moreover, there are no results of the effect of plant density on the competitiveness of these species. The purpose of this experiment was to determine if the competitiveness of the species varies according to the total density. The experiment was carried out in pots under greenhouse conditions, according to a replacement series method. Plant densities tested were 2, 4 and 8 plants per pot. The results of the replacement series diagram and those of relative crowding coefficients showed that Brassica napus was the most competitive, whatever the density is. This classification is explained primarily by leaf area. Indeed, the intraspecific competition due to B. napus has affected more its leaf area than the interspecific competition. Conversely, the intraspecific competition due to S. arvensis has less affected its leaf area than the interspecific competition. Regarding S. alba, the intraspecific competition effect was less severe than the interspecific competition effect due to B. napus and more severe than the interspecific competition effect due to S. arvensis on S. alba

Competitiveness and dry matter allocation of oilseed rape (Brassica napus L.) and two mustards (Sinapis alba L. and S. arvensis L.) under water stress conditions.

In Morocco, oilseed rape is commonly exposed to mustards competition which are not totally controlled by herbicides. To understand the competitiveness of each species, growth parameters should be studied notably dry matter allocation. The objective of this study was to confirm the competitiveness of oilseed rape with regard to Sinapis alba and S. arvensis and to investigate how the dry matter is allocated. A pot experiment was undertaken with a quartz sand as substrate. Two plant densities were tested (one and two plants). The binary density was either a monoculture or a mixture. Half the pots were maintained at field moisture capacity and the other half was irrigated up to 70% of its water holding capacity. Dry matter allocation of each species at density two was compared to that of the same species at density one. Results of replacement series diagrams and those of the relative crowding coefficient (based on total dry matter) showed that Brassica napus was more competitive than S. alba. S. arvensis was the least competitive. Under competition, B. napus irrigated at water holding capacity allocated more dry matter to stem when compared to its dry matter at density one. Under the same condition, when reducing water supply, B. napus allocated more dry matter to leaves. In case of S. alba, dry matter percent in leaves and roots were respectively low and high in normally irrigated plant and inversely under water shortage. S. arvensis allocated high and low dry matter percent respectively to root than to leaves when sufficiently irrigated. But no clear tendency was noticed under water shortage, for this species.

Critical period of weed control in oilseed rape in two Moroccan regions.

The determination of critical period of weed control in oilseed rape is necessary to know the weed control period. To determine the critical period, two fields experiments were carried out during 1995-96 growth season in Loukkos and Saïs regions at two oilseed densities (D1 = 24 and D2 = 36 plants m(-2)). Ten treatments corresponding to plots left weed free or weeded plots until four leaves, flowers bud, flowering, puds formation, and maturity stages of oilseed rape were tested. Density and biomass of weeds were determined at each oilseed stages. Results showed that weed density and biomass were higher in Saïs than in Loukkos sites. For a 10% yield loss, critical period of weed control in Loukkos was from 458 to 720 degree days after emergence (D degrees AE) and from 480 to 720 D degrees AE in oilseed conducted at densities D1 and D2, respectively. In Saïs, critical period of weed control was from 474 to 738 D degrees AE and from 468 to 675 D degrees AE in oilseed conducted at D1 and D2, respectively. It was concluded that the length of the critical period of weed control in oilseed rape grain yield seems to be dependant of the level of the infestation.

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.

[Competitiveness of hard wheat (Triticum durum Desf.) varieties against ripgut brome (Bromus rigidus Roth)]. / Compétitivité des varietés de blé dur (Triticum durum Desf.) vis à vis du brome raide (Bromus rigidus Roth.).

Varieties with an excellent competitiveness against ripgut brome (Bromus rigidus Roth.) would be very important to reinforce others methods to control ripgut brome weed. This study was carried out in 1999-2000 season in a greenhouse experiment to test the aggressiveness degree of six varieties of hard wheat (Oum Rabia, Isly, Marzak, Karim, Sebou, and Massa) combined with ripgut brome. Plant density was fixed at 16 plants of wheat or Bromus for pure crop and 8 plants for wheat and 8 for Bromus mixture. The results showed that the numbers of kernels/spikes were higher in the mixture for on pure composition. For the kernel weight, the result was opposite except for Isly and Marzak varieties. Karim and Isly varieties obtained the highest grain yield and were more competitive in mixture composition but Sebou and Massa varieties were less competitive against ripgut brome. Results of ripgut brome productivity and water use efficiency were similar and were used to determine the aggressiveness coefficient of hard wheat varieties against ripgut brome. The reduction of the shoot dry matter of brome was 22 to 56% at flowering. The grain yield of brome was reduced from 57 to 81%.

[Evaluation of the seed stock and dynamics of ripgut brome (Bromus rigidus Roth) in the cultivation of wheat in the Sais area of Morocco]. / Estimation du stock semencier et dynamique du brome raide (Bromus rigidus) dans la culture du blé au Sais Maroc.

The study was conducted on experimental plots differing in cultivation treatment (deep or shallow) at the National School of Agricultural station for three years. The objective was to study the influence of the tillage practices on vertical distribution of the seeds of ripgut brome (Bromus rigidus Roth) in the soil profile. Four tillage methods were tested: Zero tillage (SD), disc plough (PDL) and a disc harrow at two depths, 20 cm (CDM) and 30 cm (CDP). The results show that the type of cultivation affected the distribution of the seeds of ripgut brome. Shallow plots were highly infested by Bromus rigidus (876 plant/m2). The total number of seeds of ripgut brome was 96 and 45% in 0-4 cm of the soil, 3 and 29% in 4-15 cm and 1 and 26% in 15-30 cm, respectively of the deep (CDP) and shallow soil (SD). Deep tillage reduced the seed bank of ripgut brome by 96.6% and 66.7% for shallow. Seeds of ripgut brome survive more than three years at the deep soil. Processes of germination of this weed became functional after 98 days in the soil. The disc plough reduced significantly the brome population and seed bank compared to other tillage methods.

[Cartography and geographical spread of the adventitious species of brome (Bromus spp.) among cereals in the Sais area of Morocco]. / Cartographie et répartition géographique des espèces de bromes adventices des céréales dans le Sais Maroc.

Bromus spp is causing serious problems in wheat in the Sais area. However, the damage of this weed varies from one region to another according to the agro-climatic conditions and crop systems. The characterization of the infestation level in each situation is a prerequisite to develop a control strategy adapted to each environment. This study was undertaken in order to determine the infestation level and geographical spread of the weedy brome (Bromus spp) on wheat in Sais following crop systems and pedo-climatic conditions. The results obtained during two consecutive years (1998-99 and 1999-2000) revealed that ripgut brome (Bromus rigidus Roth.) was the most dominant species in wheat fields in the surveyed regions, followed by B. rubens L., B. sterilis L., B. madritensis L. and B. mollus L. Among, 18 regions and 100 infested wheat fields, 16.67% of fields were slightly infested (Plant density of Bromus (Dbr < 90 plants/m2, 61.11% were moderately infested (90 < Dbr < 290 plants/m2) and 22.22% were highly infested (Dbr > 400 plants/m2). The maximum relative frequency was obtained with Bromus rigidus (47.15%) and the coverage was 40.43%. But, for B.rubens, B. madritensis and B. sterilis, the relative frequencies were respectively 31.42; 26 and 15% and their coverages were respectively 28.9, 20.4 and 12.5%.