Crop rotation is the oldest, and perhaps the best cultural practice for reducing the risk of take-all. The effects of crops sown before wheat in a rotation are known in detail, but we know little about the opportunities for reducing take-all risk by planting certain crops in the summer period between wheat harvest and the planting of a subsequent winter wheat crop. We investigated the effects on take-all of five summer fallow crops, two soil tillage treatments and a fungicide seed treatment, in a five site-year experiment. We tested the effects of oats, oilseed rape, mustard, ryegrass and volunteer wheat crops. Bare-soil plots were also included. Take-all epidemics varied with year and site. Summer fallow crops had a greater effect on tilled plots. The incidence and severity of take-all were significantly higher in the wheat volunteer plots, whereas maintaining bare soil provided the lowest level of disease. Oilseed rape had no significant effect on take-all incidence in our experiment. The best candidates for reducing take-all risk appeared to be oats, mustard and ryegrass. These summer fallow crops decreased disease levels only when associated with conventional tillage. Summer fallow crops did not alter take-all decline in the same way as a break crop after a wheat monoculture.Abbreviations: AUDPC -area under the disease progress curve; Ggt -Gaeumannomyces graminis var. tritici; GLM -generalised linear model; Gri201, Gri601, Gri702, LR202 and LR203 -field experiment codes (Gri for Grignon and LR for Le Rheu, followed by the order of the assessed wheat crop [2 for second wheat crop, 6 for sixth wheat crop or 7 for seventh wheat crop] and the harvest year [2001, 2002, or 2003]); GS -Zadoks growth stage; GS 15 -5 leaves unfolded; GS 30 -pseudostem elongation; GS 32-33 -midstem elongation; GS 65 -flowering; GS 89 -ripening; F+/F) -with/without fungicide seed treatment; Till/no-till -conventional tillage/direct drilling.

The incidence and severity of take-all, caused by Gaeumannomyces graminis var. tritici (Ggt), in susceptible crops depend on climate, soil characteristics and cropping practices. Take-all can be controlled by modifying crop rotation, crop management and fungicide treatment. When available, fungicides are used as a seed treatment and are partially effective. There is currently no reliable method for helping farmers to optimise their choice of cropping system to improve take-all control. In this study, we defined 16 models, based on various mathematical functions and input variables, for predicting disease incidence in a wheat crop as a function of soil characteristics, climate, crop rotation and crop management. The parameters of these models were estimated from field experiments carried out at six sites in the north of France over a ten-year period. The root mean squared error of prediction (RMSEP) values of the models were estimated by cross validation and compared. RMSEP was in the range 16.34-65.93% and was higher for the models based on multiplicative functions. The lowest RMSEP value was obtained for a dynamic model simulating disease incidence during the crop cycle and which included among input variables the percentage of diseased plants determined at GS3

Brassicas contain glucosinolates (GSL) which decomposition is able to reduce the growth of populations of soil-borne fungi, bacterias or nematodes. These biocid effects on soil-borne microorganisms make a form of allelopathy phenomenon. The allelopathic properties depends on the GLS composition of the Brassicas: Indian mustard and in a lower extend Oilseed rape could have the most powerfull action, White mustard would have a weaker action. These properties also depends on crop residues: green manure with quick decomposition would result with a higher action than crop residues after grain harvest. The main mechanisms are known. In vitro, isothiocyanates obtained from the GSL decomposition inhibit all the phases of the cycle of Aphanomyces eutiches, the fungus responsible for root rot of peas. The mycelian growth of Gaeumannomyces graminis tritici, the fungus responsible for the wheat take all is inhibited by some isothyocyanates at low concentration. Furthermore, several studies give the evidence that the incorporation of Brassicas residues into the soil does inhibit the growth of both soil-borne pathogens. At last, the presence of roots of Brassicas inhibits the germination of the mycorhizes known to improve the mineral nutrition of its host plant. This phenomenon could explain the depressive effect of oilseed rape on the nutrition of a subsequent maize. This knowledge of Brassicas effects into cropping systems offers issues for a better management of precedent effects of Brassicas; these effects being positive (integrated cop protection) or negative (management of subsequent crop nutrition after Brassicas).

Effet allélopathiques des Brassicacées sur les champignons telluriques Cas d'Aphanomyces euteiches, responsable de la pourriture molle du poisNous nous intéresserons ici plus particulièrement à l'influence des cultures de Brassicacées sur un premier champignon pathogène tellurique, le champignon pathogène tellurique : Aphanomyces euteiches, responsable de la pourriture molle du pois. La pourriture molle du pois (Pisum sativum) due à A. euteichesLa pourriture molle du pois (Pisum sativum) est due à un champignon oomycète, Aphanomyces euteiches. Ce champignon est capable de provoquer des pertes de rendement très conséquentes suite à la destruction plus ou moins précoce du système racinaire. Ces pertes peuvent atteindre 10 à 30 q/ha, selon le niveau d'infestation du champ et les conditions climatiques. De nouveaux cas de nécroses racinaires dus à A. euteiches sont signalés chaque année. L'absence de méthodes de protection, hormis la prévision des risques, explique que ce problème soit devenu, depuis les années 1993-1994, une grande préoccupation pour les agriculteurs des régions les plus touchées (grand Bassin parisien en particulier). Parmi les méthodes de lutte envisagées, la réduction du potentiel infectieux du sol par un choix judicieux de plantes « de coupure » semble être une piste intéressante.Plusieurs études concernant l'effet précédent des Brassicacées sur la pourriture molle du pois (A. euteiches) ont été réalisées aux États-Unis à partir des années 60. Nous nous intéresserons dans un premier temps à l'effet des amendements organiques constitués par des enfouissements de Brassicacées sur le potentiel infectieux d'un sol infesté par A. euteiches. Dans un deuxième temps, nous essaierons d'analyser les mécanismes d'action.Voir la première partie dans OCL ; volume 12, n o 3, mai-juin 2005.