Phoma stem canker is a worldwide disease of oilseed rape, responsible for major economic losses. The main control methods are the use of resistant cultivars, cropping practices and spatial territory ...organization, involving large-scale spatial processes. A participatory approach can be useful for dealing with this problem, which requires stakeholders' coordination as regards to the timing and spatial layout of cropping practices. The scenario concept is used to plan possible future cropping systems and to reveal their main drivers. In this paper, we test a method to build quantitative land use scenarios and to test them with an existing spatially-explicit model to assess the effects of various scenarios on phoma stem canker management. It was built from previous participatory methods. The method we tested is composed of six steps: stakeholder identification, building with them a common vision of the disease behaviour, collective scenario design, and discussion with stakeholders of model-based scenario evaluations. We tested this method on a regional case study application in France. This application revealed benefits of the method with respect to the diversity of the designed scenarios (predictive and exploratory scenarios; driven by local or global context change) and the diversity of results on phoma stem canker management. Based on this application, recommendations for participation improvement and model acceptance are made: (1) build a partnership with a key local stakeholder; (2) describe and discuss precisely model functioning with stakeholders (avoid the “black box”); and (3) facilitate interpretation of scenario assessment by adapting model outputs. This method, combining a participatory approach (qualitative and quantitative construction of scenarios and their evaluation with an existing model) highlights the potential benefits of involving stakeholders in attempting to solve a local problem, in this case, phoma stem canker management.
•We combined participatory workshops and an available model for a scenario study.•Stakeholder trust in the model required a dialogue on disease-practices interactions.•Stakeholders designed context-dependent predictive and exploratory scenarios.•Model-based scenario evaluation provided information on management options.•The tested method could help the use of existing models for local management issues.
To durably control phoma stem canker (Leptosphaeria maculans/Leptosphaeria biglobosa) in oilseed rape by preserving the efficacy of specific resistances, the design of cropping systems is required, ...combining different aspects of crop management over time and at the regional scale. Modelling is a practical means to do so. To this end, the structure of SIPPOM, a Simulator for Integrated Pathogen POpulation Management, is presented. By linking epidemiological, population and crop model approaches, it simulates both the quantitative evolution (size) and qualitative evolution (genetic structure) of L. maculans population under the influence of various cropping systems. It involves five sub-models: (i) primary inoculum production; (ii) ascospore dispersal; (iii) crop development; (iv) plant infection, disease severity, and yield loss; and (v) changes in the genetic structure of pathogen populations over time. The input variables are weather data, soil characteristics, the description of cropping systems (crop sequence and winter oilseed rape crop management, including cultivars, sowing, fungicide, and tillage) and their spatial distribution (the model is spatially explicit), plus the initial size and genetic structure of pathogen populations. The genetic evolutionary forces taken into account are migration, selection, and recombination. The model simulates disease severity and the genetic structure of the pathogen population, in addition to the attainable yield less yield loss caused by the disease. The economic and environmental performances of the simulated strategies are computed using technical operation costs, crop prices, and yields. The underlying hypotheses are discussed in light of advantages and possible improvements of the model. Possible uses of SIPPOM are proposed with respect to the design of collective strategies for the durable control of phoma stem canker on winter oilseed rape at a regional scale.
Several disease indices (DI) have been proposed to assess the severity of phoma stem canker at late growth stages. The DI commonly used in France (called G₂ DI) consists of integrating the ...distribution of the proportions of plants observed within six canker severity classes into a single index. This index uses arbitrarily chosen coefficients associated to each class of canker severity. A given value of this DI can therefore be obtained with different distributions among the canker severity classes. Consequently, it is important to assess to what extent the G₂ DI is representative of the distribution of plants in canker severity classes. We show in this study that the G₂ DI is a good indicator of the distribution of the observed canker severities, using a dataset from different years, sites and cultivars; this illustrates the robustness of the G₂ DI.
A plant growth-promoting rhizobacterium belonging to the genus Achromobacter was isolated from the oil-seed-rape (Brassica napus) root. Growth promotion bioassays were performed with oilseed rape ...seedlings in a growth chamber in test tubes containing attapulgite and mineral nutrient solution, containing NO3- as N source. The presence of this Achromobacter strain increased shoot and root dry weight by 22-33% and 6-21%, respectively. Inoculation of young seedlings with the Achromobacter bacteria induced a 100% improvement in NO3- uptake by the whole root system. Observations on the seminal root of seedlings 20 h after inoculation showed that there was an enhancement of both the number and the length of root hairs, compared to non-inoculated seedlings. Electrophysiological measurements of NO3- net flux with ion-selective microelectrodes showed that inoculation resulted in a specific increase of net nitrate flux in a root zone morphologically similar in inoculated and non-inoculated plants. The root area increased due to root hair stimulation by the Achromobacter bacteria, which might have contributed to the improvement of NO3- uptake by the whole root system, together with the enhancement of specific NO3- uptake rate. Moreover, inoculated plants showed increased potassium net influx and proton net efflux. Overall, the data presented suggest that the inoculation of oilseed-rape with the bacteria Achromobacter affects the mineral uptake.
The management of phoma stem canker (blackleg disease, caused by Leptosphaeria maculans) is an integral component of oilseed rape production. In this paper, we discuss the information about ...management strategies that is disseminated in Europe and Australia. New cultivars have been introduced with improved resistance to disease, but sometimes this resistance has been overcome as new races of the pathogen have emerged. When cultivars with single major gene resistance have been introduced into areas with high inoculum concentrations, significant economic damage has been caused by new races of L. maculans within 2-3 years. Quantitative or polygenic resistance has also been used successfully against stem canker and offers more durable disease resistance if plant breeders and farmers deploy this resistance more effectively. Strategies to improve the durability of resistance need to be developed and tested in practice. New information on the occurrence of virulence and avirulence genes in populations of Leptosphaeria maculans and modelling of the durability of resistance provide opportunities for plant breeders, specialist technical organisations, cooperatives, advisory services and farmers to collaborate and better exploit cultivar resistance. Changing economic and environmental factors influence cropping practices and, if to be considered successful, management strategies must show clear financial benefits. Technology transfer will need to address all aspects of managing stem canker and other diseases of oilseed rape and using effective written, verbal and electronic methods of communication.
With 2 figures and 4 tables At the field scale, the co-existence of different farming production systems requires strategies to prevent gene flow between adjacent crops. Oilseed rape produces pollen ...dispersed by wind and insects and the risks of pollen mediated gene flow are significant for this crop. Cleistogamy, the trait of non-opening flowers, could be used to reduce pollen flow. Cleistogamous oilseed rape genotypes were obtained by INRA in France and were bred in order to improve the stability of this trait. In this paper, we examine the reliability of the cleistogamous trait for two inbred lines. The flower opening level was measured at different dates during the flowering period in six field experiments (three sites x 2 years). The results showed that some flowers were partially opened with rates varying from 0.5% to 33% principally depending on genotypes, trials (site and year) and recording dates. Given that other studies have shown that cleistogamy could reduce pollen dispersal, we consider that, even when partially unstable, cleistogamy could be beneficially used in combination with other means in a containment strategy.
Phoma stem canker, caused by
Leptosphaeria maculans (anamorph
Phoma lingam), is one of the most serious diseases of oilseed rape world-wide. However, little is known about the effects of cultural ...practices on phoma stem canker development. We carried out a field experiment, in 2000/2001 and 2001/2002, at Grignon Experimental Unit (Paris Basin, France) to assess the effects of sowing date and nitrogen availability during vegetative stages on phoma stem canker development on two winter oilseed rape cultivars. We studied eight treatments corresponding to the combination of two sowing dates—early (beginning of August) and typical (beginning of September)—two levels of nitrogen availability during vegetative stages—application of 0 or 250
kg
N
ha
−1 before the end of autumn, subsequent spring nitrogen fertilizer application being adjusted according to the needs of the crop—and two cultivars—Bristol (susceptible to phoma stem canker) and Pollen (slightly susceptible). Early sowing resulted in smaller crown cankers, whereas high nitrogen availability during the vegetative stage favoured crown canker development. Significant interactions between cultivar susceptibility and cultural practices were observed in the second year of the experiment. Crown canker development was more strongly limited by early sowing for Pollen than for Bristol. Similarly, high nitrogen availability during the vegetative stage increased crown canker development more strongly for Pollen than for Bristol. The results presented here should facilitate integration of the risk of phoma stem canker development into the choice of the sowing date and nitrogen management within the cropping system.
Weather-based models (Improved Blackleg Sporacle and SporacleEzy) to predict the date of onset of seasonal release from oilseed rape debris of ascospores of Leptosphaeria maculans or L. biglobosa, ...causes of phoma stem canker, were developed and tested with data from diverse environments in Australia, Canada, France, Poland and the UK. Parameters were estimated, using the same datasets from experiments in the UK and Poland, with an accuracy of root mean squared deviation (RMSD) of 7·4 (with a bias of -4·54, L. maculans) and 8·5 (with a bias of 0·30, L. biglobosa) days for Improved Blackleg Sporacle, and of 2·9 (with a bias of -0·06, L. maculans) and 7·3 (with a bias of -1·18, L. biglobosa) days for SporacleEzy. When tested with data independent of those used for parameter estimation, overall predictions agreed well with observed data in five countries, both for Improved Blackleg Sporacle (R² = 0·96, slope = 1·00, standard error = 0·03, P > 0·05, n = 46) and SporacleEzy (R² = 0·96, slope = 0·98, standard error = 0·03, P > 0·05, n = 46). However, SporacleEzy performed better in Australia, Canada, Poland and the UK (RMSD = 10·6, 9·7, 5·4 and 3·4 days, respectively) than Improved Blackleg Sporacle (RMSD = 11·7, 11·0, 5·6 and 6·5 days, respectively). In contrast, the prediction from Improved Blackleg Sporacle (RMSD = 8·0 days) was better in France than that from SporacleEzy (RMSD = 15·9 days). Sensitivity analysis showed that better parameter estimation could improve the quality of prediction of SporacleEzy (RMSD = 7·6 days) under French conditions. These models are capable of estimating the first seasonal release of ascospores of organisms causing phoma stem canker on oilseed rape under many climates and thus could contribute to development of strategies for control of the disease.
•Spatial distributions of cropping systems were assessed for their impact on phoma.•Agronomic and epidemiological criteria were used to characterize phoma control.•Main explanatory cropping practices ...differed between the criteria.•Weather significantly impacted epidemiological criteria of phoma control.•Sustainable strategies all included a small proportion of RlmX-cultivars.
In agricultural landscapes, pest and disease control mainly rely on cropping system characteristics and location. We have combined a participatory approach and a spatially-explicit model, to design and assess cropping system scenarios for future contextual changes in the small region of Picardie, France. Phoma stem canker of winter oilseed rape (WOSR), a widespread disease responsible for major economic losses, was used as a case study to investigate the effects of modifying cropping systems, at a regional scale, on disease controlling and on the sustainability of a newly introduced specific resistance gene (RlmX). Meta-models were fitted to assess the effects of cropping practices and weather conditions included in scenarios on three complementary model outputs: size of the pathogen population, yield loss, and fraction of the virulent population on RlmX-cultivars. We ran three replicates of each cropping practice scenario, varying the location of WOSR and associated cropping characteristics within the region. Outputs differed slightly between replicates, but there were no significant differences between replicates (alpha=0.001) for each output. The size of the pathogen population was well explained by winter oilseed rape acreages, cultivar landscape composition and tillage, and the yield loss was explained by weather conditions and cultivars. The fraction of the virulent population on RlmX-cultivars was explained primarily by cultivar landscape composition. These differences in explanatory variables for the different outputs highlighted their complementarity. Cropping practices and weather impacts on the three variables remained consistent among the explored possible future contexts. Highlighting the most efficient cropping practices to be applied in the event of different future changes could help local decision-makers to design cropping practices in the face of contextual change.
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