Oilseed Rape Volunteers Research Articles

The long-term persistence of transgenic volunteers in wild mustard and rice populations

The undesired presence of GM plants outside of cultivation is one of main concerns for the ecological risk assessment and regulation of GM plants, and how long transgenic volunteers can persist in the nature remains unknown. We conducted two long-term coexistence experiments of Bt-transgenic insect-resistant crops in populations of their wild relatives, using Bt-transgenic oilseed rape (Brassica napus) in wild mustard (B. juncea) populations from 2012 to 2019, and Bt-transgenic rice (Oryza sativa) in wild rice (O. rufipogon and O. minuta) populations from 2013 to 2019. Transgenic oilseed rape volunteers survived only in the 2012 winter, because it is a spring variety and not be resistant to cold climate and competition from weeds. Transgenic rice was not survived because of its low competitive ability compared to wild rice, but survived five years in one population of wild rice O. minuta who could not tolerant to cold temperature. Our results indicated that transgenic volunteers can persist in the wild populations under natural conditions, but the fate of transgenic volunteers in the nature depends on whether the growth environment is favorable, and they could not disperse over its niche or “tolerance zone”.

Diversifying cropping sequence reduces nitrogen leaching risks

• We monitored soil mineral N during various cropping sequences. • We simulated a 20-year series of N leaching for the cropping sequences. • We found an impact of the preceding cop on N leaching after the following crop. • Catch crop and oilseed rape volunteers reduced N leaching risk. • Diversified cropping sequences can reduce N leaching by up to 40 %. Overuse of chemical fertiliser in cereal cropping systems has resulted in severe degradation of air and water quality. Diversifying cropping sequence with legumes provides a natural source of nitrogen (N), but also increases N leaching risks after their growing period. Here, we hypothesize that legumes and other break crops, i.e., crops grown to diversify the cropping sequence, reduce N leaching at the rotation scale due to their contribution to increasing nutrient use efficiency and crop N recovery of the following cereal crops. In two 4-year experiments conducted in northern France, we monitored agronomic performance and the changes in the soil mineral N content at field scale in six preceding crop-current crop combinations including winter wheat ( Triticum aestivum ), pea ( Pisum sativum L.) and oilseed rape ( Brassica napus L.). We quantified N leaching after each crop as a function of the preceding crop with a water-fluxes model based on soil mineral N content, climate data and soil characteristics. We then simulated N leaching at the rotation scale, for 20 years of climate conditions and various cropping management systems. We show that growing pea or oilseed rape reduced soil mineral N content at harvest of the following cereals (up to mean values of −28 and −19 kg N ha −1 respectively), and N leaching risks during winter of the following cereals compared to the wheat-wheat cropping sequence. Although N leaching was higher during the winter after pea was cultivated, the cumulative losses over four experimental years of the pea cropping sequences were not significantly higher than the no-break cropping sequences. Over the 20 climate years, sequences including pea, oilseed rape, volunteers or catch crops reduced simulated N leaching by up to 40 % compared to wheat monoculture. Our study confirms that N leaching not only depends on the current crop but is also affected by the preceding crop. A large potential reduction in nitrogen leaching could be achieved in many intensive cereal-growing regions with very limited cropping sequence diversity.

Herbicides Efficacy against Volunteer Oilseed Rape as Influenced by Spray Solution pH

The pH of the spray liquid is one of the factors influencing the efficacy of herbicides. Adjusting the appropriate parameters of the spraying liquid may reduce the consumption of pesticides, which is in line with the currently introduced legal standards and society’s requirements. In the greenhouse experiment, the influence of herbicides containing mesotrione, nicosulfuron, rimsulfuron, bromoxynil, and a mixture of nicosulfuron, rimsulfuron, and mesotrione on the efficacy of oilseed rape control was investigated. Oilseed rape (Brassica napus L. ssp. oleifera), apart from being an important crop, can become a nuisance weed in many fields as form of volunteer plants. Visual assessment, reduction of fresh weight, and chlorophyll fluorescence were performed. Individual herbicides influenced the tested parameters to a different extent. The pH of the spray liquid influenced the efficacy of individual plant protection products. The highest herbicidal efficacy in relation to the tested plants was observed in the case of combinations in which mesotrione was applied at a reduced and increased pH, nicosulfuron applied in an acidic and alkaline environment, rimsulfuron without pH modification, and all treatments in which bromoxynil was applied. The herbicides containing mesotrione and bromoxynil had the greatest impact on the photosystem II activity.

Effect of Winter Oilseed Rape Cropping on the Development of the Sugar Beet Cyst Nematode, Heterodera schachtii, and Control of Volunteer Plants as a Trap Crop Method

The integration of oilseed rape (OSR) into sugar beet rotation systems is restricted due to the very good host status of OSR for the beet cyst nematode (BCN) Heterodera schachtii. In contrast to sugar beet, the cultivation of winter OSR covers a longer period, but at a lower soil temperature regime. Thus, presumably one or two generations of BCN may develop during the cultivation of winter OSR, resulting in moderate multiplication rates of 1–2 in the present study. This multiplication rate was year-dependent, but not affected by different sowing times. For the first time, the present study identified volunteer OSR emerging in high densities post-harvest as a major risk for a high multiplication of BCN at optimum temperatures. The emergence of BCN females with offspring was observed very early, resulting in a significant population increase before 350-degree days (>8 °C) in inoculation experiments and in field investigations. Conducting treatment trials with glyphosate to control volunteer OSR in micro-plots and field experiments confirmed effective suppression of BCN reproduction when growth of volunteer OSR was interrupted at 250–350-degree days. Thus, data gained from BCN reproduction studies under controlled and field conditions provided a unique basis for the development of a trap crop method. The degree day model has been successfully implemented as part of an open access management tool.

Competition, reproduction ability, and control possibilities of conventional and Clearfield® volunteer oilseed rape in winter wheat

Three plot field trials (2014–2017) were carried out in Prague. The aim of the study was to evaluate the efficacy of herbicides against volunteers from Clearfield® (CL) and conventional oilseed rape (Brassica napus L.) in winter wheat (Triticum aestivum L.) and to quantify the effect of herbicide and application time on wheat yield. Autumn control (diflufenican, isoproturon, flumioxazin, metribuzin, penoxsulam, florasulam, chlorsulfuron were tested) of volunteer oilseed rape (OSR) was more effective than using the spring herbicide treatments (2,4-D, iodosulfuron, amidosulfuron, tritosulfuron, florasulam), especially against the CL OSR variety. Full control of both CL and conventional OSR was recorded only on plots treated by the combination of metribuzin + diflufenican + flufenacet. The most effective spring herbicide was 2,4-D, but its efficacy (82–95%) depended on the growth stage of OSR and application rate. Efficacy of spring herbicides against CL OSR was lower compared to that against conventional OSR, but there were large differences among tested herbicides. Efficacy of tested ALS inhibitors against volunteer CL OSR ranged between 20% (chlorsulfuron) and 77% (tritosulfuron + florasulam). Seed production of volunteer OSR ranged between 0 and 37,000 seeds m−2 while depending strongly on time of sowing and weather conditions during the autumn and winter. No seed of CL OSR matured on plots treated by metribuzin in autumn or 2,4-D at application rate 377 g ha−1 in spring. Volunteer OSR in competition with winter wheat caused almost 50% wheat yield loss on the untreated check. Although the efficacy of most spring herbicide treatments on conventional OSR was good, the competition effect of OSR on wheat during winter and early spring caused about 0.52–0.86 t ha−1 greater yield loss compared to autumn herbicide treatments.

Overcoming seed dormancy in oilseed rape (Brassica napus L.) with exogenous compounds

SummaryDormant seeds of oilseed rape (OSR) can persist in the soil and cause OSR volunteers in subsequent crops. Several approaches were tested in the laboratory and in the field to determine whether dormancy induction and seed persistence can be reduced by using dormancy‐breaking exogenous compounds. In a laboratory experiment, OSR seeds were coated with KNO3, micronutrients, or gibberellic acid (GA) prior to a secondary dormancy test. In a field experiment, seeds were coated in a manner analogous to the laboratory experiment, and then buried 10 cm deep in the soil for 2.5 months. In a practical demonstration, OSR plants were sprayed with either urea ammonium nitrate (UAN) or a commercial product containing GA prior to seed maturity. Seed coating (laboratory and field experiments) reduced secondary dormancy and seed persistence in the field by up to 99%. The efficiency of the treatments for mitigating secondary dormancy (laboratory and field experiments) in decreasing order was GA > micronutrients > KNO3 > control. With pre‐maturity spraying (practical demonstration), UAN reduced primary dormancy by up to 77% and the development of secondary dormancy by up to 38%; GA had no effect. Dormancy and seed persistence of OSR seeds may be reduced by a pre‐maturity UAN treatment of OSR mother plants, or by applying appropriate exogenous compounds to OSR seeds.

Timing and depth of post-harvest soil disturbance can reduce seedbank and volunteers of oilseed rape

Appropriate timing of post-harvest tillage to oilseed rape (OSR, Brassica napus L.) is crucial for the creation of a soil seed bank and unwanted OSR volunteers. Existing recommendations, however, can contrast with needs for early post-harvest tillage e.g. for pest control. To specify and to systematically further improve preventive volunteer management through post-harvest tillage of imidazolinone-tolerant oilseed rape (Clearfield®; CL OSR), field experiments were set up at two locations in two separate trial periods at each location (2013–2014 and 2014–2015) in south-west Germany. After OSR harvest, and average harvest losses of 1500 m−2 seeds, or artificially broadcasting of 20000 OSR seeds m−2, stubble tillage was performed at weekly intervals (immediate (0), 1, 2, 3, and 4 weeks) at each of three depths (1–2, 6–8, and 15–17cm). To depict a worst case scenario in which herbicides were ineffective, no herbicides were applied. There were significantly smaller soil seed banks found in spring the longer the period lasted between seed rain and stubble tillage; 265 vs 145 seeds m−2 referred to 0 week vs. 4 weeks on average. Depth of stubble tillage had no significant effects on the seed number in the soil. In the first spring after seed loss, 0–2.6 CL OSR volunteers m−2 were found in the winter wheat, and the number decreased with delayed timing depth of stubble tillage. These volunteers mainly emerged in the treatment of shallow stubble tillage (1–2cm), with 0.7-0.9 flowering volunteer m−2, while volunteers averaged less than 0.04 plants m−2 in the treatment “15–17cm”. OSR volunteers in winter wheat got ripened only in one out of the four fields, and produced 1.0 seed m−2 on average. The delay between harvest and stubble tillage can be limited to approximately three weeks if stubble tillage is performed at a depth of about 6–8cm; further delay did not bring additional advantage. We recommend to retain the stubble for three weeks as further delay does not bring additional advantage, and then to apply stubble tillage deeper than 6cm. Very superficial or shallow stubble tillage should be avoided. This procedure seems appropriate for avoiding oilseed rape volunteers without use of herbicides.

Reducing the build‐up of Plasmodiophora brassicae inoculum by early management of oilseed rape volunteers

Clubroot of oilseed rape (OSR), caused by Plasmodiophora brassicae, is a disease of increasing economic importance worldwide. Previous studies indicated that OSR volunteers, Brassica crops and weeds play a critical role in the predisposition of the disease. To determine the effect of timing of foliar application of the herbicide glyphosate or mechanical destruction of OSR volunteers in reduction of clubroot severity and resting spore production, a series of studies was conducted under controlled conditions with a susceptible OSR cultivar and an isolate of P. brassicae. Plants were inoculated by injecting a spore suspension beside the root hairs at growth stage 11–12 (BBCH scale) and were terminated at 7 (early) or 21 (late) days post‐inoculation (dpi). Under controlled conditions, the first symptoms on roots were observed as early as 7 dpi. The early application of glyphosate as well as early mechanical destruction resulted in significant (P ≤ 0.05) reduction in the development of clubroot symptoms, root fresh weight and the number of resting spores⁄g root. Furthermore, the effect of volunteer management on clubroot severity in the succeeding OSR was studied by inoculating plants with the resting spores obtained from treated clubbed roots. Inoculated OSR exhibited root clubs similar to the initial symptoms after 35 dpi. Plants that were inoculated with spore suspension from early treated roots resulted in significant reductions in clubroot incidence and severity. Conversely, plants inoculated with the spore suspension from the late treated roots displayed levels of clubroot similar to the plants inoculated with the spore solutions of positive controls.

Long-Term Monitoring of Field Trial Sites with Genetically Modified Oilseed Rape (Brassica napus L.) in Saxony-Anhalt, Germany. Fifteen Years Persistence to Date but No Spatial Dispersion.

Oilseed rape is known to persist in arable fields because of its ability to develop secondary seed dormancy in certain agronomic and environmental conditions. If conditions change, rapeseeds are able to germinate up to 10 years later to build volunteers in ensuing crops. Extrapolations of experimental data acted on the assumption of persistence periods for more than 20 years after last harvest of rapeseed. Genetically-modified oilseed rape—cultivated widely in Northern America since 1996—is assumed not to differ from its conventional form in this property. Here, experimental data are reported from official monitoring activities that verify these assumptions. At two former field trial sites in Saxony-Anhalt genetically-modified herbicide-resistant oilseed rape volunteers are found up to fifteen years after harvest. Nevertheless, spatial dispersion or establishment of GM plants outside of the field sites was not observed within this period.

Field history of imidazolinone-tolerant oilseed rape (Brassica napus) volunteers in following crops under six long-term tillage systems

Volunteer oilseed rape (OSR, Brassica napus L.) exhibits weedy behavior in crops, and can contribute to gene flow or unwanted seed admixture, particularly if its variety is tolerant to specific herbicides and if the proportion of OSR in a crop rotation is high. The aim of this study was to monitor the fate of seeds of imidazolinone-tolerant oilseed rape (Clearfield®; CL OSR) lost at harvest over the two years following its intentional sowing. A 5-yr experiment (2011–2015) with non-CL OSR and CL OSR in the same rotation was conducted on an existing long-term tillage experiment in south-west Germany to investigate OSR volunteer dynamics. The experiment included different modes of primary tillage (inversion tillage, non-inversion tillage, no-till, with or without additional stubble tillage prior to primary tillage). The crop sequence was non-CL OSR, winter wheat (Triticum aestivum L.), CL OSR (a medium and a high dormancy variety), winter wheat, and maize (Zea mays L.). High dormancy CL OSR resulted in a larger soil seed bank (147 vs. 58 seeds m−2), but in fewer volunteers (0.9 vs. 1.9 volunteers m−2) than the medium dormancy variety in the first year after CL OSR. Dormancy release likely resulted in different volunteer emergence rates of the two varieties. Immediate stubble tillage after CL OSR increased seed bank and volunteers by 0.93 and 12.7 times, respectively. Inversion tillage resulted in 30 times fewer volunteers in the first year after CL OSR, but in an equal volunteer number in the second year compared to non-inversion tillage. Slight segregation of imidazolinone-tolerant genes occurred in the offspring of CL OSR, likely leading to different CL herbicide-tolerance levels in volunteers though the number of these individuals was small.Sound strategies to control OSR volunteers should include (1) use of low dormancy varieties with low potential to establish a seed bank, (2) varieties with fast dormancy release to trigger more dormant seeds to germinate in a very short period, and (3) a period of time between harvest of OSR and first tillage operation to reduce the possibility of seeds entering soil seed bank.

Molecular marker-based identification of oilseed rape volunteers with different secondary dormancy levels in oilseed rape fields

Pod dehiscence of oilseed rape (OSR) occurs before and during harvest, resulting in seed losses and in seed persistence in the soil for several years. Persisting seeds can emerge as volunteers in subsequent crops. Volunteers with deviating traits and especially genetically modified (GM) oilseed rape volunteers can impair the product quality of an oilseed rape crop. Under experimental field conditions seed persistence and volunteer abundance were found to be efficiently controlled by delayed post-harvest tillage and selection of cultivars with low secondary seed dormancy.To investigate the long-term factors affecting volunteer abundance in farmer-managed fields, an on-farm survey was carried out in winter oilseed rape fields at different locations in Germany, using artificial sowing gaps as one method to detect putative volunteers. Molecular marker analysis (ISSR-PCR), which was performed for 11 out of 31 fields, confirmed that most of the plants identified within sowing gaps were indeed volunteers. In fields with low OSR cropping frequency high percentages of volunteers could be assigned to previously cultivated varieties. Results indicate that seeds of varieties with high secondary dormancy (HD) persist in the fields for longer times and in larger numbers than seeds of varieties with low secondary dormancy. However, cultivation of HD varieties did not necessarily result in high volunteer abundance, as location and management factors have further impact on long-term seed survival. Nevertheless, with respect to GM oilseed rape cultivation proper variety selection will be an important means to assure co-existence with conventional oilseed rape.

Response of imidazolinone‐tolerant and ‐susceptible volunteer oilseed rape (Brassica napus L.) to ALS inhibitors and alternative herbicides

Imidazolinone-tolerant oilseed rape (Brassica napus L.) varieties are currently grown in Canada, North America, Chile and Australia with high acreage. A Europe-wide introduction has started and will be pushed further for both spring and winter varieties. The primary aim of this study was to evaluate the impact of imidazolinone tolerance for future volunteer oilseed rape control in subsequent crops, particularly winter wheat. A greenhouse bioassay showed cross-tolerance of imidazolinone-tolerant oilseed rape towards sulfonylureas, triazolopyrimidines and sulfonylaminocarbonyltriazolinones (resistance factors between 5 and 775), with a homozygous variety expressing a much higher tolerance level compared with a heterozygous variety. Calculated ED90 values suitable for controlling tolerant plants were always much higher than the recommended herbicide dose. Generally, results were confirmed under field conditions, but with higher efficacies than expected in some cases (e.g. florasulam). Herbicides with an alternative mode of action were found to be effective in controlling imidazolinone-tolerant volunteers in subsequent winter wheat crops. Herbicide strategies have to be adjusted for volunteer control in subsequent crops if imidazolinone-tolerant oilseed rape varieties are to be grown. However, agronomic tools (harvest date, harvest technique, tillage) should be used conscientiously in the first place to keep volunteer oilseed rape densities at the lowest possible level.

Competitiveness and yield impact of volunteer oilseed rape (Brassica napus) in winter and spring wheat (Triticum aestivum)

Volunteer oilseed rape is a relevant weed in many crop rotations due to seed persistence and dormancy. With the intro-duction of imidazolinone-tolerant oilseed rape varieties in Europe, herbicide-based control strategies of volunteers in cereals may become ineffective in the future. Experiments were conducted on experimental fields and in outdoor pots in Bingen (Germany) to quantify the effect of oilseed rape volunteers on yield and quality parameters of wheat. To simulate competition, oilseed rape was sown into wheat plots at a range of 2 to 320 plants m−2. Both spring and winter varieties of oilseed rape and wheat were used in the experiments. Crop yield parameter were expressed as the number of heads m−2, net yield as kg ha−1 and hectolitre−1 weight. Wheat moisture content, percentage of dockage, wheat thousand-kernel weight, and crude protein content were determined. Significant negative correlations were detected between the yield parameters heads m−2 and yield on the one hand, and oilseed rape density on the other hand. Moisture content of wheat and percentage of dockage were positively correlated with the volunteer density. No clear correlation was found between volunteer oilseed rape density and thousand-kernel weight, hectolitre weight and crude protein content of wheat. The highest volunteer density of 261 plants m−2 caused a maximum yield loss of 68% in winter wheat. Based on a non-linear regression analysis, a single volunteer oilseed rape plant m−2 is able to cause a yield loss of 0.74 to 1.61% in the field, which corresponds to 26.3 kg ha−1 (spring oilseed rape in spring wheat (SOSR × SW)) and 147.3 kg ha−1 (winter oilseed rape in winter wheat (WOSR×WW)), respectively. However, the introduction of imidazolinone-tolerant oilseed rape varieties will challenge farmers in terms of volunteer management. Control of volunteers is important to reduce yield losses. Accurate, delayed tillage after oilseed rape harvest and control of imidazolinone-tolerant volunteers with herbicides with other modes of action than those grouped into HRAC B will contribute to the successful avoidance and removal of imidazolinone-tolerant volunteers from subsequent crops.

Marker-assisted identification of oilseed rape volunteers in oilseed rape (Brassica napus L.) fields

Seed losses of oilseed rape (OSR) occur before and during harvest. Seeds can persist in soils for several years and often appear as volunteers in successive crops. Oilseed rape volunteers (OSRV) can harm the product quality if they emerge in subsequent OSR crops differing in fatty acid profile or other quality traits. Several factors can affect volunteer abundance. Important factors identified under controlled conditions are OSR post-harvest management (stubble tillage) and OSR variety selection in terms of the genotypic secondary dormancy potential. In the growing seasons 2009/10 and 2010/11, OSR volunteer abundance was surveyed on agricultural OSR fields in Germany. The main objective was to assess factors affecting volunteer abundance under on-farm conditions by a prediction model. Volunteer numbers were determined by two different approaches: 1. Cultivation of a semi-dwarf hybrid OSR variety, and 2. Survey of OSR volunteers between wide rows in OSR crops. Data analysis taking into account farmers´ questionnaires revealed that the factor “variety selection” was not feasible for the prediction model. As an alternative approach to assess the impact of variety selection on volunteer abundance, the genotypic origin of volunteers was investigated by DNA fingerprints using ISSR (Inter Simple Sequence Repeat)-PCR. Molecular marker analysis confirmed that OSR volunteers were to a large extent identified correctly. In four of seven selected fields, plants could be assigned to open pollinating varieties cultivated previously. In two of these fields, a high dormancy (HD) variety was found to account for a large proportion of the volunteers. In contrast, low dormancy varieties appeared only rarely as volunteers. Hybrid varieties could never be identified, due to genetic segregation in the F2 generation. Taken together, the results indicate that HD varieties substantially contribute to high OSR volunteer abundance in agricultural fields, although more data are needed to confirm this. Keywords: Brassica napus , ISSR-PCR, secondary dormancy, seed persistence, volunteers, winter oilseed rape Marker-vermittelte Identifizierung von Durchwuchsraps in Rapsfeldern Samenverluste entstehen bei Winterraps vor und wahrend der Ernte. Die Samen konnen im Boden fur Jahre uberdauern und erscheinen oft als Durchwuchsraps in Folgekulturen. Durchwuchsraps gentechnisch veranderter Sorten kann die Produktqualitat schmalern, wenn er in nachfolgend angebautem Raps mit verandertem Fettsauremuster oder anderen speziellen Qualitatsmerkmalen auftritt. Mehrere Faktoren konnen die Abundanz von Durchwuchsraps beeinflussen. Wichtige Einflussfaktoren, die unter kontrollierten Bedingungen festgestellt wurden, sind die Stoppelbearbeitung nach der Rapsernte und die Rapssortenwahl auf Grund der genotypisch beeinflussten sekundaren Dormanz. In den Anbaujahren 2009/10 und 2010/11 wurde auf Rapsfeldern in Deutschland das Auftreten von Durchwuchsraps untersucht. Hauptziel war es, Ergebnisse aus vorherigen Studien durch ein Prognosemodell fur Durchwuchsraps unter Praxisbedingungen zu bestatigen. Die Abundanz von Durchwuchsraps wurde mit zwei Methoden ermittelt: 1. Aussaat einer Halbzwerg-Hybridrapssorte, und 2. Erhebung von Durchwuchsraps in Rapsfeldern mit grosen Saatreihenabstanden. In der statistischen Auswertung unter Einbeziehung der von den Landwirten erhaltenen Informationen erwies sich der Faktor „Rapssortenwahl“ jedoch auf Grund der Vielzahl der nacheinander angebauten Sorten als unbrauchbar. Alternativ wurde daher die Sortenherkunft von Durchwuchsrapspflanzen mit Hilfe von genetischen Fingerabdrucken unter Verwendung der ISSR (Inter Simple Sequence Repeat)-PCR untersucht, um auf diese Weise eine Beziehung zwischen der Rapssortenwahl und der Abundanz von Durchwuchsraps zu prufen. Der Einsatz der molekularen Marker zeigte, dass die Durchwuchspflanzen bei der Felderhebung weitgehend korrekt erfasst wurden. Auf vier von sieben ausgewahlten Feldern konnten die Pflanzen Liniensorten zugeordnet werden, die in den vorangegangenen Jahren angebaut worden waren. Auf zwei dieser Felder machte eine hoch dormante (HD) Liniensorte den Grosteil des Durchwuchses aus. Im Gegensatz trugen gering dormante Sorten kaum zum Raps-Durchwuchs bei. Hybridsorten konnten auf Grund der genetischen Aufspaltung in der F2-Generation in keinem Fall identifiziert werden. Zusammengefasst weisen die Ergebnisse darauf hin, dass HD-Sorten wesentlich zur Abundanz von Durchwuchsraps auf landwirtschaftlichen Flachen beitragen, auch wenn dies noch durch zusatzliche Daten bestatigt werden muss. Stichworter: Brassica napus , Durchwuchsraps, ISSR-PCR, Samenuberdauerung, sekundare Dormanz, Winterraps

Crop management for optimal low-linolenic rapeseed oil production—Field experiments and modelling

Oil of conventional oilseed rape (OSR) varieties with 7–10% alpha-linolenic acid content (LAC) might oxidize when heated, resulting into an unpleasant odor. Varieties with low (around 3%) LAC have been bred to provide industries with a new raw material for frying media production. However, high-oleic low-linolenic (HOLL) OSR quality could be compromised by conventional OSR through pollen flow or volunteers. Both nearby fields and volunteers of conventional OSR growing in the HOLL field or in its margins could thus be the cause of a reduced quality. Crop management practices such as regional field pattern, crop rotation, weed control and soil tillage might be decisive. The GeneSys model was initially developed to quantify the effects of cropping systems on gene flow between genetically-modified (GM) and non-GM crops. In this work, it was improved and then used to predict LAC of OSR harvests, particularly HOLL ones, in different situations. Field experiments carried out at the experimental station in Changins (VD), Switzerland, in 2005–2006 showed that LAC was controlled by two additive quantitative genes. Consequently, an additive model was used for calculations with GeneSys. Results also showed that beyond a 20 m distance, a field of conventional OSR caused only a minor increase in LAC in a neighbouring HOLL OSR field, meaning that it is highly unlikely that pollen dispersal will compromise HOLL OSR quality under farmers’ conditions. These data were also used to evaluate the prediction quality of GeneSys. Briefly, the final LAC was slightly underestimated by the model, especially in the case of a high amount of conventional OSR volunteers leading to high LAC. Both experiments and simulations showed that the presence of volunteers of conventional OSR in the HOLL field had the most dramatic effect. In a short crop rotation, an important amount of volunteers significantly increased the LAC, but this can be controlled by adequate tillage and weed control in other crops of the rotation. Furthermore, in Switzerland, OSR is usually grown with an interval of at least 4 years in normal crop rotations, which is usually enough to prevent major contamination by volunteers if they are correctly managed.

Persistence of an oilseed rape transgene in the environment

Transgenic bromoxynil (BX)-resistant spring oilseed rape ( Brassica napus L.) was grown commercially in Canada only for two crop seasons – 2000 and 2001. We investigated the persistence of suspected BX-resistant oilseed rape volunteers in a 64-ha wheat field in Saskatchewan, Canada in 2007, 7 years after the BX-resistant cultivar BX Armor was grown. A small oilseed rape volunteer population, estimated at less than 100 plants, was observed in three main areas or patches in the field. These patches were located in low-lying areas that were too wet to plant or spray with herbicides in 2007. Viable seed was collected from 35 mature volunteers and F 1 progeny screened with BX at 280 g ai/ha in the greenhouse. Progeny of all of the volunteers were visually rated as BX-resistant; the presence of the Oxy 235 transgene in leaf tissue of progeny of all volunteers was confirmed by PCR analysis. This study has documented the longest persistence of oilseed rape volunteers in Canada. Volunteers were not observed in 2008 or 2009, because of drought conditions in spring of both years. Results support the findings from previous studies that persistence of volunteer oilseed rape populations in western Canada is generally ephemeral or transitory in the absence of seed bank immigration. However, this study shows that oilseed rape transgenes can persist in the environment for a number of years even after all cultivars with the conferred trait are removed from the market.

You reap what you sow – or do you? – volunteers in organic row-sown and broadcast-sown oilseed rape fields

The frequency and origin of oilseed rape volunteers in organic row and broadcast-sown oilseed rape fields was evaluated using DNA markers (ISSR) for analysis of potential volunteers in nine organic oilseed rape fields with different history. Using the software AFLPOP, the potential volunteers were assigned to variety by comparing their ISSR fingerprints with those of present and previous varieties. Results showed that two of the five row-sown fields, had high numbers of volunteer in the row (5 and 9 volunteers m −2), and as inter-row volunteers were also present (0.9 and 3.6 volunteers m −2), the recommended inter-row hoeing should not be neglected. Potential volunteers were also identified in the broadcast-sown fields, but their identity could not be proven. In a scenario where GM oilseed rape is cultivated previous to the organic oilseed rape, the present results indicate that the frequency of GM volunteers would exceed the threshold of 0.9%, and thus GM labelling would be demanded. Some of the volunteers belonged to varieties cultivated 8–11 years previously, indicating a long persistence of volunteer populations. What you reap might be added in the past – with consequences for organic farmers’ production and earning.

How to model and simulate the effects of cropping systems on population dynamics and gene flow at the landscape level: example of oilseed rape volunteers and their role for co-existence of GM and non-GM crops

Agricultural landscapes comprise cultivated fields and semi-natural areas. Biological components of these compartments such as weeds, insect pests and pathogenic fungi can disperse sometimes over very large distances, colonise new habitats via insect flight, spores, pollen or seeds and are responsible for losses in crop yield (e.g. weeds, pathogens) and biodiversity (e.g. invasive weeds). The spatiotemporal dynamics of these biological components interact with crop locations, successions and management as well as the location and management of semi-natural areas such as roadverges. The objective of this investigation was to establish a modelling and simulation methodology for describing, analysing and predicting spatiotemporal dynamics and genetics of biological components of agricultural landscapes. The ultimate aim of the models was to evaluate and propose innovative cropping systems adapted to particular agricultural concerns. The method was applied to oilseed rape (OSR) volunteers playing a key role for the coexistence of genetically modified (GM) and non-GM oilseed rape crops, where the adventitious presence of GM seeds in non-GM harvests (AGMP) could result in financial losses for farmers and cooperatives. A multi-year, spatially explicit model was built, using field patterns, climate, cropping systems and OSR varieties as input variables, focusing on processes and cultivation techniques crucial for plant densities and pollen flow. The sensitivity of the model to input variables was analysed to identify the major cropping factors. These should be modified first when searching for solutions limiting gene flow. The sensitivity to model processes and species life-traits were analysed to facilitate the future adaptation of the model to other species. The model was evaluated by comparing its simulations to independent field observations to determine its domain of validity and prediction error. The cropping system study determined contrasted farm types, simulated the current situation and tested a large range of modifications compatible with each farm to identify solutions for reducing the AGMP. The landscape study simulated gene flow in a large number of actual and virtual field patterns, four combinations of regional OSR and GM proportions and three contrasted cropping systems. The analysis of the AGMP rate at the landscape level determined a maximum acceptable GM OSR area for the different cropping systems, depending on the regional OSR volunteer infestation. The analysis at the field level determined minimum distances between GM and non-GM crops, again for different cropping systems and volunteer infestations. The main challenge in building spatially explicit models of the effects of cropping systems and landscape patterns on species dynamics and gene flow is to determine the spatial extent, the time scale, the major processes and the degree of mechanistic description to include in the model, depending on the species characteristics and the model objective. These models can be used to study the effects of cropping systems and landscape patterns over a large range of situations. The interactions between the two aspects make it impossible to extrapolate conclusions from individual studies to other cases. The advantage of the present method was to produce conclusions for several contrasted farm types and to establish recommendations valid for a large range of situations by testing numerous landscapes with contrasted cropping systems. Depending on the level of investigation (region or field), these recommendations concern different decision-makers, either farmers and technical advisors or cooperatives and public decision-makers. The present simulation study showed that gene flow between coexisting GM and non-GM varieties is inevitable. The management of OSR volunteers is crucial for containing gene flow, and the cropping system study identified solutions for reducing these volunteers and ferals in and outside fields. Only if these are controlled can additional measures such as isolation distances between GM and non-GM crops or limiting the proportion of the region grown with GM OSR be efficient. In addition, particular OSR varieties contribute to limit gene flow. The technical, organisational and financial feasibility of the proposed measures remains to be evaluated by a multi-disciplinary team.

Dispersal and persistence of genetically modified oilseed rape around Japanese harbors

The possibility of gene transfer from genetically modified oilseed rape (OSR) to its cultivated or wild relatives is of concern since its commercial cultivation, because of its potential weediness and impact on the environment. Introgression of modified genes can affect conservation of agricultural crops, because there are many cultivars and wild Brassicaceae that may cross with genetically modified OSR (Brassica napus) in Japan. Japan imports more than 2 million tons of OSR a year from Canada and other countries. Since volunteers of GM OSR were found around harbors in 2004, a lot of feral GM OSR was discovered in Japan. To consider the way how to keep domestic Brassicaceae from GM contamination, we surveyed and analyzed the dispersal and persistence of GM OSR around Japanese harbors. We present the cause and abundance of GM OSR in Japan by this paper. Survey of the feral OSR was performed several times a year at different seasons when domestic OSR either grows or does not around port areas. Detection of herbicide tolerance in feral B. napus was done by test papers that cross react with the modified gene product. Two kinds of herbicide tolerance (glyphosate and glufosinate) were tested. The feral B. napus were discovered around all 13 harbors that import rapeseeds from foreign countries. Genetically modified, herbicide-tolerant OSR were frequently found in the surveyed populations. Two kinds of herbicide-tolerant OSR (glyphosate- and glufosinate-tolerant) were discovered in a natural condition 40 km from port to an oil factory where 60,000 tons of OSR seed are processed a year. The cause of voluntary growth of OSR is seed spillage during transportation by trucks from harbors to oil factories and other processing facilities. Some of the feral OSR growing along the roadsides of transport paths exhibited perennial growth spilling their seeds around the places. Alteration of the generation of feral GM OSR was discovered for the first time in Japan as a result of this study. We studied the yearly change of feral OSR abundances focusing on Yokkaichi port over the 4 years since 2004. The rate of GM OSR increases year to year, and reaches nearly 90% in 2008. The possibility and consequences of gene transfer from the genetically modified OSR to domestic species (B. rapa and B. juncea) were discussed in relation to impact on domestic agriculture and on environments. Evolutional meaning of the gene transfer was also discussed with respect to the gene construct of GM OSR. This study shows the importance of another pathway of modified gene transfer to non-GM relative species by seed transportation in addition to pollen transfer from commercial cultivation of genetically modified OSR. We identified unintended dispersal and persistence of GM OSR around Japanese harbors that import OSR from Canada and other countries. Both glyphosate- and glufosinate-tolerant feral B. napus were discovered. The cause of volunteer OSR is spillage of the seeds during transportation by truck to oil factory. The feral GM OSR sometimes showed perennial growth in Japanese phonological conditions which are not observed for domestic Brassicaceae. In addition, we confirmed an alteration of generations by feral GM OSR in Japan. The possibility of cross pollination and GM gene introgression to domestic varieties can occur in these environments. To improve the situation, each responsible organization, company, administration, or government should establish measures how to stop the dispersal and persistence of GM OSR in nature. Also, the GM plant developers are responsible for revising this situation.

Comparative study of the efficiency of buffer zones and harvest discarding on gene flow containment in oilseed rape. A modelling approach

Oilseed rape (OSR) genes can escape fields in space via pollen and seeds and in time via volunteers resulting from seeds lost before or during oilseed rape harvests. Previous simulation studies and field observations showed that co-existence at the landscape level of contrasting OSR varieties such as genetically modified (GM) and non-GM varieties require costly measures that are difficult to implement, such as isolation distances between OSR fields and stringent volunteer control in all fields and road margins. In the present study, two local strategies, non-GM buffer zones around GM fields and discarding the harvest of boundary plants of non-GM fields, were tested in a simulation study using the GENESYS model. This model, which was modified here to improve the prediction of volunteer reproduction and pollen dispersal, quantifies the effects of cropping system on gene flow in landscapes over the years. The evaluation of the improved model version with independent field observations showed that cross-pollination of fields was accurately predicted up to 50 m and systematically underestimated above that distance, though fields were still ranked correctly. A corrective factor should therefore be applied to predictions in case of low regional OSR and GM proportions (which result into large distances between fields). To study the effects of the two local strategies, simulations were carried out in four contrasted case studies, based on different landscapes, regional OSR and GM proportions, cropping systems and OSR varieties. In these situations, harvest discarding was needless when volunteers were well controlled because the GM impurity in non-GM harvests was well below the EU labelling thresholds; it was useless when OSR contained male-sterile plants or when the landscape was infested by volunteers because large parts of the fields had to be discarded to respect impurity thresholds, which is financially unacceptable. Buffer zones were useful if the non-GM varieties comprised male-sterile plants or if the non-GM fields were small, but only if volunteers were well controlled and harvest impurity was already close to the labelling threshold. Buffer zones appeared considerably more efficient in reducing harvest impurity than harvest discarding because they not only increase the distance between GM and non-GM fields but also diminish the proportion of GM pollen in the total pollen cloud over landscapes. Harvest discarding could possibly be interesting for isolated OSR crops surrounded by bare ground or small crops, an effect that was not tested here. The present study showed that efforts should be dedicated to characterizing and modelling of gene flow at the landscape level, as well as the collection of datasets for the evaluation of these models in many landscapes and configurations. Local measures tested here are insufficient for ensuring harvest purity. Therefore, future work should focus on finding additional measures are necessary to manage OSR volunteers which constitute the major risk factor for OSR harvest purity.