Winter Oilseed Rape Fields Research Articles

Efficient qPCR estimation and discrimination of airborne inoculum of Leptosphaeria maculans and L. biglobosa, the causal organisms of phoma leaf spotting and stem canker of oilseed rape.

Detection of the inoculum of phytopathogens greatly assists in the management of diseases, but is difficult for pathogens with airborne fungal propagules. Here, we present experiments to determine the abundance and distribution frequencies of the ascospores of Leptosphaeria (Plenodomus) species that were collected on the tapes of volumetric Hirst-type traps near oilseed rape fields in Poznan, Poland and Harpenden, UK. Fungal detection and species discrimination were achieved using a SYBR-Green quantitative polymerase chain reaction (qPCR) with two different pairs of primers previously reported to differentiate Leptosphaeria maculans (Plenodomus lingam) or L. biglobosa (P. biglobosus). Detection was successful even at fewer than five spores per m3 of air. The primer pairs differed in the correlation coefficients obtained between DNA yields and the daily abundance of ascospores that were quantified by microscopy on duplicate halves of the spore trap tapes. Important differences in the specificity and sensitivity of the published SYBR-Green assays were also found, indicating that the Liu primers did not detect L. biglobosa subclade 'canadensis', whereas the Mahuku primers detected L. biglobosa subclade 'canadensis' and also the closely related Plenodomus dezfulensis. Comparisons confirmed that application of qPCR assays to spore trap samples can be used for the early detection, discrimination and quantification of aerially dispersed L. maculans and L. biglobosa propagules before leaf spot symptoms are visible in winter oilseed rape fields. The specificity of the primers must be taken into consideration because the final result will greatly depend on the local population of the pathogen. © 2023 Society of Chemical Industry.

Temporal Dynamics of CO2 Fluxes Measured with Eddy Covariance System in Maize, Winter Oilseed Rape and Winter Wheat Fields

The full understanding of variation and temporal changes in carbon dioxide (CO2) fluxes in cropland may contribute to a reduction in CO2 emissions from agriculture. The aim of this study was to determine the CO2 exchange intensity in the three most popular crops in Poland. The CO2 fluxes in summer maize, winter oilseed rape and winter wheat fields were measured using the eddy covariance system. The seasonal dynamics of CO2 fluxes for all studied crops varied from each other due to individual dynamics in atmospheric CO2 assimilation of each species through the growing season. The weighted average values of CO2 fluxes calculated for the entire vegetation period were −22.22 µmol CO2 m−2 s−1, −14.27 µmol CO2 m−2 s−1 and −11.95 µmol CO2 m−2 s−1 for maize, oilseed rape and wheat, respectively. All the studied agro-ecosystems were carbon sinks during the growing season. The highest negative values of CO2 fluxes (−36.31 µmol CO2 m−2 s−1 and −33.56 µmol CO2 m−2 s−1) were observed in the maize field due to the high production of biomass. However, the maize field was also the most significant carbon source due to slow growth of plants at the beginning of the growing season, and due to leaving the field fallow after harvest until the next sowing. In these two periods, the CO2 fluxes ranged from 0.59 µmol CO2 m−2 s−1 to 3.72 µmol CO2 m−2 s−1. CO2 exchange over wheat and oilseed rape fields was less intense, but more even throughout the growing season. In the wheat field, the CO2 fluxes ranged from −1.70 µmol CO2 m−2 s−1 to −23.49 µmol CO2 m−2 s−1 and in the oilseed rape field they ranged from −1.40 µmol CO2 m−2 s−1 to −22.08 µmol CO2 m−2 s−1. In addition, the catch crop in the oilseed rape field contributed to the intensive absorption of CO2 after harvesting the main crop.

Cold winters drive consistent and spatially synchronous 8-year population cycles of cabbage stem flea beetle.

Population cycles have been observed in mammals as well as insects, but consistent population cycling has rarely been documented in agroecosystems and never for a beetle. We analysed the long-term population patterns of the cabbage stem flea beetle Psylliodes chrysocephala in winter oilseed rape over 50 years. Psylliodes chrysocephala larval density from 3045 winter oilseed rape fields in southern Sweden showed strong 8-year population cycles in regional mean density. Fluctuations in larval density were synchronous over time across five subregional populations. Subregional mean environmental variables explained 90.6% of the synchrony in P. chrysocephala populations at the 7-11year time-scale. The number of days below -10°C showed strong anti-phase coherence with larval densities in the 7-11year time-scale, such that more cold days resulted in low larval densities. High levels of the North Atlantic Oscillation weather system are coherent and anti-phase with cold weather in Scania, Sweden. At the field-scale, later crop planting date and more cold winter days were associated with decreased overwintering larval density. Warmer autumn temperatures, resulting in greater larval accumulated degree days early in the season, increased overwintering larval density. Despite variation in environmental conditions and crop management, 8-yearcycles persisted for cabbage stem flea beetle throughout the 50 years of data collection. Moran effects, influenced by the North Atlantic Oscillation weather patterns, are the primary drivers of this cycle and synchronicity. Insect pest data collected in commercial agriculture fields is an abundant source of long-term data. We show that an agricultural pest can have the same periodic population cycles observed in perennial and unmanaged ecosystems. This unexpected finding has implications for sustainable pest management in agriculture and shows the value of long-term pest monitoring projects as an additional source of time-series data to untangle the drivers of population cycles.

Clopyralid applied to winter oilseed rape (Brassica napus L.) contaminates the food products nectar, honey and pollen

Clopyralid is a systemic herbicide used in oilseed rape and other crops. It was found in Danish honey from 2016 in concentrations exceeding the maximum residue level (MRL) of 0.05 mg kg−1. About 50% of the Danish honey is based on nectar from winter oilseed rape. In 2019 and 2020, winter oilseed rape fields were sprayed with clopyralid just before the assigned spraying deadline. At flowering, nectar and pollen samples were collected and the content of clopyralid was measured. Honey and pollen samples were also collected from beehives next to ten conventional winter oilseed rape fields sprayed with clopyralid. Clopyralid was found in nectar and pollen from the experimental fields, and in honey and pollen from beehives next to the conventional fields. For most samples the content in nectar and honey exceeded the MRL. The concentrations found, may not pose any health risk for consumers, as the MRL is based on the original detection limit and not on toxicological tests. However, it can have a significant economical consequence for the beekeepers, who are not allowed to sell the honey if the concentration of clopyralid exceeds 0.1 mg kg−1. Reducing the acceptable applicable rate of clopyralid or implementing an earlier deadline for spraying of clopyralid may reduce the risk of contaminating bee food products. However, if it is not possible to obtain a satisfactory effect of clopyralid on the weed flora under these conditions, spraying with pesticides containing clopyralid should be restricted in winter oilseed rape. Determination of an MRL value based on toxicological tests might result in a higher value and make it acceptable selling the honey containing higher levels of clopyralid.

Nitrification inhibitors reduce N2O emissions induced by application of biogas digestate to oilseed rape

Winter oilseed rape (WOSR) is the major oil crop cultivated in Europe and the most important feedstock for biodiesel. Up to 90% of the greenhouse gas (GHG) emissions from biodiesel production can occur during oilseed rape cultivation. Therefore, mitigation strategies are required and need to focus on direct nitrous oxide (N2O) emission as one of the largest GHG contributors in biodiesel production. Earlier studies show that nitrification inhibitors (NIs) can reduce N2O emissions derived from N-fertilization. Since information on the effect of biogas digestates with or without NIs on N2O emissions from WOSR fields is scarce, the aim of this study was to evaluate their effects on N2O emissions, mineral N dynamics, and oil yield in WOSR production fertilized with digestate. The study was conducted at five sites across Germany over three years resulting in 15 full site-years data sets. Across all sites and years, N2O emission from WOSR fertilized with biogas digestate (180 kg NH4+-N ha−1yr−1) ranged between 0.2 and 3.5 kg N2O–N ha−1 yr−1. Due to the reduction of the nitrate concentrations following digestate application, application of NI significantly reduced annual N2O emission by 36%. Our results demonstrate that NI can be an effective measure for reducing N2O emissions from digestate application, but its effectiveness depends on soil and weather conditions, and ultimately on the site-specific potential for N2O production and release. There was no effect of NI application on grain and oil yield.

Evaluating predictive performance of statistical models explaining wild bee abundance in a mass‐flowering crop

Wild bee populations are threatened by current agricultural practices in many parts of the world, which may put pollination services and crop yields at risk. Loss of pollination services can potentially be predicted by models that link bee abundances with landscape‐scale land‐use, but there is little knowledge on the degree to which these statistical models are transferable across time and space. This study assesses the transferability of models for wild bee abundance in a mass‐flowering crop across space (from one region to another) and across time (from one year to another). The models used existing data on bumblebee and solitary bee abundance in winter oilseed rape fields, together with high‐resolution land‐use crop‐cover and semi‐natural habitats data, from studies conducted in five different regions located in four countries (Sweden, Germany, Netherlands and the UK), in three different years (2011, 2012, 2013). We developed a hierarchical model combining all studies and evaluated the transferability using cross‐validation. We found that both the landscape‐scale cover of mass‐flowering crops and permanent semi‐natural habitats, including grasslands and forests, are important drivers of wild bee abundance in all regions. However, while the negative effect of increasing mass‐flowering crops on the density of the pollinators is consistent between studies, the direction of the effect of semi‐natural habitat is variable between studies. The transferability of these statistical models is limited, especially across regions, but also across time. Our study demonstrates the limits of using statistical models in conjunction with widely available land‐use crop‐cover classes for extrapolating pollinator density across years and regions, likely in part because input variables such as cover of semi‐natural habitats poorly capture variability in pollinator resources between regions and years.

Effect of soil compaction and different soil tillage systems on chemical properties of soil and presence of earthworms in winter oilseed rape fields

Effect of soil compaction and different soil tillage systems on chemical properties of soil and presence of earthworms in winter oilseed rape fields

Overwintering of pollen beetles and their predators in oilseed rape and semi-natural habitats

Semi-natural habitats (SNH) maintain high levels of biodiversity and ecosystem functioning within agroecosystems. While management recommendations for SNH to promote biodiversity and optimize natural pest control, have mostly focused on improving food resources for predators, overwintering conditions have hitherto received less attention. The success of conservation biological control is often hampered by a lack of knowledge on how different habitats and their associated traits drive the overwintering of both, crop pests and their natural enemies. Moreover, there are concerns that SNH may act as reservoirs for crop pests.We investigated the overwintering of pollen beetles (Meligethes spp.) and their predators (predatory ground beetles) across 40 habitats of all major types of SNH as well as 8 winter oilseed rape (WOSR) fields, to identify the importance of type and key traits of habitats. Overwintering of pollen beetles was higher in WOSR fields (7 individuals per 0.25 m2) and forest edges (4) compared to flower strips (2) or forest interiors (1). Similarly, overwintering of predatory ground beetles was higher in forest edges and WOSR fields (11 and 10 individuals, respectively) than in flower strips, meadows or hedgerows (4, 4 and 2 individuals). The predator-prey ratio (number of predatory ground beetles / number of pollen beetles) was higher in forest edges than in flower strips, meadows or hedgerows, and intermediate in WOSR fields. Pollen beetle numbers were negatively associated with increasing litter cover and positively with increasing bare soil, while predatory ground beetles were positively associated with soil bulk density and bare soil cover. The proportion of SNH at the landscape level (1 km radius) did not affect overwintering pollen beetles, predatory ground beetles or predator-prey ratio.We conclude that WOSR fields, rather than SNH are the major overwintering habitat and source of spring colonisation of WOSR by pollen beetles. Forest edges promote predatory ground beetles rather than pollen beetle populations according to their disproportionally high value of overwintering individuals. Agri-environmental measures to promote predatory ground beetles rather than pollen beetles should promote overwintering habitats with compact soils and high litter cover.

Landscape configuration affects herbivore\u2013parasitoid communities in oilseed rape

It is crucial to consider the effects of large-scale drivers on species presences and ecological interactions to understand what structures communities. In our study, we investigated how the species composition and the potential interaction networks of herbivore and parasitoid communities in oilseed rape fields are affected by agricultural landscape characteristics. Insect communities of 26 winter oilseed rape fields in southern Sweden were captured in water traps over a continuous time span of 30 ± 2 days. In total, 31% of the variation in the composition of herbivore host communities was explained by a combination of the surrounding oilseed rape area in the study year and the previous year and distance to the nearest forest. The oilseed rape area in the study year and distance to forest also explained 14% of the variation in the composition of parasitoid communities. Distance to the nearest forest together with the area of oilseed rape in the previous year explained 45% of the variation in asymmetry of interaction webs. These results indicate that several measures of landscape configuration are important both for the composition of host and parasitoid communities and also for the structure of interaction networks. Our results support the view that it is an appropriate strategy to cultivate oilseed rape in landscapes that are far away from forests, in order to minimize recolonization by pest species and at the same time to attract parasitoid species from the open landscape.

Effectiveness of field isolation distance, tillage practice, cultivar type and crop rotations in controlling phoma stem canker on oilseed rape

Modern agriculture has led to simpler agricultural landscapes that favour the spread of pathogens and increase pressure from pests and diseases. Landscape-dependent interactions between crops and pathogens, including disease related dispersal patterns, and the benefits of reducing pathogen significance call for the design of disease-suppressive landscapes. Model-based assessment is the most efficient method of choosing among management strategies. Based on a case study in France, we ranked the effectiveness of different crop mosaics for control of phoma stem canker on winter oilseed rape (WOSR). Assessed crop mosaics were developed from strategies defined by local stakeholders: (1) isolating target from source fields (all WOSR or only WOSR harbouring RlmX specific resistance), and (2) specifying tillage on WOSR stubble according to cultivar type (with or without RlmX). Model simulations highlighted the effectiveness of WOSR-isolation as compared to RlmX-isolation. Our analyses suggest that tillage (mouldboard ploughing) was the most important factor in explaining the size and genetic structure of the pathogen population (determinant in explaining the breakdown of resistance), and yield loss. While the pathogen population and yield loss decreased with intensive management of non-RlmX-cultivars (85% of WOSR), the same management with RlmX-cultivars modified the genetic structure of the pathogen population. Increasing isolation distances led to reductions in pathogen population and yield loss only in the strategy of WOSR-isolation. Isolating source and target RlmX-cultivar had no effect on the evolution of the population's genetic structure. Although effective in phoma stem canker control, changing tillage can require significant changes for farms. Isolation distance would require extensive information on the landscape, and imply an aggregation of crops that might or might not be possible depending on a farm's spatial organization. This study could lead to the design of a Decision Support System targeting high risk (diseased) WOSR fields to be ploughed or isolated from the following year's cultivation.

Landscape greening and local creation of wildflower strips and hedgerows promote multiple ecosystem services

Abstract The explicit and implicit aims of creating ecological focus areas (EFAs) and implementing greening measures in European agro‐ecosystems include the promotion of regulatory ecosystem services (ES) to sustain crop production in conventional cropping systems. However, the extent to which these goals are achieved with current policy measures remains poorly explored. We measured insect‐mediated pollination and natural pest control service provisioning in 18 winter oilseed rape fields as a function of the independent and interactive effects of local EFA establishment─sown wildflower strips and hedgerows─and landscape‐scale greening measures within a 1 km radius around focal fields and quantified their contribution to crop yield. Insect pollination potential and pest predation increased on average by 10% and 13%, respectively, when landscape‐scale greening measures share was increased from 6% to 26%. For pollination, the increase was stronger in fields adjoining an EFA (14%) than in fields without adjacent EFA (7%). Agricultural management practices were the main drivers of crop yield. Neither insect pollination potential or natural pest control (pest predation and parasitism) nor adjacent EFAs and landscape‐scale greening significantly affected crop yield in addition to agricultural management. Synthesis and applications. Local establishment of perennial, species‐rich wildflower strips and hedgerows, combined with landscape‐scale greening measures in agricultural landscapes, can promote multiple ecosystem services (ES) in conventional production systems. Benefits may be maximized when local and landscape measures are combined. However, enhanced pollination and natural pest regulation seem to contribute relatively little to final crop yield compared to local agricultural management practices in the high‐input conventional production system studied. Further research is needed to better understand how to improve the effectiveness of ecological focus areas and other greening measures in promoting regulatory ES. Potential improvements include minimising trade‐offs while promoting synergies between ES provision, food production and biodiversity conservation.

Wild pollinators enhance oilseed rape yield in small-holder farming systems in China

BackgroundInsect pollinators play an important role in crop pollination, but the relative contribution of wild pollinators and honey bees to pollination is currently under debate. There is virtually no information available on the strength of pollination services and the identity of pollination service providers from Asian smallholder farming systems, where fields are small, and variation among fields is high. We established 18 winter oilseed rape (Brassica napus L.) fields along a large geographical gradient in Jiangxi province in China. In each field, oilseed rape plants were grown in closed cages that excluded pollinators and open cages that allowed pollinator access. The pollinator community was sampled by pan traps for the entire oilseed rape blooming period.ResultsOilseed rape plants from which insect pollinators were excluded had on average 38% lower seed set, 17% lower fruit set and 12% lower yield per plant, but the seeds were 17% heavier, and the caged plants had 28% more flowers and 18% higher aboveground vegetative biomass than plants with pollinator access. Oilseed rape plants thus compensate for pollination deficit by producing heavier seeds and more flowers. Regression analysis indicated that local abundance and diversity of wild pollinators were positively associated with seed set and yield/straw ratio, while honey bee abundance was not related to yield parameters.ConclusionsWild pollinator abundance and diversity contribute to oilseed rape yield by enhancing plant resource allocation to seeds rather than to above-ground biomass. This study highlights the importance of the conservation of wild pollinators to support oilseed rape production in small-holder farming systems in China.

Pollinators, pests and soil properties interactively shape oilseed rape yield

Pollination, pest control, and soil properties are well known to affect agricultural production. These factors might interactively shape crop yield, but most studies focus on only one of these factors at a time. We used 15 winter oilseed rape (Brassica napus L.) fields in Sweden to study how variation among fields in pollinator visitation rates, pollen beetle attack rates and soil properties (soil texture, pH and organic carbon) interactively determined crop yield. The fields were embedded in a landscape gradient with contrasting proportions of arable and semi-natural land. In general, pollinator visitation and pest levels were negatively correlated and varied independently of soil properties. This may reflect that above- and below-ground processes react at landscape and local spatial scales, respectively. The above-ground biotic interactions and below-ground abiotic factors interactively affected crop yield. Pollinator visitation was the strongest predictor positively associated with yield. High soil pH also benefited yield, but only at lower pest loads. Surprisingly, high pest loads increased the pollinator benefits for yield. Implementing management plans at different spatial scales can create synergies among above- and below-ground ecosystem processes, but both scales are needed given that different processes react at different spatial scales.

Optimising the attractiveness of winter oilseed rape fields as foraging habitat for the West Pannonian Great BustardOtis tardapopulation during winter

SummaryWinter oilseed rape represents an important food source for Great Bustards. Great Bustard surveys during four consecutive winters (2005/2006–2008/2009) were used to identify characteristics of oilseed rape fields, which increase their attractiveness for the species in its West Pannonian wintering area. The study was conducted in study areas in Eastern Austria, around the Austrian–Slovakian–Hungarian border and in the Hungarian Moson Plain. To test for effects of field size and isolation of fields from other rape fields, and the distance to the nearest paved road on occurrence and abundance of Great Bustards (maximum number of birds counted in individual rape fields per winter), we calculated generalized linear mixed models (GLMMs) including all three predictor variables as fixed effects and winter as random effect for each of the three study areas. Field size most strongly affected occurrence and abundance of Great Bustards. The availability of large (>>15 ha) winter rape fields far from paved roads is recommended as a prime conservation measure to improve the quality of rape fields as foraging habitat for Great Bustards during the winter months (November–March).

Consumption of flea beetles (Phyllotreta, Coleoptera: Chrysomelidae) by spiders in field habitats detected by molecular analysis

AbstractFlea beetles, Phyllotreta Chevrolat (Coleoptera: Chrysomelidae) species, are often found in oilseed rape (OSR), Brassica napus Linnaeus (Brassicaceae). Among predators in the generalist predator complex present in agricultural fields, wolf spiders (Araneae: Lycosidae) are found on the ground and cobweb spiders (Araneae: Theridiidae) build webs in the foliage. We present group-specific primers developed for five flea beetle species within the genus Phyllotreta and study the incidence of predation of flea beetles by these spider groups using DNA-based gut-content analysis. Wolf spiders of the genus Pardosa Koch and the cobweb spider, Phylloneta impressa (Koch), were collected in three winter OSR fields. Flea beetle densities as well as the occurrence of predators and alternative prey were monitored. In total 19.4% of the collected Pardosa tested positive for flea beetle DNA in the polymerase chain reaction analyses, whereas 10% P. impressa were positive. Pardosa were more likely to be positive for flea beetle DNA when Pardosa activity density was low. Phylloneta impressa were more likely to be positive for flea beetle DNA if they were positive for pollen beetle DNA. Implications of these results for conservation biological control and future studies of food webs in OSR are discussed.

Pollinators and pollination of oilseed rape crops (Brassica napus L.) in Ireland: ecological and economic incentives for pollinator conservation

Pollinators are beneficial for many wild and crop plants. As a mass-flowering crop, oilseed rape has received much focus in terms of its pollination requirements but despite a threefold increase in area of cultivation of this crop in Ireland over the past 5 years, little is known about its pollination here. We surveyed the flower visiting insects found in commercial winter oilseed rape fields and evaluated the importance of different pollinator groups, investigated the contribution of insect pollination to oilseed rape seed production, and estimated the economic value of insect pollination to the crop at a national level. Our data showed that winter oilseed rape is visited by a wide variety of insect species, including the honeybee, bumblebees, solitary bees, and hoverflies. The honeybee, Eristalis hoverflies and bumblebees (especially Bombus sensu stricto and B. lapidarius) were the best pollinators of winter oilseed rape based on the number of pollen grains they carry, visitation rates per flower and their relative abundance per field. Exclusion of pollinators resulted in a 27 % decrease in the number of seeds produced, and a 30 % decrease in seed weight per pod in winter crops, with comparable values from a spring oilseed rape field also. The economic value of insect pollination to winter oilseed rape was estimated as €2.6 million per annum, while the contribution to spring oilseed rape was €1.3 million, resulting in an overall value of €3.9 million per annum. We can suggest the appropriate conservation and management of both honeybees and wild pollinators in agricultural areas to ensure continued provision of pollination services to oilseed rape, as a decrease in insect numbers has the potential to negatively influence crop yields.

Landscape and site effects on Collembola diversity and abundance in winter oilseed rape fields in eastern Austria

Soil animals are rarely considered in landscape ecology although recent findings show that landscape composition and habitat fragmentation may exert a strong influence on their communities. We assessed the relationships between landscape parameters and the species richness of Collembola (springtails) in agricultural eastern Austria, hypothesizing that the richness of surface active (epigeic) species are more significantly correlated with landscape-scale parameters than soil living (endogeic) species. We used pitfall traps and soil samples to measure species richness and abundance of the two life forms in 29 oilseed rape fields in differently structured landscapes.Epigeic species richness was positively correlated to landscape parameters like landscape diversity, habitat richness, isolation of open habitats and area of oilseed rape fields at small to medium (250–1000m) and at larger (1000–1750m) landscape scales around the investigated sites. Endogeic species richness was also significantly correlated with landscape parameters like landscape diversity and road-side strip length. Total species richness was significantly correlated with landscape diversity at a larger scale, isolation of open habitats and proportion of woody area at a smaller spatial scale. Landscape diversity measures explained a higher percentage of the diversity of epigeic (42%) than of endogeic diversity (32%). Epigeic abundance was not significantly correlated to any of the site parameters, but with landscape parameters like oilseed rape area, woody area and minimum distance to dry grassland. Endogeic abundance was only correlated to oilseed rape cover.Our results suggest that parameters associated with landscape diversity can be good predictors of Collembola diversity at two spatial scales: At small scales probably due to active migration from bordering hedges, forests or grasslands; and at larger scales possibly due to passive wind dispersal. Soil ecologists rarely take landscape-scale variables into account, and our findings may contribute to broader recognition of the importance of landscape parameters in investigations of soil biota.

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.

Re-evaluation of the role of the grey partridge Perdix perdix as a disperser of arable weed seeds

The endozoochorous dispersal of weed seeds, mediated by birds and without any adaptation to frugivory, has been studied very rarely. We studied the endozoochorous dispersal of viable seeds by the grey partridge Perdix perdix in agricultural landscape. We assessed the content of intact seeds in 609 grey partridge droppings coming from 21 sampling sites in Poland that included three land-cover types (winter cereals, winter oil-seed rape and stubble fields). We found 159 intact seeds of 13 plant species. Most of them are classified as plants without any evolved adaptations to dispersal. The number of intact seeds retrieved from droppings was positively correlated with the proportion of seeds and negatively correlated with total proportion of leaves in the diet. This result may indicate that the consumption of large numbers of seeds increases the possibility that some of them will resist digestion and be excreted with faeces. Our results showed that the highest number of intact seeds recovered from the droppings coming from stubble fields was the consequence of the importance of weed seeds in the diet of grey partridge in this type of land-cover. The grey partridge is a poor seed disperser and rather, it plays an important role as a predator of weed seeds.

Occurrence and distribution of important weed species in German winter oilseed rape fields

Data on weed species currently found in winter oilseed rape, the extent of their occurrence and regional distinctions were collected in autumn 2005, 2006 and 2007 from a total of 1463 oilseed rape (OSR) fields throughout Germany. Investigations took place in untreated parts of OSR fields at the four to six leaf stage of rape. Weed frequencies and densities were determined by randomly placing a 0.1 m2 square frame ten times in each plot, identifying and counting all plants within the frame. Results presented here mainly focus the distribution of important weed species and differences in their frequencies and densities between German Federal states.