A study of the transport and deposition of oilseed rape (Brassica napus L.) pollen in east Fife, Scotland

It has been suggested that there is a link between the relatively recent expansion in the farming of oilseed rape (Brassica napus L.) and an increase in the incidence of respiratory illness in eastern Scotland. However, there is limited evidence of the extent to which one possible cause of this increased illness, the pollen of oilseed rape, is disseminated from fields of this crop. The present study used sedimentation traps and a portable volumetric air sampler to study the transport of pollen from rape fields in Fife, and the results confirmed the widely held view that most of the pollen travels only a short distance from its source. In this case relatively low quantities ofBrassica pollen were detected more than 200 m from fields of rape. This may have implications for the formulation of advice for those who appear to suffer from an allergic reaction to rape crops.     

Shared traits make flies and bees effective pollinators of oilseed rape (Brassica napus L.)

One of the major aims of pollination ecology has been to understand the role and relative importance of different pollinator species in both natural and agricultural systems. This study explores how the quantity of pollen delivered in a single visit to a stigma (SVD) differs across insect species from a wide range of taxa (Orders: Hymenoptera, Diptera and Coleoptera) and assesses the morphological and behavioural traits that lead to differences in pollen delivery. We used oilseed rape (OSR) (Brassica napus L.), an economically important crop with open self-fertile flowers, as a test system. Behavioural traits and SVD were measured in the field for individuals of all frequent flower-visiting species of OSR. Individuals were collected and morphological traits were measured in the laboratory. The quantities of free pollen on different body parts of flower visitors, or ‘pollen load’, were also measured. Behavioural and morphological traits were then assessed as predictors of SVD. The individuals that delivered most pollen were (in order of greatest median number of pollen grains delivered): bumblebees (Bombus spp.), mining bees (Andrenidae) and honeybees (Apis mellifera). However, all but one family of flies tested delivered a significantly greater median number of pollen grains than the control, and most delivered more than sweat bees (Halictidae). Behavioural and morphological traits were important in determining pollen delivery, with greater body length, hairiness and visit duration all resulting in greater SVD. Pollen load was measured for a proportion of individuals and we found that for momentary flower visits, a greater quantity of pollen on the head of the flower visitor was linked to a greater SVD. This study demonstrates that, while bees are important pollinators in this system, many fly taxa are also effective at delivering pollen and this is linked to morphological and behavioural traits found in both groups.     

Variation in the glucosinolate content of oilseed rape (Brassica napus L.) leaves

The glucosinolate content of oilseed rape {Brassica napus) leaves was monitored over the growth period 30–70 days after planting, and a comparison made between a single-low cultivar (low in erucic acid), Bienvenu, and a double-low cultivar (low in erucic acid and glucosinolate), Cobra. In older, fully-expanded leaves the glucosinolate concentration was very low (< 0.3 μmol/ml tissue water) and did not alter during the course of the experiment. In developing sixth leaves glucosinolate content increased rapidly and reached a maximum concentration (4–5 μmol/ml tissue water) 40 days after planting (6 days after leaf emergence). The concentration then declined, to about 1 μmol/ml after 60 days although the total glucosinolate content in leaves continued to increase until 50 days; much of the reduction in concentration was simply a result of leaf expansion. No major differences were seen between the two varieties in total glucosinolate content or in the individual compounds present. Cv. Cobra developed more quickly than cv. Bienvenu so direct comparison between leaves of the two cultivars was complex. When comparing the glucosinolate content of oilseed rape leaves, between cultivars or between treatments, it is vital to ensure that carefully matched leaves of comparable developmental age are selected.     

Correlations between gametophytic (pollen) and sporophytic (seed) generations for polyunsaturated fatty acids in oilseed rape Brassica napus L.

Summary Lipids were extracted from the diploid seed and haploid pollen of Brassica napus L. Two fractions of pollen lipids, namely the diploid-specified pollen-coat and the haploid-specified internal cytoplasmic lipids were obtained. Significant correlations exist between pollen and seed generations for linoleic (182) and linolenic (183) acids. In pollen internal storage lipids, the level of 183 is positively correlated and the level of 182 is negatively correlated with the level of 183 in seed lipids. Evidence is presented that strongly supports the hypothesis that lipid biosynthesis occurs within the pollen and that synthesis is specified by haploid genes. These data support the concept of pollen selection, so that selecting among living pollen grains for superior individuals has potential as a new plant breeding tool for improving seed oil quality.     

Temperature and daylength control of flower initiation in winter oilseed rape (Brassica napus L.)

The influence of low temperature and daylength on pre-floral growth and flower initiation in winter oilseed rape cv. Mikado was examined under controlled environment conditions at the University of Newcastle upon Tyne during 1985 and 1986.
The vernalisation requirement of Mikado was most effectively fulfilled by temperatures of 6 °C and 9 °C. Plants maintained at both higher and lower temperatures had an extended pre-floral growth phase. The transition from vegetative to reproductive growth in plants maintained at 12 °C was delayed by slow accumulation of the cold requirement, whereas flower initiation appeared to be delayed by limited leaf production, dry matter accumulation and/or assimilate availability in plants grown at 3 °C. The mechanism of floral induction remained unresolved but it was clear that flower initiation was not controlled by low temperature per se . Short days partially substituted for the cold requirement at 12 °C but photoperiodic induction of flower initiation was less important than the influence of low temperature.     

Foraging behaviour of honey bees (Apis mellifera L.) on transgenic oilseed rape (Brassica napus L.var. oleifera)

The impact of genetically modified oilseed rape (Brassica napus L.) on the foraging behaviour of honey bees (Apis mellifera L.) was evaluated on two different lines transformed to express constitutively heterologous chitinase in somatic tissue for enhanced disease resistance. Experiments were conducted in confinement in an indoor flight room with controlled conditions and in an outdoor flight cage with conditions more representative of the open environment. Foraging behaviour was analysed by observations of general bee behaviour (total number of visits) and of individual bee behaviour (using a video camera coupled with a special software program to process the data). The plants were analysed in terms of nectar quantity and quality (nectar volume and sugar content). The results showed no effects on bee foraging behaviour due to the modification of the genome of these plants by the introduction of a chitinase gene even though some differences between lines were found in the nectar. The methods applied in this original approach for the evaluation of the impact of genetically modified oilseed rape were shown to be sufficiently sensitive to detect changes in bee behaviour resulting from differences between plants.     

Biodiversity of nematofauna of oilseed rape (Brassica napus L.)

Few data is available on the nematodes found in Brassicaceae, except for the most important plant parasite. However, studying the structure of nematofauna could be an important database for the soil quality and in order to assess the effects of future disturbance. This is particularly important considering that the diffusion of the canola crop in the world is increasing because of its use as a bio-diesel. Very diffused is also the Bt variety of oil seed rape, and, in this case, the study of the impact on the soil health and on bio-diversity is essential. In this research we have analyzed the nematode community, used as a bio-indicator of the soil condition. The nematofauna found in canola (Brassica napus var. oleifera) fields located in Southern Italy (Metaponto - MT) was investigated. The nematode community was studied considering its abundance, genus composition and trophic structure. Maturity and biodiversity indices were also calculated. A total of 5286 nematodes were extracted. They belong to 14 families and 24 genera. Bacterial and fungal feeders, 50.18% and 42.90% of the total respectively, dominated the trophic structure. Aphelencus is the most abundant genus (23.71%) followed by Acrobeloides (20.49%) and Aphelencoides (19.18%). Among plant feeders (6.59%), Pratylenchus is the dominant genus (2.20%) and Tylenchidae the main family (3.54%). No infestation of Meloidogyne, Heterodera or Naboccus, important plant-parasitic nematodes of canola crops, was recorded. Other important phytophagous were Helycotylenchus (0.5%), Trichotylenchus (0.5%) and Filenchus (0.9%). All of them had an abundance level below injury level. The indices of biodiversity are rather low (H'=0.93, J'=0.67), as is typical for agro ecosystems. However, the nematofauna community is quite well structured (N2=6.31, D=0.16) and the maturity index rather high (EMI=1.94). These values demonstrate that oilseed rape has a lower impact on the soil compared to other crop systems and that it could be taken into consideration for crop rotation programs. Canola could follow other more stressful crops, trying to maintain soil equilibrium.     

Influence of lodging and nitrogen rate on the yield and yield attributes of oilseed rape (Brassica napus L.)

The effects of lodging and nitrogen rate were studied in a field trial of oilseed rapeBrassica napus L. Lodging decreased seed yield (16%) compared with a frame-raised crop. Yield decreased because of a significant reduction in each of the yield components coupled with a reduced plant population caused by stem breakage at the ground level. Lodging also reduced the final crop dry weight and harvest index. Seed yield was also lower when 200 kg ha^–1 nitrogen was applied than with 400 kg ha^–1. A general decrease in pod number m^–2, seed nuber pod^–1 and seed weight caused the lower yields. The use of 400 kg ha^–1 of nitrogen changed the contribution of the terminal raceme and individual branches with respect to seed yield. Seed nitrogn content and nitrogen yield increased at the 400 kg ha^–1, lowering both seed oil content and oil yield.     

Zygotic embryo cloning in oilseed rape (Brassica napus L.)

When late torpedo- to early cotyledonary-stage zygotic embryos of Brassica napus were cultured on a solidified B5 basal medium with or without 0.05 mg l⁻¹ 6-benzylaminopurine (BAP), they proliferated by direct formation on the hypocotyl surface of structures resembling accessory cotyledons and root poles. When embryos bearing these structures were transferred to slowly rotating liquid culture on the same media, proliferation continued. As the underlying tissues senesced, meristematic structures became detached which produced cotyledonary and root tissues. A random sample of plants raised from these structures by direct transfer to sterilized potting mix all showed normal morphology.     

Detection of Deformed wing virus, a honey bee viral pathogen, in bumble bees (Bombus terrestris and Bombus pascuorum) with wing deformities

Honey bees (Apis mellifera) productively infected with Deformed wing virus (DWV) through Varroa destructor (V. destructor) during pupal stages develop into adults showing wing and other morphological deformities. Here, we report for the first time the occurrence of bumble bees (Bombus terrestris, Bombus pascuorum) exhibiting wing deformities resembling those seen in clinically DWV-infected honey bees. Using specific RT-PCR protocols for the detection of DWV followed by sequencing of the PCR products we could demonstrate that the bumble bees were indeed infected with DWV. Since such deformed bumble bees are not viable DWV infection may pose a serious threat to bumble bee populations.     

Photosynthesis by developing embryos of oilseed rape (Brassica napus L.)

The aim of this study was to assess the photosynthetic potentialof developing seeds of oilseed rape (Brassica napus L.) andto compare photosynthetic properties of embryo plastids withthose of leaf chloroplasts from the same species. Measurementsof CO₂-dependent O₂ evolution show that developing seeds ofB. napus are photosynthetically active in vitro. Essentially,all of the photosynthetic activity of the developing seed isaccounted for by the embryo. The rate of photosynthesis by developingembryos increased until the onset of desiccation, after whichit declined, so that by maturity embryos were no longer photosyntheticallyactive. Photosynthetic activity was positively correlated withchlorophyll content throughout development. Comparison of thephotosynthetic characteristics of leaf and embryo chloroplastsrevealed that rates of uncoupled electron transport were 2.5-foldgreater in those from the embryo. Light-saturated rates of CO₂-dependentO₂ evolution, per unit chlorophyll, and CO₂ saturation pointswere similar for chloroplasts from both tissues. However, light-saturationpoints and chlorophyll a/b ratios were lower for embryo thanfor leaf choroplasts. Embryos and embryo chloroplasts also containedconsiderably less ribulose 1,5-bisphosphate carboxylase/oxygenaseprotein per unit total protein, than leaves. Although excisedembryos were capable of high rates of CO₂-dependent O₂ evolution(90–100 mol mg^–1 chlorophyll h^–1) under asaturating photosynthetic photon flux density (PPFD), low transmittanceof light through the silique wall (30%), together with the highPPFD required to achieve light compensation points in developingseeds (500 mol m^–2 s^–1), suggests that photosynthesisin vivo is unlikely to make a net contribution to carbon economyunder normal environmental conditions. Key words: Embryo, development, photosynthesis, chloroplast, Brassica napus L.     

Persistence of oilseed rape (Brassica napus L.) outside of cultivated fields

It is widely assumed that most cultivated plants cannot persist in natural or semi-natural habitats. Most people thus assume that the plants growing outside of fields (in particular oilseed rape along roadsides) find their origins in the current or previous year’s cultivation of that crop. One consequence of this assumption is that the identity of plants growing on road verges is thought to reflect one of the cultivars currently or recently cultivated, while another consequence is the widespread belief that transgenic plants can be simply managed and controlled by stopping their cultivation. Our work shows that this assumption is false. We identify relict plants of a now unmarketable cultivar type of oilseed rape which have persisted in a semi-natural habitat (road verges) for at least 8 years according to farmer surveys in the studied area. More generally, we confirm that the dynamics of the feral oilseed rape plants of road verges is more complex than those resulting from spillage from agricultural machines or from neighbouring arable fields cultivated the previous year. Within the scope of transgenic oilseed rape cultivation, these results suggest that more studies on the dynamics of feral oilseed rape are needed in order to assess more precisely the risks of its invasiveness and its potential impact on genetic pollution between GM fields and non-GM fields. Received: 15 June 2000 / Accepted 31 July 2000     

Desiccation of microspore derived embryos of oilseed rape (Brassica napus L.)

Summary Microspore-derived embryos from Brassica napus L. were dried to less than 15% moisture and stored dry for a minimum of 7 days. Successful plant regeneration was observed when embryos at the cotyledonary stage of development were treated with 50 uM ABA for 7 days prior to desiccation. Solid agar or liquid medium gave similar results. The rate of drying of embryos after ABA pretreatment had only minor effects on embryo survival, but for untreated embryos, slow drying gave a small degree of survival. These results are very comparable to those with alfalfa somatic embryos, suggesting that the ABA treatment of cotyledonary stage embryos may be broadly used as a pretreatment for inducing the expression of desiccation tolerance in plant embryos.     

Genetic control of oil content in oilseed rape (Brassica napus L.)

In oilseed rape (Brassica napus L.) like in most oleaginous crops, seed oil content is the main qualitative determinant that confers its economic value to the harvest. Increasing seed oil content is then still an important objective in oilseed rape breeding. In the objective to get better knowledge on the genetic determinism of seed oil content, a genetic study was undertaken in two genetic backgrounds. Two populations of 445 and a 242 doubled haploids (DH) derived from the crosses “Darmor-bzh” × “Yudal” (DY) and “Rapid” × “NSL96/25” (RNSL), respectively, were genotyped and evaluated for oil content in different trials. QTL mapping in the two populations indicate that additive effects are the main factors contributing to variation in oil content. A total of 14 and 10 genomic regions were involved in seed oil content in DY and RNSL populations, respectively, of which five and two were consistently revealed across the three trials performed for each population. Most of the QTL detected were not colocalised to QTL involved in flowering time. Few epistatic QTL involved regions that carry additive QTL in one or the other population. Only one QTL located on linkage group N3 was potentially common to the two populations. The comparisons of the QTL location in this study and in the literature showed that: (i) some of the QTL were more consistently revealed across different genetic backgrounds. The QTL on N3 was revealed in all the studies and the QTL on N1, N8 and N13 were revealed in three studies out of five, (ii) some of the QTL were specific to one genetic background with potentially some original alleles, (iii) some QTL were located in homeologous regions, and (iv) some of the regions carrying QTL for oil content in oilseed rape and in Arabidopsis could be collinear. These results show the possibility to combine favourable alleles at different QTL to increase seed oil content and to use Arabidopsis genomic data to derive markers for oilseed rape QTL and identify candidate genes, as well as the interest to combine information from different segregating populations in order to build a consolidated map of QTL involved in a specific trait.     

Cold pretreatment enhances microspore embryogenesis in oilseed rape (Brassica napus L.)

Stress is an essential component during embryogenesis induction in microspore culture. Cold pretreatment has been used in cereal microspore culture but very seldom attempted in Brassica microspore culture. The effect of cold pretreatment of flower buds subjected to a liquid medium on microspore embryogenesis was investigated in spring and winter Brassica napus, as well as in B. rapa and B. oleracea. Cold pretreatment significantly enhanced microspore embryogenesis (by 1–7 fold) compared to commonly used microspore culture protocol in B. napus, while it was less effective in B. rapa or even negative in B. oleracea. The appropriate duration of cold pretreatment was found to be 2–4 days, which stimulated the best microspore embryogenesis. Cold pretreatment was also able to promote embryo development including the improvement of embryo quality and acceleration of embryogenesis. When incorporating with medium refreshing, cold pretreatment could initiate the most microspore embryogenesis than any other treatment used. With further improvement cold pretreatment method may have a positive potential in Brassica breeding programmes.     

Molecular markers for low-glucosinolate alleles in oilseed rape (Brassica napus L.)

Two recent studies have mapped QTLs associated with the level of seed glucosinolates in oilseed rape (Brassica napus L.). It was likely that the two most significant QTLs identified in each study were the same, as they were linked to RFLP alleles identified by common DNA probes. To investigate the utility of these probes in breeding programmes, they were used to study RFLPs in a range of low- and high-glucosinolate cultivars and breeding lines. It was shown that all low glucosinolate spring and winter cultivars possessed a specific RFLP fragment identified by probe wg3f7 which is linked to theGSL-1 QTL, and all high-glucosinolate cultivars possessed a specific RFLP fragment identified by probe wg7a8, which is linked to theGSL-2 QTL. Cultivar Ariana, which has intermediate levels of glucosinolates possessed the low-glucosinolate fragment atGSL-1 but the high-glucosinolate fragment atGSL-2. A similar result was found with the cvs. Martina and Bronowski which have intermediate and variable levels of glucosinolates. There were no other RFLP fragments identified by other DNA probes which were specific to either the low- or high-glucosinolate phenotypes. The use of probes wg3f7 and wg7a8 in selection of low-glucosinolate lines in breeding programmes is discussed.     

Photosynthesis in leaves and siliques of winter oilseed rape (Brassica napus L.)

The rate of photosynthesis and its relation to tissue nitrogen content was studied in leaves and siliques of winter oilseed rape (Brassica napus L.) growing under field conditions including three rates of nitrogen application (0, 100 or 200 kg N ha^-1) and two levels of irrigation (rainfed or irrigated at a deficit of 20 mm). The predominant effect of increasing N application under conditions without water deficiency was enhanced expansion of photosynthetically active leaf and silique surfaces, while the rate of photosynthesis per unit leaf or silique surface area was similar in the different N treatments. Thus, oilseed rape did not increase N investment in leaf area expansion before a decline in photosynthetic rate per unit leaf area due to N deficiency could be avoided. Much less photosynthetically active radiation penetrated into high-N canopies than into low-N canopies. The specific leaf area increased markedly in low light conditions, causing leaves in shade to be less dense than leaves exposed to ample light. In both leaves and siliques the photosynthetic rate per unit surface area responded linearly to increasing N content up to about 2 g m^-2, thus showing a constant rate of net CO₂ assimilation per unit increment in N (constant photosynthetic N use efficiency). At higher tissue N contents, photosynthetic rate responded less to changes in N status. Expressed per unit N, light saturated photosynthetic rate was three times higher in leaves than in silique valves, indicating a more efficient photosynthetic N utilization in leaves than in siliques. Nevertheless, from about two weeks after completion of flowering and onwards total net CO₂ fixation in silique valves exceeded that in leaves because siliques received much higher radiation intensities than leaves and because the leaf area declined rapidly during the reproductive phase of growth. Water deficiency in late vegetative and early reproductive growth stages reduced the photosynthetic rate in leaves and, in particular, siliques of medium- and high-N plants, but not of low-N plants.     

Salicylic acid-induced accumulation of glucosinolates in oilseed rape (Brassica napus L.) leaves

Applying a salicylic acid soil drench to oilseed rape plantsincreased the concentration of glucosinolates in their leaves.The intensity of this ‘induction’ depended on theconcentration of salicylic acid applied and the age of the leaf:developing leaves retained enhanced levels of glucosinolateslonger than mature leaves. 2-Phenylethylglucosinolate showedthe greatest increase in concentration, with only minor increasesin other glucosinolates in developing leaves. This responseto salicylic acid is more specific than that observed followingfungal infection or damage by herbivores. The results presentedhere are among the first to demonstrate an increase in secondarymetabolite content in response to salicylic acid. The implicationsof this response are discussed in terms of the role of salicylicacid and glucosinolates in plant defence. Key words: Salicylic acid, oilseed rape, Brassica napus, glucosinolates     

Targeting of oleosins to the oil bodies of oilseed rape (Brassica napus L.)

Oleosins of Brassica napus L. (oilseed rape) synthesized by in-vitro translation were found to be very efficiently targeted to microsomal membranes but only poorly translocated to oil bodies or emulsified oil. The use of other bilayer membranes as controls showed that this interaction was specific. The rate of oleosin synthesis in the presence of microsomes was enhanced about threefold, indicative of the involvement of the signal-recognition particle in the targeting process. There is no evidence for the cleavage of the protein during targeting and the protein sequence reveals no consensus cleavage site for the signal peptide. Protection experiments using Proteinase K revealed that about 6 kDa of the protein is exposed on the cytoplasmic side of the ER but the remainder is protected. Carbonate (pH 11) washing of microsomal membranes after in-vitro translation confirmed that oleosins have a domain which remains inserted in the ER rather than the protein being transported completely into the lumen of the ER. These results indicate that oleosins are transported via the ER prior to their accumulation on oil bodies.     

Effects of pollen dilution on infection of Nosema ceranae in honey bees

Multiple stressors are currently threatening honey bee health, including pests and pathogens. Among honey bee pathogens, Nosema ceranae is a microsporidian found parasitizing the western honey bee (Apis mellifera) relatively recently. Honey bee colonies are fed pollen or protein substitute during pollen dearth to boost colony growth and immunity against pests and pathogens. Here we hypothesize that N. ceranae intensity and prevalence will be low in bees receiving high pollen diets, and that honey bees on high pollen diets will have higher survival and/or increased longevity. To test this hypothesis we examined the effects of different quantities of pollen on (a) the intensity and prevalence of N. ceranae and (b) longevity and nutritional physiology of bees inoculated with N. ceranae. Significantly higher spore intensities were observed in treatments that received higher pollen quantities (1:0 and 1:1 pollen:cellulose) when compared to treatments that received relatively lower pollen quantities. There were no significant differences in N. ceranae prevalence among different pollen diet treatments. Interestingly, the bees in higher pollen quantity treatments also had significantly higher survival despite higher intensities of N. ceranae. Significantly higher hypopharyngeal gland protein was observed in the control (no Nosema infection, and receiving a diet of 1:0 pollen:cellulose), followed by 1:0 pollen:cellulose treatment that was inoculated with N. ceranae. Here we demonstrate that diet with higher pollen quantity increases N. ceranae intensity, but also enhances the survival or longevity of honey bees. The information from this study could potentially help beekeepers formulate appropriate protein feeding regimens for their colonies to mitigate N. ceranae problems.