Oilseed Rape Cultivation Research Articles

Does insecticide resistance alone account for the low genetic variability of asexually reproducing populations of the peach-potato aphid Myzus persicae?

The typical life cycle of aphids includes several parthenogenetic generations and a single sexual generation (cyclical parthenogenesis), but some species or populations are totally asexual (obligate parthenogenesis). Genetic variability is generally low in these asexually reproducing populations, that is, few genotypes are spread over large geographic areas. Both genetic drift and natural selection are often invoked to account for this low genetic variability. The peach-potato aphid, Myzus persicae, which encompasses both cyclical and obligate parthenogens, has developed several insecticide resistance mechanisms as a consequence of intense insecticide use since the 1950s. We collected asexually reproducing M. persicae from oilseed rape and examined genetic variability at eight microsatellite loci and three insecticide resistance genes to determine whether their genetic structure was driven by drift and/or selection. We identified only 16 multilocus microsatellite genotypes among 255 individuals. One clone, which combined two insecticide resistance mechanisms, was frequently detected in all populations whatever their location over a large geographical area (the northern half of France). These unexpected findings suggest that drift is not the unique cause of this low variability. Instead, the intensification of both insecticide treatments and oilseed rape cultivation may have favored a few genotypes. Thus, we propose that selective pressures resulting from human activities have considerably modified the genetic structure of M. persicae populations in northern France in a relatively short period of time.

Life cycle and potential gene flow of volunteer oilseed rape in different tillage systems

SummaryThe study examined the effect of tillage (intensive vs. zero tillage) on potential gene flow during the life cycle of oilseed rape volunteers between July 2002 and August 2003. After growing oilseed rape, 4–29% of the seeds lost during harvest entered the soil seedbank when stubble tillage was performed immediately after the seed input. The seedbank was small (0–3%) when stubble tillage was delayed. Zero tillage resulted in seedbanks from 1 to 17% of the initial seed input. The seeds were distributed mainly in the upper soil layers after zero tillage or primary tillage with a rigid tine cultivator, whereas ploughing shifted most of the seeds into deeper layers. The highest number of volunteers (1 plant m−2) emerged and flowered in the following crop of winter wheat either when a large soil seedbank existed and/or the seedbank was located mainly in the upper soil layer. Outcrossing with other rape crops was unlikely as volunteers flowered 1 month later than rape crops sown at the normal timing. These volunteers produced a maximum of 8 viable seeds m−2. Ploughing preserved seeds in deep soil layers transferring the risk of gene flow to the future, whereas non‐inversion tillage can cause gene flow from high numbers of flowering volunteers within the first year following oilseed rape cultivation.

Application of RAPD‐PCR for Virulence Type Analysis within Verticillium dahliae and V. longisporum

AbstractA collection of 24 isolates of Verticillium dahliae, 11 isolates of V. longisporum and one isolate of V. albo‐atrum originating from different host plants and geographical regions was tested for genetic variability by random amplified polymorphic DNA‐polymerase chain reaction (RAPD–PCR). Based on nine primers, the three Verticillium species could be clearly differentiated. Likewise, this analysis provided a distinct separation of vegetative compatibility groups (VCG) 2B, 4A and 4B of V. dahliae by specific DNA banding patterns. Additionally, V. longisporum was found to segregate into two subgroups with only 88% similarity. This molecular‐genetic approach was used for the analysis of randomly selected Verticillium isolates from a field with high intensity of oilseed rape cultivation (33% in crop rotation). RAPD‐PCR analysis revealed that 95 of 100 isolates tested belonged to V. longisporum and 5 to VCG 2B of V. dahliae. This study demonstrates an adaptation of Verticillium soil populations to a specific cropping history.

A major quantitative trait locus for resistance to Turnip Yellows Virus (TuYV, syn. beet western yellows virus, BWYV) in rapeseed

AbstractTurnip yellows virus (TuYV) is responsible for a recognizable loss of yield in European winter oilseed rape cultivation. To map genes involved in TuYV resistance, a double haploid population was established by crossing a resynthesized rapeseed line (R54) as donor for TuYV resistance with an elite rapeseed line (‘Express’). Resistance was determined with 10 plants per line by double antibody sandwich‐enzyme‐linked immunosorbent assay. After screening 17 primer combinations (Pstl/Msel and EcoRI/Msel), 143 amplified fragment length polymorphism markers were mapped to 20 linkage groups representing 15 chromosomes of the rapeseed genome. Quantitative trait loci (QTL) were mapped using the composite interval mapping approach. As a result, one major quantitative trait locus was found on linkage group MS17, explaining up to 50% of the phenotypic variation. Because no other factors displaying a significant effect on the expression of resistance could be identified, a simple mode of inheritance for TuYV resistance is suggested, thus enabling marker‐assisted selection during rapeseed breeding.

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.

Herbicide‐resistant genetically‐modified crop: its risks with an emphasis on gene flow

Herbicide‐resistant genetically‐modified (GM) crops are the most widely cultivated worldwide, representing 78% of GM crops in 1999, followed by insect‐resistant GM crops with Bt gene. Gene flow is the most touching risk arising from GM crops, and is categorized as three types: within species, between species and between GM crop and other organisms. This review shows that gene flow is a reality in the plant kingdom with evolutionary change. Herbicide resistance evolves naturally and spreads dynamically in weeds. One of the most concerning crop in relation to gene flow is Brassica napus, which has a high outcrossing rate and many relative species. In contrast, frequency of gene flow via outcrossing is relatively low in inbreeding cereal crops such as rice, wheat and barley, but published reports have shown that substantial gene flow is possible. Another possible and immediate risk is herbicide‐resistant GM crops becoming volunteer weeds. Dry direct‐seeded rice is one of the most likely crops in this respect. Stacking different resistance genes in a crop would accelerate multiple resistance evolution in weeds. Multiple resistance to three major herbicides has already been observed in oilseed rape cultivation. More efforts must be made for long‐term risk assessment on GM crops in the natural ecosystem. More studies on weed biology and ecology, particularly reproductive processes in weeds, are essential for better understanding of gene flow and systematic management strategy. We hope that this review motivates researchers to analyze data available now, to collect fundamental information on crops and weeds in agro‐ecosystem, and to lead to better risk assessment and management.

The effect on the woodpigeon ( Columba palumbus) of the introduction of oilseed rape into Britain

The production of oilseed rape on a large scale in Britain began in 1973 and the woodpigeon ( Columba palumbus) quickly became a major pest of this crop. This paper uses ringing recovery data to examine the effects of the introduction of oilseed rape upon the movements and survival of the woodpigeon, and observational data to investigate changes in foraging behaviour. The mean distance travelled between ringing and recovery sites decreased in areas of high oilseed production but increased where little oilseed rape was grown. In good arable areas, the introduction of oilseed rape did not affect woodpigeon survival but it increased woodpigeon mortality in poor arable areas, probably as a result of increased shooting pressure. Oilseed rape is the preferred winter food of woodpigeons and they forage more efficiently on oilseed rape fields than pastures, the main alternative source of food in winter. After the widespread cultivation of oilseed rape, the average weight loss in a woodpigeon over the winter months became significantly less. Following the introduction of oilseed rape into Britain, overwinter mortality from starvation declined and the number of young produced each summer now has a more important effect upon woodpigeon population size.

Oilseed rape and seasonal symptoms: epidemiological and environmental studies.

There is widespread concern that the cultivation of oilseed rape leads to seasonal epidemics of respiratory symptoms in populations living in the neighbourhood, and it has been suggested that the plant is a potent allergen. A study was therefore undertaken to determine the prevalence of seasonal symptoms in rural populations close to and far from areas of oilseed rape cultivation, and to measure the levels of allergen and other potentially harmful substances released by the crop. Random samples of 1000 adults from the general practice populations of two villages surrounded by oilseed rape fields, and 1000 adults from one village far from such cultivation, were taken. The subjects completed a previously validated questionnaire on respiratory and other symptoms, including questions on symptom seasonality, occupation, and smoking habits. Pollen and fungal spore counts were made around fields of oilseed rape and in the villages. The chemicals released by oilseed rape were measured in the field. Overall, 86.8% of the subjects completed the questionnaires and the populations of the two samples were generally comparable. Spring and summer exacerbations of symptoms occurred equally in the two areas in approximately 25% of the population. There were small but significant excesses of cough, wheeze, and headaches in spring in the oilseed rape area (2.3% v 1.1%, 6.8% v 4.6%, and 4.8% v 2.8%, respectively), and cough, wheeze, and itchy skin were more prevalent in smokers. Counts of oilseed rape pollen were generally low except adjacent to fields, and counts of fungal spores were mostly higher in the rape than the non-rape areas. Oilseed rape was shown to give off terpenes and these were detected close to fields. While it is likely that a proportion of the spring symptoms occurring in people living in close proximity to oilseed rape is caused by the plant, the excess of such symptoms is small. This, together with the low levels of pollen in the area, suggests that allergy to oilseed rape pollen is uncommon. The general prevalence of seasonal symptoms in rural areas is of interest, and a proportion of these cases is likely to be caused by factors other than allergy. Release of chemicals by plants and natural rises in summer ozone levels may be contributors.

Size and shape of sampling units for estimating incidence of stem canker on oil-seed rape stubble in field plots after swathing

Further exploitation of the increasingly popular oil-seed rape crop, Brassica napus L., as a valuable break in cereal production in the U.K., is threatened by the susceptibility of the crop to a number of diseases of which the most serious is likely to be stem canker caused by Phoma lingam (Tode ex Fr. Desm.), perfect stage Leptosphaeria maculans (Desm.) Ces et de Not. (Gladders, 1977; Hewitt, 1977). This pathogen has already severely restricted the cultivation of oil-seed rape in France (Lacoste et al. 1969) and in Australia (Bokor et al. 1975; McGee & Emmett, 1977).