Jul 13, 2005

Research Projects

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The dispersal behaviour of oilseed rape plants

(2001 – 2004) Federal Biological Research Centre for Agriculture and Forestry (BBA), Institute for Plant Virology, Microbiology and Biosafety, Braunschweig

Topic

Cultivated plants have a certain feral potential irrespective of genetic modification. Oilseed rape (Brassica napus) is notable in this respect, being found very often on ruderal sites along verges and railway lines.

The aim of the research project was the morphological and molecular genetic characterisation of feral crucifer plants – like oilseed rape and its relatives – from ruderal locations. It was hoped that this would provide insights into the tendency of oilseed rape plants to spread and grow wild.

In addition, the project was to check whether oilseed rape genes can establish themselves in the gene pool of related wild plants.

No genetically modified oilseed rape plants were released for these experiments. Instead, the investigations focused on crucifer populations at ruderal locations.

Summary

The aim of the project was to assess the potential of ruderal oilseed rape to grow wild, and to gather base data for the question concerning the establishment of oilseed rape genes in related wild crucifers.

• A total of 74 sites, some of them with several patches of ruderal oilseed rape, were mapped and examined. On about half the sites, ruderal oilseed rape appeared in only one of the four research years. As molecular genetic tests showed, even patches that appeared in several years were often the result of new arrivals. A rape seed potential was found in only a few soil samples from ruderal sites.
• In contrast with the current cultivation situation, there was quite a high incidence of plants with a high glucosinolate content in the seed on ruderal sites.
• No wild crucifers that are crossable under field conditions were found in the research area. The charlock populations identified on ruderal sites were, as is typical of wild plants, much more genetically variable than the ruderal oilseed rape that had been feral for only a short period.

Experiment description

Mapping and botanical identification of the crucifer plants

Crucifer plants at various ruderal locations in a selected region of Lower Saxony were morphologically identified from 2001 to 2004 over a period of several months per year. Samples were taken for molecular genetic analysis and cultivation in the greenhouse, and the places where they were found were mapped.

Ascertaining the rape seed potential in the soil

In 2002 and 2003 soil samples were taken from thirty selected sites to investigate the presence of an oilseed rape seed bank in the soil. The viable rape seeds were identified in a germination test. Leaf samples were taken from the germinated plants for molecular genetic tests.

Population dynamics of ruderal oilseed rape and wild crucifers

In order to ascertain the propagation potential, characteristics of the ruderal plants relevant for population dynamics, such as growth, development and seed formation, were evaluated using suitable formulae. Model experiments were carried out with seedlings under different site conditions and the evaluation formula arrived at in this manner was used to estimate the propagation potential of oilseed rape and wild crucifers for each location.

Molecular genetic tests

Molecular genetic tests were carried out for the genetic representation of the relationships between the collected crucifers, known oilseed rape varieties and related wild species like wild turnip, wild radish and charlock. The objective was to add to the knowledge concerning population dynamics and gene flow in oilseed rape and related crucifers.

Analysis of the erucic acid and glucosinolate content

In the past, a high erucic acid content used to make the rapeseed oil bitter, while toxic glucosinolate made the seeds unusable as animal feed. Through breeding, today’s cultivated oilseed rape contains only small amounts of these substances (these are the so-called 00 varieties). Exceptions are high erucic acid varieties, which are still cultivated to a limited extent.

Spectroscopic analyses were used to investigate the erucic acid and glucosinolate content of seeds from cultivated oilseed rape varieties and from the ruderal oilseed rape sampled in 2001 and 2002.

Results

Mapping and botanical identification of the crucifer plants

Oilseed rape: A large proportion of the 54 sites where oilseed rape was found in the first evaluation year (2001) contained no ruderal oilseed rape in 2002. Because of the low reappearance rate (20 sites = 37 per cent), the investigations in the second year were extended to a further twenty sites. In the spring of 2003, oilseed rape plants were found at only nine of the sites that had produced oilseed rape the year before, representing a reappearance rate of only 23 per cent, which can be explained by unfavourable climatic conditions and high pest infestation. In 2004 the reappearance rate was 55 per cent. Eleven per cent of the sites from 2001 did not produce oilseed rape plants in 2002 but did again in 2003.

Charlock: In the research years 2001-2003 charlock was the only potentially crossable wild crucifer (although the probability outdoors is extremely low) found in relevant population sizes at several ruderal sites. Samples of individual plants from the years 2002 and 2003 from a total of 18 sites were available for the molecular genetic test. Charlock was found at five of these sites (i.e. 28 per cent) in both years and samples were taken.

Determining the rape seed potential in the soil

Only in a few soil samples – almost exclusively in those from a site close to an oil mill – was it possible to demonstrate the presence of germinating oilseed rape plants.

One particularly noteworthy finding was that many of the sites that had a large number of oilseed rape plants in 2001, and therefore a high expected seed volume, produced no plants in subsequent years. The hypothesis that ruderal oilseed rape possesses a high potential to spread and to grow wild can not be proved on the basis of this finding, which was repeated in three subsequent years.

Population dynamics of ruderal oilseed rape

The number of ruderal rape seeds formed per site was very variable, reaching very high values in some individual cases. However, another deciding factor for the establishment potential of plant populations is whether the seeds have sufficient chances on site to germinate and develop. Here it can be concluded from the results of the model experiments that the establishment possibilities are generally to be considered low; only open, gravelly sites offer good early development.

The establishment potential estimated for the research years from theoretical calculations corresponded only in part with the frequency of occurrence of oilseed rape registered during the experiments. A possible reason for this discrepancy is the omission from the population dynamics modelling of factors like weather conditions, seed loss through seed predators and new seed input.

Molecular genetic tests

Ruderal oilseed rape: According to the molecular genetic tests, a reemergence or new arrival of oilseed rape plants of the same variety the following year is likely only in isolated cases. At most of the sites it must be assumed that there was new input of different varieties of oilseed rape in successive following years. It was possible to identify some of the individual plants as certain oilseed rape varieties that are commonly cultivated in Lower Saxony. Overall, it was apparent that ruderal rape, like cultivated rape varieties, is not very genetically variable – a known effect of crop breeding.

Wild crucifers: The charlock populations found at ruderal sites are clearly distinct from oilseed rape in molecular genetic terms. Compared with ruderal rape, the examined charlock was much more genetically variable, both within the site where it was found and when compared over different years. It also appears that the majority of the examined plants can be grouped genetically by site.

Analysis of the erucic acid and glucosinolate content

The examination of seed samples from 2001 und 2002 using near-infrared spectroscopy (NIRS) found glucosinolate and erucic acid values that generally correspond to the 00 varieties currently cultivated on approx. 97 per cent of areas in Germany. In contrast to the current cropping situation however, there were also a considerable number of plants with high or increased erucic acid and/or glucosinolate content, some of them at the same sites in consecutive years. The occurrence of this type of ruderal rape could stem from handling losses of seeds from glucosinolate-rich varieties that occurred a long time ago, or from hybridisations between different varieties. It is possible that this type of rape, which was last cultivated in Germany in the late 1980s, has a better survival ability because of the substances it contains.

In several cases, it was possible to classify plants with high erucic acid and low glucosinolate contents to corresponding varieties. However, no classification was possible for ruderal rape plants with high erucic acid and glucosinolate values.