Nov 3, 2010

Research Projects

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Oilseed rape with low persistence – a strategy for controlling gene transfer through volunteer rape

(2008 – 2011) University of Hohenheim, Faculty of Agricultural Science, Institute for Crop Production and Grassland Research, Stuttgart

Topic

Seeds from the crop plant oilseed rape can survive for a long time in the soil, and often do not germinate until years later, appearing as volunteer plants in the following crops. This can lead to adventitious mixing and outcrosses in subsequent oilseed rape crops.

The aim of this project is to test whether, and to what extent, the cultivation of oilseed rape lines with little or no persistence (secondary dormancy) reduces the occurrence of volunteer rape plants in the crop rotation, thereby preventing varieties becoming mixed e.g. with transgenic traits, within an oilseed rape crop.

The project will develop reliable laboratory and field methods which

• identify genotypes with low persistence in the rape variety spectrum and
• determine the suitability and stability of this trait for reducing volunteer rape under field conditions with conventional rape.

Experiment description

The following projects will be carried out on the basis of a multi-stage methodological approach using laboratory, greenhouse and field trials:

• Assessing oilseed rape varieties for the secondary dormancy trait and selection of non-dormant genotypes. In addition to conventional genotypes, two transgenic lines and their isogenic check lines will be examined in the laboratory. A quick test for dormancy will also be developed.
• Developing an on-farm estimation frame and model for predicting the occurrence of volunteer rape in the crop rotation. Data will be collected on farms growing conventional oilseed rape. The data collected will include the level of shattering losses during threshing and the level of the soil seed bank.
• Crop rotation experiments to establish the persistence of rape seeds and the occurrence and fitness of conventional volunteer rape in subsequent oilseed rape crops. Volunteer rape will be deliberately established with conventional varieties in various different agricultural crops. The number of volunteers will then be quantified by crop species and the fitness level in the plant population in question will be assessed.

The project is part of the joint project on “Developing and testing confinement strategies for oilseed rape”. The network partners - the University of Hohenheim, the University of Göttingen and the Julius Kühn-Institut (JKI) - are collaborating on laboratory analyses, the use of trial fields and data exchange for modelling.

Results

Testing oilseed rape varieties for the dormancy trait

In the 2008/2009 and 2009/2010 growing seasons, a cultivar trial was carried out with ten conventional winter rape varieties, with four repetitions on two sites.

The seeds of low-dormancy individuals were sown in August of the trial year on small plots together with the parent varieties. The seeds were harvested the following year and tested for the dormancy trait. The results for the 2008/2009 trial year are now available. Within the spectrum of varieties tested, there was a broad, variety-based variability in the dormancy trait at both sites. A difference of just under 40 percentage points was found in the dormancy level between the high-dormancy and low-dormancy lines.

Developing a rapid test for the dormancy trait

A rapid test was developed to test large quantities of seed material from field samples for the ‘secondary dormancy trait’. Pods with ripe seeds were rolled in commercial paper towels and incubated in a plastic tub half-filled with water for 7 or 14 days at 20ºC. The germinated seeds were then counted.

‘On-Farm’ estimation frame

In the 2008/2009 and 2009/2010 trial years, samples were taken from a total of 49 farm fields in order to assess the level of seed shedding losses, the soil seed bank in the first spring following the rape harvest, and the number of volunteer rape plants emerging in the following crop.

To measure the seed lost during threshing, cloths were laid at right angles to the threshing direction before the rape plants flowered, fixed in place and levelled. After threshing, the cloths were collected in and the fallen seeds were counted. The average seed loss for the 2009 and 2010 harvests was 4000 seeds per square metre. This represents about one hundred times the number of seeds sown.

Crop rotation experiments

Simulating seed shedding: Seeds of the low-dormancy variety Express (15% dormancy) and of the high-dormancy variety Smart (95% dormancy) were scattered at a rate of 10,000 seeds per square metre around the usual time for rape threshing and then immediately incorporated in the soil (shallow tillage). This was followed by non-inversion basic tillage. Winter turnip rape, winter wheat, summer barley and grain peas were sown as the follow-on crop (winter turnip rape to simulate winter oilseed rape, whilst making it possible to spot volunteer rape among the turnip rape plants).

Counting volunteer rape plants: In the following spring, the soil seed bank of oilseed rape seed was measured and flowering volunteer rape plants were assessed. The soil seed bank varied between 1% and 10% of the quantity of seed originally scattered, depending on the variety. Flowering volunteer rape plants were found particularly in the winter turnip rape (between three and 12 plants per square metre), while all the other crops had a maximum of 0.5 volunteer rape plants per square metre.

seed survival

Various rape genotypes were tested for seed survival in a burial experiment. Seeds from each variety were sown into fabric sacks and buried for six months at a depth of 10 cm around the rape threshing date. At the start of the growing season, any seeds that had not yet germinated were recovered, counted and tested for viability. All the seeds that germinated during the trial died inside the sacks. The survival rate of the seeds in the spring was dependent on the variety and varied between 7% and 95%. Varieties with high seed dormancy (Smart) displayed a much higher seed survival rate in the soil than varieties with lower seed dormancy (Express).