spread

Feral and volunteer crop populations in the arable environment

Not all the seed from crop plants is harvested; many seeds are lost, either falling to the ground within the field or dispersed by machinery, birds, etc. to end up beyond the field margins. In some cases the seeds survive in the seedbank giving rise to volunteer populations within subsequent crops or feral populations outside of the cropped area.  The persistence and spread of volunteer and feral populations can lead to significant weed problems while providing a bridge for the dispersal and escape of traits present in cultivated populations.

Volunteer oilseed rape

In the cultivation of oilseed rape (Brassica napus L.), large numbers of seed are shed and fall to the ground before and during harvest. Given the right environmental conditions a proportion of these seeds will become dormant and enter the seedbank, emerging later if subjected to appropriate germination triggers. This has led to the presence of volunteer weed populations within arable fields and to persistent seed bank populations.

The persistence and spread of novel genes

A transgenic, that is genetically modified, oilseed rape (Brassica napus) provides the model system with which we have investigated the dynamics of novel genes in local populations. A stochastic, spatially explicit individual based model (IBM) was developed to simulate the dynamics of the transgene introduced into a non-transgenic population. The model combines life-history and management processes with environmental drivers to examine the effect of these on the spread and persistence of the transgene and the conferred trait.

The model has been used to explore a number of features of this system:

Gene flow patch diagramSpread and persistence in patchy populations - Plant populations, including arable weeds, typically exhibit spatial heterogeneity, that is patchiness, in their distribution. Together with the localised nature of plant to plant interactions this has the potential to affect the dynamics of a population and the spread and persistence of the genes they posses. Model simulations have shown that small scale spatial heterogeneity in the distribution of transgenic plants combined with localised pollen dispersal reduces mixing between populations and acts to limit the spread of the gene through the population.

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