Geneflow and persistence

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Geneflow and persistence

• Geoff Squire

Scottish Crop Research Institute
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Concerns

• Ecological
• feral populations or hybrids with wild relatives
  interfere with the habitat
• Food purity
• outcrossing between nearby fields
• feral populations contributing to yield

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The system

• Soil - genesis, resilience
• Primary production crops and weeds
• Decomposition bacteria, fungi, protozoa,
  nematodes, collembola, etc.
• Element cycling
• Herbivory nematodes, insects, cattle/sheep
  humans

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The scales

• Fine soil structure bacterial, fungal
• Field patch plant populations
• Field management unit
• Farm or group of farms
• Landscape

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Soil is a complex medium
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Oilseed rape

• Reappeared as a common crop in 1970s
• Most Brassica napus, some B. rapa
• As a break crop in cereals
• Oil has a wide range of uses
• Outcrossing (contact, wind, insect)
• Feral descendents (pod shatter, inducible
  dormancy)

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It has joined joined the seedbank

• In this small plot of 200 m-2
• 10,000 original OSR crop plants
• gt100,000 seed shed at harvest
• 100 feral plants one year later
• gt1000 feral seeds still in the seedbank

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It has good regional coverage
1 km
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1. Will it disturb the habitat?

• Soil structure
• Habitat processes
• Other organisms

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Other arable plants

• Seedbank 1000 to gt10,000 individuals in a
  square metre
• 10 target weeds
• 30 common, 150 less common species
• Non-target species highly valuable to arable food
  web
• From glacial and more recent

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Common Cruciferae
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Will OSR affect rest of seedbank ?
Community-scale
properties
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Will it affect transmission through food webs ?
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Ecological impact - conclusions

• Ferals and hybrids -
• Negligible effect on integrity of soil
• Negligible effect on main habitat processes
• Mainly fill vacant space ferals typically 100
  m-2
• But might alter seedbank species abundance or
  species composition
• And some transmission of effect to food web

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2. Impurities in yield

• Distance and frequency
• Persistence over time
• Food quality
• Perception and preference

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Distance and time?
1 km
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Gene flow depends on context
f
d
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Analysis in progress (2002)
2 km
Green oilseed rape fields Black GM oilseed
rape fields
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Impurities in OSR decay slowly
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Impurity in yield - conclusions

• Not preventable in oilseed rape under present
  arable cropping
• at low frequency over several km, mediated by a
  range of insect vectors and wind-borne pollen
• regional process depending on the configuration
  of fields in a locality
• cross pollination between nearby fields is 1 in
  1000 or less (higher to fields of partial male
  fertility)
• In-field ferals can contribute more (i.e. 1 in a
  100) to impurities
• Can be limited
• lt 0.1 not practicable
• lt 1 uncertain and only with the most rigorous
  standards

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Conclusions

• Of ferals and hybrids
• Ecological effects small
• Low level of impurity in harvest will be
  difficult to manage
• First conclusion might have to be modified if
  field practice changes