Geneflow and persistence

Geoff Squire

Scottish Crop Research Institute

ConcernsEcological • feral populations or hybrids with

wild relatives interfere with the habitat

Food purity • outcrossing between nearby fields • feral populations contributing to

yield

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

The scales

• Fine soil structure – bacterial, fungal

• Field patch – plant populations• Field – management unit• Farm or group of farms• Landscape

3D View 2D View3D View 2D View

Soil is a complex medium

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)

It has joined joined the seedbank

In this small plot of 200 m-2

• 10,000 original OSR crop plants

• >100,000 seed shed at harvest

• 100 feral plants one year later

• >1000 feral seeds still in the seedbank

1 km

It has good regional coverage

1. Will it disturb the habitat?

• Soil structure • Habitat processes• Other organisms

Other arable plants

• Seedbank – 1000 to >10,000 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

Common Cruciferae

Brassica napus Brassica rapa

Raphanus raphanistrum

Sinapis arvensis

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10

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0 200 400 6000

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Will OSR affect rest of seedbank ?

Community-scale properties

Will it affect transmission through food webs ?

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

2. Impurities in yield

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

preference

1 km

Distance and time?

Gene flow depends on context

f

d

2 km

Green – oilseed rape fields

Black – GM oilseed rape fields

Analysis in progress (2002)

Impurities in OSR decay slowly

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0.2

0.4

0.6

0.8

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0 3 6 9 12 15

time (years)

co

nta

min

ati

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herbicide

no herbicide

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 < 0.1% not practicable< 1% uncertain and only with the most rigorous

standards

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