|
Back to SCIENCE Homepage
Swede breeding in Scotland
Dr John E. Bradshaw
Scottish Crop Research Institute
Invergowrie, Dundee DD2 5DA, Scotland
Filed 23 Oct 04
©www.land-care.org.uk
Introduction
Swedes (Brassica napus) have been grown
in the UK to provide winter forage for cattle and sheep since the
early 1800s. Today they are also an important vegetable for culinary
use.
During the 19th century many new strains and varieties
were produced by visual selection of attractive looking roots which
were then seeded together in isolation from other multiplications.
They were, however, very variable as a result of insects making
cross-pollinations between plants in an isolation site.
Figure 1: Dr John E. Bradshaw
Plant Breeder, SCRI
For an enlarged view Click
Here
(Photograph by courtesy of SCRI)
Between 1900 and 1930 the chemical composition
of swedes was determined with a view to improving their feeding
value, but opinions differed over the relationship between chemical
composition and feeding value. Research workers in Scotland concluded
that the swede with the highest dry-matter yield per unit area was
the most profitable one to grow, and from 1930 this became the main
selection criterion in the breeding programme at the Scottish Plant
Breeding Station (SPSB) in Edinburgh. (The work of SPBS was incorporated
into SCRI on its formation in 1981.) Furthermore, the desire to
produce high yielding, uniform cultivars became the major influence
on the choice of breeding method and type of cultivar.
Figure 2: Swede breeding from single
seed descent
Bag-selfing from 1994 -1999
For an enlarged view Click
Here
(Photograph by courtesy of SCRI)
In recent years more attention has been paid to
disease resistance, particularly to powdery mildew and clubroot,
and to an attractive appearance for culinary use.
Pure-line breeding
Although swedes are insect-pollinated, Davey at
SPBS showed that they are usually self-fertile and that inbreeding
depression is mild. He produced uniform lines from variable commercial
cultivars by a number of generations of natural self-pollination
in insect-proof bags (bag-selfing), but did not consider the best
ones to be sufficiently superior or distinct from their parent cultivars
for release as new cultivars. Interestingly, however, two lines
which were produced in the 1980s for genetical research have been
released. A line from cultivar Criffel is being grown in New Zealand
as an improved and distinct cultivar, Highlander, and a superior
line from the shopping swede Acme is being marketed in the UK as
an improved stock of Acme.
Pedigree inbreeding
During the 1930s, Davey changed his approach to
combining desirable characteristics from different cultivars, strains
and pure lines through hybridizations, followed by bag-selfing and
selection for a number of generations to produce true breeding lines
with the required attributes. This pedigree method which he developed
has now been in use for over 70 years. The cultivars Angus and Melfort
came from crosses made in 1967 and were placed on the NIAB Recommended
List of Swedes in 1982. Airlie was National Listed in 1991, Brora
in 1993, Kenmore in 1994 and Invitation in 1995.
Airlie is a general purpose swede with very high
fresh yields of low dry matter content resulting in average yields
of dry matter. It has purple skinned, intermediate shaped roots
with cream coloured flesh. It has good resistance to powdery mildew.
Invitation was SCRI’s first cultivar with
resistance to clubroot as well as to powdery mildew. Clubroot resistance
was introduced from a stubble turnip (in fact European Clubroot
differential 04) through a synthetic B. napus produced in
1976. Four backcrosses to modern cultivars with selection for clubroot
resistance ensued before commencing four generations of selfing
with family selection for agronomic characters, as well as single
plant selection for clubroot resistance. Invitation is a general
purpose, winter hardy swede with high yields of dry matter at a
high dry matter content. It has purple skinned, intermediate shaped
roots with yellow coloured flesh. It is resistant to the most prevalent
races of clubroot found in the UK but can not be guaranteed resistant
to all races.
Single seed descent
When the government stopped funding brassica
breeding in 1991, the commercial company which became Advanta Seeds
UK Limited saw the need for new swede cultivars and commissioned
a breeding programme at SCRI. Naturally they wanted a fast cost
effective programme and SCRI swede breeder John Bradshaw (Figure
1) opted for single seed descent. He had already used the
method on a small scale for research into the genetical basis of
heterosis (hybrid vigour) and knew it worked because he had also
been able to produce the cultivar Virtue which was national listed
in 1997.
Figure 3: Swede breeding by single
seed descent
Yield trial of over 1000 lines in 1999
For an enlarged view Click
Here
(Photograph by courtesy of SCRI)
In 1993 fifteen crosses were made between parents
which complemented each other for desirable chacteristics, including
the cross between Airlie and Invitation. Then in 1994, a few plants
of each of the 15 hybrids (F1 generation) were raised in a glasshouse
and bag-selfed (Figure 2) to produce what we call
F2 seed. Seed is in fact sown in a warm glasshouse in October and
the seedlings grown at 15 to 20 degC until December when the temperature
is set at frost-free (5 degC) to allow natural vernalization (cold
requirement for flowering) over winter. Then in 1995, 120 F2 plants
from each cross, making a total of 1800, were grown in the glasshouse
and bag-selfed to produce F3 seed. The process was repeated in 1996
(F4 seed), 1997 (F5 seed) and 1998 (F6 seed). Each F5 plant traced
back to a single unique F2 plant, hence the name single seed descent.
Over 1000 of the F5 plants produced enough seed
for assessment as F6 families in a yield trial in 1999 (Figure
3). One could see that the families were uniform inbred
lines with big differences between lines which showed all combinations
of the parental traits, as predicted back in 1865 by Mendel, the
founder of modern genetics. Colleagues from Advanta helped me and
my trials’ officer, Ralph Wilson, select 50 lines for further
seed production in 2000 and trialling in 2001. We involved Scottish
growers in helping us to choose six out of the 50 lines for multiplication
in polythene tunnels in 2002, using blowflies as pollinators. More
extensive trials involving Scottish growers followed in 2003 and
in 2004 we entered two of the lines from the cross between Airlie
and Invitation into Official National List Trials. One has recently
been named Gowrie, as a result of a competition run at SCRI’s
Open Day. The winner of the name the swede competition was eight
year old Rory Lawson from Birkhill near Dundee (1).
Figure 4: Gowrie swedes - the product
For an enlarged view Click
Here
(Photograph by courtesy of SCRI)
Gowrie is a high yielding swede with intermediate
dry matter content, excellent powdery mildew resistance, resistance
to the most prevalent races of clubroot in the UK, and an attractive
globe shape with purple skin and yellow flesh (Figure 4).
It is suitable for culinary use and for feeding to sheep and cattle.
Future needs and possibilities
High yield , disease resistance, an attractive
appearance and uniformity have all been achieved in inbred line
cultivars. Whether or not even greater uniformity and desirable
combinations of traits can be achieved more readily in F1 hybrid
cultivars remains an open question. SCRI certainly has the technology
and germplasm to produce hybrids, but seed production and hence
the resulting seed would be more expensive. In other words, commercial
judgements will need to be made. As for additional desirable traits,
one only has to see swedes being grown under fleece to realise that
root flies are the major pest problem. In-built resistance to these
and other pests such as flea beetles, caterpillars and aphids are
highly desirable but require further research and then a ten year
breeding programme which raises the eternal question of who pays,
government or industry or both?
21 October 2004.
©www.land-care.org.uk
Reference
1. Editorial (2004). Gowrie swede:
a new variety
See SCIENCE Homepage, filed 19 Oct 04, www.alnd-care.org.uk
Click Here
to View
Finis
|
