Download Managing Blackleg Resistance Breakdown and Trade Barriers through Blackleg

Managing Blackleg Resistance Breakdown
and Trade Barriers through Blackleg
Resistance Stewardship in Canola
Dilantha
Fernando
Department
of
Plant
Science
University
of
Manitoba
MB Agronomists Conference, Dec 15, 2010
What is Blackleg?
Where does it attack & cause symptoms?
Major
Problems
at
the
Present
Time
•  The
pathogen
is
reappearing
and
there
is
more
disease
in
the
farmers’
fields
•  A
trade
barrier
on
the
export
of
canola
seed
to
China
General
Blackleg
Management
PracEces
•  Resistant
culEvars
–
very
effecEve
•  Adequate
rotaEon
of
canola
with
other
crop
species
•  IsolaEng
canola
producEon
from
previously
infected
fields
by
a
specified
distance
•  Efficient
weed
and
volunteer
control
•  The
use
of
cerEfied
seed
and
seed
treatment
Blackleg
is
not
a
new
problem
•  It
was
well
managed
with
good
geneEcs
(resistance)
for
almost
3
decades.
•  However,
New Problems with Blackleg!!
•  The disease is emerging in farmers’ fields even on MR and Rrated cultivars – outbreaks are now more common!
•  New races (strains) have been found since 2002
•  China has introduced restrictions on the import of canola seed
•  Several growers practicing Tighter Rotations with canola
•  Minimum or zero tillage can aggravate the problem
Is
Plant
Resistance
the
Best
Strategy?
•  Use
of
plant
resistance
is
one
of
the
most
aSracEve
approaches
to
suppressing
plant
disease.
–  1.
Requires
no
ac0on
by
the
farmer
during
the
growing
season.
Therefore,
low
produc0on
costs.
–  2.
Is
not
disrup0ve
to
the
environment.
i.e
Limits
pes0cide
applica0on.
low
produc0on
costs
–  3.
Is
generally
compa0ble
with
other
disease
management
techniques.
–  4.
Most
oEen
singularly
sufficient
to
suppress
disease
to
tolerable
levels
(But
not
always
a
good
method
to
do
so!!)
.
8
What are the Types of Resistance we have?
•  Resistance
•  Two types:
1.  Major gene/qualitative/vertical
•  single gene
•  gene-for-gene interactions
2.  Minor gene/quantitative/horizontal
•  many genes each with small impact
Pathogenicity
Gene
Host
Gene
Rlm1
Qualita4ve
Resistance
Quan4ta4ve
Resistance
Single gene resistance
Major effects
Avrlm1
Avrlm1
Avrlm1
QTL1
QTL2
QTL3
QTL4
QTL5
Multiple gene resistance – minor effects
Two types of resistance to L. maculans
Quantitative
resistance (partial
resistance)
R gene-mediated
resistance (complete
resistance)
susceptible
resistant
Canadian Blackleg Situation
% Incidence of Blackleg stem canker
Infected Plants
% plants infected with blackeg
50
Manitoba
Saskatchewan
Alberta
45
40
35
30
25
20
15
10
5
0
2003
2004
2005
2006
2007
2008
2009
2010
Courtesy Clint Jurke and Faye Dokken-Bouchard
Blackleg Situation
•  Outbreaks of blackleg more common
•  New races of blackleg appearing
•  Short rotations and zero tillage increase disease
risk.
•  How durable is the blackleg resistance?
Do Rotations of crop help?
•  Crop Rotations
•  Getting tighter
•  Increase risk for disease development
How should resistance be deployed?
•  Resistance
can
fail
if
it
is
not
applied
correctly,
as
has
happened
in
Australia
and
France.
Lessons from other canola growing countries:
Situation in France
•  In France, the large-scale use of single Rlm1 gene for ten
years (1990 to 2000) shifted the population of isolates from
Avrlm1 to others (Rouxel et al., 2003) .
•  Therefore the efficiency of resistance of the commercially
successful cultivars harboring Rlm1 decreased consistently
between 1995 and 2003 in France. (Rouxel et. al. 2003)
Frequency of isolates harboring AvrLm1 or avrLm1 from
Cultivars with the major resistance gene Rlm1
Virulent strains
Rouxel et. al. 2003
Lessons from other canola growing countries:
Situation in Australia
•  The Surpass 400 (LepR3 gene resistance) derived cultivars
became susceptible to blackleg within 2 years after being
released – ‘Boom and Bust’!
•  Cause - due to large-scale use of single gene resistance
(2001 to 2003) – loss $ 5 – 10 million / year
•  Dominant single gene resistance being easily overcome by
pathogen population shifts (Li et al, 2003).
Blackleg
•  Australian experience
•  Surpass 400 (LepR3) released
commercially in 2001
•  Epidemic in 2003.
Hyola 60 – LepR3 resistance
Conventional Resistance
Situation in Western Canada in early 2000’s
Chen and Fernando, 2006 Can J of Plant Pathology
Blackleg symptoms on R-Rated canola cultivar
Distribution of New Pathogenicity groups
How
does
one
isolate
react
to
different
culEvars
with
known
R‐genes?
•  Visual
indica0on
of
the
varia0on
observed
on
the
various
R
genes.
This
isolate
is
05‐08,
which
is
one
of
the
isolates
recovered
from
the
canola
debris
that
Coreen
Franke
collected
at
the
Killam
site
in
2005.
Percentage
of
isolates
carrying
avirulence
allele
AvrLm2
at
each
site
Kutcher et al. 2010
Overcoming Glacier which has Rlm2 (Plum Coulee)
Percentage
of
isolates
carrying
avirulence
allele
AvrLm3
at
each
site
Kutcher et al. 2010
Rlm3 not effective in Brandon, Carberry, Plum Coulee
Percentage
of
isolates
carrying
avirulence
allele
AvrLm4
at
each
site
Kutcher et al. 2010
Avrlm4 – not so good in the west
The success in Breeding for disease resistance - the future?
Mean Incidence (% of Total Plants Surveyed)
12%
10%
8%
6%
Blackleg
4%
2%
0%
1999
2000
2001
2003
2004
2005
2006
2007
2008
2009
Year
Courtesy
Faye
Dokken‐Bouchard
Strategy for stable resistance deployment
•  Therefore
resistance
should
be
deployed
as
part
of
a
larger
strategy
to
control
this
disease.
•  Stewardship
of
blackleg
resistance
and
agronomic
prac0ces
designed
to
control
blackleg
should
be
recommended
together.
Pathogenicity
Gene
Host
Gene
Rlm1
Avrlm1
Rlm1
Quan4ta4ve
Resistance
Avrlm1
Avrlm1
Qualita4ve
Resistance
QTL1
QTL2
QTL3
QTL4
QTL5
Fitness
cost
of
virulence
can
be
used
as
indicator
of
durability
of
the
corresponding
R
gene
•  Near
isogenic
isolates
at
AvrLm1
or
AvrLm4
loci
•  Host
without
the
corresponding
R
gene
(no
selec0on
pressure)
Avr gene in
L .maculans
population
Deploy
Brassica
napus R
gene
L. maculans
evolves to
virulence
Remove
Brassica
napus R
gene
Consequence for
L. maculans
Consequence
for Brassica
napus
AvrLm4
Rlm4
Point mutation
No Rlm4
Large fitness
cost of virulence
Can redeploy
Rlm4
Rapid selection
for AvrLm4
avrLm4
AvrLm1
Rlm1
Deletion of gene
No Rlm1
Rlm2
Rlm3
?
May be able
to redeploy
Rlm1
Less rapid
selection for
AvrLm1
avrLm1
AvrLm2
AvrLm3
Smaller fitness
cost of virulence
No Rlm2
No Rlm3
avrLm2
avrLm3
Time (years)
No fitness cost of
virulence
No selection for
AvrLm2, AvrLm3
Cannot
redeploy
Rlm2, Rlm3
Durability of Brassica napus resistance
Fitness cost of virulence at L. maculans locus
Fitness cost of virulence & potential durability of R gene resistance
Blackleg
•  Known:
•  R-rated cultivars can and do break down
•  Pathogen diversity is high
•  Virulence genes available to
compromise most R genes
•  Tight rotations recipe for epidemic
What factors decide the
durability of resistance?
•  Resistance Durability
•  Resistance may not be durable if:
•  pathogen diversity is high
•  pathogen gene flow is high
•  pathogen reproductive capacity is high
•  Canola resistance diversity is low
QuanEtaEve
resistance
•  Not
race
specific
•  QuanEtaEve
resistance
is
non
race
specific
•  QuanEtaEve
resistance
is
durable
•  Difficult
to
screen
for
‐
at
seedling
stage
•  Screening
for
quanEtaEve
resistance
currently
relies
on
field
assessment
at
harvest
Keeping Resistance to Blackleg Alive!
•  How should resistance be deployed?
Pathogenic
Diversity
low
high
high
Gene
flow
low
R
genes
&
quant.
Use
resist.
in
mulE‐lines
quanEtaEve
or
regional
resistance
deployment
Gene
flow
high
Pyramid
R
genes
low
Use
R
gene
McDonald
BA.
and
Linde
C.
EuphyFca
124
(2):
163‐180,
2002
Pathogenicity
Gene
Host
Gene
Rlm1
Avrlm1
Avrlm1
Quan4ta4ve
Resistance
QTL1
QTL2
QTL3
QTL4
QTL5
Blackleg
Resistance Stewardship Options
(Falls well within Environmental Stewardship)
•  Want current resistance genes to last
•  What are the options?
1.  Long rotations
2.  Rotating resistance genes
3.  Resistance genes with minor genes
Acknowledgements
• 
• 
• 
• 
Randy
Kutcher,
Agriculture
&
Agri‐Food
Canada,
Melfort,
SK
Clint
Jurke,
Canola
Council
of
Canada
Khaled
Al‐Taweel,
University
of
Manitoba
Yu
Chen,
University
of
Manitoba
(Cargill
Inc.,
SK)
•  Natural
and
Science
and
Engineering
Research
Council
of
Canada
•  Agriculture
Research
Development
Ini0a0ve,
MB
•  Canola
Council
of
Canada
–
CARP
Program
•  Seed
Industry
Carman Blackleg Nursery
Thank you
41
Identification of 16 races among 87 isolates of L. maculans from
western Canada collected between 1997-2005 – R. Kutcher et.al
Race designation1
Number of isolates
of each race
Frequency
(%)
Number of
avirulence alleles
Av1-2-3-4-5-(6)-7-(8)-9-10(LepR3)2
1
1.2
8
Av1-2-4-5-(6)-7-(8)-9-10(LepR3)
1
1.2
7
Av1-2-3-6-(8)-9-10-(LepR3)
1
1.2
6
Av1-2-4-6-7-(8)-10-(LepR3)
1
1.2
6
Av1-4-5-6-7-(8)-10-(LepR3)
1
1.2
6
Av2-3-6-(8)-9-10-LepR3
7
8.1
6
Av2-4-6-7-(8)-10-LepR3
13
14.9
6
Av1-2-6-7-(8)-10-(LepR3)
1
1.2
5
Av1-2-6-(8)-9-10-(LepR3)
20
23.0
5
Av1-4-6-7-(8)-10-(LepR3)
1
1.2
5
Av2-4-6-7-(8)-10
1
1.2
5
Av2-6-7-(8)-10-LepR3
3
3.5
5
Av2-6-(8)-9-10-LepR3
19
21.8
5
Av4-6-7-(8)-10-LepR3
1
1.2
5
13
14.9
4
3
3.5
4
Av1-2-6-(8)-10-(LepR3)
Av2-6-(8)-10-LepR3
Air‐borne
ascospores
R
gene
resistance
Phoma
leaf
spots
Infec0on
QTL
resistance
Damage
Severe
canker
(harvest)
QTL
resistance
Early
canker
Major
gene
mediated
resistance
•  Race
specific,
high
risk
of
overcoming
resistance
•  EffecEve
only
if
corresponding
Avr
allele
is
predominant
in
pathogen
populaEon
•  InformaEon
on
pathogen
races
is
essenEal
•  Many
factors
(e.g.
host
culEvar,
pathogen
fitness
cost,
temperature)
affect
race
composiEon
of
populaEons
Temperature affects R gene resistance
Resistant
15°C
25°C
Susceptible
Darmor
DarmorMX (Rlm6)
Huang et al., 2006, New Phytologist, 170, 129-141
Monitoring
pathogen
populaEon
R gene is effective only if corresponding Avr
allele is predominant in pathogen population,
so it is needed to monitor pathogen population
•  Collec0on
of
isolates
from
leaf
spots
or
stem
cankers
•  Collec0on
of
ascospores
from
air
samplers
•  Determina0on
of
pathogen
race
structure
using
pathogenicity
test
or
specific
PCR
primers
Detect
Avr
allele
by
inoculaEon
(Pathogenicity
Test)
Air
sampling
to
determine
alleles
b
Spore sampler surrounded
by diseased OSR stem debris
Van de Wouw et al., 2010
Advantages
 Samples
larger
populaEon
 Quicker,
cheaper
 
Less
laborious
than
cotyledon
assays
Temperature affects quantitative resistance
Mean internal stem canker severity
100
80
Darmor
Eurol
60
40
20
0
15°C
25°C
Darmor (with quantitative resistance)
Eurol (without quantitative resistance)
Huang et al., 2009, Plant Pathology
Growth
in
stem
(internal)
Resistant
Darmor
Susceptible
Eurol
Huang et al., 2009, Plant Pathology
Management
of
Blackleg
of
Canola
Cultural
control:
Crop
rotation
for
at
least
3
years.
Tillage
–
conventional
tillage
helps
reduce
inoculum
Weeds
and
volunteer
canola
removed.
Pathogen-free
seed.
Genetic
resistance:
Resistant
cultivars
—
the
most
important
and
sustainable
means
of
blackleg
control
in
Canada
for
the
past
three
decades.