Late blight in 2012 – status report
David Cooke
Alison Lees
Allison Chapman
Julie Squires & Louise Sullivan
Louise Cooke – AFBI, Northern Ireland
Moray Taylor – Fera
Blight scouts, Potato Council, Scottish Government
2011
2012 summary to date Dry planting but subsequently very wet. Blight active
early with extreme disease pressure
Many Smith Periods up until July 11th (5587 cf 1034 at
same time in 2011)
335 outbreaks to date (183 in 2011) first outbreak Cornwall early May (cf Fife 28th June 2011) Herefordshire by 16th May Scottish Borders 30th May
SSR fingerprinting completed on 55 samples
2012
GB P. infestans 2011 population update
74 138 73 899 Isolate no. 1452 1118 522 247 426
Regional distribution of genotypes
England & Wales (n=75) Scotland (n=341)
Effect of temperature on different P. infestans genotypes
6_A1 more aggressive than 13_A2 at higher temperatures
Field competition experiments show 13_A2 dominates 6_A1 and others
0
10
20
30
40
50
120 160 184 200 216 232 248 264 280 296 320 336 352 368 384 400
Day Degrees (°C/days)
Ave
rage
lesi
on
siz
e (
mm
2 )
6_A1
13_A2
Low temperature infection
Approx. 50% of isolates infected at 6°C
Not specific to particular genotypes
More windows of opportunity for
infection than currently realised
Recent study also examining interaction of
temperature and different time periods at
high humidity
0
20
40
60
80
100
6 8 10 12 14 16 18 20
Temperature (°C)
Infe
ctio
n (
%)
Green33 status (as per Feb 2012)
Fluazinam was less effective against a green33 isolate compared to a blue13
isolate in an artificially inoculated field experiment under very high disease
pressure and long spray intervals in Lelystad in 2011
The cause (reduced sensitivity, increased aggressiveness...?) not yet known
The link between green33 and reduced effectiveness of fluazinam not
established and under investigation.
Lineage defined by WUR group (Wageningen) where it comprised 20% of popn
in 2011. SSR profile shared with D. Cooke in October 2011
GB population 2003-2011 screened for presence of green33 and only two
isolates found. These are from volunteer potatoes in a carrot crop in Norfolk
sampled in early October 2011.
Amongst samples collected during 2008-10 (BayerCropScience & Syngenta)
and fingerprinted at JHI green33 was found only in NL
Close collaboration between EU scientists allowing good communication and
shared findings
Kessel, Evenhuis & Schepers (Wageningen UR, NL)
Green33 sensitivity testing update
A collection of green33, 13_A2 and other isolates have now been tested at Plant
Research International (Wageningen, NL) to evaluate the EC50 to fluazinam
A wide range of sensitivity to fluazinam exists in the Phytophthora infestans
population. For example, all 13_A2 isolates tested were highly sensitive to very
low doses. Amongst isolates of green33 some were more sensitive than others;
the isolate from the 2011 Dutch field trial was amongst the least sensitive.
Trials suggest that, in the absence of fluazinam, green33 is less competitive than
13_A2 and it may have been the higher usage patterns in the Netherlands that
resulted in the green33 type becoming established.
Green33 is sensitive to all other fungicides. Best practice guidelines should be
followed with Shirlan comprising no more than 50% of blight sprays in a season.
Mark Bullen (Syngenta) and Kessel, Evenhuis & Schepers (Wageningen UR, NL)
Green33 status (Aug 2012 update) Green33 found in NR21 (Norfolk) in early October 2011
We have focussed on testing samples from the earliest outbreaks in this area
and have detected no green33 (33_A2) amongst 50 samples tested to date
NR10 22 Jun 6_A1 NR10 26 Jun 6_A1 & 13_A2 NR10 4 Jul 6_A1
PE20 26 Jun 6_A1 PE20 3 Jul 6_A1
NR29 2 Jul 13_A2
NR11 28 Jun 6_A1
CT7 13 Jun 13_A2 CT7 14 Jun 13_A2
2011
Jersey samples (Howard Hinds) 6_A1, 13_A2, 1_A1
Oospores The primary inoculum for a few GB outbreaks each year
appears to be derived from oospores.
Warm wet springs increase the risk of oospore germination.
Recent dry/cool springs has decreased the threat in GB
Danish industry (Nielsen, Hansen & Bødker, 2011) reported an
early and severe start to 2011 blight season that coincided with
rainfall events in May & high infection pressure in Late May-
June. Ridomil worked well to keep such infection in check.
Oospores could still cause problems to the GB industry should
weather conditions be suitable early in the season.
Long rotations - the best strategy to counter threat of oospores
The oospore threat in other parts of Europe
Dominant clonal types
plus a collection of
diverse novel genotypes
- the result of sexual
recombination.
From such recombinants
come successful clonal
types with traits that
make blight more
difficult to manage (e.g.
13_A2, 6_A1 and 33_A2)
Nordic populations
similarly diverse
Geert Kessel, Trudy van den Bosch et al PRI Wageningen – Euroblight meeting Russia Oct 2011
13_A2
6_A1
Less pathogen diversity in NW Europe (2008-10)
13_A2 still present in many areas (less due to reduced Metalaxyl use?)
A high proportion of novel ‘misc’ types particularly in East
New clonal genotypes in East and NL
Active collaboration among EU scientists helps industry
Thanks to Bayer and Syngenta, Howard Hinds, Vangelis Vellios
n=350
Conclusions
Late blight severe in 2012 but robust regimes with a range of
active ingredients are enabling effective management
P. infestans able to infect below 10oC – but Smith Periods still
offer a good indication of disease activity
No evidence spread of green33 genotype in early infections in
GB. Follow Syngenta best practice advice for Shirlan
Population change can be driven by new genotypes that emerge
from germinating oospores. Maintain long rotations and manage
discard piles and volunteers to minimise all primary inoculum.
Ongoing/planned work
Completing the isolation and genotyping of GB 2012 samples
European and global population diversity in collaboration with
industry and other partners
Studies on the interaction between pathogen genotype,
aggressiveness and response to temperature and humidity for
blight outbreak prediction using modified Smith period criteria for
improved decision support
Longer-term prediction/modeling of epidemic progress of
different genotypes to optimise management to minimise
emergence of new virulences or fungicide resistance
Ongoing testing of pathogen effector diversity for long-term
strategies of breeding durable resistance
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