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