© Laetitia Chartrain

Staying ahead of changing

disease threats

James BrownJohn Innes Centre, Norwich

james.brown@jic.ac.uk

Septoria

FusariumMildewEyespot

Brown rust Yellow rust

© Laetitia Chartrain

© Bob Powelson © James Brown

Wanted: Resistance to all significant diseases(+ yield + quality + standing power + maturity…)

Major achievement in wheat breeding: durable resistance to powdery mildew

Brown 2015, Annual Review of Phytopathology© Govt of W.Australia

Disease resistance : a two-stage process

Recognition Defence

Strong is not Stable in disease resistance

• Resistance triggered by recognition of pathogen

• Fungus mutates: avoids recognition, evades defences

Brown 2015, Ann. Rev. Phytopathol.

Strong is not Stable in disease resistance

• mlo mildew resistance : much stronger defence

• In most current barley varieties

Brown 2015, Ann. Rev. Phytopathol.

“There is no free lunch” : trade-offs of mlo

Strong resistance to mildew

Greater susceptibility to spotting diseases…

BlastFusariumSpot blotch

…notably Ramularia leaf spot

mlo mildew resistance in barley increases susceptibility to Ramularia leaf spot

Mildew-susceptible varieties mlo lines Trials at 6 sites in Bavaria & Scotland, 2013

Ram

ula

ria

seve

rity

(%

max

)

McGrann et al. 2014, Journal of Experimental Botany

How do breeders develop durable disease resistance?

Breeding mimics Darwinian evolution

Variation in many plant traits+

which affect fitness+

& are inherited

Evolution by natural selection

Improved crop varieties

Plant breeding : an international industry

Variety selection in multi-national field trials

Septoria Fusarium

Tan spot

Brown rust

© Michael Trolove

• Cheap & easy travel• Free movement of seed within EU• EU-level Plant Variety Rights

Variety selection in multi-national field trials

Ramularia

Ramularia

Net blotch

© Michael Trolove

• Cheap & easy travel• Free movement of seed within EU• EU-level Plant Variety Rights

Yellowrust

Variety selection in multi-national field trials

© Michael Trolove

• Cheap & easy travel• Free movement of seed within EU• EU-level Plant Variety Rights

Successful wheat breeding: durable resistance of wheat to powdery mildew

• Many genes with small individual effects

• Built up over ~40 years

Brown 2015, Annual Review of Phytopathology© Govt of W.Australia

Advances and challenges in durable resistance to Septoria

Milder, wetter winters

The Septoria / Yield Challenge: Important genes which increase yield & promote Septoria are linkedArraiano & Brown 2017 Mol Pl Path

Loss of fungicide activity

Nitrogen fertiliser

LG Sundance 7.3 KWS Siskin 6.8Crusoe, Dunston, Freiston, Graham 6.7etc

© Laetitia Chartrain

Wheat yellow rust: global changes, local threats

Ali et al. 2017, Frontiers Plant Sci.

• Mix of non-durable recognition genes

• & more durable defence genes

Fungicides support breeding for resistance

• Ramularia severe from 1998

• Over 15 years, barley varieties with better resistance released

• Finding good trial sites• Accumulating defence genes• Understanding role of mlo

• Fungicides are essential to defend against new diseases

The future of disease resistance in cereals

• Field scoring is the limiting step in breeding

• Widespread & growing use of DNA markers• E.g. Pch1 resistance to eyespot

• Drones: accelerate field scoring?

• Foreseeable new technology• Electronic noses: detect fungal compounds

• Hand-held scanners: colour detection

• Genomic selection: select many genes simultaneously

• Disease profile changes• (Re-)emerging diseases: tan spot? stem rust???

© URSULA Agriculture

© Arybelle Technologies

© N Dakota State Univ © USDA-ARS

Take-home messages

• Choose varieties with all-round disease resistance, to maximise income and minimise pressure on fungicides

• Follow label guidance to maintain the effectiveness of fungicides

• Breeding industry needs unhindered access to Europe, including travel, exchange of seed, and variety licensing