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© Laetitia Chartrain
Staying ahead of changing
disease threats
James BrownJohn Innes Centre, Norwich
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