Reducing Fusarium head blight (FHB) and deoxynivalenol (DON) accumulation in cereals requires identifying sources of genetic resistance, as resistance is quantitative and no variety exhibits complete resistance, and eliminating factors that increase susceptibility, such as the RhtD1b semi-dwarfing gene which is associated with reduced FHB resistance due to impaired anther extrusion. Breeding efforts aim to combine major resistance genes/QTL from sources like Sumai 3 wheat with additional genes/mechanisms to provide robust multi-genic FHB and DON resistance adapted to European wheat backgrounds.

1. Reducing the risk of DON accumulation in cereals
Paul Nicholson
John Innes Centre

2. FHB and disease resistance – a challenge to breeders
Not just yield loss – mycotoxin contamination DON
Resistance can only be assessed in adult plants at flowering
Susceptibility varies throughout flowering
Resistance is quantitative (controlled by quantitative trait loci (QTL))
No variety exhibits complete resistance
Resistance is greatly affected by environment.
- low disease pressure: all varieties appears resistant
- high disease pressure: all varieties appear susceptible
Genetic analysis requires testing across multiple years and environments
Wheat is hexaploid and has a genome size of approx. 17Gb

3. Classical ‘types’ of Resistance
Type 1:
Resistance to initial infection
Efficient anther extrusion reduces
FHB susceptibility

4. Classical ‘types’ of Resistance
Type 1:
Resistance to initial infection
Type 2:
Resistance to fungal spread from infection site

5. Wheat

6. Wheat
Fungus

7. Wheat

8. Wheat
DON

9. Wheat

10. Wheat

11. Wheat

12. Barley

13. Barley
Fungus

14. Barley

15. Barley

16. Barley

17. Barley

18. DON
o Mycotoxin/phytotoxin
o Virulence factor in wheat
• Promotes fungal spread in wheat
• Bleaching above infection site predominantly the result of DON
oNot a virulence factor in barley

19. Sources of resistance to FHB: wheat
•Sumai 3 (China), 3B, 5A, 6B
•Type 1 resistance:
•Chromosome 5A (QTL)
•Type 2 resistance:
•chromosome 3B (Fhb-1)
•Chromosome 6B (Fhb-2).
•Qs.
•How well do these resistances work in European winter wheat backgrounds?
•How many are required to provide robust resistance?
Photo by Guihua Bai.• Need to complement the Sumai 3 resistance with additional
genes to provide high level resistance to FHB.

20. Sources of resistance: wheat
• Other varieties:
• Frontana (Brazil), 3A – (type 1) not stable?.
• Aurora (Russia), 5A, 1BL/1RS - (type 2),
• T. macha (land race), type 1 and type 2.
• Arina (Switzerland), QTL of only moderate effect . Three QTL studies all identified
different genomic regions for FHB resistance. Not suitable for Marker Assisted
Selection (MAS).
• Wild species – Leymus racemosus – Fhb3 (whole of short arm on 7AS)

21. Watkins Collection : wheat lines collected in 1930’s from across
the globe.
Additional sources of FHB resistance:
land races and wild relatives
Triticum timopheevii
Difficult to introduce the positive elements into new varieties without
dragging along negative ones.
Simon Orford

22. Resistance to FHB: barley
Two row barely is generally more resistant than
six row barley
The ‘Denso’ dwarfing gene on 4H can
compromise resistance when causing heads to
be partially trapped in ‘boot’.
Most FHB QTL are coincident with those for
height, flowering time and spike architecture.
Sources of resistance: ‘heritage’ varieties. E.g.
Chevallier.

23. MycotoxinFungus
Transgenic Wheat Expressing a Barley UDP-Glucosyltransferase Detoxifies
Deoxynivalenol and Provides High Levels of Resistance to Fusarium graminearum.
Li et al (2015) Mol Plant Microbe Interact. ;28:1237-46
Credit: Chem. Res. Toxicol.
DON
3-glucosyl-DON
One mechanism for resistance to FHB
Note: this is relevant to DON-producing species

24. Fusarium head blight (FHB)

25. FHB
quantitative trait loci
(QTL)
Bai, et al (1989) Acta Agriculturae Shanghai 5: 17-23
1989
6BL
Sumai3
5AS
3BS

26. FHB
quantitative trait loci
(QTL)
Cuthbert et al (2006)
Plant Breeding 128: 1-26
2006
6BL
‘Mendelised to Fhb2’
Sumai3
5AS
Centromeric - too fine to map
3BS
‘Mendelised to Fhb1’

27. FHB
quantitative trait loci
(QTL)
Buerstmayr et al (2009)
Plant Breeding 128: 1-26
2009
6BL
‘Mendelised to Fhb2’
Sumai3
5AS
Centromeric - too fine to map
3BS
‘Mendelised to Fhb1’
Over 100 FHB QTL reported dispersed across all 21 chromosomes

28. 2016 - Fhb1: revealed at last?
Rawat, et al (2016) Wheat Fhb1 encodes a chimeric lectin with agglutinin domains and a pore-forming toxin-
like domain conferring resistance to Fusarium head blight. Nature 2016
Filing of Patent WO 2017/173318 Fhb1 identified as a mutation in a ‘susceptibility’ gene
- a histidine-rich calcium binding protein-like gene, named TaHRC. Zhenqi et al (2017) Kansas State University
Jia, et al. A journey to understand wheat Fusarium head blight resistance in the Chinese wheat landrace
Wangshuibai (2018) Crop Journal 6:4859
Li et al (2019) and Su et al (2019) papers confirm TaHRC mutation as conferring resistance.

29. Rht-D1brht-tall Rht-B1b
Green revolution semi-dwarf wheat
Rht1 Rht2
T. Draeger
RhtB1
RhtD1
❑ Wheat genome: three homoeologous chromosome sets.
(Peng et al. 1999)
Rht-B1b and Rht-D1b mutations are highly similar

30. FHB and plant height
Hilton et al (1999) Plant Pathology
Taller varieties tend to be more resistant to FHB than shorter varieties
Mechanisms?
Pleiotropy?
Linkage?

31. Arina (tall) (FHB resistant Swiss variety) x Riband (Rht-D1b) (UK (they are all susceptible) variety)
Soissons (Rht-B1b) (FHB resistant French variety) x Orvantis (Rht-D1b) (FHB susceptible French variety)
Arina (tall) x Riband (Rht-D1b) (Draeger et al 2007)
Major QTL at RhtD1b – large negative effect on FHB resistance
Soissons (Rht-B1b) x Orvantis (Rht-D1b) (Srinivasachary et al 2008)
Major QTL at RhtD1b – large negative effect on FHB resistance
No FHB QTL associated with Rht-B1b
FHB resistance in European winter wheat
Q. Why is Rht-D1b associated
with FHB susceptibility?
Linkage or pleiotropy

32. Anthers and type 1 resistance
Pollen contain compounds (choline and betain) that promote growth of germinating Fusarium conidia
(Strange et al 1978)
Wheat varieties with fully extruded anthers tend to be more resistant to FHB
Wheat lines carrying RhtB1b or RhtD1b have shorter anther filaments and greater susceptibility to FHB.
Rht-D1b anther retention more
severe than Rht-B1b (Buerstmayr &
Buerstmayr 2016)
Conclusion: the difference in FHB
susceptibility between Rht-B1b and
Rht-D1b is due to difference in
anther extrusion.

33. Rht-B1c and Rht-D1c dwarf lines both show increased type 2 resistance
0
2
4
6
8
10
12
rht tall rht 3 rht 10
numberofdiseasesedspikelets
Mercia NIL
Spray inoculation
0
2
4
6
8
10
12
14
16
rht tall rht 3 rht 10
numberofdiseasedspikelets
Mercia NIL
Point inoculation
Rht-D1c mutation is a 4 fold
duplication of the Rht-D1b
mutation
Chris Burt

34. FHB susceptibility: due to Rht or a nearby gene?
Recombinant near isogenic Rht-D1a/Rht-D1b lines
2,743 point inoculations to assess disease spread (Type 2)
16,598 FHB observations
Result
The susceptibility is not due to the Rht-D1 allele itself.
The problem is a near-by gene introduced alongside Rht-D1b.
Chris Burt

35. Role of phytohormone signalling pathways in Fusarium resistance
Ethylene Auxin Brassinosteroid Gibberellin ABA
Susceptibility Susceptibility SusceptibilityNo effect
Type 1 Type 2
SusceptibilityResistance
Type 1 Type 2
Chen et al
(2009)
Steed et al
(unpublished)
Goddard et al
(2014)
Srinivasachary et al
(2009)
Susceptibility ?
Buhrow et al (2016)
Phytopathology 106:986-996
Paul Cannon Paul Cannon
Luo et al
(2016)
Qi et al
(2016)
Haidoulis
(unpublished)

36. Introducing barley resistance into wheat
o Barley possesses potent type II resistance
• Which barley chromosomes carry resistance?
• Can barley chromosomes confer type II resistance in a wheat genetic
background?
o Wheat lines with barley chromosome additions developed by
Márta Molnár-Láng

37. Selected wheat-barley additions
4A 4B 4D +4H
0
10
20
30
40
50
60
70
Percentageofinfectedspikelets
Genotype
Point inoculated 2012 polytunnel experiment
Fungus

38. Selected wheat-barley additions
4A 4B 4D +4H
0
10
20
30
40
50
60
70
Percentageofinfectedspikelets
Genotype
Point inoculated 2012 polytunnel experiment
Fungus

39. Wheat-barley 4H(4D) substitution
4A 4B 4D +4H
0
10
20
30
40
50
60
70
Percentageofinfectedspikelets
Genotype
Point inoculated 2012 polytunnel experiment
Fungus

40. 0
1
2
3
4
5
6
7
8
9
CS CSDT15(4DL) CSDTE15(4DS) N4AT4D N4DT4B
Spikeletsinfectedup
Line
Point inoculated 2013 glasshouse experiment
Lacks 4DS
10 dpi
17 dpi
21 dpi
Lacks 4DL
Fungus
Effect of loss of short arm of 4D chromosome on FHB type 2 resistance
Type 2 susceptibility factor
carried on short arm of 4D

41. Fusarium head blight phenotyping Brazilian spring wheat populations

42. Unlike European wheat, Rht genes have a lesser effect on FHB susceptibility
Minor FHB QTL: 4 – 11% variance
1B, 4A, 4D (Rht-D1b), 5B, 7A
Major height QTL: 40 – 80% variance
Rht-B1b (4B) and Rht-D1b (4D)
4% 80%

43. Major mycotoxin (DON) accumulation QTL : 18 – 25% variance
4B and 4D
No association with other traits (Rht, FHB visual symptoms or FDK)
0
50
100
150
200
250
300
350
0 5 10 15 20
FHBAUDPC
DON (ppm)
Relevance to European wheat? Same as Oakley x Esket 4B mycotoxin QTL?
Identification of mycotoxin QTL

44. Summary
• Wheat:
Type 1: Increased plant height and anther extrusion
Type 2: Large-effect resistance QTL (e.g. Fhb1 and Fhb2)
Elimination of FHB susceptibility factors (RhtD1b associated and
chromosome 4D FHB susceptibility factors).
Increased DON detoxification through glycosyltransferase activity
Reduced DON accumulation (4B chromosome effect).
Genomic selection offers a route for breeders to increase the rate of
resistance enhancement without a need for a mechanistic understanding.

45. Acknowledgements
Ex-group:
Nick Gosman
Srinivasachary
Richard Draeger
Antoine Peraldi
Robert Saville
Chris Burt
JIC:
Brande Wulff
Burkhard Steuernagel
Sanu Arora
Kumar Gaurav
Cristobal Uauy
Nikolai Adamski
Ricardo Ramirez Gonzalez
Simon Griffiths
Jon Clarke
Horticultural Services
EI: Chris Watkins
Fiona Doohan
Gerhard Adam
Marc Lemmens
Embrapa:
Pedro Scheeren
Jessica Rosset Ferriera
Eduardo Caierao
Luciano Consoli
Gisele Torres
Yukio Tosa