Field evaluations highlight the

importance of the pre-symptomatic

phase in supporting strong partial

resistance against Zymoseptoria tritici

James Gerard Hehir, Cliona Connolly, Aoife O'Driscoll, Joseph Lynch, John

Spink, James Brown, Fiona Doohan, Ewen Mullins

2

Zymoseptoria tritici, the causal

agent of septoria tritici blotch

Yield losses of up to 50% (Eyal et

al., 1987)

Long pre-symptomatic phase

(latent period)

Active sexual cycle

Septoria tritici blotch (STB) of wheat

(O’Driscoll et al., 2014)

Pre-symptomatic phase (latent period)

3

Epidermal layer

Mesophyll Layer

Latent period- Last up to 7-28 days

Leaf surface

Lesions bearing asexual pycnidia

Switches to aggressive necrotropic lifestyle

Necrotrophic phase

4

Active sexual cycle

30% end of season

Pathogen evolution

Septoria tritici blotch (STB) of wheat

(O’Driscoll et al., 2014)

Current control measures

Control almost entirely reliant on

fungicides

European fungicide input - 70%

(>€400 million) (Fones & Gurr 2015)

Fungicide efficacy decreasing year

on year: azoles & SDHIs

(H152R mutation) (Dooley et al., 2016a)

Regulation (EC) No 1107/2009-

prohibition of DMI-based fungicides

Need to shift reliance from fungicides to more durable

resistant varieties

Azole resistance: Ireland

(Kildea, et al., unpublished)

766x less

sensitive

6x less

sensitive

Durable resistant varieties?

6

Over-reliance on selection based on yield:

Narrow spectrum of resistant genotypes (Arraiano & Brown, 2016)

21 major resistance gene mapped

89 QTL- (Quantitative resistance)

Alternative approach: Broaden genetic

spectrum using wild relatives

Synthetic hexaploids – rich source STB

resistance

Is resistance durable in the field?

Synthetic hexaploidsGene Chromosome Resistance source

Stb1 5BL Bulgaria 88

Stb2 1BS Veranopolis

Stb3 7AS Israel 493

Stb4 7DS Tadinia

Stb5 7DS Synthetic 6x

Stb6 3AS Flame, Hereward

Stb7 4AL ST6

Stb8 7BL Synthetic W7984

Stb9 2BL Courtot, Tonic

Stb10 1Dc Kavkaz-K4500

Stb11 1BS TE9111

Stb12 4AL Kavkaz-K4500

Stb13 7BL Salamouni

Stb14 3BS Salamouni

Stb15 6AS Arina, Riband

StbSm3 3AS Salamouni

Stb16q 3DL SH M3

Stb17 5AL SH M3

Stb18 6DS Balance

StbWW 1BSWW1842, WW2449,

WW2451

TmStb1 7AmSMDR043 (T.

monococcum

Major genes resistance to STB

(Brown et al., 2015)

Gene Chromosome Resistance source

Stb1 5BL Bulgaria 88

Stb2 1BS Veranopolis

Stb3 7AS Israel 493

Stb4 7DS Tadinia

Stb5 7DS Synthetic 6x

Stb6 3AS Flame, Hereward

Stb7 4AL ST6

Stb8 7BL Synthetic W7984

Stb9 2BL Courtot, Tonic

Stb10 1Dc Kavkaz-K4500

Stb11 1BS TE9111

Stb12 4AL Kavkaz-K4500

Stb13 7BL Salamouni

Stb14 3BS Salamouni

Stb15 6AS Arina, Riband

StbSm3 3AS Salamouni

Stb16q 3DL SH M3

Stb17 5AL SH M3

Stb18 6DS Balance

StbWW 1BSWW1842, WW2449,

WW2451

TmStb1 7AmSMDR043 (T.

monococcum(Image adapted from Zhang et al. et al., 2004)

Gene Ref

STB5 Arraiano et al. (2001b)

STB8 Adhikari et al. (2003)

STB16q Tabib Ghaffary et al. (2012)

STB17 Tabib Ghaffary et al. (2012)

Background to Study

7

15 20 25 30 35

Stigg

Dunmore

Oakley

JB Diego

Gator

Kielder

Croft

Glasshouse study: Latent Period

(Zt_IPO323)

Stigg : 38dpi Kielder: 38dpi

Days

8

Questions?

1, Is the strong partial resistance phenotype

in Stigg reflective across different disease

environments?

2, Does extended latency period correlate to

field resistance?

Experimental plan:

Variety STB Rating (HGCA)

Stigg (SH) 8

Dunmore 6

JB Diego 5

Kielder 5

Gator 5

Croft 4

Gallant 3

Field study: 2 years (2013-2015), across 3

three locations

No fungicide treatment

Intensive assessments of STB severity: twice

weekly on second leaf and flag leaf (>20)

Cultivars selected based STB resistance

ratings/glasshouse LP

12.5

13

13.5

14

14.5

15

15.5

16

Waterford Carlow Norwich60

65

70

75

80

85

90

Waterford Carlow Norwich

Mean daily temperature (°C) 01May -31August 2015

Mean monthly rainfall (mm)1June -31August 2015

NorwichCarlowWaterford

% S

TB

seve

rity

fl

ag

le

af

(GS

71)

0

10

20

30

40

50

60

70

80

90

100

Stigg Dunmore JB Diego Kielder Gator Croft Gallant

Norwich

1, Is the strong partial resistance phenotype in Stigg

reflective across different disease environments?

a*

b b b

c

bb

2014-2015 growing season

*Different letter indicates significance between cultivars (Tukey P0.05)

% S

TB

seve

rity

fl

ag

le

af

(GS

71)

0

10

20

30

40

50

60

70

80

90

100

Stigg Dunmore JB Diego Kielder Gator Croft Gallant

Carlow

Norwich

1, Is the strong partial resistance phenotype in Stigg

reflective across different disease environments?

e

a

c

b

d

cd

b

% S

TB

seve

rity

fl

ag

le

af

(GS

71)

0

10

20

30

40

50

60

70

80

90

100

Stigg Dunmore JB Diego Kielder Gator Croft Gallant

Waterford

Carlow

Norwich

1, Is the strong partial resistance phenotype in Stigg

reflective across different disease environments?

a

b b

c

d

cd

d

1, Is the strong partial resistance phenotype in Stigg

reflective across different disease environments?

1, Is the strong partial resistance phenotype in Stigg

reflective across different disease environments? ✓

Untreated Yield 10 t/ha 6.5 t/ha

Stigg Gallant

Waterford 2015

14

Stigg

CroftDunmore

Gallant

Gator JB Diego

Kielder

Stigg

Croft

Dunmore

Gallant

Gator

JB Diego

Kielder

y = -61.132x + 3783.1R² = 0.5746

500

1000

1500

2000

2500

3000

3500

4000

12 17 22 27 32 37

AU

DP

C

Latency period* (days)

▪▪

Carlow

Waterford

*Latency period defined as days from Flag leaf emergence to first visible symptoms of pycnidia on the leaf

2, Does extended latency period correlate to partial field

resistance?

2, Does extended latency period correlate to partial field

resistance? ✓

15

Epidemiological differences between partial resistance and

susceptibility?

LP (degree days) =ln (

𝑐𝑦 − 𝑎

− 1)

−𝑏+ 𝑚

1, Latent phase

Profile of STB Disease Progression- Carlow 2015

𝑦 = 𝑎 +𝑐

(1 + 𝑒 −𝑏 × 𝑥−𝑚 )

Y= disease severity

a, b, c, m, x = fitted coordinates of the

logistic curve

*Estimations of disease progression were calculated once the accuracy of fit was deemed significant

^Degree Days were calculated using a base temperature of 0°C at flag leaf emergence and

accumulated from flag leaf emergence to senescence.

Y= disease severity of 1%

1, Latent Phase- Disease Establishment

16

Gator Dunmore Kielder Gallant Croft JB

Diego

Stigg Difference in mean cultivar oday v. oday Stigg

Carlow 663^ 663 667 683 777 786 920 213 ( 23%)

Waterford 639 589 588 * 564 608 742 164 ( 22%)

Flag leaf emergence – first pycnidia (1% disease)

Carlow

Difference Carlow-Waterford =132 oday

* Gallant (waterford) removed as estimations of disease progression was not significant

Waterford

Gator Dunmore Kielder Gallant Croft JB

Diego

Stigg Difference in mean cultivar oday v. oday Stigg

Carlow 663^ 663 667 683 777 786 920 213 ( 23%)

^Approximate values based on model

17

Epidemiological differences between partial resistance and

susceptibility?

2, Rate of

disease

progression

Rate of disease progression slope =

𝑏 × 𝑐 × 𝑒(ln (

𝑐𝑦−𝑎

−1))

(1 + 𝑒(ln (

𝑐𝑦−𝑎

−1)))2

Profile of STB Disease Progression- Oakpark 2015

Y= disease severity

a, b, c, m, x = fitted coordinates of the logistic

curve

18

-----------------

------

T

-----------------------

-----------

40% 841 869 832 805 924 912 993 129 ( 13%)

Slope

(m=)

0.75 0.42 0.62 0.75 0.80 0.89 0.88 20%

% STB

Severity oday

Gator Dunmore Kielder Gallant Croft JB

Diego

Stigg Difference in mean

cultivar oday v. oday

Stigg

20% 790 811 784 772 887 877 969 148 ( 15.4%)

Slope

(m=)

0.50 0.27 0.41 0.50 0.52 0.59 0.81 43%

Stigg: increased RDP at a later degree day

Rate of disease progression

Carlow 2015

19

T

40% 754 800 784 752 795 916 139 ( 15.2%)

Slope

(m=)

0.69 0.54 0.41 0.53 0.58 0.43 22%

% STB

SeverityGator Dunmore Kielder Croft JB

Diego

Stigg Difference in mean

cultivar oday v. oday

Stigg

20% 718 752 717 704 749 863 135 ( 15.6%)

Slope

(m=)

0.45 0.34 0.22 0.33 0.37 0.30 12%

Stigg: same RDP at a latter degree day

------------------------

---------

-----------------

Waterford 2015

Rate of disease progression

Site Average RDP

(slope)

Average oday

(20% severity)

Carlow .51 842

Waterford .33 751

Conclusion

What is driving resistance?

Stigg: strong levels of partial phenotypic STB resistance

characterised by a lengthened pre-symptomatic phase or “latent

period”

Once LP concluded, followed by a rate of disease progression

comparable to that observed in susceptible genotype

Genetics that underpin a longer Latent period?

Current work

Acknowledgments

21

Cliona Connolly

Dr. Ewen Mullins

Dr Joesph lynch

Deirdre Doyle

John Spink

Dr. Steven Kildea

Dr. Petra Kockapplegren

www.VICCI.ie

Dr. Harriet Benbow

Prof. Fiona Doohan

James Brown