rp resistance rp1-d-virulent isolates fungicides

• Rp resistance• Rp1-D-virulent isolates• fungicides

Effect of rust on sweet corn yieldEAR WEIGHT

Y = 99.4 - 0.58 Xr = 0.81 n = 232

0

20

40

60

80

100

120

140

0 10 20 30 40 50 60 70

Rust severity (%) one week before harvest

Pe

rce

nt

ma

xim

um

yie

ld (

ea

r w

eig

ht)

Rp-resistance

Bands of chlorotic flecks (no sporulation)

In the 1990s, Rp resistanceadded at least $3 million*annually to the value ofprocessing sweet corn in the Midwest * based on four, relatively conservative assumptions

250,000 A processing sweet corn Midwest

1. x 1/2 exposed to common rust

125,000 A exposed to rust

2. x 6.2 tons per A

775,000 tons

3. x $50 per ton

$38,750,000

4. x 15% rust severity*

x 0.5 % loss per 1% severity

$2,906,250 loss

* an average of 15% rust severity or more for hybrids rated MR to S

Rust severity %and (estimated Reactions of sweet corn hybridsyield reductions)** R MR M MS S 0-10% (3%) 0.63 0.26 0.11 0.11 0.1110-20% (9%) 0.37 0.47 0.16 0.11 020-30% (15%) 0 0.26 0.63 0.26 0.1630-40% (21%) 0 0 0.11 0.32 0.2640-50% (27%) 0 0 0 0.21 0.32>50% (>30%) 0 0 0 0 0.16 * probability based on 19 trials in 18 years of evaluations in University of Illinois sweet corn hybrid disease nurseries - plants inoculated as seedlings

** yield loss estimated by multiplying rust severity by 0.6

Probability* of severe rust

Susceptible Rp-resistant

Rp1-D resistant hybrid

Rock Falls, IL September 1999

Rp1-D resistance Los Mochis, Mexico

March 2000

1. How will hybrids react to the Rp1-D-virulent race? - non-Rp hybrids - Rp hybrids

2. Does Rp1-D have any “residual” effect on the new race?

Questions about theRp1-D-virulent race

Reactions of non-Rp hybrids

r = 0.90* * for non-Rp hybrids

0

10

20

30

40

50

60

70

0 10 20 30 40 50 60 70

Severity (%) of rust Rp1-D avirulent isolates

Sev

erit

y (

%)

of

rust

R

p1-

D v

iru

len

t is

ola

tes

Rp1-D hybrids

RpX hybrids

Reactions to Rp1-D-virulent and avirulent isolates

2001 UI hybrid disease nursery

0

10

20

30

40

50

60

70

0 10 20 30 40Severity of rust (%)

Rp1-D-avirulent isolates

Se

ve

rity

of

rus

t (%

)R

p1

-D-v

iru

len

t is

ola

tes

Rp inbreds

r = 0.76 among non-Rp inbreds

2001 UI inbred disease nursery

Reactions to Rp1-D-virulent and avirulent isolates

Hybrids that do not have theRp1-D gene have the samereaction to Rp1-D-virulentand Rp1-D-avirulent rust

Reactions of Rp hybrids

- inoculated with Rp1-D-virulent rust

Populations of Rp hybrids compared to non-Rp hybrids

0

10

20

30

40

50

60

0 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60

Severity of rust (%) - Rp1-D virulent isolates

Num

ber

of h

ybrid

s

Rp1-Dnon Rp1-D

n Mean S.D.137 32.8 8.4 176 33.8 10.7

Rp1-D-virulent isolates - 2001

2001 UI hybrid disease nursery

Pairs of Rp hybrids and

non-Rp hybrids

- inoculated with Rp1-D-virulent rust

Pairs of Rp and non-Rp hybrids

non-Rp hybrid Rp hybrid

Bodacious Bodacious RustDay Star Morning Star GG Code 8 GG Code 23Primetime Prime PlusSch 5005 ChieftainSS 8102 SS 8102 R

0

10

20

30

40

50

60

0 10 20 30 40 50 60

Severity (%) - non-Rp hybrid or inbred

Seve

rity

(%

) -

Rp h

ybrid o

r in

bre

d

r = 0.96 n = 43

slope = 0.95

Reactions of Rp and non-Rp pairs to Rp1-D-virulent rust

2001 UI Rp hybrid trial

• no residual resistance from Rp1-D

• no linkage of general resistance near rp1 region

Rp hybrids and

non-Rp hybrids

- inoculated with a mixture of Rp1-D-virulent and avirulent rust

0

5

10

15

20

25

30

35

0 1-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60

Severity of rust (%) - mixture of isolates

Nu

mb

er o

f h

yb

rid

s

Rp1-D

non Rp1-D

n Mean S.D. 86 15.5 6.4 156 27.5 11.4

Mixture of virulent and avirulent isolates - 2000

2000 UI hybrid disease nursery

Pairs of Rp and non-Rp hybrids

Pair 2000 (mix) 2001 (vir)CnS 710 R 15% 34%CnS 710 36% 37% Incredible Rust 10% 29%Incredible 24% 30%

Morning Star 22% 34%Day Star 41% 35%

Prime Plus 16% 39%Primetime 32% 40%

If virulence is frequent

Hybrids with Rp1-D have similar reactions as non-Rp hybrids - population distributions alike - Rp and non-Rp versions alike

If virulence is infrequent

Hybrids with Rp1-D are infected less severely than non-Rp hybrids - additional research on simple ways to detect frequency of virulence and relate frequency to potential severity

If virulence is infrequent

Rp hybrid non-Rp hybrid

Paired hybrid monitor plotsnon-Rp hybrid Rp hybrid

similar number of pustules per leaf - virulence frequent

fewer pustules on leaves of Rp hybrid - infrequent

Conclusions for Rp1-D are applicable to otherRp genes when virulence against those Rp genes are prevalent

Rp-G, Rp1-E, Rp1-I, Rp1-K compound rust genes

Fungicides• EBDCs

• TILT

• strobilurins (QUADRIS, F-500)

Fungicides*• fungicides are preventative• fungicides ARE NOT curative

Rule of thumb: one or two early applications are superior to multiple late applications • juvenile tissue is more susceptible• infection occurs in the whorl • pustules on lower leaves = inocula for 2o infection (5,000 urediniospores per pustule)

* EBDCs, Tilt

Early applications of fungicides

~ 2% severity

* EBDCs, Tilt

Later applications of fungicides

> 5-10% severity

* EBDCs, Tilt

Strobilurins

may change use of fungicides on sweet corn

• more efficacious • may have different thresholds ?

Rust & NLB - 'Florida XP-7' Leaf area necrotic (%) Rick Raid - UF-Belle Glade Planted: 17 Feb 1997

0

10

20

30

40

50

60

70

Non-treated

Manzate Tilt Folicur Quadris Tilt +Manzate

Folicur +Manzate

Quadris+Manzate

Quaddris+ Tilt

Lea

f ar

ea n

ecro

tic

(%)

Common rust - 'Silver Queen' Leaf area infected (%)

Helene Dillard, NYAES- Geneva Planted: 21 June 2000

0

5

10

15

20

25

30

Non-treated Quadris 0.38 28 July 09 August

Quadris 0.77 28 July 09 August

Tilt 0.25 28 July 09 August

Quadris 0.38 09 August 21 August

Quadris 0.77 09 August 21 August

Tilt 0.25 09 August 21 August

Per

cen

t le

af a

rea

infe

cted

Thresholds

• can rust be controlled if strobilurins are first applied at higher thresholds?

OR

• can strobilurins be applied after we determined that virulent isolates are frequent enough to cause severe infection?

Location: Urbana, IL - May 29, 2001

Hybrids: Snow White, Sterling

Compounds: Tilt, BASF F-500, Quadris (low, high rate)

Application: July 5 (2 to 4-leaf) 5% July 11 (4 to 6-leaf) 15%

July 17 (6 to 8-leaf) 30% July 24 (row tassel) 40%

21 treatments

• 3 replicates, 4-row plots 27.5 ft length, ~ 40 plants/row • 2 inoculated “spreader” rows adjacent to each plot (constant source of urediniospores) • rated rust weekly (severity - %) • harvested 20 consecutive plants/row

Snow White - % yield Y = 99.1 - 0.57 X

r2 = 0.83

50

60

70

80

90

100

10 20 30 40 50 60 70Rust severity (%)

Yie

ld (

% m

ax

imu

m)

Rust fungicide trial - 2001

% yield

Sterling - % yield Y = 100.3 - 0.42 X

r2 = 0.71

50

60

70

80

90

100

10 20 30 40 50 60 70Rust severity (%)

Yie

ld (

% m

axim

um

)

Rust fungicide trial - 2001

% yield

Rust fungicide trial - 2001

Non-treated

Non-treated

strobilurin-treated

strobilurin-treated

Controls - Snow White

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

non-treated check

Tilt 4 oz. - July 5,11,17,24

Application at 5% severity - Snow White

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%)

Non-treated

Tilt - 4 applications

Tilt 4 oz. July 5

Strobilurins July 5

Application at 15% severity - Snow White

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t se

verit

y (%

)

Non-treated

Tilt - 4 applications

Tilt 4 oz. July 11

Strobilurins July 11

Application at 30% severity - Snow White

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

Non-treated

Tilt - 4 applications

Tilt 4 oz. July 17

Strobilurins July 17

Application at 40% severity - Snow White

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

Non-treated

Tilt - 4 applications

Tilt 4 oz. July 24

Strobilurins July 24

Controls - Sterling

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

non-treated checkTilt 4 oz. July 5,11,17,24

Application at 5% severity - Sterling

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

non-treated Tilt 4 oz. 4 applicationsTilt 4 oz. July 5Strobilurins July 5

Application at 15% severity - Sterling

0

10

20

30

40

50

60

70

5 July 11 July 16 July 23 July 30 July 7 August

Rus

t sev

erity

(%

)

non-treated Tilt 4 oz. 4 applicationsTilt 4 oz. July 11Strobilurins July 11

5.5

6

6.5

7

7.5

8

5% 15% 30% 40% Tilt weekly Check

Yie

ld (

ton

s/A

Tilt Strobilurin

Rust fungicide trial - 2001

Sterling

• yield was reduced about 4% to 6% for each 10% rust severity Snow White• one application of strobilurin at 5%, 15% or 30% gave about the same level of control as weekly applications of Tilt Sterling • applications at 15% and 30% did not control as well as applications at 5%, but yield did not differ between applications at 5% and 15%

• Application thresholds for strobilurins may be high enough to determine whether or not Rp1-D-virulent rust is frequent enough or cause damage. • Thresholds for strobilurins probably will be in the 5% to 15% range.

Tentative conclusions

general or partial resistance

susceptible

Common rustfield corn vs. sweet corn - 2000 Field corn• 1573 field corn lines x FR 1064 • 1 replicate • 1 to 9 scale (~sq. rt. of %) PI accessions - 2001• 2000 accessions (So. America)• 2 replicates • 1 to 9 scale (~sq. rt. of %)

n = 244 n = 1573mean = 24% mean = 4.97SD = 11.6% SD = 0.67 BLSD = 6.7%

0

0.1

0.2

0.3

0.4

0.5

1-2% 2-4% 4-6% 7-10%

11-15%

16-20%

21-25%

26-30%

31-35%

36-40%

41-50%

>50%

Fre

quen

cy

Sweet corn Field corn

Common rust - 2000

sweet corn vs. field corn

Severity (%) or 1 to 9 rating (squared)

Reactions of PI accessions - 2001

0

50

100

150

200

250

300

350

0 > 0 to < 0.5

0.5 to < 1

1 to < 2 2 to < 3 3 to < 4 4 to < 5 5 to < 6 > = 6

Rust rating

Nu

mb

er

of

ac

ce

ss

ion

s

Antioquia, Columbia Ancash, PeruBoyaca, Columbia Apurimac, PeruCauca, Columbia Cajamarca, Peru

Lima, PeruJunon, Peru

B93 (PI 539871) B108 (PI 597926) IA DS61* (NSL 75976) * source of resistance to P. polysora

Sources of accessions with partial rust resistance?

Early Cogent Hawaii #9 Silver SucroEsteem Lancelot Sugar 73GG Code 27 Miracle Sugar 74 btGG Code 61 PX 9314639 Tendertreat EHGG Code 74 Seneca Horizon

Partial rust resistance in active* sweet corn hybrids

Champ GG Code 6 SensorGH 2757 Merlin Tuxedo

AVX 2539 Sugar Time Sweetie 82Dinner Time Sun 2577 SS 8801GG Code 14 Sun 2642 Tastee TreatPrime Pak Sun 2733 WH 3125Sugar Loaf Sweetie 76 Wintergreen

Partial rust resistance in inactive* sweet corn hybrids

• Rp genes• fungicides• general resistance

Jerald Pataky Department of Crop Sciences

University of Illinois

j-pataky@uiuc.eduwww.sweetcorn.uiuc.edu