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Rp resistance Rp1-D-virulent isolates fungicides. Effect of rust on sweet corn yield EAR WEIGHT. Rp-resistance. Bands of chlorotic flecks (no sporulation). In the 1990s, Rp resistance added at least $3 million* annually to the value of processing sweet corn in the Midwest

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Rp-resistance

Bands of chlorotic flecks

(no sporulation)


In the 1990s, Rp resistance

added at least $3 million*

annually to the value of

processing 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


Probability* of severe rust

Rust severity %

and (estimated Reactions of sweet corn hybrids

yield reductions)** R MR M MS S

0-10% (3%) 0.63 0.26 0.11 0.11 0.11

10-20% (9%) 0.37 0.47 0.16 0.11 0

20-30% (15%) 0 0.26 0.63 0.26 0.16

30-40% (21%) 0 0 0.11 0.32 0.26

40-50% (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



Rp1-D resistant hybrid

Rock Falls, IL

September 1999


Rp1-D resistance

Los Mochis, Mexico

March 2000


Questions about the

Rp1-D-virulent race

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?


Reactions of

non-Rp hybrids




Hybrids that do not have the

Rp1-D gene have the same

reaction to Rp1-D-virulent

and Rp1-D-avirulent rust


Reactions of

Rp hybrids


Populations of Rp hybrids

compared to

non-Rp hybrids

- inoculated with Rp1-D-virulent

rust


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 hybridRp hybrid

Bodacious Bodacious Rust

Day Star Morning Star

GG Code 8 GG Code 23

Primetime Prime Plus

Sch 5005 Chieftain

SS 8102 SS 8102 R




Rp hybrids

and

non-Rp hybrids

- inoculated with a mixture of

Rp1-D-virulent and avirulent rust



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 plots

non-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 other

Rp 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 ?


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


% yield

Rust fungicide trial - 2001


% yield

Rust fungicide trial - 2001







Sterling

Rust fungicide trial - 2001


  • 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%


Tentative conclusions

  • 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.


general or partial

resistance

susceptible


Common rust

field 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 %)


Common rust - 2000

sweet corn vs. field corn

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


Sources of accessions with

partial rust resistance?

Antioquia, Columbia Ancash, Peru

Boyaca, Columbia Apurimac, Peru

Cauca, Columbia Cajamarca, Peru

Lima, Peru

Junon, Peru

B93 (PI 539871)

B108 (PI 597926)

IA DS61*(NSL 75976)* source of resistance to P. polysora


Partial rust resistance in active*

sweet corn hybrids

Early Cogent Hawaii #9 Silver Sucro

Esteem Lancelot Sugar 73

GG Code 27 Miracle Sugar 74 bt

GG Code 61 PX 9314639 Tendertreat EH

GG Code 74 Seneca Horizon

Champ GG Code 6 Sensor

GH 2757 Merlin Tuxedo


Partial rust resistance in inactive*

sweet corn hybrids

AVX 2539 Sugar Time Sweetie 82

Dinner Time Sun 2577 SS 8801

GG Code 14 Sun 2642 Tastee Treat

Prime Pak Sun 2733 WH 3125

Sugar Loaf Sweetie 76 Wintergreen



Jerald pataky department of crop sciences university of illinois

Jerald Pataky

Department of Crop Sciences

University of Illinois

[email protected]

www.sweetcorn.uiuc.edu


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