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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 Rp1-D-virulent isolates fungicides

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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

* 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)**RMRMMSS

0-10% (3%)0.630.260.110.110.11

10-20% (9%)0.370.470.160.110

20-30% (15%) 00.260.630.260.16

30-40% (21%)000.110.320.26

40-50% (27%)0000.210.32

>50% (>30%)00000.16

* 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


Susceptible Rp-resistant


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


Reactions to Rp1-D-virulent and avirulent isolates

2001 UI hybrid disease nursery


Reactions to Rp1-D-virulent and avirulent isolates

2001 UI inbred disease nursery


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


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


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 R15%34%

CnS 71036% 37%

Incredible Rust10%29%

Incredible24%30%

Morning Star22%34%

Day Star41%35%

Prime Plus16%39%

Primetime32%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


Rust fungicide trial - 2001


Non-treated


Non-treated


strobilurin-treated


strobilurin-treated


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, ColumbiaAncash, Peru

Boyaca, ColumbiaApurimac, Peru

Cauca, ColumbiaCajamarca, 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 CogentHawaii #9 Silver Sucro

EsteemLancelot Sugar 73

GG Code 27Miracle Sugar 74 bt

GG Code 61PX 9314639 Tendertreat EH

GG Code 74Seneca Horizon

ChampGG Code 6 Sensor

GH 2757Merlin Tuxedo


Partial rust resistance in inactive*

sweet corn hybrids

AVX 2539Sugar TimeSweetie 82

Dinner TimeSun 2577SS 8801

GG Code 14Sun 2642Tastee Treat

Prime PakSun 2733 WH 3125

Sugar LoafSweetie 76Wintergreen


  • Rp genes

  • fungicides

  • general resistance


Jerald Pataky

Department of Crop Sciences

University of Illinois

j-pataky@uiuc.edu

www.sweetcorn.uiuc.edu


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