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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

  • Rp resistance

  • Rp1-D-virulent isolates

  • fungicides


Rp resistance rp1 d virulent isolates fungicides

Effect of rust on sweet corn yield

EAR WEIGHT


Rp resistance rp1 d virulent isolates fungicides

Rp-resistance

Bands of chlorotic flecks

(no sporulation)


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

Susceptible Rp-resistant


Rp resistance rp1 d virulent isolates fungicides

Rp1-D resistant hybrid

Rock Falls, IL

September 1999


Rp resistance rp1 d virulent isolates fungicides

Rp1-D resistance

Los Mochis, Mexico

March 2000


Rp resistance rp1 d virulent isolates fungicides

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?


Rp resistance rp1 d virulent isolates fungicides

Reactions of

non-Rp hybrids


Rp resistance rp1 d virulent isolates fungicides

Reactions to Rp1-D-virulent and avirulent isolates

2001 UI hybrid disease nursery


Rp resistance rp1 d virulent isolates fungicides

Reactions to Rp1-D-virulent and avirulent isolates

2001 UI inbred disease nursery


Rp resistance rp1 d virulent isolates fungicides

Hybrids that do not have the

Rp1-D gene have the same

reaction to Rp1-D-virulent

and Rp1-D-avirulent rust


Rp resistance rp1 d virulent isolates fungicides

Reactions of

Rp hybrids


Rp resistance rp1 d virulent isolates fungicides

Populations of Rp hybrids

compared to

non-Rp hybrids

- inoculated with Rp1-D-virulent

rust


Rp resistance rp1 d virulent isolates fungicides

Rp1-D-virulent isolates - 2001

2001 UI hybrid disease nursery


Rp resistance rp1 d virulent isolates fungicides

Pairs of Rp hybrids

and

non-Rp hybrids

- inoculated with Rp1-D-virulent

rust


Rp resistance rp1 d virulent isolates fungicides

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 resistance rp1 d virulent isolates fungicides

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

2001 UI Rp hybrid trial


Rp resistance rp1 d virulent isolates fungicides

  • no residual resistance

  • from Rp1-D

  • no linkage of general

  • resistance near rp1 region


Rp resistance rp1 d virulent isolates fungicides

Rp hybrids

and

non-Rp hybrids

- inoculated with a mixture of

Rp1-D-virulent and avirulent rust


Rp resistance rp1 d virulent isolates fungicides

Mixture of virulent and avirulent isolates - 2000

2000 UI hybrid disease nursery


Rp resistance rp1 d virulent isolates fungicides

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%


Rp resistance rp1 d virulent isolates fungicides

If virulence is frequent

Hybrids with Rp1-D have similar

reactions as non-Rp hybrids

- population distributions alike

- Rp and non-Rp versions alike


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

If virulence is infrequent

Rp hybrid non-Rp hybrid


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

Fungicides

  • EBDCs

  • TILT

  • strobilurins

  • (QUADRIS, F-500)


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

Early applications of fungicides

~ 2% severity

* EBDCs, Tilt


Rp resistance rp1 d virulent isolates fungicides

Later applications of fungicides

> 5-10% severity

* EBDCs, Tilt


Rp resistance rp1 d virulent isolates fungicides

Strobilurins

may change use of fungicides

on sweet corn

  • more efficacious

  • may have different thresholds ?


Rp resistance rp1 d virulent isolates fungicides

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?


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

  • 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


Rp resistance rp1 d virulent isolates fungicides

% yield

Rust fungicide trial - 2001


Rp resistance rp1 d virulent isolates fungicides

% yield

Rust fungicide trial - 2001


Rp resistance rp1 d virulent isolates fungicides

Rust fungicide trial - 2001


Rp resistance rp1 d virulent isolates fungicides

Non-treated


Rp resistance rp1 d virulent isolates fungicides

Non-treated


Rp resistance rp1 d virulent isolates fungicides

strobilurin-treated


Rp resistance rp1 d virulent isolates fungicides

strobilurin-treated


Rp resistance rp1 d virulent isolates fungicides

Sterling

Rust fungicide trial - 2001


Rp resistance rp1 d virulent isolates fungicides

  • 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%


Rp resistance rp1 d virulent isolates fungicides

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.


Rp resistance rp1 d virulent isolates fungicides

general or partial

resistance

susceptible


Rp resistance rp1 d virulent isolates fungicides

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 %)


Rp resistance rp1 d virulent isolates fungicides

Common rust - 2000

sweet corn vs. field corn

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


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

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


Rp resistance rp1 d virulent isolates fungicides

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 resistance rp1 d virulent isolates fungicides

  • Rp genes

  • fungicides

  • general resistance


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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