SUPPRESSION OF RUST RESISTANCE IN WHEATMina Talajoor

Department of Plant Sciences & Plant PathologyMontana State University

Triticum turgidum (2n=4x, AABB)

Origins of Wheat

Triticum aestivum(2n=6x, AABBDD)

Aegilops tauschii(2n=2x, DD)

Triticum urartu (2n=2x, AA)

Aegilops speltoides(2n=2x, SS) Photos courtesy of Li Huang

Wheat Rust

•Leaf RustPuccinia triticina

Obligate biotrophic fungus

Wheat Rust

•Leaf Rust

•Stem Rust

•Leaf Rust

•Stem Rust

Puccinia triticina

Puccinia graminis f. sp. tritici

Photo courtesy of NCERA-184 & WERA-97

Obligate biotrophic fungus

Wheat Rust

•Leaf Rust

•Stem Rust

•Stripe Rust

Puccinia triticina

Puccinia graminis f. sp. tritici

Puccinia striiformis f. sp. tritici

Photo courtesy of NCERA-184 & WERA-97

Obligate biotrophic fungus

Breeding for Resistance• R-gene nomenclature

• Leaf Rust: Lr• Stem Rust: Sr• Stripe (Yellow) Rust: Yr

• R-genes confer resistance in a race-specific manner

Lr21Confers resistance toleaf rust race PRTUS6

Suppression of stem rust resistance

• Stem rust-specific suppressor on Canthatch 7DL

7DL

1

2

3

4

5

6

7

A B D

Su

Sr7

Sr9Sr16Sr12

OBJECTIVEInvestigate the specificity of the Canthatch suppressor- Is it stem rust-specific?- Is suppression related to genomes or

chromosome locations?

Objective• Investigate the stem rust specificity of the suppressor• Genetic characteristic of the suppressor• Absence of leaf rust or stripe rust resistance genes in the Canthatch background

Approach

Location Lr Yr Sr4A Sr7b2B Lr16 Yr5 Sr363B

Objective• Identify patterns of suppression related to genomes or chromosome locations

Approach

  A B D

1   Sr31Lr26

Sr18Lr21

2Sr34   Lr11Sr21    Lr17

Yr8

Sr9g    Sr36Sr16    Yr5

Lr16Sr6

3 Sr27 Sr12 Sr24Lr24

4Sr7a

Sr7b   

5   Lr52Yr47 Sr30

6 Sr8 Lr9 Sr5

7 Sr22Lr47

Sr17Yr2Yr6

Lr34Yr18

Genome

Chro

mos

ome

Control Crosses• Other suppressors in D genome (Bai & Knott, 1991)• Suppression may or may not be from our suppressor

• Cross with mNS1-Can

• If resistance is suppressed, it is not because of our suppressor

• If resistance is expressed, it supports our hypothesis that it is because of our suppressor.

Quantifying Infection Type

Roelfs, A. & Singh, R. Rust diseases of wheat: Concepts and methods of disease management. 81 (Agribookstore/Winrock: 1992).

Resis. Susc.

SAMPLE ANALYSIS

Canthatch

Su Su srx srx

Su might suppress SrX

Su does not suppress SrX

All Resistant

All Susceptible

SrX

x

su su SrX SrX

Su su SrX srx

F1 plants:

Screen F1 plants with race avirulent to SrX

mNS1-Can

su su srx srx

There is another suppressor in the background that suppresses SrX

There is no other gene suppressing expression of SrX in this background

All Resistant

All Susceptible

SrX

x

su su SrX SrX

su su SrX srx

F1 plants:

Screen F1 plants with race avirulent to SrX

Statistical Analysis• Test 20 seeds

• A significant difference 1/20 = 0.05

• Should be all resistant or all susceptible

Crossing Log

Sample Infection Type (IT) Data

su su srx srx

x

Su Su SrX SrX

resistant

Alpowa SrX

Su su SrX srx

F1 plants:

F1 plants:

Su__ SrX__ su su SrX__ Su __ srx srx

su su srx srx

F2 plants:

39 13: : :

resistant susceptible susceptible?

resistant

Su su SrX srx

Su__ SrX__ su su SrX__ Su __ srx srx

su su srx srx

F2 plants:

39 13: : :

resistant susceptible susceptiblesusceptibleresistant

Su su SrX srx

F1 plants:

3 : 1 Alpowa suppressor does not suppress SrX

resistant

resistant : susceptible

9 : 7 Alpowa suppressor suppresses SrX