# Presentation: 032989

## Disease resistance in black 

**University of Idaho**
**Department of Forest Resources**
**Moscow, Idaho 83844-1133**

**Disease resistance in black **
**cottonwood and its hybrids  **

## Absence of residual effects of a defeated resistance gene 

- Are race-specific resistance genes completely neutralized by matching virulence, or do they demonstrate residual effects (Nelson, R.R. 1981. Crops Soils Mag. 34:7-9)?
- To what extent is partial resistance to disease the product of defeated major genes (Nelson, R.R. 1978. Annu. Rev. Phytopathol. 16:359-378).

## Objective  

- To test a hypothesis that a defeated major gene for resistance to *M. medusae* contributes to partial resistance to *M. *x*columbiana*, the hybrid offspring of *M. medusae*.

## Materials and methods 

- Three-generation hybrid poplar pedigree (Tony Chen’s)
- 93-968 X S7C4 (grandparents); family 55 (F1); family 822 (F2)
- Greenhouse inoculation with a KY isolate of *Mmd*.
- 269 F2 clones in early April 2001 to determine infection type
- Field assessments of partial resistance
- 346 F2 progeny (Frewen et al. 2000. Genetics 154:837-845)
- In 1997, infection type and uredinial density
- In 2000, infection type and rust severity (0-100 Schreiner’s)

## Infection types of hybrid poplar F2 clones inoculated with a Kentucky isolate of Melampsora medusae to determine the presence of a single gene for resistance.

**Infection types of hybrid poplar F****2**** clones inoculated with a Kentucky isolate of *****Melampsora medusae***** to determine the presence of a single gene for resistance.**

- Z Given that one F1 parent was a resistant heterozygote and the other a
-   susceptible recessive homozygote, we expected  a 1:1 segregation.

## A single gene inherited from P. trichocarpa for resistance to a Kentucky isolate of M. medusae

***P. trichocarpa***** – Rr**
**       ****(93-968)**

***P. deltoides***** – rr**
**       ****(S7C4)**

**F****1**** – TxD – Rr x rr**

**F****2**** – TDxTD – 1R:1S**

## In the field in both 1997 and 2000, there was no evidence of the resistant infection type noted in the greenhouse study (all clones in family ‘822’ possessed a susceptible infection type).

## No evidence of the partial resistance of a defeated major gene

| Traits | 2   | df | P-value |
| --- | --- | --- | --- |
| Uredinial density
(1997 in the field) | 0.412 | 1 | 0.521 |
| Rust severity
(2000 in the field) | 0.011 | 1 | 0.917 |

- Kruskal-Wallis One-Way ANOVA for 2 quantitative traits: independent variables are infection types of hybrid poplar F2 clones inoculated with a Kentucky isolate of *M. medusae*.

## Group 1 is the set of clones that were shown in the inoculation to possess a gene for resistance to M. medusae and group 2 is the set of clones that were not shown to possess a gene for resistance. 

**Group 1 is the set of clones that were shown in the inoculation to possess a gene for resistance to *****M. medusae***** and group 2 is the set of clones that were not shown to possess a gene for resistance. **

## Group 1 is the set of clones that were shown in the inoculation to possess a gene for resistance to M. medusae and group 2 is the set of clones that were not shown to possess a gene for resistance. Each bar is clone means of the Schreiner scale.

- Group 1

- Group 2

**Group 1 is the set of clones that were shown in the inoculation to possess a gene for resistance to *****M. medusae***** and group 2 is the set of clones that were not shown to possess a gene for resistance.**** Each bar is clone means of the Schreiner scale.**

## Our results conflict with the hypothesis of partial resistance by “defeated” resistance genes (Nelson, R.R. 1978. Annu. Rev. Phytopathol. 16:359-378).
A single gene for resistance to M. medusae did not contribute to partial resistance to M. xcolumbiana.

- A single gene for resistance to *M. medusae* did not contribute to partial resistance to *M*. x*columbiana*.

**Conclusion   **

## Partial rust resistance in the field near Corvallis, Oregon was independent of the gene for resistance to M. medusae.

**Conclusion   **

## Contrasting inheritance of exapted resistance to foliar diseases of poplar

- Near Kelsey Bay north of Campbell River on Vancouver Island
- 2 pedigrees: TxD and TxM
- 3 foliar diseases (*Venturia *leaf and shoot blight, *Taphrina *leaf blister, and *Linospora* leaf blight)

## Contrasting inheritance of exapted resistance

- Single recessive gene for R to *Venturia*
- Single recessive gene for R to *Taphrina*

- Two dominant genes for R to *Venturia*
- Single dominant gene for R to *Taphrina*

- Contingency testing for linkage of the two recessive genes inherited from D: χ2 = 4.1 (P = 0.04)

**D**

**M**

## A TxM pedigree has been planted this fall and will be challenged with an isolate of M. xcolumbiana other than the Mxc13 pathotype employed last year (In progress). 

**Other tasks**

## Field inoculation in Kentucky in June 2002: 
An isolate of Septoria musiva from western Kentucky is  being maintained in the U of I Forest Pathology Lab
To determine the inheritance of resistance to Septoria canker in progenies of the commercial clone ‘NM-6’
Progenies were produced by Toby Bradshaw (UW) and Rick Hall (ISU).
Westvaco Corp. is maintaining the trial.

- An isolate of *Septoria musiva* from western Kentucky is  being maintained in the U of I Forest Pathology Lab
- To determine the inheritance of resistance to *Septoria* canker in progenies of the commercial clone ‘NM-6’
- Progenies were produced by Toby Bradshaw (UW) and Rick Hall (ISU).
- Westvaco Corp. is maintaining the trial.

**Other tasks**

## Develop a co-culture assay for rust and its putative mycoparasite, Sphaerellopsis filum 
To determine whether S. filum is host-specific 
Collaborating with Larissa May Del Mio in Brazil in regarding that S. filum affects rust epidemics there as well

Determine whether S. filum is a mycoparasite, or an opportunistic necrotroph associated with rust 
This fungus is thought to be a “nonspecific fungal hyperparasite of rust” that occurs on most of the thousands of rust fungi in temperate zones and the tropics alike. 

- To determine whether *S. filum* is host-specific
- Collaborating with Larissa May Del Mio in Brazil in regarding that *S. filum* affects rust epidemics there as well
- Determine whether *S. filum* is a mycoparasite, or an opportunistic necrotroph associated with rust
- This fungus is thought to be a “nonspecific fungal hyperparasite of rust” that occurs on most of the thousands of rust fungi in temperate zones and the tropics alike.

**Bio-control strategies**

## Sphaerellopsis filum occurs on poplar leaf rust in the U.S. only in the Southeast (observed and collected 4 consecutive years [1997-2000])

- Two hyperparasitic phenotypes

## U.S. Department of Energy, Biomass Energy Technology Division 
Oregon State University subcontract of a USDA National Research Initiative grant awarded to Steve Strauss
Westvaco Corp. 
Toby Bradshaw
Rozi Mohamed 
Tony Chen and Joel Davis 
Amanda Osuch 

- Oregon State University subcontract of a USDA National Research Initiative grant awarded to Steve Strauss
- Westvaco Corp.
- Toby Bradshaw
- Rozi Mohamed
- Tony Chen and Joel Davis
- Amanda Osuch

**Acknowledgements **