George Newcombe and KwanSoo Woo

1
Disease resistance in black cottonwood and its
hybrids
George Newcombe and Kwan-Soo Woo University of
Idaho Department of Forest Resources Moscow,
Idaho 83844-1133
2
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. 347-9)?
• To what extent is partial resistance to disease
  the product of defeated major genes (Nelson, R.R.
  1978. Annu. Rev. Phytopathol. 16359-378).

3
Objective

• To test a hypothesis that a defeated major gene
  for resistance to M. medusae contributes to
  partial resistance to M. xcolumbiana, the hybrid
  offspring of M. medusae.

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Materials and methods

• Three-generation hybrid poplar pedigree (Tony
  Chens)
• 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
  154837-845)
• In 1997, infection type and uredinial density
• In 2000, infection type and rust severity (0-100
  Schreiners)

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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.
Z Given that one F1 parent was a resistant
heterozygote and the other a susceptible
recessive homozygote, we expected a 11
segregation.  
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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)
F1 TxD Rr x rr
F2 TDxTD 1R1S
7

• 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).

8
No evidence of the partial resistance of a
defeated major gene
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.
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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.
10
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.
11
Conclusion

• Our results conflict with the hypothesis of
  partial resistance by defeated resistance genes
  (Nelson, R.R. 1978. Annu. Rev. Phytopathol.
  16359-378).
• A single gene for resistance to M. medusae did
  not contribute to partial resistance to M.
  xcolumbiana.

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Conclusion

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

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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)

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Contrasting inheritance of exapted resistance
D
M

• 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 ?2 4.1 (P
0.04)
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Other tasks

• 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).

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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.

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Bio-control strategies

• 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.

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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
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Acknowledgements

• 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