Identification and Development of Rust- Resistant Soybean Germplasm

Transcription

1 Identification and Development of Rust- Resistant Soybean Germplasm David R. Walker USDA-ARS Soybean/Maize Germplasm, Pathology and Genetics Research Unit & University of Illinois, Urbana, IL, USA

2 Resistance to soybean rust (Phakopsora pachyrhizi) may involve: Reddish-brown (RB) instead of Tan lesions Type 0 infection type Low disease severity or lesion density Fewer uredinia per lesion or unit area Slower development of disease on infected tissue Slower movement of disease upwards through the foliar canopy Limited sporulation from uredinia PI A (RB lesions) Dillon (Tan lesions)

3 Resistance genes reported in literature Gene Source Resistance reaction Linkage group Position on LG (cm) Rpp1 PI HR/RB G Rpp1-b PI A RB lesions Rpp2 PI RB lesions J Rpp2[?] Rpp3 PI RB lesions C Rpp(?)Hyuuga PI RB lesions C Rpp4 PI B RB lesions G ~80 Rpp4[?] Rpp5 (Dominant) PI RB lesions N Rpp5 (Incompl Dom) PI rpp5 (Recessive) PI RB lesions N 40-44

4 Challenges to identifying alternative sources of resistance Influence of environmental conditions on epidemiology and disease development Effect of plant maturity on disease development 13 maturity groups (MGs) of soybean Lesion type (RB or tan) is not always obvious Bossier City, Louisiana, September 2007 MG VII uniform test MG VI uniform test Photo: J. Blair Buckley

5 Challenges to evaluating resistance Potential geographic and temporal variation among Phakopsora pachyrhizi populations Injury and lesions caused by other pests and pathogens Quincy, Florida, 30 Oct 2007 PI PI PI A

6 Infection types described by Bromfield et al. (1980) Type 0 No macroscopically visible symptoms Type RB Low infection type Reddish brown lesions ~0.4 mm 2 in diameter Average of 0-2 uredinia per lesion Type TAN High-infection type Tan-colored lesions ~0.4 mm 2 in diameter Average of 2-4 uredinia per lesion Bromfield et al Phytopathol. 70:17-21

7 Variation in reactions Benning (MG VII) Upper surface 10 X Lower surface 20 X

8 Variation in reactions PI (MG VIII) Upper surface Upper surface 10X Lower surface Lower surface 10X

9 Variation in reactions PI A (MG VIII) Upper surface Upper surface 10X Lower surface Lower surface 10X

10 Variation in reactions PI B (MG IX) Upper surface Upper surface 10X Lower surface Lower surface 10X Lower surface

11 Field evaluations in Southeastern USA ( ) Plant late in growing season (ideally in mid-august) Optional treatments: Extend natural photoperiod using portable lighting units Inoculate with spore suspensions Use agricultural streptomycin to reduce bacterial disease lesions Methods devised by Roger Boerma and Dan Phillips (University of Georgia) in 2005

12 USDA germplasm evaluation tests Bossier City Blackville Alexandria Attapulgus Baton Rouge Fairhope Quincy

13 Collaborators in field evaluations of USDA germplasm accessions ( ) Collaborator Affiliation Location Randy Nelson USDA-ARS, Urbana, IL Urbana, IL Emerson Shipe & John Mueller Roger Boerma, Dan Phillips & Donna Harris David Weaver & Ed Sikora Glen Hartman & Monte Miles Ray Schneider Clemson U U of Georgia Auburn U USDA-ARS, Urbana, IL LSU Blackville, SC Attapulgus, GA Fairhope, AL & Fairhope, AL Baton Rouge, LA Steve Moore LSU Alexandria, LA Blair Buckley LSU Bossier City, LA

14 Rating resistance to SBR Quincy, Florida, early November 2009

15 Looks can be deceiving: MG VIII entries in Fairhope, AL 2007* Accession Lesions/cm 2 Sporul (1-5) Severity (1-9) Uredinia/cm 2 PI PI PI PI > PI PI PI PI *Fairhope data provided by Glen Hartman

16 Rust Index used for a quick and simple assessment of resistance in 2009 Rust Index (RI) = severity x sporulation Severity rated on a 1-5 scale In which 1 = no SBR lesions and 5 = lesions as dense as those on susceptible controls Sporulation rated on a 1-5 scale In which 1 = no sporulating lesions found and 5 = profuse sporulation, similar to that occurring on susceptible controls Inspect low-sporulating leaf samples with a microscope if possible Possible range for RI: 1 to 25

17 Reactions of lines with known soybean rust resistance (Rpp) genes at ( ) Entry Gene MG (Les/cm 2 ) Sporul (1-5) RI (1-25) RI (1-25) LG Rpp1 III Williams 82 - III > PI Rpp1 VII PI Rpp2 VII > PI Rpp(?) VII > (Hyuuga) Hyuuga FT-2 (LG C2) VII Kuell - VII PI Rpp3 VIII PI B Rpp4 VIII

18 P. pachyrhizi virulence diversity between Paraguay and Mississippi (S. Li, 2009) 3 P. pachyrhizi isolates from Mississippi (1 from 2006 and 2 from 2007) were used to challenge: 10 PIs resistant to SBR in Paraguay in 2006 PIs with Rpp1-4 PI (Rpp1) was most resistant of the PIs with a known resistance gene PI B was only one of the Paraguayan PIs with a level of resistance similar to PI Small but significant differences among three MS isolates were found for both mean severity and mean sporulation Li, S Crop Sci. 49:

19 Assessment of P. pachyrhizi virulence diversity within the U.S. Pham et al. (2009): 2004 isolates from Mobile Co. and Baldwin Co., AL, and from near Baton Rouge, LA Each produced a unique reaction pattern when inoculated on 20 soybean entries Paul and Hartman (2009) 2006 isolates from FL, IL, MS, and SC, and 2007 isolates from FL and TX All produced similar reactions on each of the 16 accessions inoculated with them

20 But everything is hotter in Louisiana 2009 Rx in Southeast Resistant (RI 1-10) 2009 Rx in Bossier City, LA Resistant (RI 1-10) Mod. resistant (RI 11-19) Highly susceptible (RI 20-25) No. of PIs 6 (11%) 5 (10%) 34 (62%) Mod. resistant (RI 11-19) Resistant (RI 1-10) Mod. Resistant (RI 11-19) Highly susceptible (RI 20-25) Total

21 Evidence for virulence diversity in 2009 P. pachyrhizi populations Quincy Fairhope Bossier (FL) (AL) City (LA) Entry MG Rust index Rust index Rust index (1-25) (1-25) (1-25) NC-Raleigh VII ~20-25 PI (Rpp1) VII 1.7 ~3.0 4 PI VII PI VII PI VII PI VII PI A VII PI VII

22 Ft. Detrick Retests Re-evaluation of some of the Ft. Detrick rejects in the field: Test one group of PIs with resistance ratings just below Ft. Detrick resistance threshold in 2 nd round of evaluation Test another group with highly susceptible ratings in 2 nd round of Ft. Detrick greenhouse assays In 2008, three out of 56 MG IX and X accessions screened in and Fairhope, AL (5%) were resistant in both locations In 2009 these and several other accessions appeared to be resistant in the Southeast

23 Other 2009 germplasm evaluations in Quincy 70 Glycine soja accessions 207 G. max x G. tomentella backcross lines developed by Dr. Ram Singh

24 Development of breeding/mapping populations High-yielding parent x SBR-resistant PI parent Modified singleseed descent Backcrossing of Rpp genes into elite genetic backgrounds Recombinant inbred lines (RILs)

25 Breeding programs that have field-tested lines Institution Researchers Field evaluations USDA-ARS, Urbana, IL Iowa State Univ. Univ. of Missouri - Columbia North Carolina State Univ. Canadian breeders Univ. of Georgia Univ. of Missouri - Portageville David Walker & Randy Nelson Silvia Cianzio & Leonora Leandro Henry Nguyen, David Sleper, Tri Vuong Andrea Cardinal Albert Tenuta, Vaino Poysa, Elroy Cober Roger Boerma, Donna Harris, Dan Phillips Grover Shannon Attapulgus, GA

26 Lessons learned from germplasm evaluations No universally ideal rating method or scale Lesion type and disease severity can be informative, but sporulation ratings are also important A two-tier rating method may be the best compromise between efficiency and accuracy Rate plots in field to eliminate clearly susceptible entries Examine leaves from resistant plots with a microscope Inspection of leaves with a microscope often reveals a few sporulating lesions on even the most resistant accessions (Complete immunity has not been found) Apparent resistance should be confirmed after ~2 wk

27 Acknowledgements USDA-ARS United Soybean Board Auburn University Clemson University University of Florida North Florida Research and Education Facility University of Georgia Louisiana State University

28 Acknowledgements David Wright NFREC Jim Marois NFREC Debbie Green NFREC Tristan Mueller NFREC Maynard Douglas NFREC Kelley O Brien NFREC Chuck Dickson NFREC Brian Kidd NFREC Pratibha Srivastava NFREC Nick Dufault Penn State Working in Quincy Katey Pauls USDA-ARS Urbana & Quincy Aly Hyrkas USDA-ARS Urbana Todd Bedford USDA-ARS Urbana

29 Questions?