Proceedings of the 2007 CPM Short Course and MCPR Trade Show December 4 6, 2007 Minneapolis Convention Center Do not Reproduce or Redistribute Without Written Consent of the Author(s)
The Application and Effectiveness of the Rag1 Gene for Resistance to Soybean Aphid Brian Diers, Univ. of Illinois Matt O Neal, O Iowa State Univ.
Outline Background on soybean aphids. Background on resistance. Mapping of aphid resistance genes. Aphid isolate interaction testing. Results from evaluations of experimental lines with the aphid resistance gene Rag1. Future and ongoing research.
Take Home Message Varieties with the aphid resistance gene Rag1 (and other genes) will be available in the near future. The Rag1 resistance gene is not the complete answer, aphids can defeat this gene. Will still need to scout fields planted to aphid resistant varieties.
Soybean Aphid Resistance Soybean aphids (Aphis glycines Matsumura) were first identified as a soybean pest in North America in 2000. Native to Asia. Spread throughout the northern US soybean production region and southern Canada.
Soybean Aphid Management Insecticides Biological Control Host Plant Resistance
Insecticides are the Main Management Option for Growers Growers are recommended to treat aphid populations with a foliar insecticide when they exceed 250 aphids per plant. Insecticide use targeting aphids in Iowa 2003 ~ 4 million acres (http://www.ipm.iastate.edu/ipm/icm/node/53) 2004 ~100-250,000 acre (http://www.ipm.iastate.edu/ipm/icm/2005/6-27/survey.html) 2005 ~2 million acres http://www.ipm.iastate.edu/ipm/icm/2005/10-10/aphids.html) 2005 - spider mite outbreaks in eastern Iowa 2006 - ~500,000 acres (low estimate) 2007- ~50% of Iowan soybeans treated at least once.
Host Plant Resistance Antixenosis The inability for an insect pest to find and feed on the plant. Antibiosis The inability for the pest to grow and reproduce while feeding on a resistant plant. Tolerance The ability of the plant to yield despite insect feeding.
Screening for Resistance to the Soybean Aphid Germplasm Commercial cultivars (MG II, II, IV) Asian cultivars Number tested 818 106 Number resistant 0 0 Pubescent lines Ancestral lines Diverse collection of germplasm accessions 11 101 >3000 0 9 85 Hill, C.B., Y. Li, and G. L. Hartman. 2004. Resistance to the soybean aphid in soybean germplasm. Crop Science 44: 98-106.
Antibiosis Resistance in Dowling, Jackson and PI 200538 Aphid Mortality Adults Nymphs Survival rate (% 100 90 80 70 60 50 40 30 20 10 0 Jackson Dowling PI200538 Pana 0 2 4 6 8 10 Days Survival rate (%) 100 90 80 70 60 50 40 30 20 10 0 0 2 4 6 Days Jackson Dowling PI200538 Pana Li, Y., C.B. Hill, and G.L. Hartman. 2004. Effect of three resistant soybean genotypes on the fecundity, mortality, and maturation of soybean aphid (Homoptera : Aphididae). Journal of Economic Entomology 97: 1106-1111. 1111.
Antibiosis Resistance in Dowling, Jackson and PI 200538 Aphid fecundity Progeny/female/10 days 25 20 15 10 5 0 L1 L2 L3 Leaf number Dowling Jackson PI 200538 Pana
Mapping Aphid Resistance The maturities of Dowling (MG VIII), Jackson (MG VII) and PI 200538 (MG VIII) make them incompatible for production in the Midwest. The resistance gene(s) need to be bred into northern soybean backgrounds. This breeding would be more efficient if the locations of the resistance gene(s) were known.
Resistance in Dowling, Jackson and PI 200538 Mapped Resistance was mapped in a population of F 2 plants. The populations were evaluated for resistance in a greenhouse tests.
Map Location of the Aphid Resistance Gene (Rag1( Rag1) ) on LG M Across Dowling Crosses Jackson x Loda 0.0 Satt150 0.0 3.1 7.3 Satt540 Satt435 Rag1 15.4 18.9 20.8 Satt540 Satt435 Rag 15.2 20.0 25.5 28.0 Satt463 Satt245 Satt323 Satt220 28.5 31.6 35.3 Satt463 Satt245 Satt220
Backcrossing Aphid Resistance In 16 months five backcrossed were made to move the Rag1 gene from Dowling into the background of the MG II variety Loda. Developed BC4F 1 plants in 3 other backgrounds. Backcross F 1 plants Dowling X
2005 Field Evaluations Tested the equivalent of BC1F 2 -derived resistant and susceptible lines in 2005. Compared approximately 15 resistant to 15 susceptible lines. Small plots in screened cages at U of I and Michigan State University. Inoculated with aphids and protected from predators. Insecticide treated and not treated plots in Illinois.
Results from U of I Cage Test There were significantly fewer aphids on resistant plants then susceptible plants. Trait Aphid rating (6-28) Aphid rating (7-22) Plant height (inches) Seed yield (g) Res. 0.8 1.6 35.8 79.9 Susc. 2.3 3.3 30.0 19.2 Aphid rating: 0 = no aphids, 4 = severe plant damage. Difference between resistant and susceptible genotypes significant for all traits (P<0.05). Difference between resistant and susceptible genotypes was significant at P<0.05) for all traits.
Aphid Resistant Line Aphid Susceptible Line
Aphid Infestations (7-11 11-05) Resistant Line Susceptible Line
Agronomic Evaluations of Resistant and Susceptible BC Lines. Noninfested Yield tests across 2006-2007 of BC3F2 lines (Loda) and BC2F2 lines (Dwight). Trait Loda Maturity (date) Plant height (in) Yield (bu/acre) Dwight Maturity (date) Plant height (in) Yield (bu/acre) Res. (32) 9-19 35.9 56.3 (19) 9-20 37.0 63.2 Susc. (22) 9-17 35.2 55.6 (24) 9-18 36.2 62.6
Commercial Development of Varieties with Rag1 University of Illinois has developed experimental lines with Rag1 in MG II-IV backgrounds. This germplasm has been licensed to commercial breeding companies. Increases of our varieties is occurring this winter but commercial quantities of seed will not be available until 2009. Seed from commercial companies will be available 2009.
Aphid Resistance: The Bad News Aphid biotypes exist that can overcome Rag1. Biotype = an insect population that is resistant to the defenses of the host plant. Soybean aphid biotype found resistant to Rag1. Biotype found in Ohio. Unofficial reports of these isolates in other locations.
Aphid Isolate x Soybean Genotype Interaction Test Tested aphid resistance sources and aphid susceptible genotypes with a soybean aphid isolate from Illinois (obtained from Glen Hartman) and from Ohio (obtained from Rouf Mian). Conducted two non-choice tests that were each replicated three times. Each replicate was a single caged plant.
Aphid Isolate x Soybean Genotype Interaction Test Dwight Aphid Isolate Illinois Ohio ---No. of Aphids Plant -1 --- 468bc 398c Williams 82 Dowling (Rag1) LD05-16611(Rag1) Jackson (Rag) PI 200538 (Rag2) PI 567597C (MSU) 726a 15d 29d 11d 10d 21d 574abc 639ab 627ab 414c 7d 7d
How Common are the Ohio Type Aphid Biotypes in Fields? We don t really know. This Ohio biotype is are of the diversity present in the U.S, not selected. Evidence can be gleaned from experiments conducted by a project funded by the NCSRP. David Ragsdale (U of M) and Matt O Neal (ISU) lead this program. Aphid resistant lines are being tested in different Midwest field locations.
Host plant resistance Iowa (Matt O Neal) O Resistant (Rag1) and susceptible isolines artificially infested with 10 aphids per plant and caged. 2500 Average aphids per plant (+SEM) 2000 1500 1000 500 0 Aphid resistant soybeans Aphid susceptible soybean 13-Jul 17-Jul 20-Jul 25-Jul 31-Jul The resistant soybean contains the Rag1 gene. The susceptible soybean is an isoline that does not contain the Rag1 gene. Resistant soybeans slowed aphid reproduction.
Host Plant Resistance (Matt O Neal) O Plots of each variety were kept aphid free (yellow) or left untreated (blue). Susceptible soybean Resistant (Rag1) soybean
Host Plant Resistance Soybean aphid resistance tested on naturally occurring populations. Resistant soybeans were not aphid free, reaching threshold by 31 July 2007.
Host Plant Resistance Iowa Soybean aphid resistance tested on naturally occurring populations. Average aphids per plant (+SEM) 4000 3500 3000 2500 2000 1500 1000 500 0 Aphid resistant soybean Aphid susceptible soybean 3- Jul 10- Jul 17- Jul 24- Jul 31- Jul 7- Aug 14- Aug Resistant soybeans were not aphid free, reaching threshold by 31 July 2007.
Host Plant Resistance Iowa Yield reductions occurred due to aphids. Average bu/acre (+SEM) 75 70 65 60 55 50 45 40 35 untreated aphid-free untreated aphid-free Soybean aphid resistant Soybean aphid susceptible
Host Plant Resistance Minnesota (David Ragsdale) Yield reductions did not occur due to aphids. Average bu/acre (+SEM) 35 30 25 20 15 10 5 0 Aphid free Resistant Untreated control Susceptible Peak aphid populations: Susceptible ~ 500, Resistant ~ 100 aphids per plant
Host Plant Resistance Illinois (Kevin Steffey) Yield reductions did not occur due to aphids. Average bu/acre (+SEM) 75 70 65 60 55 50 45 40 35 untreated aphid-free untreated aphid-free Soybean aphid resistant Soybean aphid susceptible Peak aphid populations: Susceptible = 478, Resistant = 224 aphids per plant
Host Plant Resistance - Illinois (Kevin Steffey) Number of Aphids / Plant 1000 800 600 400 200 0 Susceptible 1-Aug 8-Aug 15-Aug Rag1 resistant SD01-76R LD05-16060 LD05-16519 LD05-16529 LD05-16621 LD0516611
Test of U of I Developed Line with Rag1 by Channel Bio Owatonna, MN Prepared bytodd Vagts Technical Support Agronomist Aphid Resistant Aphid Susceptible Channel Bio is a registered trademark of Channel Bio Corp. BioFuture SM is a service mark of Channel Bio Corp.
Host Plant Resistance - Wisconsin Wisconsin (est. Aphids per Plant) commercial variety #1 Resistant Susceptib KS5004N LD05-16519 LD05-16621 SDX04R-68-1-8 SD01-76R E06901 E06902 E06905 E06906 K1639 LD05-16060 LD05-16529 LD05-16611 SDX04R-68-1-3 SDX04R-68-1-9 0 100 200 300 400 500 600 700 800 Avg. Aphids per Plant Average number of aphids/plant on August 9, 2007
New Aphid Resistance Genes are Being Used Soybean varieties are being developed with aphid resistance from a number of germplasm sources. Dechun Wang at Michigan State University developed lines show good resistance in the field. They are further from commercializing these lines than Rag1 germplasm.
Other Sources of Resistance - Iowa Iowa Resistant Susceptible commerical variety # 3 commerical variety #2 commerical variety #1 KS1639 LD05-16519 LD05-16611 LD05-16621 SDX04R-68-1-8 E06901 E06902 E06905 E06906 KS5004N LD05-16060 LD05-16529 SD01-76R SDX04R-68-1-3 SDX04R-68-1-9 0 10000 20000 30000 Average cumulative aphid days (+SEM)
Other Sources of Resistance - Wisconsin Wisconsin (est. Aphids per Plant) commercial variety #1 Resistant Susceptib KS5004N LD05-16519 LD05-16621 SDX04R-68-1-8 SD01-76R E06901 E06902 E06905 E06906 K1639 LD05-16060 LD05-16529 LD05-16611 SDX04R-68-1-3 SDX04R-68-1-9 0 100 200 300 400 500 600 700 800 Avg. Aphids per Plant Average number of aphids/plant on August 9, 2007
New Aphid Resistance Genes are Being Used Rag2 from PI 200538 shows a high level of resistance of our isolate that overcomes Rag1. Will have field tests of Rag2 lines this summer. Stacking Rag1 and Rag2. Glen Hartman (U of I) recently identified 40 accessions from Asia that show a high level of aphid resistance. Starting to study the genetics of resistance from these sources.
Conclusions Resistance to soybean aphids exists. Aphid resistant varieties with Rag1 are the closest to commercialization. There are aphid biotypes that can overcome this resistance gene. Varieties with aphid resistance genes other than Rag1 will be available during the next few years. Will need to scout fields of aphid resistant varieties!
Contributors Glen Hartman Matt O Neal Curt Hill Ki-Seung Kim Yan Li David Ragsdale
Acknowledgements We are grateful for funding from the following:
Marker Assisted Selection Polyacrylamide gels ABI 377 sequencer Light Cycler SNP detector
Results from Michigan Cage Test, and Wisconsin and South Dakota Field Test Test Michigan Cage (0-5 scale) Wisconsin Field (% plants colonized) South Dakota Field (No. of aphids) Res. 3.5 10% 184 Susc. 3.9 32% 593 Michigan rating: 0 = no aphids, 4 = severe plant damage.
60 45 30 15 0 Soybean aphid-susceptible vs. -resistant soybean varieties Whiteside County, University of Illinois 52 * 57 54 49 * 57 54 -- 46 -- 48 56 54 53 51 SD01-76R+ LD05-16060 LD05-16060+ LD05-16519 LD05-16519+ LD05-16529 LD05-16529+ LD05-16621 LD05-16621+ LD0516611 LD05-16611+ SD01-76R Mean yield (bushels per A)
1000 800 600 400 200 0 131 Host Plant Resistance - Illinois (Kevin Steffey) ) 1 August 2007 290 262 250 171 84 84 26 32 28 43 38 LD05-16060 LD05-16060+ LD05-16519 LD05-16519+ LD05-16529 LD05-16529+ LD05-16621 LD05-16621+ LD0516611 LD05-16611+ SD01-76R+ SD01-76R Mean no. aphids per plant
1000 900 800 700 600 500 400 300 200 100 0 420 940 751 544 296 195 235 376 119 76 153 113 LD05-16611+ Host Plant Resistance - Illinois (Kevin Steffey) ) 8 August 2007 LD05-16060 LD05-16060+ LD05-16519 LD05-16519+ LD05-16529 LD05-16529+ LD05-16621 LD05-16621+ LD0516611 SD01-76R SD01-76R+ Mean no. aphids per plant
1000 800 600 400 200 0 131 Host Plant Resistance - Illinois (Kevin Steffey) ) 1 August 2007 290 262 250 171 84 84 26 32 28 43 38 LD05-16060 LD05-16060+ LD05-16519 LD05-16519+ LD05-16529 LD05-16529+ LD05-16621 LD05-16621+ LD0516611 LD05-16611+ SD01-76R+ SD01-76R Mean no. aphids per plant
1000 800 600 400 200 0 Host Plant Resistance - Illinois (Kevin Steffey) ) 15 August 2007 6 1 4 2 3 15 12 4 7 3 2 5 SD01-76R+ LD05-16060 LD05-16060+ LD05-16519 LD05-16519+ LD05-16529 LD05-16529+ LD05-16621 LD05-16621+ LD0516611 LD05-16611+ SD01-76R Mean no. aphids per plant