Resistance to the soybean aphid in soybean germplasm and other legumes C.B. Hill1, Y. Li1, and G. Hartman1,2 1Dept. of Crop Sciences, Univ. of Illinois, Urbana, IL, USA; 2USDA-ARS

Sources of Resistance to the Soybean Aphid The soybean aphid, Aphis glycines Matsumura, invaded North Effects of antibiosis on soybean aphids Choice-test, 9 days after aphid infestation America in 2000. It has since become a serious pest in the central Fecundity of soybean aphids over 10 days on resistant 250 states, prompting the spraying of millions of hectares with insecticides and susceptible genotypes to control it. We began the search for genetic resistance to the aphid 18 b 200 soon after the arrival of the pest. Using a systematic approach 16

14 150 and taking advantage of the convenience of the USDA Soybean Germplasm Collection at our location, we screened thousands of 12 100 commercial and non-commercial germplasm accessions for resistance 10 8 Number of aphids/plant Number 50 in an air-conditioned greenhouse dedicated to this effort. We found 6 a resistance in a few ancestors of North American cultivars. Over 4 a 0 2

Number of offspring/viviparous aptera of offspring/viviparous Number a Dowling Jackson PI71506 Ina Pana Williams Loda the last couple of years, we have characterized the expression of 82 0 Genotypes resistance, studied the effects on aphid biology, and looked for other Dowling (R) Jackson (R) Loda (S) Pana (S) Cultivars Non-choice test, 12 days after aphid infestation possible secondary soybean aphid hosts. In addition, we began to

120 determine the genetics of resistance in the known resistance sources Percent of 1st instars that matured to adults on resistant 100 while continuing to search for new sources of resistance. We have also and susceptible genotypes formed collaborative relationships with public and private breeding 80 80 organizations to help expedite the development and release of new 60 70

soybean aphid resistant cultivars. 60 40

Number of aphids/plant 50 20 40 0 30 Jackson Dowling PI71506 Williams Pana Ina Loda 82 20

Genotypes maturation to adults Percent 10 Expression of resistance in Dowling and Jackson is primarily 0 antibiosis, while resistance in PI71506 is antixenosis. Dowling (R) Jackson (R) Loda (S) Pana (S) Cultivars Additional Sources of Resistance Under Study Percent survival of 1st instar soybean aphid nymphs on Number of aphids 14 days after infestation in a choice test resistant and susceptible genotypes Glycine Number Entry species of aphids 100 Sato (PI548409) max 15 a b 90 soja Taichung 38 (PI518282) 19 a b c 80 Sugao Zarai (PI200538) max 20 a b 70 Dowling Jackson (PI548657) max 20 a b 60 Jackson 50 Palmetto (PI548480) max 26 b c Loda 40 Pana CNS (PI548445) max 26 b c 30 Percent survival Percent Dowling (PI548663) max 28 b c d e 20 Moyashimame (PI87059) max 61 c d e f 10 0 Showa No. 1-4 (PI88508) max 67 e f g 0 2 4 6 8 Taichung 37 (PI518281) soja 70 f g Days after aphid transfer Ina max 230 h i j k Secondary Host Range of Soybean Aphids Williams 82 max 269 i j k l Fecundity, maturation, and survival of soybean aphids Pana max 311 j k l Colonization of soybean aphids on various legume species was significantly reduced on resistant genotypes. PI522212B soja 337 k l 14 days after soybean aphid infestation in a choice test

Loda max 437 l 9 Mean 105 8 7 6 5 4 3 2

Aphid colonization index 1 0 Inheritance of Resistance

Observed F2 segregation Comparison of Dowling and a susceptible soybean cultivar, Vicia faba Vicia sativa F Vicia villosa Vigna aureus Glycine soja 1 Lens culinaris Pisum sativum treated or untreated with imidacloprid, 4 weeks after exposure to Vigna angularis Medicago sativa Trifolium repens Cross phenotype Resistant Susceptible χ2 (3R:1S) P Lotus corniculatus Lablab purpureusPhaseolusTrifolium lunatus pratense Phaseolus vulgaris Onobrychis vicifolia Phaseolus coccineus Resistant Glycine max soybean aphids beginning at the R1 (first flower) stage Trifolium subterraneum Susceptible Glycine max Dowling (R) x Loda (S) R 128 44 0.03 0.86 Species Aphid colonization index: 0 = no aphids or plant damage observed - 9 Dowling (R) x Pana (S) R 17 6 0.01 0.90 dense aphid population with severe plant damage, stunting, or death. Dowling (R) x Williams 82 (S) R 131 46 0.09 0.76

Colonization of soybean aphids on Glycine species 9 R = no aphid colonization; S = aphid colonization, 14 days after infestation in a choice test. days after infestation in a choice test Resistance in Dowling is conditioned by a single dominant gene.

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40 Number of aphids/plant Number 20 References

0 Hill, C.B., Y. Li, and G.L. Hartman. 2004. Resistance to the soybean aphid in soybean germplasm. Crop Science 44: 98-106. G. soja G. falcata G. curvata G. latifolia G. cyrtoloba G. tabacina G. canescens G. tomentella G. clandestina G. microphylla Resistant G. max Susceptible G. max Hill, C.B., Y. Li, and G.L. Hartman. 2004. Resistance of Glycine spe- Glycine species cies and various cultivated legumes to the soybean aphid (Homoptera: Aphididae). J. Economic Entomology: in press. Susceptible Glycine genotypes appeared to be better Li, Y., C.B. Hill, and G.L. Hartman. 2004. The effect of three resistant secondary hosts for the soybean aphid than other soybean cultivars on the fecundity, mortality and maturity rate of the legume species. � soybean aphid, Aphis glycines. J. Economic Entomology: in press.