Resistance to the Soybean Aphid in Soybean Germplasm

severe aphid infestation (Wang et al., 1996). An additional threat posed by the aphid is its ability to transmit certain With an efficient greenhouse screening method, the first resistance plant viruses to soybean such as Alfalfa mosaic virus, Soyto the soybean aphid (Aphis glycines Matsumura) was found in cultivated soybean [Glycine max (L.) Merr.] germplasm. No resistance was bean dwarf virus, and Soybean mosaic virus (Sama et al., found in 1425 current North American soybean cultivars, 106 Maturity 1974; Iwaki et al., 1980; Hartman et al., 2001; Hill et al., Group (MG) 000 through VII Asian cultivars, and in a set of 11 ‘Clark’ 2001; Clark and Perry, 2002). isolines possessing different pubescence traits. Dense pubescence did Aphis glycines and close relative A. gossypii, the cotton not provide protection against the soybean aphid. Resistance was or melon aphid, are the only aphid species found colonizdiscovered and established in three ancestors of North American ing soybean in the USA. In other parts of the world, A. genotypes: ‘Dowling’, ‘Jackson’, and PI 71506. Expression of resiscraccivora, Aulacorthum solani, and other species have tance in those genotypes was characterized in choice and nonchoice been found colonizing soybeans (D. Voegtlin, personal tests. In choice tests, significantly fewer aphids occurred on Dowling, communication, 2003). Jackson, and PI 71506 plants compared with susceptible cultivars (P Aphis glycines has a heteroecious, holocyclic life-cycle 0.05). Aphid populations did not develop on Dowling and Jackson in nonchoice tests, indicating that there was a negative impact on pattern (Guang-xue and Tie-sen, 1982). Rhamnus catharaphid fecundity on those cultivars. That evidence combined with obtica (buckthorn) is the primary host of A. glycines (Hartservations of aphid mortality on those cultivars suggested that antibioman et al., 2001) and soybean is a secondary host. In sis-type resistance contributed to the expression of resistance. Possible autumn, when the soybean crop matures, the aphid moves donors of resistance to Dowling and Jackson were identified. In nonto R. cathartica, where mating and oviposition occurs. The choice tests, population development on PI 71506 was not sigegg stage overwinters on R. cathartica. During the follownificantly different from development on susceptible cultivars, indicating spring, the eggs hatch and a few generations are proing that antixenosis was more important in that genotype. Resistance duced before alatae (winged females) fly to soybean. was expressed in all plant stages. Dowling provided season-long proBecause A. glycines is a recent pest in the USA, a comtection against aphids equal to the use of the systemic insecticide imiprehensive integrated management approach to control dacloprid {1-[(6-Chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine} in a field test. Four other germplasm accessions, ‘Sugao Zarai’, the aphid has yet to be developed. Research to evaluate ‘Sato’, ‘T260H’, and PI 230977, had levels of resistance not significantly the efficacy of currently available insecticides and other different from Dowling, Jackson, and PI 71506 in a choice test control measures has just begun. Researchers in Minne(P 0.05). sota have developed recommendations for the use of insecticides to control the aphid (Ostlie, 2002). Until other components of integrated pest management S is a major crop in the USA, with 75 million (IPM) are developed, soybean producers will need to Mg of grain produced in 2000 (USDA, 2002). A new rely on the use of insecticides to control the aphid. threat to soybean production in the USA, the soybean An integral component of an IPM program to control aphid, recently arrived. aphids is plant resistance (Auclair, 1989; Harrewijn and A native of Asia, the soybean aphid was first found in Minks, 1989). Insect resistance can significantly reduce the Midwest in 2000 (Hartman et al., 2001). It rapidly input costs for producers (Luginbill, 1969). Resistance spread throughout the region and into other parts of North was reported in G. soja (Sun et al., 1990), a close relative America (Patterson and Ragsdale, 2002). High aphid popof G. max (Hymowitz, 1970), and other wild relatives ulations can reduce crop production directly when their (Zhuang et al., 1996). There are no reports of resistance feeding causes severe damage such as stunting, leaf distorin G. max. A report from Indonesia indicated that there tion, and reduced pod set (Sun et al., 1990). Yield losses was no resistance in a test of 201 soybean cultivars and attributed to the aphid in some fields in Minnesota during breeding lines (Sama et al., 1974). 2001, where several thousand aphids occurred on individThere are three basic kinds of resistance: tolerance, ual soybean plants, were 50% (Ostlie, 2002) with an antixenosis, and antibiosis (Smith, 1989). Knowledge of average loss of 101 to 202 kg ha 1 in those fields (Patterson the mechanism of resistance is necessary to develop efand Ragsdale, 2002). In earlier reports from China, soyfective screens to identify resistant plants. Choice tests, bean yields were reduced up to 52% when there was an where aphids are allowed to choose their preferred hosts, average of about 220 aphids per plant (Wang et al., 1994) help identify resistance, but do not distinguish between and plant height was decreased by about 210 mm after the types of resistance. Nonchoice tests, where aphid movement is restricted to a single host, help distinguish C.B. Hill and Y. Li, Dep. of Crop Sci.; G.L. Hartman, USDA-ARS antibiosis, the effect of resistance on the biology of the and Dep. of Crop Sci., Univ. of Illinois, 1101 West Peabody Dr., aphid, from antixenosis, nonhost preference. Field tests Urbana, IL 61801. Received 10 Mar. 2003. *Corresponding author to measure yield in the presence of aphid infestation ([email protected]). Published in Crop Sci. 44:98–106 (2004).  Crop Science Society of America Abbreviations: IPM, integrated pest management; MG, maturity group; RH, relative humidity; VIPS, Variety Information Program for Soybeans. 677 S. Segoe Rd., Madison, WI 53711 USA