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ABSTRACT
With an efficient greenhouse screening method, the first resistance to the soybean aphid (Aphis glycines Matsumura) was found in cultivated soybean [Glycine max (L.) Merr.] germplasm. No resistance was found in 1425 current North American soybean cultivars, 106 Maturity Group (MG) 000 through VII Asian cultivars, and in a set of 11 'Clark' isolines possessing different pubescence traits. Dense pubescence did not provide protection against the soybean aphid. Resistance was discovered and established in three ancestors of North American genotypes: 'Dowling', 'Jackson', and PI 71506. Expression of resistance in those genotypes was characterized in choice and nonchoice tests. In choice tests, significantly fewer aphids occurred on Dowling, Jackson, and PI 71506 plants compared with susceptible cultivars (P = 0.05). Aphid populations did not develop on Dowling and Jackson in nonchoice tests, indicating that there was a negative impact on aphid fecundity on those cultivars. That evidence combined with observations of aphid mortality on those cultivars suggested that antibiosis-type resistance contributed to the expression of resistance. Possible donors of resistance to Dowling and Jackson were identified. In non-choice tests, population development on PI 71506 was not significantly different from development on susceptible cultivars, indicating that antixenosis was more important in that genotype. Resistance was expressed in all plant stages. Dowling provided season-long protection against aphids equal to the use of the systemic insecticide imidadoprid {1-[(6-Chloro-3-pyridinyl)methyl]-N-nitro-2-imidazolidinimine} in a field test. Four other germplasm accessions, 'Sugao Zarai', 'Sato', 'T260H', and PI 230977, had levels of resistance not significantly different from Dowling, Jackson, and PI 71506 in a choice test (P = 0.05).
Abbreviations: IPM, integrated pest management; MG, maturity group; RH, relative humidity; VIPS, Variety Information Program for Soybeans.
SOYBEAN IS A MAJOR CROP in the USA, with >75 million Mg of grain produced in 2000 (USDA, 2002). A new threat to soybean production in the USA, the soybean aphid, recently arrived.
A native of Asia, the soybean aphid was first found in the Midwest in 2000 (Hartman et al., 2001). It rapidly spread throughout the region and into other parts of North America (Patterson and Ragsdale, 2002). High aphid populations can reduce crop production directly when their feeding causes severe damage such as stunting, leaf distortion, and reduced pod set (Sun et al., 1990)....