Soybean Aphid - Host Plant Resistance

Host Plant Resistance

Several varieties of soybean have demonstrated resistance to the soybean aphid. Resistance may be conferred by antibiosis, antixenosis, or tolerance. In some instances, such as with the soybean cultivars 'Dowling', 'Jackson', and 'Palmetto', resistance to the soybean aphid results from a combination of both antibiosis and antixenosis. In the 'Dowling' cultivar, resistance is conferred by a single dominant gene (Rag1). Soybean plants that are resistant to the soybean aphid can cause both reduced fecundity and longevity in soybean aphids. In the case of antibiosis, certain life stages of the soybean aphid may be more susceptible than others. For example, nymphs have higher rates of metabolism than other life stages, ingest more phloem, and are thus exposed to larger quantities of antibiotic compounds. Expression of antibiotic factors in resistant soybean plants that negatively affect soybean aphids has been shown to remain constant throughout the growing season, remaining unaffected by the physiological maturity of the plant. Colonization of resistant soybean cultivars can vary between years depending upon the level of infestation, with resistant plants showing lower levels of resistance in years with significant levels of soybean aphid infestation. Physical characteristics of soybean, such as dense pubescence, have thus far proven incapable of reducing colonization by soybean aphids.