Antixenosis to the Soybean Aphid in Soybean Lines

The soybean aphid, Aphis glycines, is a pest of soybean in Asia, and it has become a major pest of this crop in North America with large outbreaks that cause significant yield loss. Host-plant resistance is one management tactic being developed against soybean aphid in North America, and resistance may be manifested as antixenosis, antibiosis, or tolerance. In this study, choice tests were conducted to identify antixenosis to soybean aphids in several soybean lines. The soybean lines ‘Dowling,’ PI 230977, ‘Jackson,’ ‘Cobb’ and ‘Palmetto’ had strong antixenosis to soybean aphid, and lines PI 71506, G93-9223, ‘Braxton,’ ‘Cook,’ ‘IAC-1,’ ‘Ripley,’ and ‘Tie feng 8’ were moderately antixenotic. The intermediate level of antixenosis in PI 71506 contrasts with previous results, and suggests biotypic differences in the responses of soybean aphid to this line. Shoot length, shoot width, and seedling dry mass were also measured to test for any association between aphid host choice and plant size. Plant-size parameters varied by soybean line in all tests. However, the relation between aphid host choice and plant-size parameters was generally weak and not consistent across tests, suggesting that other undetermined plant characteristics were important in host selection. The identification of antixenosis in several soybean lines provides soybean breeders and pest management practitioners with additional options for managing soybean aphid through host-plant resistance. Antixenosis may be important on its own, and it may prove be complimentary to the antibiosis mode of resistance by reducing selection on resistance-breaking biotypes of soybean aphid, thereby prolonging the usefulness of plant resistance as a non-chemical means of managing soybean aphid.