No soybean cultivars exhibit resistance to larval damage by the cerambycid, Dectes texanus LeConte, in the United States. Selected soybean varieties and plant introductions (PIs) in maturity groups VI to VIII from the U.S. Department of Agriculture National Soybean Germplasm Collection were evaluated for D. texanus resistance in a series of field and laboratory experiments from 2005 through 2008. In field cage experiments, the numbers of oviposition punctures (OPs) per plant were determined as indicators of oviposition antixenosis and the ratio of OPs per live D. texanus larvae (OP/Lv) served as an indicator of plant antibiosis to larvae. A D. texanus-susceptible variety treated with the systemic insecticide fipronil was used as a positive antibiosis control. Plant introduction PI165673 had the highest OP/Lv ratio, indicating that even if oviposition was successful, an antibiosis factor in PI165673 significantly reduced egg hatch and the resulting number of live D. texanus larvae. Factorial analyses indicated that maturity group is not a significant factor in the expression of resistance. Thus, PI165673 appears to be a potential source of resistance to D. texanus. In related field studies, the preferred D. texanus oviposition site was localized to leaf petioles in the upper four or five nodes of the plant canopy. Histomorphological analyses of petiole cross-sections of plant introductions PI171451, PI165676, and PI165673 indicated that leaf petiole morphology may be related to reduced D. texanus oviposition on petioles of PI171451 and PI165676, but that resistance in PI165673 is independent of petiole morphology.
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Vol. 105 • No. 2