Unintended impacts of value added plant breeding: linolenic acid and soybean

Linolenic acid is a precursor to volatile comnponents in the plant’s defense response to Hemiptera. Commercial soybean varieties with altered levels of linolenic acid have been developed for their improved oil qualities. We examined how seed linolenic acid level affects soybean aphid, Aphis glycines Matsumara (Hemiptera: Aphididae) population dynamics and how the aphid impacts yield and grain composition of these specialty beans. In a field experiment soybean varieties with varying concentrations of linolenic acid in the seed (ultra-low, low, and commodity) were grown in micro-plots covered by insect exclusion cages at a research farm in Story Co. Iowa. Plants were artificially infested with soybean aphids at the V2 to V3 growth stage. Aphid populations were monitored from initial infestation to leaf senescence. Early season population growth was used to determine intrinsic rates of growth. Seed was collected at the end of the season to measure yield and grain composition. Fatty acid profiles of seeds were measured using GC-MS. We observed no difference among treatments after analyzing early season aphid populations and seasonal plant exposure to aphids. We measured a decrease in linolenic acid accumulation under high aphid populations. The results of this experiment suggest no changes are necessary for management of altered linolenic acid soybean varieties.