Temperature conditioning of soybean seedlings influences expression of resistance to soybean aphid (Aphis glycines) Biotype 1

The Rag1 gene has been shown to confer resistance to biotype 1 soybean aphids (SBA) Aphis glycines, but little is known about whether plant exposure to temperature alters the expression of resistance. To test for indirect plant-mediated temperature effects on SBA, individual soybean seedlings (V-0 stage) containing Rag1 resistance were exposed to either low (20⁰C) or high (30⁰C) temperature for different durations (0, 3 or 5 days) at 25⁰C prior to infestation with a single neonate aphid. We hypothesized that conditioning plants to high temperatures would cause resistance to break down, and that the effect would be enhanced by longer exposure. Four aphid responses were evaluated: pre-adult development time, survival to adult, lifetime progeny produced per female, and adult longevity. When plants were conditioned at 20⁰C, there were no statistically-significant effects of conditioning duration on SBA development or adult longevity. However, percent survival and numbers of progeny decreased significantly as plant conditioning time increased, suggesting that the expression of Rag1 resistance is modified by the length of plant exposure to low temperature. In contrast, at 30⁰C conditioning time had no effect on any aphid response, and survival was significantly lower compared to any of the treatments at 20⁰C. These results suggest that SBA may be responding directly to abiotic stress. However, we cannot discount that high temperature did not have an effect on resistance, which may have occurred quickly after plants were transferred. Thus, it is possible that SBA responses are a result of both temperature and plant resistance effects.