Integrating plant tolerance into breeding programs for soybean aphid (Aphis glycines Matsumura) management

Since its introduction in North America, the soybean aphid has caused significant economic losses in soybean. Although monogenic soybean aphid resistant soybean (Rag genes) has been deployed, the development of polygenic or aphid tolerant soybeans remains unexplored. The research objective was to characterize the peroxidase activity in soybean genotypes in the presence and absence of aphids, and also identify a phenotypic method to screen aphid-tolerant recombinant inbred lines (RIL). Enzyme kinetic assays documented the total peroxidase activity for soybean KS4202 (tolerant), SD01-76R (susceptible), U09-105007 (high yield) and U11-611112 (high yield) during two vegetative stages (V1 and V3) at 4, 6 and 8 days post aphid introduction (dpi). Analyses using qPCR were also performed to compare the differential expression of two peroxidase transcripts, Glyma06g15030 and Glyma14g35440. Peroxidase basal levels were similar among the genotypes for both V1 and V3 stages within the time points analyzed. Under aphid infestation, V3-KS4202 aphid-infested plants had significantly higher peroxidase activity than their respective control plants at 4 and 6 dpi and U11-611112 at 4 dpi. There were no apparent trends when comparing the expression of the two specific peroxidase transcripts (Glyma06g15030 and Glyma14g35440) in the absence of aphids in both V1 and V3 stage; however, there was a tendency for greater expression of Glyma06g15030 in KS4202 when aphids were present. The different patterns observed when comparing KS4202 with the high yield and susceptible soybean at the V3 stage suggests that total peroxidase activity in response to aphid feeding may be useful for screening RIL in a breeding program for soybean aphid tolerance.