Update:
refer to final results

The soybean aphid is the most important arthropod pest of soybean in North America.
The prevalence of the aphid in soybean fields has resulted in increased time spent on
scouting and the increased use of insecticides as both seed treatments and foliar sprays
leading to a significant increase in the cost of production. The current strategy to limit the
economic losses caused by the aphid is to increase host plant resistance. The discovery of
several aphid resistant genes in various cultivars have greatly aided the process. However,
specific soybean aphid biotypes have already been identified around the country that
specifically overcome the resistant genes. In order to overcome this adaptation and to
generate broad spectrum resistance against not only the soybean aphid but also against
other pathogens such as the soybean cyst nematode, the goal of this proposal has been to
evaluate transgenic soybean that express the PHYTOALEXIN DEFICIENT4 (PAD4) gene.
Transgenic plants that express this gene have previously been shown to provide resistance to
aphids and nematodes in other crop plants. As part of a previously funded project, transgenic
soybean plants the overexpress soybean PAD4 were generated. In this project period, the
transgenic plants (T3 generation) were evaluated for resistance to the soybean aphid.
The T1 transgenic plants derived from the five independent transformation events
were evaluated for the presence and expression of the transgene. The plants were also
evaluated for the response to soybean aphid infestation.
• Four T1 plants from the transgenic events E1, E2, & E5 and five T1 plants from the
transgenic events E3 & E6 were evaluated. Tissue collected from unifoliate leaves from
plants at the V0 stage were used for DNA extraction. Polymerase chain reaction
indicated that although all plants contained the BAR gene (Selectable marker indicating
presence of pVN001) not all of them contained the PAD4 gene (Fig 1).
• The T1 plants were also evaluated PAD4 expression using RT-PCR (Fig. 2). RNA
collected from the plants derived from each individual transformation event were pooled.
High levels of PAD4 expression were observed in E2, E3 & E4 plants compared to E1
and E6 plants (Fig. 2).
• The plants derived from the transgenic events E2, E3 and E4 show increased resistance
to soybean aphids (Fig. 3). On the other hand, plants derived from the E1 and E6
transformation events that show little to no expression of PAD4 (Fig. 2) support aphid
populations similar to those observed on the non-transgenic control, Jack (Fig. 3).
• Seeds collected from the T2 plants were evaluated for response to aphid infestation
(Fig. 4A). In the T2 generation, we observed that plants derived from the five
independent transgenic experiments showed enhanced resistance to aphid infestation.
• A similar response was observed in the T3 generation (Fig. 4B).