Influence of soil type on Cry3Bb1 expression and efficacy in the field

Greater than expected injury by western corn rootworm (WCR) (Diabrotica virgifera virgifera) to Cry3Bb1 expressing hybrids has been reported in southwestern Nebraska. Affected areas of fields are often characterized by high pH, calcareous soils where corn growth is poor.  As part of a comprehensive study to understand potential causes of unexpected injury, experiments were conducted in 2013 and 2014 to ascertain whether poor soil and associated poor corn growth leads to reduced expression of Cry3Bb1. Standard soil sampling procedures were conducted to establish the soil pH and soil texture of patches within fields. Quantitative determination of Cry3Bb1 protein expression levels in root tissues from corn planted in good and poor soils of multiple fields was compared at the V5- V6 plant growth stage using the enzyme-linked immunosorbent assay. Adult WCR emergence was also recorded from artificially infested corn plants in poor and good soils in multiple fields. The expression of Cry3Bb1 protein was not significantly impacted by soil type as the Cry3Bb1 expression level was similar in plants from poor and good soils.  Also, WCR survival from plants in each soil type was not significantly different. There was no correlation between soil pH and either the expression level of Cry3Bb1 protein or emergence of WCR.  Results suggest that Cry3Bb1 expression levels are sufficient to provide adequate root protection against WCR regardless of soil type which enables us to rule out lowered Cry3Bb1 expression as a contributing factor to the greater than expected WCR injury observed in some southwestern Nebraska cornfields.