Exploring genetic mechanisms of resistance by western corn rootworm to corn producing Gpp34/Tpp35Ab1

The western corn rootworm is a serious pest of corn in the Midwest. Management of rootworm injury includes the use of genetically engineered corn hybrids that express insecticidal proteins derived from the bacteria Bacillus thuringiensis (Bt). These plant-incorporated protectants, such as the Bt toxin Gpp34/Tpp35Ab1, disrupt the midgut of susceptible rootworm, leading to mortality. Starting in 2013, resistance to Gpp34/Tpp35Ab1 corn hybrids was identified in Iowa, and elsewhere in the western Corn Belt. Currently, there is a dearth of published work identifying genetic markers for resistance to Gpp34/Tpp35Ab1 in western corn rootworm. To address this knowledge gap, Bt-resistant western corn rootworm adults were collected in 2018 from two field in Iowa planted with Gpp34/Tpp35Ab1 corn that suffered high levels of rootworm feeding injury. These field-collected individuals were crossed with a Bt-susceptible non-diapausing strain, and then reselected on Gpp34/Tpp35Ab1 corn. From these strains, family lines were initiated by conducting reciprocal crosses between Bt-resistant and Bt-susceptible parents. Following random mating among F1 progeny, resulting F₂ larvae were reared on either Gpp34/Tpp35Ab1 corn or non-Bt corn. Nucleotide variants were predicted among parents and F₂ progeny from genotyping-by-sequencing markers, and quantitative trait locus (QTL) mapping performed to identify genomic region(s) linked to inheritance of Gpp34/Tpp35Ab1 resistance. QTL markers generated from this study can contribute to improved resistance monitoring and management efforts and provide insight into the genetic basis of Gpp34/Tpp35Ab1 resistance. This will provide a broader understanding of resistance evolution by western corn rootworm and help improve current and future approaches for resistance management.