Mechanism and DNA-based detection of field-evolved resistance to transgenic Bt corn in fall armyworm (Spodoptera frugiperda)

Rahul Banerjee,James Hasler,Fangneng Huang,Rodney Nagoshi,Juan Luis Jurat-Fuentes,Kenneth Narva,Lucas Hietala,Robert Meagher

doi:10.1038/s41598-017-09866-y

Abstract

Evolution of resistance threatens sustainability of transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt). The fall armyworm (Spodoptera frugiperda) is a devastating pest of corn in the Western Hemisphere initially controlled by transgenic Bt corn producing the Cry1Fa insecticidal protein (event TC1507). However field-evolved resistance to TC1507 was observed in Puerto Rico in 2007 and has subsequently been reported in a number of locations in North and South America. Early studies on Puerto Rico fall armyworm populations found that the resistance phenotype was associated with reduced expression of alkaline phosphatase. However, in this work we show that field-evolved resistance to Cry1Fa Bt corn in Puerto Rico is closely linked to a mutation in an ATP Binding Cassette subfamily C2 (ABCC2) gene that functions as a Cry1Fa receptor in susceptible insects. Furthermore, we report a DNA-based genotyping test used to demonstrate the presence of the resistant (SfABCC2mut) allele in Puerto Rico populations in 2007, coincident with the first reports of damage to TC1507 corn. These DNA-based field screening data provide strong evidence that resistance to TC1507 in fall armyworm maps to the SfABCC2 gene and provides a useful molecular marker for detecting the SfABCC2mut allele in resistant fall armyworm.

Highlights

Pest control efficacy and the potential for higher net returns have driven increasing adoption of transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt crops) during the past 20 years[1]
In this study we report SfABCC2 as a functional Cry1Fa/Cry1A receptor in S. frugiperda and identify a mutation tightly linked to field-evolved resistance to transgenic corn event TC1507
We demonstrate the detection of this mutant allele (SfABCC2mut) in current and archived field-collected S. frugiperda genetic samples

Summary

Introduction

Pest control efficacy and the potential for higher net returns have driven increasing adoption of transgenic crops producing insecticidal proteins from the bacterium Bacillus thuringiensis (Bt crops) during the past 20 years[1]. In the US, Bt corn and cotton adoption represent about 80% of the national acreage devoted to the two commodities[2]. This high level of adoption increases selection pressure for the evolution of resistance to Bt toxins in targeted pests. Reduced expression of an alkaline phosphatase gene (SfmALP2) was associated with resistance to Cry1Fa corn in Spodoptera frugiperda We report a mutation in an ABCC2 gene as linked to field resistance to Bt corn producing the Cry1Fa protein in S. frugiperda from Puerto Rico and describe a DNA-based method to monitor for resistance in field samples. We demonstrate the feasibility of using this strategy on archived samples to provide a historical reconstruction of resistance evolution and dispersal

Methods

Results

Conclusion