Inheritance patterns, dominance and cross-resistance of Cry1Ab- and Cry1Ac-selected Ostrinia furnacalis (Guenée).

Tiantao Zhang,Mingxia He,Kanglai He,Qing Li,Angharad M R Gatehouse,Zhenying Wang,Martin G Edwards

doi:10.3390/toxins6092694

Abstract

Two colonies of Asian corn borer, Ostrinia furnacalis (Guenée), artificially selected from a Bt-susceptible colony (ACB-BtS) for resistance to Cry1Ab (ACB-AbR) and Cry1Ac (ACB-AcR) toxins, were used to analyze inheritance patterns of resistance to Cry1 toxins. ACB-AbR and ACB-AcR evolved significant levels of resistance, with resistance ratios (RR) of 39-fold and 78.8-fold to Cry1Ab and Cry1Ac, respectively. The susceptibility of ACB-AbR larvae to Cry1Ac and Cry1F toxins, which had not previously been exposed, were significantly reduced, being >113-fold and 48-fold, respectively. Similarly, susceptibility of ACB-AcR larvae to Cry1Ab and Cry1F were also significantly reduced (RR > nine-fold, RR > 18-fold, respectively), indicating cross-resistance among Cry1Ab, Cry1Ac, and Cry1F toxins. However, ACB-AbR and ACB-AcR larvae were equally susceptible to Cry1Ie as were ACB-BtS larvae, indicating no cross-resistance between Cry1Ie and Cry1Ab or Cry1Ac toxins; this may provide considerable benefits in preventing or delaying the evolution of resistance in ACB to Cry1Ab and Cry1Ac toxins. Backcrossing studies indicated that resistance to Cry1Ab toxin was polygenic in ACB-AbR, but monogenic in ACB-AcR, whilst resistance to Cry1Ac toxin was primarily monogenic in both ACB-AbR and ACB-AcR, but polygenic as resistance increased.

Highlights

Bacillus thuringiensis (Bt) is a valuable source of insecticidal proteins used in pest control, both in spray formulations and when expressed in genetically modified crops
LC50 values for both sets of F1 offspring produced from reciprocal crosses between Asian corn borer (ACB)-AbR and ACB Bt susceptible colony (ACB-BtS) were intermediate to those of the parents, and were not significantly different from each other (Table 1)
When reciprocal crosses were performed between ACB-AbR or ACB-AcR and the susceptible colony ACB-BtS, the F1 offspring showed no significant differences, and the data were in agreement with autosomal inheritance of the resistance with no maternal effects

Summary

Introduction

Bacillus thuringiensis (Bt) is a valuable source of insecticidal proteins used in pest control, both in spray formulations and when expressed in genetically modified crops. Bt transgenic crops have been highly successful and beneficial to the agricultural industry, leading to lower yield losses and reducing the use of chemical pesticides and fossil fuels. Despite these benefits, there remains the ever-present concern that insects will evolve resistance to the Bt toxins currently in use, seriously threatening the longevity of this technology. Since the global commercialization of transgenic Bt crops the total planted area has increased more than 100-fold from 1.7 million hectares in 1996 to 175 million hectares in 2013, making biotech crops the fastest adopted crop technology in the history of modern agriculture [2].

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Conclusion