Commentary by Prof. Joe Cummins

The article below puts the refuge strategy into question. The article shows that when low levels of Bt cry 1 toxin are produced in transgenic cotton the inheritance pattern is codominant and as somewhat higher toxin levels are produced in cotton the inheritance shows weak codominance. Only crops that produce high levels of toxin show the recessive inheritance that makes the refuge work.Codominant cry 1 inheritance makes the refuge an accelerator for spreading the resistance gene. Refuge has been taken to heart by government bureaucrats and many environment groups opposing GM crops. Five years ago I began to point out that refuge had an achilles heal and that defect was dominant or codominant resistance! Blind and unthinking adherence to dogma is very unwise, particularly in the world of GM crops.

Much more efforts should be spent studying the inheritance of resistance to Bt in crop pests and to think of stopping the planting of GM crops where codominant inheritance is detected.

Laboratory selection increased resistance of pink bollworm (Pectinophora gossypiella) to the Bacillus thuringiensis toxin Cry1Ac. Three selections with Cry1Ac in artificial diet increased resistance from a low level to >100-fold relative to a susceptible strain. We used artificial diet bioassays to test F1 hybrid progeny from reciprocal crosses between resistant and susceptible strains. The similarity between F1 progeny from the two reciprocal crosses indicates autosomal inheritance of resistance. The dominance of resistance to Cry1Ac depended on the concentration. Resistance was codominant at a low concentration of Cry1Ac, partially recessive at an intermediate concentration, and completely recessive at a high concentration. Comparison of the artificial diet results with previously reported results from greenhouse bioassays shows that the high concentration of Cry1Ac in bolls of transgenic cotton is essential for achieving functionally recessive inheritance of resistatance.

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