Resistance of cotton with δ-endotoxin genes from Bacillus thuringiensis var. kurstaki on selected lepidopteran insects

Transgenic cotton (Gossypium hirsutum L.) plants that express truncated versions of insect control protein genes cryIA (c) and CryIIA of Bacillus thuringiensis Berliner var. kurstaki (Bt) have been developed for managing lepidopteran pests. However, agronomic traits and pest resistance can vary among transformation events. We examined selected agronomic traits and resistance, in laboratory and field, against tobacco budworm [Heliothis virescens (F.)] and bollworm [Helicoverpa zea (Boddie)] for various transformation events of the cryIA(c) and CryIIA genes. Monsanto events with cryIIA were as resistant to tobacco budworm and bollworm as the M531 Bt event of cryIA (c), but showed some yield loss. Calgene events ST 807, ST 808, and ST 317 expressing cryIA(c) were similar to the M531 Bt event of cryIA (c) in control of tobacco budworm and bollworm. Eackcrossed cultivars NuCOTN 33 B and NuCOTN 35 B from Delta & Pine Land Co. with event M531 Bt of cryIA(c) were highly resistant to tobacco budworm, producing more than 1400 kg ha -1 (vs. 0 on nontransgenic recurrent parents) under high levels of tobacco budworm infestation. These NuCOTN cultivars also yielded 450 to 550 kg ha -1 more lint than the recurrent parents under high levels of natural infestation of tobacco budworm in the insecticide control treatment; in the absence of tobacco budworm, NuCOTN yields were equal to or greater than for recurrent parents. The Paymaster Technologies lines with event M757 Bt of cryIA (c) were not pure for the gene, but showed excellent field resistance to tobacco budworm. Lines HX2 BG and HX3 BG showed resistance equal to the donor event M757 and yields equal to H1244. Reduced performance of event M757 in HX6 BG relative to other Paymaster lines with this event indicates a significant genotype x event interaction. Laboratory survival of bollworm after 7 d on transgenic leaves and squares was greater than survival of tobacco budworm; however, weight of surviving larvae of each species was only 10 to 15% of that on nontransgenic controls. Survival of fall armyworm [Spodoptera frugiperda (J.E. Smith)] at 7 d was only slightly lower than on nontransgenics, and weights were slightly lower. Careful evaluation of transgenic events and cultivars is necessary to ensure that the final cultivar is both resistant to target pests and has acceptable yield.