Partial characterization of cotton plants expressing two toxin proteins from Bacillus thuringiensis: relative toxin contribution, toxin interaction, and resistance management

Abstract

Laboratory studies were performed to characterize the lepidopteran toxicity of cotton plants expressing two different toxin proteins from Bacillus thuringiensis (Bt), in order to assess insect resistance management implications of a commercial, two‐toxin transgenic cotton. An independent and additive interactive effect of two Bt δ‐endotoxins expressed by the transgenic cotton variety 15985 was demonstrated by examining the responses of Heliothis virescens (F.), Helicoverpa zea (Boddie), and Spodoptera frugiperda (J.E. Smith) larvae to field‐ or greenhouse‐grown tissue from genetic near‐isolines, which expressed Cry1A only, Cry2Ab only, or both toxins. In all cases, the Cry2Ab component was the larger contributor to total toxicity in the two‐toxin isoline. Toxin‐specific, quantitative enzyme‐linked immunosorbent assay (ELISA) tests confirmed that the levels of each toxin in tissues of the two‐toxin isoline were not statistically different (P > 0.05) from the levels found in the corresponding tissues of the respective single‐toxin isoline. Resistance management considerations were discussed. Considering the additive interaction of toxins, a relatively simple insect resistance‐monitoring procedure was proposed for the monitoring of commercial cotton varieties expressing both toxins.

Potential shortfall of pyramided transgenic cotton for insect resistance management

“…However, unlike our results showing similar seasonal declines of about threefold in Cry1Ac and Cry2Ab in DP 164 B2RF, previous studies with other cultivars found that the seasonal decline in toxin concentration was generally less for Cry2Ab (35)(36)(37) than Cry1Ac (38)(39)(40)(41)(42). In any case, seasonal declines in the concentration of Bt toxins could be an important factor affecting redundant killing because there is extensive variation among cotton cultivars in patterns of production of Bt toxins (43).…”

Comparative Study of <i>Helicoverpa armigera</i> (Hubner) (Lepidoptera: Noctuidae) Preference for Bt and Non-Bt Soybean Cultivars

“…Treatments Bt7 and Bt8 were considered repellants for H. armigera, suggesting that the physical and chemical factors act in different ways among cultivars and these factors are fundamentally important for the behavioral analysis of insects [36].…”

Enhancing Sustainability of Cotton Production Systems in West Africa: A Summary of Empirical Evidence from Burkina Faso

“…In Bollgard II, these proteins, Cry1Ac and Cry2Ab, are encoded by genes originating from the common soil bacterium Bacillus thuringiensis (Bt). These Cry proteins are both highly effective in killing certain lepidopteran larvae (caterpillars) [23]. Once ingested, the Cry proteins bind to specific molecular receptors on the lining of the caterpillar's gut, create holes in the gut, and quickly cause death [57].…”