Transgenic Bt-producing Brassica napus: Plutella xylostella selection pressure and fitness of weedy relatives

¹ Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, K. W. Neatby Bldg., Ottawa, Ontario, K1A 0C6, Canada
² Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, S7N 0X2, Canada
³ Environment Canada, National Water Research Institute, 11 Innovation Blvd., Saskatoon, Saskatchewan, S7N 3H5, Canada
⁴ Dept. of Plant Sciences and Landscape Systems, 2431 Centre Drive, Ellington Plant Sciences, University of Tennessee, Knoxville, TN 37996-4561, USA

Corresponding author: masonp@agr.gc.ca

Abstract

Release of transgenic insect-resistant crops creates the potential not only for the insect pest to evolve resistance but for the escape of transgenes that may confer novel or enhanced fitness-related traits through hybridization with their wild relatives. The differential response of diamondback moth (Plutella xylostella) populations in eastern and western Canada to Bt-producing (GT) Brassica napus and the potential for enhanced fitness of GT B. napus and weedy GT Brassica rapa × B. napus hybrid populations (F₁, BC₁, BC₂) were studied. Comparative bioassays using neonates and 4th instars showed that GT B. napus and GT B. rapa × B. napus hybrids are lethal to larvae from both populations. No measurable plant fitness advantage (reproductive dry weight) was observed for GT B. napus (crop) and GT B. rapa × B. napus hybrid populations at low insect pressure (1 larva per leaf). At high insect densities (>10 larvae per leaf), vegetative plant weight was not significantly different for GT B. napus and non-GT B. napus, whereas reproductive plant weight and proportion of reproductive material were significantly higher in GT B. napus. Establishment of the Bt trait in wild B. rapa populations may also increase its competitive advantage under high insect pressure.