Agronomic effects of gene flow: multiple herbicide resistance in volunteer crop plants

摘要

Gene stacking in volunteer crop plants was first reported in canola, Brassica napus. Herbicide resistant Brassica napus resistant to glyphosate, glufosinate, bromoxynil or imidazolinone herbicides has been widely accepted by Canadian producers since 1996, occupying approximately 85% of B. napus acres. Volunteer canola is also a significant weed, ranking between 16th and 20th in relative abundance amongst weeds in western Canada in recent post-herbicide weed surveys. It survives in the seed bank for 4 or 5 years following the canola crop. Plant-to-plant outcrossing rates in B. napus are approximately 20%. Outcrossing diminishes with distance to less than 1% at boundaries between adjacent fields and further to less than 0.2% at greater distances. Outcrossing has been identified up to 3 km distance from the pollen source. Gene flow via pollen, in combination with volunteer survival results in multiple herbicide resistant volunteers, with two or three different resistance genes stacking in a single plant. The longevity of volunteer canola in the seed bank, outcrossing rates and multiple herbicide resistance prohibit the easy extinction of traits once they have been released. Resistant and multiple resistant volunteers have necessitated the modification of agronomic practices for their control. Most producers rely on herbicide mixtures containing auxinic herbicides like 2, 4-D which control all canola volunteers. The risks of gene flow and modified agronomic practices must be balanced against the gains to the industry and the environment. The use of herbicide resistant canola has reduced the amount of herbicide used in western Canada by 6,000 tonnes annually, and decreased tillage and consequent use of diesel fuel by 31.2 million liters. While much can be learned from the Canadian example, decisions on the introduction of future traits for crops must continue to be trait, environment and crop specific.