No fitness cost in Brassica rapa (wild turnip) populations associated with transgenic glyphosate and non-transgenic AHAS-inhibiting herbicides resistance

Abstract

Brassica rapa is an annual species cultivated for centuries for food consumption and oil. Its wild form is a common weed in temperate climates around the world, including Argentina, interfering in more than 20 crops. The adoption of genetically modified (GM) and non-GM Brassica napus herbicide-resistant cultivars and the possibility of introgression with B. rapa gave rise to new weedy biotypes. In Argentina, in 2012, natural populations of transgenic (GM) glyphosate-resistant B. rapa were found and one of these populations also showed (non-GM) AHAS-inhibiting resistance. The study of the pleiotropic effects on fitness cost in this species could determine whether these resistances could persist in agricultural fields. The aim of the present study was to assess the effect of the glyphosate transgene (GT73) and AHAS Trp574Leu mutation on B. rapa vegetative and reproductive traits. Two trials were carried out, one with a homogenous genetic background and another with a different genetic background, both in two growing seasons. We found no differences in either trial between the resistant and susceptible biotypes in any of the fitness traits evaluated. It was also noted that in winter, the biotypes showed a better performance than plants growing in spring. Based on these results, glyphosate resistance and AHAS-inhibiting resistance are likely to persist in Brassica rapa populations even without the herbicide selection. This is in agreement with the area invaded by this weed in Argentina over the last ten years.