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

Abstract

The adoption of genetically modified (GM) and non-GM Brassica napus herbicide-resistant cultivars, along with the possibility of introgression with B. rapa, has led to the emergence of new weedy biotypes. In Argentina, in 2012, natural populations of transgenic (GM) glyphosate-resistant and non-GM AHAS-inhibiting resistant B. rapa were detected. The investigation of the pleiotropic effects between herbicide resistance and fitness in these biotypes can help determine the potential persistence of these resistances in agricultural fields. The aim of this study was to assess the effect of the glyphosate transgene (GT73) and AHAS Trp574Leu mutation on B. rapa vegetative and reproductive traits. Fitness components were compared between susceptible (S) and resistant (R) populations in two trials in a common garden experiment. Each assay was performed in the spring and winter season. One trial was carried out using populations with homogeneous genetic background, and the other using populations with different genetic backgrounds. Plants grown during the winter season exhibited superior performance compared to those grown in spring. No differences were found between R and S biotypes in the parameters evaluated in populations with homogeneous genetic background, except for siliques per main inflorescence where the S biotype produced more siliques than the R, although this later compensated with more seeds per silique. When comparing R and S biotypes with different genetic backgrounds, no significant differences were found in the evaluated parameters. Therefore, glyphosate and AHAS-inhibiting resistances are likely to persist in Brassica rapa populations, even in the absence of herbicide selection pressure.