Brassica rapa L. is an annual Brassicaceae species cultivated for oil and food production, whose wild form is a weed of crops worldwide. In temperate regions of South America and especially in the Argentine Pampas region, this species is widely distributed. During 2014, wild B. rapa populations that escaped control with glyphosate applications by farmers were found in this area. These plants were characterized by morphology and seed acidic profile, and all the characters agreed with B. rapa description. The dose-response assays showed that the biotypes were highly resistant to glyphosate. It was also shown that they had multiple resistance to AHAS-inhibiting herbicides. The transgenic origin of the glyphosate resistance in B. rapa biotypes was verified by an immunological test which confirmed the presence of the CP4 EPSPS protein and by an event-specific GT73 molecular marker. The persistence of the transgene in nature was confirmed for at least 4 years, in ruderal and agrestal habitats. This finding suggests that glyphosate resistance might come from GM oilseed rape crops illegally cultivated in the country or as a seed contaminant, and it implies gene flow and introgression between feral populations of GM B. napus and wild B. rapa. The persistence and spread of the resistance in agricultural environments was promoted by the high selection pressure imposed by intensive herbicide usage in the prevalent no-till farming systems.

No abstract

Two introduced wild species Helianthus annuus L. and H. petiolaris Nutt. have become widespread in central Argentina and overlap the sunflower crop region. Intermediate off-type plants between the wild and cultivated species are often found, which is of concern because of the recent release of imidazolinone resistant varieties and the likely use of genetically modified sunflower cultivars. The progeny of 33 off-type plants obtained from 14 representative sites of the diffusion area were studied to confirm hybrid origin. Germination, survival, morphological traits and days to flowering confirmed hybridization between crop and both wild species, when compared to eight accessions of typical wild plants. Some progenies were presumably crop-wild H. annuus hybrids, some originated from the cross of cultivated plants and H. petiolaris, and two were the advanced generation of a cultivated hybrid. Hence, morphological traits are a good clue for the identification of spontaneous hybrid plants at field. The results indicate that crop-wild hybridization and introgression occur at various places in central Argentina. This fact may represent a way to herbicide resistance escape and future transgene escape if GM sunflower cultivars are released for commercial use.