Assessment of Brassica napus gene flow potential to wild relatives in northern South Africa

Abstract

The Brassicaceae, distributed throughout South Africa, is a family in which hybridization may occur between cultivated species and its wild and weedy relatives. Hybridization with transgenic varieties could increase the potential invasiveness and weediness of a species by conferring beneficial transgenic traits to the F1 generation. Gene flow from transgenic Brassica napus to related genera is highly likely since these related genera occur frequently throughout South Africa. While no transgenic B. napus is approved for cultivation in South Africa, glyphosinate tolerant B. napus is imported as food and feed. This study aimed to assess the likelihood of gene flow from B. napus to adjacent reproductively compatible populations with emphasis placed on their spatial distribution and overlap in populations should transgene escape occur. This study will contribute to future risk assessments of transgenic B. napus for cultivation in South Africa. The spatial distribution of the Brassicaceae throughout the northern provinces of South Africa was determined with the use of specimen data collected from 12 major herbaria. Seventy-six Brassicaceae species from 23 genera and 10 tribes were identified. These are widespread in the entire study area, with the most species found where (1) anthropological activity is the highest, (2) rainfall is above 300 mm, and (3) when located within the Dry Highveld Grassland and Mesic Highveld Grassland bioregions. Ten species were identified as reproductively compatible with B. napus. Five phytochoria were identified for the distribution of the Brassicaceae based on rainfall and mountainous environments. Four criteria were used to determine which reproductively compatible species presented the highest likelihood for gene flow to occur. Prevalence, spatial overlap, gene flow rate and distribution by anthropological activities, were identified from the literature and standardized for quarter degree grid cell data, and scored in order to identify high risk areas. The area presenting the highest risk for potential gene flow to occur was Gauteng followed by a high risk area stretching from the north-east of the study area along the eastern border through to the south-east. Possible implications of gene flow between transgenic B. napus and its reproductively compatible relatives were identified, and mitigation strategies suggested. Further studies is required on the potential for gene flow to occur between B. napus and its reproductively compatible relatives that are indigenous to South Africa.