An Investigation of Tradeoffs in Herbicide Resistant Brassica rapa: Effects on Pollen and Ovule Production, Biomass and Development

For decades, herbicides have been used to control weeds and increase crop yields, a practice resulting in a growing number of weeds that are herbicide resistant. Like the problem of antibiotic resistance for medicine, herbicide resistant weeds present a significant agricultural challenge. To meet this challenge, we need management strategies informed by a more complete understanding of the biology of herbicide resistance. With this goal in mind we investigated tradeoffs in growth and reproduction of Atrazine Resistant (AR) versus Atrazine Susceptible (AS) Brassica rapa grown at two temperature regimes. Between the strains, tradeoffs were evident for pollen production and overall plant development. AS plants produced significantly more pollen per flower compared to AR plants. Additionally, development was significantly delayed in AR as compared to AS plants. Atrazine resistant plants took 20.5% longer than atrazine susceptible plants to produce their first true leaves, 13.0% longer to produce buds and 8% longer to produce the first flower as compared to the atrazine susceptible strain. Biomass, ovule count and pollen count were all greater in the cool treatment, however growth was significantly delayed as compared to the warm treatment. Plants in the cool treatment had significantly greater above ground biomass (26.5%) than plants in the warm treatment, but there was no effect of strain on biomass. Similarly, we found a significant effect of temperature, but not strain, on the average number of ovules produced per flower, with the warm treatment plants producing significantly fewer ovules than plants in the cool treatment. Warm temperatures also had a significant negative effect on pollen production. This study expands our understanding of tradeoffs associated with herbicide resistance to include effects on components of both male and female fitness.