Characterizing Genetic Factors Involved in 2,4-D Resistance using the Red Clover

2,4-Dichlorophenoxyacetic acid (2,4-D), the first herbicide that selectively controlled dicot species, is an important weedicide against broad-leaf weeds. Despite being used for more than 70 years, the precise molecular mode of action of 2,4-D has been poorly understood. Several dicot weeds species have been reported to show resistance to 2,4-D and with the new releases of 2,4-D resistant engineered crops, this is expected to increase. Further, exploring the genetics underpinning 2,4-D resistance in naturally occurring resistant species can help enlighten molecular biology as well as generate resistant cultivars without the need of transgenic system. This study is aimed towards characterizing the genes involved in a 2,4-D resistant Trifolium pratense L. (red clover) developed using conventional breeding approach. The University of Florida Forage Breeding Program has just released a 2,4-D resistant cultivar, FL24D, using recurrent phenotypic selection (6 cycle, C0 : C6). In order to locate the resistance imparting genes, we bulk sequenced the base population (C0, susceptible) and FL24D (C6, resistant). Subsequently, with the help of draft red clover genome assembly, we identified genomic regions showing significant shift in the allele frequency from the C0 to C6 generation. Initial comparative genomic analysis has shown presence of auxin pathway genes in the vicinity of the regions of interest. These regions can prove useful for marker-assisted breeding of 2,4-D resistance into elite cultivars.  Further studies are ongoing to validate the candidate genes which can help discern the biology behind 2,4-D resistance in the red clover. Such knowledge can provide insight into the molecular mechanism of 2,4-D in dicots and can significantly contribute towards understanding and control of evolution of weeds resistant to 2,4-D. Results and discussion of these study will be presented.