A New Red Clover 2,4-D-Resistant Cultivar to Improve Broadleaf Weed Control and Elucidate the Molecular Mechanism of Resistance

Abstract

Using recurrent phenotypic selection we have developed a red clover (Trifolium pratense L.) cultivar (FL24D) resistant to 2,4-Dichlorophenoxyacetic acid (2,4-D) after six cycles. Approximately 20,000 seeds were broadcast seeded into metal flats and sprayed with 1.1 kg a.i. ha^-1 2,4-D at 4 week (3 trifoliate leaf stage). One month later, 385 (1.95 %) plants were selected for intercrossing. Selection criteria were based on survival and regrowth. Following cycles were based on recurrent half-sib selection. While standard red clover cultivars (susceptible to 2,4-D) died after the recommended 2,4-D application rates, FL24D established a stand with no decrease in total yield relative to the unsprayed treatment. Under unsprayed conditions, FL24D presented one of the highest yields compared to commercially available cultivars. Additionally, FL24D is earlier in spring growth than any other known cultivar in the market. Despite the economic importance of 2,4-D and its use for more than 60 years, remarkably little is known about the underlying genetic architecture or the genetic process by which resistance is acquired in plants. Using remnant seed from the cultivar development, cycle 0 (susceptible) through cycle 6 (resistant), we are studying both the process of acquired resistance and the molecular mechanism involved in such resistance.