Files
Abstract
White clover (Trifolium repens L.) is a key pasture legume in temperate regions worldwide. The high protein content of white clover herbage makes it an ideal component of pastures to complement grasses. In addition, its ability to fix atmospheric nitrogen improves soil fertility. The breeding efforts for white clover have been focused on improving yield, persistence, disease resistance, and abiotic stress tolerance. There isn’t much research on improving herbicide resistance in white clover. Therefore, the choice of herbicides as chemical weed control in white clover is very limited. Selective post-emergence herbicides are needed as emerging clover seedlings development is slow and not competitive with faster-growing weeds. In this study, we developed 2,4-D tolerant white clover through mutation breeding and recurrent phenotypic selection. We also performed transcriptomic analysis to find candidate genes responsible for 2,4-D tolerance in white clover. A local white clover ecotype “Durana” was used as recipient of EMS mutation. The concentration of 0.4% EMS resulted in a 72.3% germination rate, indicating it was the optimal dose. An effective dose (ED90) of 2241.7 g ae ha-1 2,4-D was determined and used to screen mutagenized seedlings in the greenhouse. Surviving plants were crossed back with “Durana” plants to create a base population for recurrent selection. After 6 cycles, the survival rate following a 2,4-D rate (4483.4 g ae ha-1) that was two times the ED90 reached 80%. Field and greenhouse experiments comparing resistance levels of the mutant population and three commercial cultivars (“Durana”, Renovation, and Regalgraze) showed greater resistance in the experimental population, with GR50 values of 1785.03 g ae ha-1 and 3240.61 g ae ha-1 in the greenhouse and field trials, respectively. A genetic gain of 9% per cycle was observed in cycles 6 and 9. This study demonstrates that EMS mutagenesis and recurrent selection are effective methods for inducing 2,4-D tolerance in white clover. Transcriptome analysis of 2,4-D tolerant (Experimental cycle 6) white clover and susceptible (“Durana”) revealed stress response, metabolism, and photosynthesis-related genes are responsible for 2,4-D resistance in white clover.