A dinitroaniline herbicide resistance mutation can be nearly lethal to plants

Background

Lolium rigidum (annual ryegrass) is the most important weed in Australian agriculture and the pre-emergence dinitroaniline herbicides (e.g. trifluralin) are widely and persistently used for Lolium control. Consequently, resistance evolution to dinitroaniline herbicides has been increasingly reported.

Resistance-endowing target-site 𝛼-tubulin gene mutations are identified with varying frequencies. The present study investigated the putative fitness cost associated with the common resistance mutation Val-202-Phe, and the rare resistance mutation of Arg-243-Met causing helical plant growth.

Results

Results showed a deleterious effect of the Arg-243-Met mutation on fitness when plants are homozygous for this mutation. This was evidenced as high plant mortality, severely diminished root and aboveground vegetative growth (lower relative growth rate) and very poor fecundity when compared to the wild type, which led to a nearly lethal fitness cost of > 99.9% in competition with a wheat crop. A fitness penalty in vegetative growth was evident, but to a much less extent, in plants heterozygous for the Arg-243-Met mutation. In contrast, plants possessing the Val-202-Phe mutation exhibited a fitness advantage in vegetative and reproductive growth.

Conclusion

The α-tubulin mutations Arg-243-Met and Val-202-Phe incur contrasting effects on fitness. These results help understand the absence of plants homozygous for the Arg-243-Met mutation and the high frequency of plants carrying the Val-202-Phe mutation in dinitroaniline resistant L. rigidum populations. The α-tubulin Arg-243-Met mutation can have an exceptional fitness cost with nearly lethal effects on resistant L. rigidum plants.