Genetic inheritance of dinitroaniline resistance in an annual ryegrass population

The increasing number of weedy species resistant to dinitroaniline herbicides warrants studies on the evolutionary factors contributing to resistance evolution, including genetic inheritance of resistance traits. In this study, we investigated the genetic control of trifluralin resistance in a well-characterised Lolium rigidum Gaud. population from Western Australia. This population was purified to contain plants homozygous for the Val-202-Phe α-tubulin mutation, and used as the resistant (R) parents and crossed with susceptible (S) parents to produce eight reciprocal F1 families. Trifluralin dose response curves of the eight F1 families indicate that trifluralin resistance in this population is inherited as an incomplete recessive nuclear trait. The F1 plants were crossed within each families to establish eight pseudo-F2 (ψ-F2) families. Segregation ratio of resistance and susceptibility in ψ-F2 families were determined using the discriminating trifluralin rates of 120 and 480 g a.i. ha^-1. At 480 g a.i. ha^-1 trifluralin, the segregation ratio in almost all ψ-F2 families (except one) was fit to 1:3 (resistance: susceptibility) one recessive gene control model. However, at 120 g a.i. ha^-1 trifluralin, the segregation ratios in half of the families did not fit this model, indicating involvement of one or more genes in resistance at the lower rate. These results showed complexity of genetic inheritance of trifluralin resistance in this L. rigidum population possessing the Val-202-Phe α-tubulin mutation.