Lolium rigidum

Resistance to the herbicide pyroxasulfone is slowly but steadily increasing in agricultural weeds. The evolved resistance of one Lolium rigidum population has been attributed to…

We have previously demonstrated that an aldo-keto reductase (AKR) from Echinochloa colona (EcAKR4-1) can metabolize glyphosate and confers glyphosate resistance. This study aims to investigate if the EcAKR4-1 orthologs from Lolium rigidum also play a role in glyphosate resistance in non-target-site based, glyphosate-resistant (R) L. rigidum populations from Western Australia.

Lolium rigidum 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.

Lolium rigidum (annual ryegrass) is a species that is prone to evolve resistance to a wide range of herbicide modes of action. Rapid detection of herbicide-resistant weed populations in the field can aid farmers to optimise the use of effective herbicides for their control.

The herbicide pyroxasulfone was widely introduced in 2012, and cases of evolved resistance in weeds such as annual ryegrass (Lolium rigidum Gaud.) and tall waterhemp [Amaranthus tuberculatus (Moq.) Sauer] have started to emerge.

AHRI researchers have show in this report that a single P450 gene in a cross-pollinated weed species L. rigidum confers resistance to herbicides of at least five modes of action across seven herbicide chemistries.

Most Australian crop farm populations of the grass weed Lolium rigidum are multiple herbicide-resistant. Most resistant populations exhibit target site mutations (e.g. ACCase, ALS), as well as metabolic resistance due to cytochrome P450, catalysed by enhanced rates of herbicide metabolism.

Cinmethylin is a new (old) herbicide being commercialised by BASF that is pre-emergent selective in wheat. Cinmethylin has been shown to be an inhibitor of acyl ACP thioesterase (Campe et al 2018).

The research by AHRI PhD student Jinyi Chen (now Dr Jinyi Chen!) documents both target site and non-target site resistance to dinitroaniline herbicides in Lolium individuals. We are long accustomed to documenting multiple mechanisms of resistance existing within Lolium individuals/populations because of the high genetic diversity and obligate cross-pollination between Lolium which enables multiple resistance mechanisms to be a frequent occurrence.  In this particular Lolium population, resistance to dinitroaniline herbicides is due to a mutation in the alpha tubulin gene (Val-202-Phe) and non-target site enhanced rates of dinitroaniline herbicide trifluralin metabolism.   Unequivocal evidence for the target site Val-202-Phe mutation endowing resistance was obtained by expressing in transgenic rice, where it endowed resistance.

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, the researchers investigated the genetic control of trifluralin resistance in a well-characterised Lolium rigidum Gaud. (annual ryegrass) 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.