Lolium rigidum

The obvious evolutionary reality is that persistent use of harvest weed seed control (HWSC) is a selection pressure for any mechanisms enabling L. rigidum seed to avoid HWSC. For example, seed shatters before grain harvest or a greater percentage of retained seed at a height below that at which the crop is cut in the harvesting operation.

Weed control failures due to herbicide resistance are an increasing and worldwide problem significantly impacting crop yields. Metabolism-based herbicide resistance (referred to as metabolic resistance) in weeds is not well characterized at the genetic level.

Problem weeds in agriculture, such as Lolium rigidum Gaud., owe some of their success to their large and dormant seed banks, which permit germination throughout a crop-growing season. Dormant weed seed banks could be greatly depleted by application of a chemical that stimulates early-season germination and then kills the young seedlings. Fluridone, a phytoene desaturase-inhibiting herbicide that can also break seed dormancy, was assessed for its efficacy in this regard.

The auxinic herbicide 2,4-D amine is known, in vitro, as a cytochrome P450 inducer. The current study uses 2,4-D pre-treatment, at the whole plant level, to study mechanism(s) of non-target site based herbicide resistance to the ACCase-inhibiting herbicide diclofop-methyl in Lolium rigidum.

The potential for low rates of diclofop-methyl to result in rapid evolution of herbicide resistance in a herbicide-susceptible Lolium rigidum (annual ryegrass) population was demonstrated in a recent cropfield study.

A wild population of a plant species, especially a cross-pollinated species, can display considerable genetic variation. Genetic variability is evident in differential susceptibility to an herbicide because the population can show continuous phenotypic variation.

α-Amylase in grass caryopses (seeds) is usually expressed upon commencement of germination and is rarely seen in dry, mature seeds. A heat-stable α-amylase activity was unexpectedly selected for expression in dry annual ryegrass (Lolium rigidum) seeds during targeted selection for low primary dormancy.

Pyroxasulfone is a new pre-emergence herbicide that provides effective control of Lolium rigidum, including populations with evolved resistance to multiple herbicide modes of action.

Sequestration of paraquat away from its target site in the chloroplast has been proposed as a mechanism of paraquat resistance. However, no consensus has been reached as to where paraquat is sequestered. This study quantifies paraquat in leaf protoplasts of paraquat resistant (R) and susceptible (S) Lolium rigidum.

Twenty-two amino acid substitutions at seven conserved amino acid residues in the acetohydroxyacid synthase (AHAS) gene have been identified to date that confer target-site resistance to AHAS-inhibiting herbicides in biotypes of field-evolved resistant weed species.