In Australia, glyphosate resistance has been observed in rigid ryegrass in several states including New South Wales (NSW) and South Australia (SA). Several populations of glyphosate-resistant rigid ryegrass were analyzed for the inheritance of glyphosate resistance. Eight glyphosate-resistant populations were crossed to the same susceptible population to create first filial generation (F₁) families. Individuals from the F₁ families were subsequently treated with glyphosate. The response to glyphosate of F₁ families from all eight crosses was more similar to the resistant parent than the susceptible parent. Within crosses, dose responses of reciprocal F₁ families were not significantly different from each other, indicating glyphosate resistance is encoded on the nuclear genome in all eight populations. The level of dominance observed in dose–response experiments ranged from partial to total within the herbicide doses tested. F₁ individuals from five of the populations were crossed with susceptible (S) individuals to create backcross (BC) populations. Most of the families from these BC populations segregated in a manner consistent with a single gene controlling glyphosate resistance. These results indicate that resistance is inherited as a single dominant allele in four out of the five glyphosate-resistant rigid ryegrass populations. Such information is vital in the development of management strategies for glyphosate resistance in Australia.

Nomenclature: Glyphosate; rigid ryegrass, Lolium rigidum Gaud. LOLRI.