Towards large‐scale prediction of Lolium rigidum emergence. II. Correlation between dormancy and herbicide resistance levels suggests an impact of cropping systems

Abstract

Owen MJ, Michael PJ, Renton M, Steadman KJ & Powles SB (2011). Towards large‐scale prediction of Lolium rigidum emergence. II. Correlation between dormancy and herbicide resistance levels suggests an impact of cropping systems. Weed Research51, 133–141.SummaryThis study investigated a possible link between seed dormancy and herbicide resistance status of Lolium rigidum (annual or rigid ryegrass). Mature seeds were collected from 406 populations across the 14‐million hectare grain belt of southern Western Australia. For each population, initial dormancy and change in dormancy over a 6‐month period were measured, and resistance status of seedlings to four herbicides (diclofop‐methyl, sethoxydim, clethodim and sulfometuron‐methyl) was assessed. Greater seed dormancy correlated with higher levels of herbicide resistance for all four herbicides tested. The herbicides represented two modes of action (acetyl CoA carboxylase‐ and acetolactate synthase inhibitors) and a contrast of generalist (metabolic) and target‐site mutation mechanisms. The coexistence of dormancy and herbicide resistance is suggested to be an adaptation to decades of intense cropping; the plants that are most likely to successfully reproduce are those that exhibit delayed germination (avoiding pre‐seeding weed control strategies) and possess herbicide resistance (surviving subsequent in‐crop herbicide application). We propose that herbicide resistance status may have a role as a predictive tool in modelling dormancy in L. rigidum at a large spatial scale.