Understanding Lolium rigidum Seeds: The Key to Managing a Problem Weed?

Abstract

The 40 million hectare southern Australian winter cropping region suffers from widespread infestation by Lolium rigidum (commonly known as annual or rigid ryegrass), a Mediterranean species initially introduced as a pasture plant. Along with its high competitiveness within crops, rapid adaptability and widespread resistance to herbicides, the dormancy of its seeds means that L. rigidum is the primary weed in southern Australian agriculture. With the individuals within a L. rigidum population exhibiting varying levels of seed dormancy, germination can be staggered across the crop-growing season, making complete weed removal virtually impossible, and ensuring that the weed seed bank is constantly replenished. By understanding the processes involved in induction and release of dormancy in L. rigidum seeds, it may be possible to develop strategies to more effectively manage this pest without further stretching herbicide resources. This review examines L. rigidum seed dormancy and germination from a weed-management perspective and explains how the seed bank can be depleted by control strategies encompassing all stages in the lifecycle of a seed, from development to germination

Resistance to herbicides inhibiting the biosynthesis of very‐long‐chain fatty acids

“…Lolium rigidum in Australia is often present in crop fields, and herbicide resistance, since first reported, now extends to many herbicides and is very widespread across the Australian grain‐growing regions . The genus Lolium was introduced into Australia from southern Europe as a pasture plant and over the past 200 years has been repeatedly selected for highly productive varieties adapted to local Australian conditions …”

“…58 -61 The genus Lolium was introduced into Australia from southern Europe as a pasture plant wileyonlinelibrary.com/journal/ps and over the past 200 years has been repeatedly selected for highly productive varieties adapted to local Australian conditions. 62 In Australia the first documented case of resistance in L. rigidum to the herbicide diclofop-methyl (ACCase inhibitor, group A) was reported in 1982, 57 with subsequent characterisation of cross-resistance between group A and B herbicides in 1986. 63 This population was herbicide selected in the field by repeated use of trifluralin (one application per growing season over 10 years), followed by four applications of trifluralin and diclofop (one application per year).…”

RIM: Anatomy of a Weed Management Decision Support System for Adaptation and Wider Application

“…Shallow cultivation only stimulates the germination of ryegrass without control, whereas moulboard ploughing is a radical option targeting both ryegrass plants and seedbank, almost resetting the ryegrass population size to zero. For simplicity, given the relatively short life span of ryegrass seeds (Goggin et al 2012), neither differential seed redistribution throughout the soil profile nor cultivation depths were modelled. However, the possibility of returning buried viable seeds to the surface was taken into account with a lower proportion of kill when the duration between two ploughs was not sufficient to allow for natural mortality to fully occur (i.e., 3 yr).…”

A “Stressed” Alfalfa-Based Cropping System Leads to the Selection of Quizalofop-Resistant Italian Ryegrass (Lolium perennessp.multiflorum)

“…are prone to rapidly evolve resistance under herbicide selection pressure because of the combination of three characteristics: high genetic variability, adaptability, and fecundity (Gill et al 1996;Holt et al 2013). Moreover, they produce dense and highly competitive infestations (Lemerle et al 2001), have a weak dormancy (Goggin et al 2012), and seed production can be as high as a few thousand seeds per plant (Pedersen et al 2007), with up to 45,000 seeds m À2 (Rerkasem et al 1980). However, the seed longevity of Lolium spp.…”