Seed Germination Ecology of South Eastern Australian Rigid Ryegrass (Lolium rigidum) Populations

Abstract

Herbicide resistance is an increasing issue in many weed species, including rigid ryegrass (Lolium rigidum Gaudin); a major weed of winter cropping systems in southern Australia. Recently, this weed has also been found in summer crops in the south eastern region of Australia. Effective control of this herbicide resistant weed across south eastern Australia requires alternative management strategies. These strategies can be informed from analyses on the interaction of germinable seeds with their regional environment and by identifying the differences between populations of varying herbicide resistance levels. In this study, we explore how various environmental factors differentially affect the seed germination and seedling emergence of three L. rigidum populations, including one glyphosate-resistant population (GR), one glyphosate-susceptible population (GS) and one population of unknown resistance status (CC04). Germination was greater than 90% for all populations at each temperature regime except 15/5 C. Populations germinated at a lower rate under 15/5 C, ranging from 74 to 87%. Salt stress had a similar effect on the germination of all populations, with 0% germination occurring at 250 mM salt stress. Population GS had greater tolerance to osmotic stress with 65% germination at −0.4 MPa compared to 47% and 43% germination for CC04 and GR, respectively; however, germination was inhibited at −0.8 and −1.6 MPa for all populations. All populations had lower germination when placed in complete darkness as opposed to alternating light/dark. Germination in darkness was lower for CC04 (69%) than GR (83%) and GS (83%). Seedling emergence declined with increasing burial depth but retained 37% emergence at 8 cm when averaged over the populations. These results indicate that L. rigidum Gaud. can survive under a range of environmental variables and the extent of survival differs based on population, however, there was no difference based on herbicide resistance status.

Influence of burial depth and soil disturbance on the emergence of common weed species in the Iberian Peninsula

“…The seed densities chosen ensured enough seedling emergence to properly characterize emergence patterns with individual seedlings representing a small fraction of the cumulative emergence (∼ 0.2% to 7%). Seedling recruitment in the present study was similar to or higher than other experiments conducted under similar conditions (Nosratti et al 2017; Thompson et al 2021).…”

A Comparison of Germination Responses on Italian Ryegrass (diploid vs tetraploid) Seeds to Interactive Effects of Salinity and Temperature

“…[13,27,28] studies about P. turgidum, Leymus chinensis and Lolium multiflorum noted similar trends with this study. Previous studies have shown there is usually a negative correlation between salt tolerance and germination percentage in Lolium species [29,30,31]. Germination energy, which is called the first few days of the germination stage, in higher temperature affects more negatively than salt levels in this study.…”

Differential response of winter- and summer-emerging accessions of rigid ryegrass (Lolium rigidum Gaudin) to postemergence herbicides in Australia

“…A recent Australian study reported that rigid ryegrass accessions can germinate across a wide range of diurnally fluctuating temperatures, from 15/5 C to 35/25 C (day/night temperatures) (Thompson et al 2021). More than 90% of seeds germinated at 30/20 C and 35/25 C, suggesting that this weed could germinate in the summer months in Australia provided that soil moisture is sufficient.…”

“…More than 90% of seeds germinated at 30/20 C and 35/25 C, suggesting that this weed could germinate in the summer months in Australia provided that soil moisture is sufficient. Although rigid ryegrass is a well-recognized problem in winter crops and winter fallow, there are recent reports of its occurrence in summer crops (e.g., cotton) and summer fallow in the southeastern region of Australia (Thompson and Chauhan 2022;Thompson et al 2021).…”