Zarka Ramiz

Brome grass (Bromus diandrus) is a winter annual weed with similar growth habits to wheat. Native to Europe and Mediterranean regions, brome grass is found in southern Australian cropping regions typified by cool, wet winters and hot dry summers. Annual ryegrass (Lolium rigidum) was originally introduced as a pasture species, and is now one of the most persistent and troublesome weeds in the southern Australian cropping system. These annual weeds typically emerge at the same time as crop seedlings.

Historically, herbicides are an efficient way of controlling crop weeds but their continual use is selecting for weeds survivors, which then dominate the population and become problematic for growers. Surviving weeds may be able to enzymatically detoxify the herbicide, or they may contain an altered herbicide target site that prevents the herbicide from binding, or perhaps another mechanism of resistance is present. Greater weed seed dormancy is also being selected for by long-term use of herbicides, because these weeds physically avoid the herbicide treatment. For this situation, studies on seed germination ecology are valuable.

Weed ecology and germination patterns of problematic weeds have been studied previously. However, none have asked why there is so much variation in germination percentages and emergence patterns, between different populations of the same species, nor how these are controlled at the genetic level. The question of if there are genes responsible for causing germination variation among these populations is yet to be answered. This research will focus on brome grass and ryegrass seed behaviour under conditions of ecological stress, their germination percentages, genetic factors influencing dormancy and differing between early and late germinating weed seeds, and how best to control them.
The study objectives are to:
• Investigate germination percentages and emergence patterns over time for germinating ryegrass and brome grass populations, within different rainfall zones;
• Determine the biochemical basis of dormancy in populations with delayed emergence;
• Identify genes involved in dormancy for brome grass and ryegrass;
• Deduce strategies for more effective control of brome grass and ryegrass when using pre-emergent herbicides.
Knowledge gained from this project will assist with the development of effective integrated weed management (IWM) strategies to slow the rate of resistance evolution and to successfully manage already resistant ryegrass and brome grass populations.