Mr Rajesh Barua

Herbicide Resistance in Winter Grass (Poa annua) and its Management

Supervisors: Prof Christopher Preston, A/Prof Gurjeet Gill and Dr. Peter Boutsalis

Poa annua, also commonly known as annual meadow grass, winter grass or bluegrass, belongs to the family Poaceae and is a common weed wherever cool-season turf-grasses are grown. It is a problematic weed of turf worldwide due to its unsightly appearance, competition with desirable species, and its upright growth habit producing an uneven surface that affects ball roll in golf and other sports. It is also present as a weed in 38 crops such as vegetables, cereals, sugar beet, potatoes, and orchards in 80 countries. This species is usually controlled by herbicides in turf. However, in the recent years, herbicide resistance has been identified in P. annua. In Australia, resistance to 5 herbicide modes of action has been identified in populations of P. annua collected from golf courses including: ALS inhibitors, Photosystem II inhibitors, tubulin biosynthesis inhibitors, glyphosate and endothall. Although there are several previous studies on herbicide resistance in P. annua, there is limited information available on the mechanisms of resistance to herbicides in this species. The aim of this study is to identify the extent of resistance and the mechanisms of resistance associated with herbicide resistance in P. annua and also develop alternate management strategy.

The main objectives of this project are to:

* Screen P. annua populations for resistance to different herbicide groups

* Undertake detailed dose-response experiments to assess the level of resistance (LD50 and GR50) in different P. annua populations

* Explore the herbicide resistance mechanism including the mutations that confer resistance by sequencing target enzymes as well as non-target site mechanisms where needed

* Identify the mode of inheritance of herbicide resistance of different herbicide groups by segregation of crosses

* Determine the fitness penalty for resistance to different herbicide groups in F2 populations developed from crosses between R and S populations

* Identify alternate herbicides to control the resistant P. annua populations

This project will provide comprehensive information on the nature of resistance to the different herbicides in P. annua and the extent of resistance in turf across Australia. This will help determine management options by suggesting possible approaches to management, including non-chemical approaches where appropriate. Resistance is now suspected in P. annua to propyzamide, which has become an extremely important herbicide for the control of multiple herbicide resistant Loilum rigidum populations. Lessons learned from research on propyzamide resistant P. annua could be highly useful for the management of herbicide resistant L. rigidum in the future.