Dispersal and genetic variability of Sonchus oleraceus L. in relation to its resistance to ALS-inhibiting herbicides.

Abstract

The work described in this thesis investigates the existence and level of acetolactate synthase (ALS)-inhibiting herbicide resistance in Sonchus oleraceus in Australia. It further discusses the sensitivity of different S. oleraceus populations to different dose rate treatments of the ALS-inhibiting herbicide, chlorsulfuron. Thirdly the movement or not of the resistance gene between S. oleraceus plants. Gene movement is investigated in light of S. oleraceus being self pollinated and possessing a wind dispersed seed. Finally using molecular tools the genetic diversity and seed movement in S. oleraceus is investigated. Although much is known about the evolution of plant based genetic resistance to herbicides there is less known as to the specific resistance gene movement in differing weed species. The first approach undertaken in this study was to collect a broad spectrum of S. oleraceus seed from a number of Australian states and test the progeny from this seed for resistance to chlorsulfuron. Subsequent to this DNA extractions were made from S. oleraceus plant material for use in AFLP and sequencing techniques. The results of this study indicate that ALS-inhibiting herbicide resistance to chlorsulfuron in S. oleraceus is now widespread in Australia. The movement of the resistance gene within populations is low (<4%), however, population dendrograms indicate seed has been dispersed across large distances in Australia facilitating the movement of the resistance gene. In addition sequence analysis indicates numerous independent mutation events. With the identification of previously unknown levels of resistance in Australia and gene movement knowledge, extension of improved management practises is possible.