Resistance of ryegrass (Lolium spp.) to paraquat and glyphosate in the Western Cape

Eksteen, Frederik Heinrich (2007-12)

Dissertation (PhD) -- University of Stellenbosch, 2007.

Thesis

ENGLISH ABSTRACT: The origin of this study dates back to 2001 when ryegrass (Lolium spp.) from a vineyard near Tulbagh was found by the author to be resistant to glyphosate. Several other populations of glyphosate resistant ryegrass were found on nearby farms. In attempts to eliminate what was initially thought to be a very localised resistance problem, paraquat was applied at several of these sites. It soon became apparent that significant numbers of these ryegrass populations were also resistant to paraquat. Populations that were susceptible to glyphosate but resistant to paraquat were also found. This was the first recorded incidence of paraquat resistance in ryegrass. Further screening of Western Cape ryegrass resulted in the identification of populations that showed multiple resistance to glyphosate, paraquat and ACCase inhibitors. In laboratory trials this study established that the mechanism which confers resistance to paraquat is based on the failure of the herbicide to reach its site of action in the plant. This lack of trans location was ascribed to sequestration of the active ingredient in a non-physiologically active site in the plant, such as the vacuole. This form of resistance was overcome by applying glufosinate ammonium, either prior to, or together with the paraquat application. The same degree of synergy was observed using photosystem II inhibitors with paraquat. The resistance mechanism is overcome by these products by either preventing paraquat from being 'sequestrated and/or freeing up of herbicide which had already been bound. Mixtures containing paraquat, glufosinate ammonium and a photosystem II inhibitor such as terbuthylazine gave the best control of resi~tant ryegrass populations. Independent confirmation, of the findings in the laboratory perfonned trials, was done in field trials, conducted during the 2007 season by Syngenta SA on paraquat resistant ryegrass populations in the Western Cape.

AFRIKAANSE OPSOMMING: Die oorsprong van die studie dateer terug na die jaar 2001 toe raaigras deur die outeur, vanuit 'n wingerd naby Tulbagh posetief getoets is vir weerstand teen glifosaat. Verskeie ander populasies van glifosaat weerstandbiedende raaigras is ook op nabygelee plase gekry. In 'n poging, in wat aanvanklik gedink is 'n baie gelokaliseerde weerstandsprobleem is, is paraquat toegedien op verskeie van die populasies. Dit het egter gou duidelik geword dat baie van die raaigras populasies ook bestand was teen paraquat. Raaigras populasies wat vatbaar is vir glifosaat maar weerstandbiedend teen paraquat is, is ook gevind. By verdere ondersoek na raaigras in die Wes-Kaap is daar ook populasies geldentifiseer wat veelvuldige weerstand getoon het teen glifosaat, paraquat en die ACCase inhibeerdes. In 'n laboratorium studie is vasgestel dat die meganisme wat verantwoordelik is vir die weerstand van paraquat, gebasseer is op die onvermoee van die onkruiddoder om die setel van werking in die plant te bereik. Die onvermoee van die onkruiddoder om in die plant getranslokeer te word kan toegeskryf word aan sekwistrasie van die aktiewe bestanddeel na 'n nie-fisiologies aktiewe setel in die plant soos die vakuool. Hierdie vorm van weerstand kan oorkom word deur die toediening van glufosinaat ammonium voor of saam met 'n paraquattoediening. Dieselfde graad van sinergie is ook gevind tussen die fotosisteem II inhibeersders en paraquat. Die weerstandsmeganisme is oorkom deur dat die produkte voorkom dat die paraquat gesekwistreer word en/of deur die onkruiddoder wat reeds vasgele is weer beskikbaar gemaak word. Mengsels van paraquat, glufosinaat ammonium en 'n fotosisteem II inhibeerder soos terbutilasien het die beste beheer gegee van die weerstandbiedende raaigraspopulasies. Die bevindings in die studie is onafhanklik bevestig gedurende die 2007 seisoen in veldproewe wat deur Syngenta SA uitgevoer is op paraquat weerstandbiedende raaigraspopulasies in die Wes-Kaap.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/50744
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