Weed Research (2015) 55, 173-184

M. Okada, B.D. Hanson, K.J. Hembree, Y. Peng, A. Shrestha, C.N. Stewart Jr., S.D. Wright and M. Jasieniuk (2015)
Evolution and spread of glyphosate resistance in Conyza bonariensis in California and a comparison with closely related Conyza canadensis
Weed Research 55 (2), 173-184
Abstract: Glyphosate-resistant weeds are an increasing problem in perennial cropping systems in the Central Valley of California, USA. To elucidate the evolutionary origins and spatial spread of resistance, we investigated the geographical distribution of glyphosate resistance and the population genetic diversity and structure of Conyza bonariensis and compared the results with previously studied C. canadensis. Thirty-five populations from orchards and vineyards across the Central Valley were sampled. Population genetic structure was assessed using microsatellite markers. Population-level resistance was assessed in glasshouse screening of plants grown from field-collected seed. Bayesian clustering and analyses of multilocus genotypes indicated multiple origins of resistance, as observed in C. canadensis. Pairwise F_ST analysis detected spatial spread of resistance in the south of the Central Valley, also similar to C. canadensis. The results strongly indicate that the southern valley was an environment markedly more suitable than the northern valley for resistance spread and that spread in Conyza species was driven by increased uniformity of strong selection in the southern valley, due to recent regulation on herbicides other than glyphosate. Accordingly, resistant C. canadensis individuals occurred at high frequencies only in the southern valley, but interestingly resistant C. bonariensis occurred at high frequencies throughout the valley. Expression of resistance showed varying degrees of plasticity in C. bonariensis. The lower selfing rate and substantially greater genotypic diversity in C. bonariensis, relative to C. canadensis, indicate greater evolutionary potential over shorter time periods. Interspecific hybridisation was detected, but its role in resistance evolution remains unclear.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): Marie Jasieniuk, Anil Shrestha

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Erigeron canadensis (weed)
	Erigeron bonariensis (weed)		U.S.A. (SW)