Growth and Reproduction of Glyphosate-Resistant and Susceptible Populations of Kochia scoparia.

Vipan Kumar,Prashant Jha,Mark Gijzen

doi:10.1371/journal.pone.0142675

Abstract

Evolution of glyphosate-resistant kochia is a threat to no-till wheat-fallow and glyphosate-resistant (GR) cropping systems of the US Great Plains. The EPSPS (5-enol-pyruvylshikimate-3-phosphate synthase) gene amplification confers glyphosate resistance in the tested Kochia scoparia (L.) Schrad populations from Montana. Experiments were conducted in spring to fall 2014 (run 1) and summer 2014 to spring 2015 (run 2) to investigate the growth and reproductive traits of the GR vs. glyphosate-susceptible (SUS) populations of K. scoparia and to determine the relationship of EPSPS gene amplification with the level of glyphosate resistance. GR K. scoparia inbred lines (CHES01 and JOP01) exhibited 2 to 14 relative copies of the EPSPS gene compared with the SUS inbred line with only one copy. In the absence of glyphosate, no differences in growth and reproductive parameters were evident between the tested GR and SUS inbred lines, across an intraspecific competition gradient (1 to 170 plants m-2). GR K. scoparia plants with 2 to 4 copies of the EPSPS gene survived the field-use rate (870 g ha-1) of glyphosate, but failed to survive the 4,350 g ha-1 rate of glyphosate (five-times the field-use rate). In contrast, GR plants with 5 to 14 EPSPS gene copies survived the 4,350 g ha-1 of glyphosate. The results from this research indicate that GR K. scoparia with 5 or more EPSPS gene copies will most likely persist in field populations, irrespective of glyphosate selection pressure.

Highlights

Kochia scoparia (L.) Schrad. is a monoecious, diploid (2n = 18) weed species, prevalent across the northern and central Great Plains of North America [1,2,3]
The enolpyruvylshikimate3-phosphate synthase (EPSPS) gene copy number did not correlate with vegetative growth parameters, including plant height, canopy width, primary branches, total leaf area, and shoot biomass of GR or SUS K. scoparia, whether the plants were grown at intraspecific densities of 1 (Fig 1a, 1d, 1g, 1j, and 1m), 85 (Fig 1b, 1e, 1h, 1k, and 1n), or 170 (Fig 1c, 1f, 1i, 1l, and 1o) plants m-2
The amplified copies of the EPSPS gene in GR K. scoparia did not affect other enzymes involved in the shikimate pathway [14]

Summary

Introduction

(kochia) is a monoecious, diploid (2n = 18) weed species, prevalent across the northern and central Great Plains of North America [1,2,3]. It is one of the most problematic, summer annual broadleaf weeds in cropland and non-cropland areas of this region. A single plant can produce more than 100,000 seeds, and manifests a unique mechanism of seed dispersal through tumbling [3, 4]. A mature plant breaks off at the base of the stem and tumbles across the landscape with the prevailing wind, dispersing seeds over a long distance [3, 4]. Because of the PLOS ONE | DOI:10.1371/journal.pone.0142675 November 18, 2015

Objectives

Methods

Results

Conclusion