Fitness Outcomes Related to Glyphosate Resistance in Kochia (Kochia scoparia): What Life History Stage to Examine?

Abstract

A fast-spreading weed, kochia (Kochia scoparia), has developed resistance to the widely-used herbicide, glyphosate. Understanding the relationship between the occurrence of glyphosate resistance caused by multiple EPSPS gene copies and kochia fitness may suggest a more effective way of controlling kochia. A study was conducted to assess fitness cost of glyphosate resistance compared to susceptibility in kochia populations at different life history stages, that is rate of seed germination, increase in plant height, days to flowering, biomass accumulation at maturity, and fecundity. Six kochia populations from Scott, Finney, Thomas, Phillips, Wallace, and Wichita counties in western Kansas were characterized for resistance to field-use rate of glyphosate and with an in vivo shikimate accumulation assay. Seed germination was determined in growth chambers at three constant temperatures (5, 10, and 15 C) while vegetative growth and fecundity responses were evaluated in a field study using a target-neighborhood competition design in 2014 and 2015. One target plant from each of the six kochia populations was surrounded by neighboring kochia densities equivalent to 10 (low), 35 (moderate), or 70 (high) kochia plants m−2. In 2015, neighboring corn densities equivalent to 10 and 35 plants m−2 were also evaluated. Treatments were arranged in a randomized complete block design with at least 7 replications. Three kochia populations were classified as glyphosate-resistant (GR) [Scott (SC-R), Finney (FN-R), and Thomas (TH-R)] and three populations were classified as glyphosate-susceptible (GS) [Phillips (PH-S), Wallace (WA-S) and Wichita (WI-S)]. Of the life history stages measured, fitness differences between the GR and GS kochia populations were consistently found in their germination characteristics. The GR kochia showed reduced seed longevity, slower germination rate, and less total germination than the GS kochia. In the field, increases in plant height, biomass accumulation, and fecundity were not clearly different between GR and GS kochia populations (irrespective of neighbor density). Hence, weed management plans should integrate practices that take advantage of the relatively poor germination characteristics of GR kochia. This study suggests that evaluating plant fitness at different life history stages can increase the potential of detecting fitness costs.

Seedbank persistence, germination and early growth of glyphosate‐resistant Kochia scoparia

“…Kumar and Jha () determined that most GR K. scoparia populations from Montana also had delayed and reduced germination compared with GS populations at various temperature regimes. Moreover, similar findings were observed for GR and GS populations from Kansas (Osipitan & Dille, ).…”

“…The majority of GR K. scoparia populations from Montana had delayed and reduced germination at various temperature regimes compared with glyphosate‐susceptible (GS) populations (Kumar & Jha, ). Similar results were found in a study of populations from Kansas, USA (Osipitan & Dille, ). With the relatively recent occurrence of GR K. scoparia populations across western Canada, there is renewed interest in determining these basic weed biology data because of potential management implications.…”

Impact of Cover Crop Management on Level of Weed Suppression: A Meta‐Analysis

“…Globally, the adoption of cover crops is gaining more attention, especially in reduced and no-tillage systems, partly due to increasing interest in reducing the development of herbicide-resistant weeds, and enhancing the sustainability of agroecosystems (Teasdale, 1993;Dorn et al, 2015;SARE/CTIC, 2017). Cover crops could provide weed suppression physically through smothering (Hutchinson and McGiffen, 2000); ecologically through competition for limited resources such as nutrients, water, and light (Teasdale, 1996;Hartwig and Ammon, 2002;Mirsky et al, 2013;Adigun et al, 2014;Osipitan and Dille, 2017); or chemically through release of allelochemicals from living and dead biomass (Barnes et al, 1987;Weston, 1996;Caamal-Maldonado et al, 2001;Kunz et al, 2016). Cover crops could provide weed suppression physically through smothering (Hutchinson and McGiffen, 2000); ecologically through competition for limited resources such as nutrients, water, and light (Teasdale, 1996;Hartwig and Ammon, 2002;Mirsky et al, 2013;Adigun et al, 2014;Osipitan and Dille, 2017); or chemically through release of allelochemicals from living and dead biomass (Barnes et al, 1987;Weston, 1996;Caamal-Maldonado et al, 2001;Kunz et al, 2016).…”

Weed Interference and Control in Cowpea Production: A Review

“…The magnitude of yield depends on crop variety, weed density, type of weeds, weed persistence, duration of weed interference and crop management practices (Lagoke et al, 1982;Cousen, 1985;Kropff et al, 1992;Li et al, 2004;Milberg & Hallgren, 2004;Osipitan & Dille, 2017). For instance, among four cowpea cultivars examined by Nangju and Wanki (1980), the yield reductions due to weeds were 25% for VITA 1, 33% for VITA 5, 46% for ER-1 and 54% for TVX33-IG.…”