Ozone Enhances Adaptive Benefit of Glyphosate Resistance in Horseweed (Conyza canadensis)

Abstract

Since the first identification of glyphosate resistance in horseweed in California in 2005, the glyphosate-sensitive (GS) biotype has become rare, whereas the glyphosate-resistant (GR) biotype has become dominant in the eastern San Joaquin Valley (SJV). This is an area exposed to regular usage of glyphosate and to high levels of ambient ground-level ozone (O3). A previous study showed that SJV biotypes of GR are more robust than GS in the absence of ozone. This advantage was reduced, though not eliminated, at elevated O3. This suggests that the rapid evolution of resistance to glyphosate was not linked to evolution of resistance to O3. In this study, we contrasted these responses to O3 in the presence of concurrent glyphosate pressure. The GR and GS biotypes differed in growth and injury, reflecting their known differential sensitivities to glyphosate, but responded similarly to O3 with no O3 × biotype interaction. Ozone imposed an unexpected, but ecologically important, impact that enhanced the performance advantage of GR over GS. In the presence of the combination of glyphosate and O3 the biomass of GR was reduced to low but viable levels, whereas the biomass of GS was reduced to nonviable levels that effectively removed it from the population. These data do not support a genetic linkage between resistance to glyphosate and to O3, but suggest that air pollution may have accelerated the fixation of glyphosate-resistance alleles in California horseweed populations.

Diel trends in stomatal response to ozone and water deficit: a unique relationship of midday values to growth and allometry in Pima cotton?

“…) were located in the greenhouse, as previously described (Grantz et al . , ) and illuminated with natural sunlight. Air with appropriate O 3 concentration (4, 59 and 114 ppb; 12‐h means, 07:00–19:00 h) was introduced at one complete air exchange per minute into each CSTR.…”

“…At 10 or 12 days after planting (DAP; Run 1 or 2, respectively), when cotyledons were fully expanded and the first true leaf was emerging, two pots were transferred to each of nine cylindrical, Teflon O 3 exposure chambers. These chambers (continuously stirred tank reactors, CSTRs; Heck et al 1978) were located in the greenhouse, as previously described (Grantz et al 2008(Grantz et al , 2010 and illuminated with natural sunlight. Air with appropriate O 3 concentration (4, 59 and 114 ppb; 12-h means, 07:00-19:00 h) was introduced at one complete air exchange per minute into each CSTR.…”

“…Ozone was generated by corona discharge (Model SGC-11; Pacific Ozone Technology, Brentwood, CA, USA) from purified oxygen (Series ATF-15, Model 1242; SeQual Technologies Inc., San Diego, CA, USA) and regulated in a single CSTR with a dedicated O 3 monitor (Model 49C; Thermo Fisher Scientific, Waltham, MA, USA), with computerised feedback control (Grantz et al 2008). The O 3 concentrations in the other CSTRs were maintained proportionally and determined every 15 min with a separate O 3 monitor (Model 49C) through continuously purged Teflon dust filters and tubing.…”

Climate change and weed adaptation: can evolution of invasive plants lead to greater range expansion than forecasted?

“…, 2005). Glyphosate‐resistant alleles were fixed more rapidly in Conyza canadensis (L.) Cronquist (horseweed) in the San Joaquin Valley of California, USA, when exposed to elevated ozone levels, illustrating how selection for multiple traits may promote range expansion under changing environmental conditions (Grantz et al. , 2008; Table 2).…”

Invasive herbaceous respond more negatively to elevated ozone concentration than native species

“…Competition can often interact with other abiotic factors (Larson et al, 2018; Low‐Décarie et al, 2011) and is affected by elevated O 3 concentration (McDonald et al, 2002; Scebba et al, 2006). Moreover, invasive weeds in weed–crop experiments are more tolerant to O 3 , thereby resulting in greater competitive success of specific crop species (Grantz et al, 2006,2008,2019; Paudel et al, 2016; Shrestha & Grantz, 2005). Therefore, it is important to consider the potential interaction between competition and O 3 when assessing plant invasiveness.…”