A Pro₁₀₆to Ala Substitution is Associated with Resistance to Glyphosate in Annual Bluegrass (Poa annua)

Abstract

Glyphosate is used in the transition zone to control annual bluegrass in fully dormant warm-season grasses. A suspected resistant (R) biotype of annual bluegrass was identified on a golf course in South Carolina after at least 10 consecutive years of glyphosate application. Greenhouse bioassays revealed the R biotype was 4.4-fold resistant to glyphosate compared with a standard susceptible (S) biotype. Further studies were conducted to investigate the mechanism conferring glyphosate resistance in the R biotype. Leaf discs of both biotypes accumulated shikimate in response to increasing glyphosate concentration, but the glyphosate concentration resulting in 50% EPSP synthase inhibition as a result of shikimate accumulation (I50) was 4.2-fold higher in the R biotype compared with the S biotype. At the whole plant level, similar levels of shikimate accumulation were observed between biotypes at 6 and 24 h after treatment (HAT) with glyphosate, but greater shikimate accumulation occurred in the S biotype at 72, 120, and 168 HAT. Shikimate levels decreased in the R biotype after 72 HAT. There were no differences in14C-glyphosate absorption between biotypes. However, more14C-glyphosate translocated out of the treated leaf in the R biotype and into root tissues over time compared with the S biotype. Partial sequencing of the EPSP synthase gene revealed a point mutation that resulted in an Ala substitution at Pro106. Although other mechanisms may contribute to glyphosate resistance, these results confirm a Pro106to Ala substitution is associated with resistance to glyphosate in the R annual bluegrass biotype.

Multiple target site resistance to glyphosate in junglerice (Echinochloa colona) lines from California orchards

“…The range of resistance levels reported in E. colona worldwide and among the populations screened in this study may reflect the role of different mechanisms contributing to resistance. For example, reduced translocation of glyphosate in the plant generally confers a higher level of resistance than is observed with target site mutations and more than one mechanism of resistance may be present within a plant …”

First Resistance Mechanisms Characterization in Glyphosate-Resistant Leptochloa virgata

“…Other glyphosate-resistant grass weeds such as: Bromus diandrus, Echinochloa colona, Eleusine indica, Lolium perenne spp. multiflorum, L. rigidum, Poa annua , among others (González-Torralva et al, 2012; Alarcón-Reverte et al, 2015; Chen et al, 2015; Cross et al, 2015; Fernandez et al, 2015; Salas et al, 2015; Yu et al, 2015; Malone et al, 2016), exhibited RI values that ranged between 3 to 19, and between 4 to <182 based on in their ED 50 or LD 50 , respectively. Differences in the level of glyphosate resistance between these species were due to various resistance mechanisms.…”

EPSPS duplication and mutation involved in glyphosate resistance in the allotetraploid weed species Poa annua L.

“…Data from whole‐plant dose–response experiments support the hypothesis that R is resistant to glyphosate, because R showed an RI of 17.9 when compared with S. This RI is larger than that found in any other glyphosate‐resistant biotype of P. annua reported to date, including a biotype from South Carolina with an RI of 4.4, a biotype from Tennessee with an RI of 12 and a biotype from Missouri with an RI of 5.2. The shikimic acid accumulation data support the whole‐plant dose–response findings, because R plants did not show a significant increase in shikimic acid accumulation after treatment with glyphosate, suggesting that R individuals are able to translate enough EPSPS to maintain the homeostasis of the shikimic acid pathway.…”