A threefold glyphosate tolerance was identified in two Italian ryegrass populations, T1 and T2, from Mississippi. Laboratory experiments were conducted to characterize the mechanism of glyphosate tolerance in these populations. The T1 population absorbed less 14C-glyphosate (43% of applied) compared to the susceptible (S) population (59% of applied) at 48 h after treatment (HAT). The T2 population absorbed 14C-glyphosate at levels (56% of applied at 48 HAT) that were similar to both T1 and S populations, but tended to be more comparable to the S population. The amount of 14C-glyphosate that remained in the treated leaf was significantly higher in both T1 (67% of absorbed) and T2 (65% of absorbed) populations compared to the S population (45% of absorbed) at 48 HAT. The amount of 14C-glyphosate that moved out of treated leaf to shoot and root was lower in both T1 (25% of absorbed in shoot and 9% of absorbed in root) and T2 (25% of absorbed in shoot and 11% of absorbed in root) populations compared to the S population (40% of absorbed in shoot and 16% of absorbed in root) at 48 HAT. There were no differences in epicuticular wax mass among the three populations. Treating a single leaf with glyphosate solution at the field use rate (0.84 kg ae ha−1) as 10 1-µl droplets killed the S plant but not the T1 and T2 plants (33 and 55% shoot fresh-weight reduction, respectively). Shikimic acid accumulated rapidly at higher levels in glyphosate-treated leaf segments of the S population compared to the T1 population up to 100 µM glyphosate. However, above 500 µM glyphosate, the levels of shikimate were similar in both the S and T1 populations. Furthermore, shikimic acid content was three- to sixfold more in whole plants of the S population treated with 0.22 kg ae ha−1 glyphosate compared to the T1 and T2 populations. No degradation of glyphosate to aminomethylphosphonic acid was detected among the tolerant and susceptible populations. These results indicate that tolerance to glyphosate in the T1 population is partly due to reduced absorption and translocation of glyphosate and in the T2 population it is partly due to reduced translocation of glyphosate.
You have requested a machine translation of selected content from our databases. This functionality is provided solely for your convenience and is in no way intended to replace human translation. Neither BioOne nor the owners and publishers of the content make, and they explicitly disclaim, any express or implied representations or warranties of any kind, including, without limitation, representations and warranties as to the functionality of the translation feature or the accuracy or completeness of the translations.
Translations are not retained in our system. Your use of this feature and the translations is subject to all use restrictions contained in the Terms and Conditions of Use of the BioOne website.
Vol. 56 • No. 3