Nontarget Mechanims Involved in Glyphosate Tolerance Found in Canavalia ensiformis Plants

Abstract

A glyphosate-tolerant population of Canavalia ensiformis was collected in a cover crop in citrus orchards in Veracruz (Mexico), where glyphosate had been used for the first time. A susceptible Amaranthus hybridus L. population was collected from a nearby field that had never been treated with glyphosate. Dose-response experiments indicated a glyphosate tolerance ratio [ED(50)(C. ensiformis)/ED(50) (A. hybridus)] of 7.7. The hypothesis of a high level of glyphosate tolerance was provisionally corroborated on the basis of shikimate accumulation in both species. The susceptible population accumulated 6 times more shikimic acid in leaf tissue 96 h after glyphosate application than the tolerant leguminous crop. Two different physiological factors were involved in the glyphosate tolerance of this C. ensiformis population, which were confirmed by [(14)C]glyphosate, being a lack of penetration of glyphosate through the cuticle of the leguminous plants and an impaired herbicide translocation to the roots and the rest of shoots. This paper reports that two different nontarget site-based mechanisms, limited absorption and reduced translocation, contribute to the glyphosate tolerance found in C. ensiformis.

Glyphosate tolerance by Clitoria ternatea and Neonotonia wightii plants involves differential absorption and translocation of the herbicide

“…4). These results are consistent with those of Cruz-Hipolito et al (2009), who found the legume Canavalia ensiformis to be more tolerant to glyphosate than A. hybridus.…”

“…The data from the shikimic acid assay with leaf segments are given separately for each trial in the experiment. Regression analysis was conducted with the statistical software package Sigma Plot 8.0 (Cruz-Hipolito et al 2009). …”

“…Above-ground fresh weight per pot was determined 21 days after spraying and data were expressed as percentages of the value for the untreated control. The herbicide rate inhibiting plant growth of each species by 50% with respect to the untreated control, ED 50 , was determined according to Cruz-Hipolito et al (2009). The tolerance/susceptibility ratio was computed as ED 50 (C. ternatea)/ED 50 (A. hybridus) and ED 50 (N. wightii)/ED 50 (A. hybridus).…”

“…Plants of the three species at the same stage as before were harvested for shikimic acid extraction 6, 12, 24, 48, 72 and 96 h after treatment. Leaf tissues (0.5 g fresh weight) were homogenized and samples frozen in liquid nitrogen according to Cruz-Hipolito et al (2009). Shikimic acid accumulation was determined optically on a Beckman DU-640 spectrophotometer.…”

“…Legumes have traditionally been used as cover crops in large citrus grove areas in the Mexican tropics, where they are sown in strips 2-3 m wide between tree rows (Cruz-Hipolito et al 2009). The species most commonly used for this purpose are Neonotonia wightii, Mucuna pruriens, Canavalia ensiformis and Clitoria ternatea.…”