Rice (Oryza sativa) response to drift rates of glyphosate

Abstract

Greenhouse and field studies were conducted to investigate response of two rice varieties, Priscilla and Cocodrie, to sub-lethal rates of glyphosate in terms of injury, shikimate accumulation and yield. In the greenhouse, more shikimate accumulated in Cocodrie than Priscilla at comparable glyphosate rates applied to plants at the three-leaf stage. In field studies, glyphosate was applied to both varieties when they were 74-cm tall and in the internode separation growth stage. Visual injury, plant height, and leaf-tissue samples for shikimate analysis were collected at 3, 7, 14, 21 and 28 days after treatment (DAT). Rice yield was also determined. Noticeable visual injury and height reduction to both varieties was observed as early as 7 and 3 DAT in Cocodrie and Priscilla, respectively. Shikimate levels in leaves began to increase in both varieties by 3 DAT in a dose-dependent manner and reached a peak between 7 and 14 DAT. Elevated shikimate levels were still detectable by 28 DAT. Similar levels of shikimate accumulated in both varieties at comparable glyphosate rates. However, glyphosate treatment at comparable rates reduced rice yields more in Cocodrie than in Priscilla. The highest rate of glyphosate reduced yield in Cocodrie by 92% whereas there was only a 60% yield reduction in Priscilla. Shikimate levels in glyphosate-treated rice were strongly correlated to yield reductions across both varieties and appeared to be a better predictor of yield reduction than was visual injury. Visual injury coupled with measured shikimate levels can be used collaboratively to identify glyphosate exposure and estimate subsequent rice yield reductions.

Early Detection of Crop Injury from Glyphosate on Soybean and Cotton Using Plant Leaf Hyperspectral Data

“…Reddy et al [4] found that glyphosate application on non-GR soybean could induce reduction of leaf chlorophyll content and decrease nodule biomass and leghemoglobin content. Koger et al [5] found that visual injury and plant height reduction could be observed for rice within seven days after glyphosate treatment. More recently, Reddy et al [6] reported that, in an aerial glyphosate drift experiment, chlorophyll reduction is about 80% for non-GR soybean leaves sprayed with 0.866 kg· ae/ha glyphosate solution, and higher than 40% for non-GR cotton leaves within one week after treatment.…”

Alterações no metabolismo da cana-de-açúcar em função da aplicação de maturadores

“…Matallo et al (2009), trabalhando com glyphosate e concentração de ácido chiquímico em citros, observaram que as plantas que receberam aplicação de glyphosate mostraram sempre maiores concentrações de ácido chiquímico que as plantas testemunhas. Vá-rios pesquisadores (Singh & Shaner, 1998;Wang, 2001;Mueller et al, 2003) (Mueller et al, 2003;Koger et al, 2005), algodão (Pline et al, 2002), girassol, trigo e milheto (Henry et al, 2007), soja (Singh & Shaner 1998) e trigo (Bresnahan et al, 2003.…”

“…Bresnahan et al (2003), verificando a concentração de ácido chiquímico com aplicação de glyphosate na cultura do trigo, observaram que o pico de concentração foi entre 7 e 10 dias após a aplicação e que os teores foram diminuindo até a colheita. Corroborando essa informação, Koger et al (2005) observaram que os picos de acumulação de ácido chiquí-mico ocorrem até 14 dias após o tratamento e que altos níveis foram detectados até 28 dias depois da aplicação do glyphosate.…”

Glyphosate as a tool to produce shikimic acid in plants

“…Koger et al, 2005a), to distinguish resistant from susceptible soybean and cotton cultivars (Pline et al, 2002;Bonini et al, 2009), and to check its effect on the metabolism of aromatic amino acids in Cyperus rotundus (Wang, 2001). Transitory in nature, shikimic acid accumulation has been reported to occur one day after glyphosate application, reaching peak levels between four and seven days afterwards (Koger et al, 2005b).…”