Biochemical Basis for the Time-of-Day Effect on Glufosinate Efficacy against Amaranthus palmeri

Abstract

Glufosinate, a glutamine synthetase (GS) inhibitor, often provides variable weed control depending on environmental conditions such as light, temperature and humidity at the time of application. Midday applications normally provide improved efficacy compared to applications at dawn or dusk. We investigated the biochemical basis for the time-of-day effect on glufosinate efficacy in Amaranthus palmeri. GS1/GS2 gene expression and GS1/GS2 protein abundance were assessed in different parts (young leaves, old leaves, and roots) of plants incubated in the dark compared to those in the light. The turnover of GS total activity was also evaluated overtime following glufosinate treatment at midday compared to dusk application. The results suggest that GS in A. palmeri is less expressed and less abundant in the dark compared to in the light. Midday application of glufosinate under intense light conditions following application provide full control of A. palmeri plants. Consequently, these plants are unable to recover GS activity by de novo protein synthesis. Full activity of GS is required for complete inhibition by the irreversible inhibitor glufosinate. Therefore, glufosinate applications should always be performed in the middle of the day when sunlight is intense, to prevent weed escapes from the herbicide treatment.

Unraveling the mechanism of resistance in a glufosinate-resistant Palmer amaranth (Amaranthus palmeri) accession

“…The qPCR reaction mixture followed the same methodology described in "Glutamine Synthetase Gene Copy Number Quantification" with forward and reverse primers described in Table 1. The primer pairs GS1b and GS2b amplifying GS1 and GS2, respectively, were obtained from a previous study targeting these genes in A. palmeri (Takano and Dayan 2021). The assay was conducted under the following conditions: 30 s at 98 C, 40 cycles of 98 C for 10 s, and 60 C for 30 s. After the cycle was completed, the temperature increased by 0.5 C every 5 s from 65 C to 95 C to generate melting curves.…”

Palmer amaranth (Amaranthus palmeri) control affected by weed size and herbicide spray solution with nozzle type pairings

“…According to Takano and Dayan (2021), weed control by glufosinate is highly dependent on environmental conditions (light, temperature and humidity at the time of application). Also, relative humidity was previously reported to be a critical factor in the efficacy of glufosinate to act on Palmer amaranth (Coetzer et al 2001).…”