Characterization of glyphosate-tolerant genetically modified eucalyptus

Abstract

Eucalyptus stands out as one of the most productive tree species for large-scale cultivation. However, like all cultivated crops, it requires specialized management practices, including the control of weeds, pathogens, and pests. Glyphosate is the most widely applied herbicide used in the essential weeding effort, and it ensures the sustainable management of eucalyptus cultivation in Brazil. Given the sensitivity of eucalyptus to glyphosate, existing weed control methods in young eucalyptus farms predominantly rely on protected mechanical or/and knapsack spraying. Both methods contribute to herbicide drift, which compromises tree yield and increases chemical waste due to uneven spraying. This study provides a detailed observation of the physiological parameters and long-term field performance of glyphosate-tolerant (HT), genetically modified (GM) eucalyptus developed by FuturaGene/Suzano S.A. and approved in Brazil for operational deployment. The HT GM eucalyptus events were meticulously evaluated to ensure high levels of glyphosate tolerance. This involved the direct application of herbicide on seedlings in greenhouse studies and on young trees in field conditions. The herbicide-treated GM eucalyptus in all trials demonstrated consistent growth and maintained physiological parameters comparable to their respective non-sprayed wild-type (WT) counterparts. The HT GM eucalyptus represents a significant advancement by enabling the direct application of glyphosate over the top of the trees to control the weeds within the planting row. This innovative approach minimizes the need for frequent mechanical and manual interventions, thereby lowering worker herbicide exposure, reducing the environmental impact of mechanical operations, and enhancing the overall efficiency and sustainability of HT GM eucalyptus stands.

Keywords: CP4-EPSPS; GM eucalyptus; herbicide-tolerance; photosynthesis; weed control.

Figure 1.

Phytotoxicity scale.

Figure 2.

Response of glyphosate-tolerant GM eucalyptus 751K022, 955S019 and, 955S024 and their wt-backgrounds fgn-K and FGN-S under 0, 25%, 50%, 100% and, 200% of acid equivalent ha⁻¹ of glyphosate using the commercial product Scout® at 15 days after application (DAA). (a) aerial part biomass (g), (b) phytotoxicity rating (1-5). Means followed by the same letter do not differ statistically by the Tukey test at 5% significance level.

Figure 3.

Photosynthetic parameters of GM Eucalyptus glyphosate-tolerant 751K022 and their wt-background FGN-K under the recommended dose of glyphosate (1.8 kg acid equivalent ha⁻¹ of glyphosate using the commercial product Scout®) applied 30 days post-planting and evaluated up to 5 days post-application. (a) Light compensation point (LSP), (b) maximum net photosynthetic rate (A_max), and (c) apparent quantum yield (AQY). Means followed by the same letter do not differ statistically between genotypes, within each treatment, by the Tukey test at 5% significance level.

Figure 4.

Photosynthetic parameters of GM Eucalyptus glyphosate-tolerant 955S019 and its wt-background FGN-S under the recommended dose of glyphosate (1.8 kg acid equivalent ha⁻¹ of glyphosate using the commercial product Scout®) applied 30 days post-planting and evaluated up to 5 days post-application. (a) Light compensation point (LSP), (b) maximum net photosynthetic rate (A_max), and (c) apparent quantum yield (AQY). Means followed by the same letter do not differ statistically between genotypes, within each treatment, by the Tukey test at 5% significance level.

Figure 5.

Photosynthetic parameters of GM Eucalyptus glyphosate-tolerant 955S024 and their wt-background FGN-S under the recommended dose of glyphosate (1.8 kg acid equivalent ha⁻¹ of glyphosate using the commercial product Scout®) applied 30 days post-planting and evaluated up to 5 days post-application. (a) Light compensation point (LSP), (b) maximum net photosynthetic rate (A_max), and (c) apparent quantum yield (AQY). Means followed by the same letter do not differ statistically between genotypes, within each treatment, by the Tukey test at 5% significance level.

Figure 6.

Yield performance (volume – m³ ha⁻¹ year) of glyphosate-tolerant GM eucalyptus and their backgrounds (WT) after two over-the-top applications of glyphosate at 30- and 60-days after planting. (a) field trial 1, roundwood volume evaluated 17 months after planting. (b) field trial 2, roundwood volume evaluated 36 months after planting.