Physiological and growth responses of cacao to glyphosate exposure

Abstract

Herbicide drift phytotoxicity is a problem in plantation crops due to application failures and unfavorable spray conditions. With the increased use of glyphosate in cacao plantations in Ghana, there are concerns about the effect on cacao growth and productivity from doses that potentially could be expected from drift. The aim of this study was to evaluate the physiological and growth response of young cacao plants exposed to glyphosate. Two field experiments were conducted in randomized blocks, with four replications. Glyphosate was applied at rates 0 to 720 g a.e. ha⁻¹. Crop injury, shikimate accumulation, chlorophyll content, quantum efficiency of PSІІ (Fv/Fm), height, and stem diameter were evaluated. Increased glyphosate rates increased crop injury and shikimate accumulation and decreased chlorophyll content, quantum efficiency of PSІІ (Fv/Fm), and plant growth. Glyphosate rates 360 g a.e. ha⁻¹ or higher resulted in >60% foliar injury and more than 10-fold increase in shikimate accumulation. Glyphosate reduced chlorophyll content to <10 and Fv/Fm to <0.35 at the highest rates. Glyphosate rates ≥180 g a.e. ha⁻¹ reduced height and stem diameter of plants and caused reductions in stand count. Thus, cacao showed sensitivity to glyphosate, and severe injury impaired plant growth.

Keywords:

• Herbicide drift
• shikimate
• crop injury
• chlorophyll
• Theobroma cacao L

Acknowledgments

The authors are grateful to the technical team of the Agronomy and Physiology Biochemistry Division of the Cocoa Research Institute of Ghana (CRIG) for providing technical support. This paper is published with the kind permission of the Executive Director of CRIG as manuscript number CRIG/01/2022/023/003.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data generated during the current study are available from the corresponding author on reasonable request.

Additional information

Funding

This study was funded by COCOBOD/CRIG with project code CRIG/CC/1/25.