Glyphosate excessive use chronically disrupts the shikimate pathway and can affect photosynthesis and yield in citrus trees

Autor(es)

Martinelli, Rodrigo ; Rufino, Luiz Renato ; de Melo, Ana Caroline ; Alcantara-de La Cruz, Ricardo ; das Gracas Fernandes da Silva, Maria Fatima ; da Silva, Jefferson Rangel ; Boaretto, Rodrigo Marcelli ; Monquero, Patricia Andrea ; Mattos, Dirceu ; de Azevedo, Fernando Alves

• Tipo de documento: Artigo Científico
• Fonte: Chemosphere; v. 308, p. 11-pg., 2022-12-01.

Resumo

Glyphosate excessive use is reported in Brazilian citrus orchards, whereas there is speculation about its consequences and the published studies are contradictory and inconclusive. This study aimed to describe the possible harmful effects by simulating glyphosate drift directly to the leaves of similar to 4-yr-old citrus plants. As major results, glyphosate doses >360 g ae ha(-1) increased the shikimate accumulation in leaves (up to 2.3-times above control), which was increased after a second glyphosate application (up to 3.5-times above control), even after a 240-d interval. Interestingly, shikimate accumulation was occasionally related to a dose-response of the herbicide at specific times; however, the doses had their accumulation peak on determined dates. These accumulations were directly correlated to reduced net photosynthesis even months after the glyphosate sprays. Quantum productivity based on electron transport through the photosystem II and apparent electron transport reductions up to 17% were also observed during the entire experiment course. Similarly, quantum productivity based on CO2 assimilation of glyphosate sprayed leaves decreased up to four times compared to the control after the second application. Glyphosate doses >360 g ae ha(-1) increased stomatal conductance and transpiration as the carboxylation efficiency decreased, evidencing a carbon drainage in the Calvin-Benson cycle. These metabolic and physiological disturbances suggest possible photooxidative damage and an increase in photorespiration, which may be a mitigation strategy by the citrus plants to glyphosate effects, by the cost of reducing the citrus fruit yield (up to 57%). It is concluded that glyphosate phytotoxicity damages citrus plants over time due to chronic disturbances in the shikimate pathway and photosynthesis, even when there are no symptoms. This study is the first report to demonstrate how glyphosate damages citrus trees beyond the shikimate pathway. (AU)

• Processo FAPESP: 20/12004-4 - Manejo sustentável de plantas daninhas em citros: interação entre controle químico e técnicas conservacionistas
• Beneficiário: Fernando Alves de Azevedo
• Modalidade de apoio: Auxílio à Pesquisa - Regular
• Processo FAPESP: 17/02927-5 - EMU concedido no processo 2015/13572-8: analisador de gases infravermelho (IRGA)
• Beneficiário: Dirceu de Mattos Junior
• Modalidade de apoio: Auxílio à Pesquisa - Programa Equipamentos Multiusuários