Metabolização de herbicidas inibidores do fotossistema II em cultivares de cana-de-açúcar
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Data
2021-01-20
Autores
Miranda, Valesca Pinheiro de
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Universidade Estadual Paulista (Unesp)
Resumo
Herbicidas inibidores do fotossistema II (FSII) são amplamente utilizados nos canaviais e, apesar de serem considerados seletivos, a metabolização dessas moléculas nas cultivares de cana-de-açúcar é pouco conhecida. Assim, objetivou-se avaliar a absorção e degradação dos herbicidas amicarbazone, diuron e tebuthiuron aplicados em pós-emergência em cultivares de cana-de-açúcar. Foi conduzido experimento em casa-de-vegetação, em delineamento inteiramente casualizado, e em duplicata, com 16 repetições. Aos trinta dias após o transplantio das mudas pré-brotadas CTC9001, CTC9002, RB97 5201 e RB98 5476, aplicaram-se os herbicidas amicarbazone, diuron e tebuthiuron, nas doses de 1050, 2000 e 1250 g ha-1, respectivamente, em adição ao espalhante adesivo Agral (0,5 v v-1). Foram avaliadas a taxa de transporte de elétrons (ETR), a fitointoxicação e os teores externos e internos dos herbicidas e seus metabólitos. A ETR foi monitorada nos períodos de 1, 24, 48, 72, 96, 120, 144, 168, 216, 264, 312 e 360 horas após a aplicação (HAA) em 8 repetições por tratamento, e aos 7 e 14 dias após aplicação (DAA) avaliaram-se os sintomas de fitointoxicação. Aos 2, 7 e 15 DAA determinou-se os teores externos e internos dos herbicidas e seus metabólitos, a partir da coleta, lavagem e maceração de todas as folhas das plantas. As soluções de lavagem foram analisadas para determinação dos teores externos, enquanto 0,1000 g do material macerado e liofilizado foi submetido a extração com solução metanol:água (80:20) para determinar os teores internos, ambas realizadas por cromatografia líquida de alta eficiência e espectrometria de massas (LC-MS/MS). Verificaram-se diferenças na ETR e nos teores dos herbicidas entre as cultivares. Os maiores teores internos de amicarbazone foram observados na CTC 9002, sobretudo aos 2 DAA. Nesse período, também ocorreram acentuadas reduções da ETR na mesma, sendo, portanto, superiores a absorção e a sensibilidade ao herbicida na CTC 9002. A degradação do amicarbazone nos genótipos estudados resultou na formação de dois metabólitos (DA MDK 3586 e N-Me DA 3586), sendo o segundo o principal produto formado no interior da planta. Para o diuron, aos 2 DAA foram encontradas as maiores concentrações nas plantas, sendo que a CTC 9001 e a CTC 9002 apresentaram teores absorvidos superiores, bem como as menores porcentagens de ETR, comparadas às cultivares RB. Observou-se baixa porcentagem de degradação do diuron a 3,4-DCA (inferior a 10%), independente da cultivar e período avaliados. Grande parte do tebuthiuron aplicado se manteve na superfície das folhas (superior a 80%), com porcentagem de absorção foi inferior a 14%. A CTC 9002 demonstrou maior sensibilidade ao tebuthiuron comparada aos demais genótipos, com maior teor interno e decréscimo significativo da ETR (acima de 80%) às 48 HAA. O comportamento da ETR em relação as concentrações moleculares médias de herbicida absorvido indicou que teores inferiores de amicarbazone e tebuthiuron ocasionaram uma forte inibição da ETR, enquanto o diuron foi mais absorvido pelas plantas. Assim, a absorção dos herbicidas foi inibida à medida que ocorreu intoxicação da planta, pois houve interrupção da fotossíntese, sendo observados um intenso decréscimo da ETR e superiores teores internos nas cultivares aos 2 DAA, principalmente na CTC 9002.
Photosystem II inhibitor herbicides (FSII) are widely used in sugarcane fields and, although they are considered selective, the metabolism of these molecules in sugarcane varieties is little known. Thus, the objective was to evaluate the absorption and degradation of the herbicides amicarbazone, diuron and tebuthiuron applied in post-emergence in sugarcane cultivars. An experiment was carried out in a greenhouse, in a completely randomized design, and duplicate, with 12 replications. Thirty days after transplanting the pre-sprouted seedlings CTC9001, CTC9002, RB97 5201 and RB98 5476, the herbicides amicarbazone, diuron and tebuthiuron were applied, in the doses of 1050, 2000, and 1250 g ha-1, respectively, in addition to the adhesive spreader Agral (0.5 v v-1). The electron transport rate (ETR), phytointoxication and the external and internal contents of herbicides and their metabolites were evaluated. ETR was monitored at 1, 24, 48, 72, 96, 120, 144, 168, 216, 264, 312, and 360 hours after application (HAA) in 8 repetitions per treatment, and at 7 and 14 days after application (DAA) phytointoxication symptoms were evaluated. At 2, 7, and 15 DAA, the external and internal contents of herbicides and their metabolites were determined from the collect, washing and maceration of all the leaves of the plants. The washing solutions were analyzed to determine the external contents, while 0.1000 g of the macerated and lyophilized material was subjected to extraction with methanol: water (80:20) solution to determine the internal contents, both performed by high performance liquid chromatography and mass spectrometry (LC-MS / MS). Differences in ETR and herbicide content were found between cultivars. The highest internal contents of amicarbazone were observed in CTC 9002, especially at 2 DAA. During this period, also occured accentuated reductions in ETR at the same, therefore being higher than the absorption and sensitivity to the herbicide in CTC 9002. The degradation of amicarbazone in the studied genotypes resulted in the formation of two metabolites (DA MDK 3586 and N-Me DA 3586), being the second the main product formed inside the plant. For diuron, at 2 DAA, the highest concentrations were found in the plants, with CTC 9001 and CTC 9002 presenting higher absorbed contents, as well as the lower percentages of ETR, compared to RB cultivars. A low percentage of degradation of the diuron at 3,4-DCA (less than 10%) was observed, regardless of the cultivar and period evaluated. Much of the applied tebuthiuron remained on the leaf surface (higher than 80%), with an absorption percentage below 14%. CTC 9002 demonstrated higher sensitivity to tebuthiuron compared to other genotypes, with higher internal content and a significant decrease in ETR (above 80%) at 48 HAA. The behavior of ETR in relation to the molecular concentrations means of absorbed herbicide indicated that lower levels of amicarbazone and tebuthiuron caused a strong inhibition of ETR, while diuron was more absorbed by plants. Thus, the absorption of herbicides was inhibited as intoxication of the plant occurred, because photosynthesis was interrupted, with an intense decrease in ETR and higher internal contents in cultivars at 2 DAA, mainly in CTC 9002.
Photosystem II inhibitor herbicides (FSII) are widely used in sugarcane fields and, although they are considered selective, the metabolism of these molecules in sugarcane varieties is little known. Thus, the objective was to evaluate the absorption and degradation of the herbicides amicarbazone, diuron and tebuthiuron applied in post-emergence in sugarcane cultivars. An experiment was carried out in a greenhouse, in a completely randomized design, and duplicate, with 12 replications. Thirty days after transplanting the pre-sprouted seedlings CTC9001, CTC9002, RB97 5201 and RB98 5476, the herbicides amicarbazone, diuron and tebuthiuron were applied, in the doses of 1050, 2000, and 1250 g ha-1, respectively, in addition to the adhesive spreader Agral (0.5 v v-1). The electron transport rate (ETR), phytointoxication and the external and internal contents of herbicides and their metabolites were evaluated. ETR was monitored at 1, 24, 48, 72, 96, 120, 144, 168, 216, 264, 312, and 360 hours after application (HAA) in 8 repetitions per treatment, and at 7 and 14 days after application (DAA) phytointoxication symptoms were evaluated. At 2, 7, and 15 DAA, the external and internal contents of herbicides and their metabolites were determined from the collect, washing and maceration of all the leaves of the plants. The washing solutions were analyzed to determine the external contents, while 0.1000 g of the macerated and lyophilized material was subjected to extraction with methanol: water (80:20) solution to determine the internal contents, both performed by high performance liquid chromatography and mass spectrometry (LC-MS / MS). Differences in ETR and herbicide content were found between cultivars. The highest internal contents of amicarbazone were observed in CTC 9002, especially at 2 DAA. During this period, also occured accentuated reductions in ETR at the same, therefore being higher than the absorption and sensitivity to the herbicide in CTC 9002. The degradation of amicarbazone in the studied genotypes resulted in the formation of two metabolites (DA MDK 3586 and N-Me DA 3586), being the second the main product formed inside the plant. For diuron, at 2 DAA, the highest concentrations were found in the plants, with CTC 9001 and CTC 9002 presenting higher absorbed contents, as well as the lower percentages of ETR, compared to RB cultivars. A low percentage of degradation of the diuron at 3,4-DCA (less than 10%) was observed, regardless of the cultivar and period evaluated. Much of the applied tebuthiuron remained on the leaf surface (higher than 80%), with an absorption percentage below 14%. CTC 9002 demonstrated higher sensitivity to tebuthiuron compared to other genotypes, with higher internal content and a significant decrease in ETR (above 80%) at 48 HAA. The behavior of ETR in relation to the molecular concentrations means of absorbed herbicide indicated that lower levels of amicarbazone and tebuthiuron caused a strong inhibition of ETR, while diuron was more absorbed by plants. Thus, the absorption of herbicides was inhibited as intoxication of the plant occurred, because photosynthesis was interrupted, with an intense decrease in ETR and higher internal contents in cultivars at 2 DAA, mainly in CTC 9002.
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Palavras-chave
Amicarbazone, Diuron, Saccharum spp., Seletividade, Tebuthiuron, Selectivity