Respostas fisiológicas da mandioca à aplicação de herbicidas / Cassava physiological responses to the application of herbicides

RESUMO

A análise da fluorescência da clorofila a vem sendo utilizada para melhorar o entendimento dos mecanismos da fotossíntese, bem como, na avaliação da capacidade fotossintética alterada por estresses bióticos ou abióticos. Objetivou-se com esse trabalho avaliar a sensibilidade de plantas de mandioca a herbicidas com diferentes mecanismos de ação, bem como, os danos causados pela aplicação desses herbicidas no aparato fotossintético destas plantas. Para isso foi montado um experimento no delineamento em blocos casualizados, com quatro repetições no arranjo fatorial (10 x 4), sendo  o primeiro fator referente aos herbicidas utilizados (bentazon, clomazone, fomezafen, fluazifop-p-buthyl, glyphosate, nicossulfuron, clorimuron, a mistura fluazifop-p-buthyl + fomesafen, sulfentrazone e  testemunha), o segundo fator às épocas de avaliação (aos 2, 9, 16 e 23 dias após a aplicação dos herbicidas). Os herbicidas avaliados afetaram de forma diferenciada as plantas de mandioca, sendo que, o glyphosate e sulfentrazone promoveram a morte das plantas. Os herbicidas clomazone, fomesafen, fluazifop-p-buthyl e chlorimuron-ehtyl causaram baixa intoxicação as plantas de mandioca e não afetaram a relação Fv/Fm e a ETR. No entanto, para o nicossulfuron e a mistura fluazifop-p-buthyl + fomesafen os valores da Fv/Fm estiveram abaixo do ideal nas primeiras épocas de avaliação mas as plantas tratadas com...

ABSTRACT

Analysis of chlorophyll a fluorescence has been used to improve the understanding of the mechanisms of photosynthesis, as well as in the evaluation of plant photosynthetic capacity altered by biotic or abiotic stresses. The objective of this study was to evaluate the sensitivity of cassava plants to herbicides with different mechanisms of action, as well as the damage caused by the application of herbicides on the photosynthetic apparatus of these plants. An experiment was conducted in a randomized block design with four replications. The treatments were constituted of the application of the following post- emergence herbicides in cassava bentazon, clomazone, fomesafen, fluazifop-p-buthyl, glyphosate, nicosulfuron, chlorimuron, fluazifop-p-buthyl + fomesafen, sulfentrazone, besides a control without application. The visual intoxication and chlorophyll a fluorescence assessments were performed at 2, 9, 16 and 23 days after herbicide application. The herbicides evaluated affected differently the cassava plants. Sulfentrazone and glyphosate promoted plant death. Herbicides clomazone, fomesafen, fluazifop-p-buthyl and chlorimuron-ehtyl caused low toxicity to cassava plants and did not affect the ratio Fv / Fm and ETR. However, for the mixture nicossulfuron and fluazifop-p-buthyl + fomesafen values of Fv / Fm were suboptimal in the first evaluation times but plants treated with the...