Mecanismos de resistência e resposta aos herbicidas inibidores da ALS e da PROTOX em Euphorbia heterophylla L

Abstract

Euphorbia heterophylla (EPHHL) is an important weed species in world agriculture and its control becomes difficult due to herbicide resistance. To develop proper EPHHL management strategies it is important to know the level and the mechanisms of resistance and persistence of resistant populations in the fields. Experiments were carried out to study the resistance of EPHHL to ALS and PROTOX inhibitors at biochemical, plant and population levels. The objectives on chapter I are to confirm the occurrence of resistance to ALS inhibitors and to determine whether there is cross resistance to other chemical groups, such as imidazolinone, sulfonylurea, pyrimidinyl (thio) benzoates and triazolopyrimidines in biotypes of EPHHL with multiple resistance (ALS and PROTOX). The objectives on chapter II are to confirm the existence of new EPHHL biotypes with resistance PROTOX in the states of Paraná and Rondônia and to determine whether there is cross resistance to other chemical group, such as diphenyl ethers, N-phenyl-phthalimide, triazolinone, oxadiazole and pyrimidinedione. The objectives on chapter III are to evaluate the activity of the ALS enzyme from biotypes with multiple resistance and to compare it to the enzyme activity of susceptible population in the absence and in the presence of the herbicides imazapyr, imazethapyr and nicosulfuron. The objectives on chapter IV is to characterize the activity of several antioxidant enzymes, such as peroxidase, catalase and superoxide dismutase in EPHHL biotypes treated with PROTOXinhibiting herbicides. The objective on chapter V are to identify the persistence of EPHHL populations resistant to ALS inhibitors on fields from Southwest and Western Paraná that were resistant in a previous survey and check for resistance to glyphosate in EPHHL these crops. The results support the hypothesis that EPHHL biotypes from Bom Sucesso do Sul, Vitorino, Vilhena and Medianeira have multiple resistance to ALS and PROTOX inhibitors. Four EPHHL biotypes are cross-resistant to all ALS chemical groups and five populations are cross-resistant to the PROTOX inhibitors tested. The resistance to ALS inhibitors on the EPHHL biotypes evaluated is attributed to the lower sensitivity of the herbicide target enzyme. The activity of all antioxidant enzymes, both on the resistant and susceptible biotypes, is dependent of the herbicide and on the dose used and can be one of the mechanisms of resistance to PROTOX inhibitors. The biotypes of EPHHL resistant to ALS-inhibiting herbicides remain in the area even after long-term observation of resistance. The resistance to PROTOX inhibitors also remains in areas, but less frequently.