Caracterização de biótipos de Raphanus sativus L. resistentes e suscetível a herbicidas inibidores da enzima acetolactato sintase

Abstract

The Raphanus sativus (fodder radish) is a species of winter that is characterized as weed and can be used as ground cover, before winter and summer crops. His presence, like weed in areas for grain production can cause damage due to its ability to compete. This species is normally controlled with ALS inhibitor herbicides such as enzyme-methyl iodosulfurom that due to the continued use of selected resistant biotypes. Therefore, the research objectives were to determine the dose required to control 50% of the population (C50) and reduce 50% of the mass production of dry matter of shoots (GR50) of resistant biotypes, for the susceptible biotype; check alternative herbicides for control of resistant biotypes; checking the resistance mechanism through the activity of the ALS enzyme, gene sequencing of the ALS enzyme response biotypes and applying the cytochrome P450 monooxygenase inhibitor metabolism; and estimate the adaptive value of susceptible biotypes resistant and iodosulfurom methyl-sodium. For this, experiments were conducted in a greenhouse and laboratories belonging to UFPel and Wheat Embrapa Passo FundoRS using fodder radish seeds collected in northern crops and gaucho northwest where control failures occurred after the use of iodosulfurom methyl sodium. The results demonstrate that to obtain equivalent control of resistant biotypes (B4 and B13), it is necessary dose of iodosulfurom methyl sodium than 89 252 times higher than that required for the susceptible biotype (B1). Biotypes B4 and B13 are controlled with the alternative herbicide glufosinate ammonium, paraquat dichloride, diuron + paraquat dichloride, glyphosate, saflufenacil, metribuzin, bentazon, 2,4-D amine, mesotrione, tembotrione, atrazine and fomesafen belonging to mechanisms separate action. However, B4 and B13 biotypes show resistance to metsulfurom-methyl, nicosulfuron, chlorimurom-ethyl, imazethapyr, cloransulam-methyl, flucarbazone sodium and bispyribac-sodium, all herbicides inhibitors of ALS enzyme, confirming the cross-resistance. In the assay of ALS enzyme activity, fodder radish biotypes have similar affinity for the enzyme, however B4 and B13 have greater Vmax when compared to susceptible; inhibiting ALS enzyme activity in the presence of iodosulfurom methyl-sodium herbicide showed 50% inhibition is required 0.65 and 0.82 uM to B4 and B13 respectively, resulting in a resistance factor 15 and 19 when compared with B1. It was found that mutation of resistant biotypes presented with Trp574 substitution of leucine amino acid tryptophan by confirming that the resistance was due to sensitivity of the ALS enzyme. We observed the occurrence of the silent mutations Ala122 in all biotypes which the codon GCC was substituted for GCT without causing changes in the amino acid. Biotypes have no metabolism iodosulfurom methyl-sodium cytochrome P450 complex when inhibited by the insecticide malathion or piperonyl butoxide (PBO). The fodder radish susceptible biotypes (B1) and resistant (B4) to iodosulfurom-methyl herbicide sodium generally had similar fitness.