Caracterização de biótipos de Lolium multiflorum Lam. resistentes a herbicidas inibidores da enzima acetolactato sintase (ALS)

Abstract

The selection pressure imposed by the intensive use of ALS enzyme inhibitors herbicides have selected resistant ryegrass biotypes. The characterization of resistant biotypes is indispensable to establish management strategies to prevent the spread of resistance. Thus, were conducted studies in order to evaluate the level of resistance; identify alternative herbicides to control biotypes resistant; evaluate the kinetic characteristics in vitro of the ALS enzyme; evaluate the absorption rate and metabolism of the iodosulfuron herbicide in ryegrass biotypes resistant and susceptible to iodosulfuron herbicide; identify and compare adaptive value of the resistant and susceptible ryegrass biotypes to iodosulfuron herbicide; evaluate the competitive ability between resistant or susceptible ryegrass biotypes with the wheat; and, indentify the inheritance type, the genes number involved with the resistance and the resistance degree from ryegrass biotypes. Were conducted studies with biotypes from Brazil (Col and Joi) and the USA (NC and AR). As results, a rate between 6-10 times higher herbicide is required to control and reduce 50% dry matter in resistant biotypes (Joi and Col) compared with susceptible. Alternatively in post emergence Col biotype is controlled with herbicides glyphosate and clethodim and Joi biotype with clethodim herbicide. The mechanism of resistance of the Joi and Col biotypes does not result from metabolism by P450 isoenzymes. The resistance of NC and AR biotypes follows from the insensitivity of the enzyme to iodosulfuron herbicide and the rapid metabolism in resistant biotypes may be another mechanism of resistance. In assessing the adaptive value between biotypes resistant ryegrass (Joi) and susceptible, in general, this is similar. The biotypes resistant ryegrass (Joi) or susceptible, in general, have similar adaptive value. The wheat crop has greater competitive ability in relation to ryegrass biotypes resistant (Joi) or susceptible. For the ryegrass biotype resistant (Joi) the interspecific competition is harmful. The resistance to ryegrass biotype Joi is encoded by nuclear dominant gene, and heterozygote biotype is not controlled with the registration rate of the iodosulfuron herbicide.