Resistência múltipla e habilidade competitiva de Lolium multiflorum Lam. aos herbicidas glifosato (EPSPs), iodosulfurom-metílico e piroxsulam (ALS)

Abstract

The herbicides inhibiting EPSPs and ALS are the most used for the control of ryegrass in wheat and consequently result in the selection of naturally occurring resistant biotypes in the environment. The identification and characterization of these biotypes is fundamental for the management of the weed species. Thus, the objectives of the research were to evaluate the occurrence of multiple and cross resistance in ryegrass biotypes to ALS inhibitor herbicides and EPSPs; to verify the mechanism of resistance in susceptible and resistant plants through the accumulation of shikimic acid in response to application of glyphosate; of the activity of the enzyme ALS to iodosulfuron-methyl and of the response of the biotypes to the application of glyphosate, iodosulfuron-methyl and piroxsulam after treatment with cyt-P450 monooxygenase metabolism inhibitor; to evaluate the adaptive value and competitive ability of ryegrass biotypes resistant to and susceptible to glyphosate, iodosulfuron methyl and piroxsulam herbicides. Experiments were conducted in a greenhouse and laboratory, using seeds from plants that survived the control of the suspected resistance of glyphosate and iodosulfurom-methyl, collected in crops in the State of Rio Grande do Sul (RS) and Paraná (Paraná State). The results allow us to conclude that ryegrass biotype 110 has multiple resistance to glyphosate herbicides (EPSPs), iodosulfurom-methyl and pyroxsulam (ALS), and cross-resistance to iodosulfurom methyl and pyroxsulam (ALS) herbicides of the sulfonylureas and triazolopyrimidines groups, and Susc biotype is susceptible to glyphosate and ALS inhibitors. The mechanism of glyphosate resistance of biotype 110 is not due to the insensitivity of EPSPs to glyphosate. Resistance of the biotype 110 is a result of the insensitivity of the ALS enzyme to the sodium iodosulfuromethyl methyl herbicide. The biotype 110 does not exhibit glyphosate, iodosulfuron-methyl and pyroxsulam metabolism by the cyt-P450 complex with respect to inhibition by malathion or piperonyl butoxide (PBO). There is no difference in the competitive ability between the 110 and Susc biotypes.