CHANGE IN PHYSIOLOGICAL FEATURES IN RYEGRASS BIOTYPES IN COMPETITION WITH SOYBEAN DUE RESISTANCE TO GLYPHOSATE

Herbicide resistance can cause biochemical, physiological, morphological and phenological changes in weeds, altering their competitive ability against crops. The aim of the study was to assess physiological changes and cellular damage in susceptible and resistant biotypes of ryegrass and soybeans under competition. Three experiments were conducted in a greenhouse using a completely randomized design with four replications performed in a replacement series. The ratios of soybean and to susceptible (experiment 1) and resistant ryegrass (experiment 2) and of susceptible to resistant (experiment 3) ryegrass were 100:0, 75:25, 50:50, 25:75 and 0:100. Forty days after the emergence of the soybean crop and 60 days after the emergence of the ryegrass plants, the leaves of the competing plants were collected. The following variables were assessed: the levels of carotenoids, chlorophylls and total phenolic compounds; amount of hydrogen peroxide; degrees of lipid peroxidation and electrolyte leakage; and activity of enzymes catalase, superoxide dismutase and ascorbate peroxidase. The production of phenols and increased oxidative damage due to interspecies competition with ryegrass was, in general, observed in the soybeans; the ryegrass biotypes, susceptible and resistant to glyphosate, coexisting with soybean have generally higher oxidative damage due to intraspecific competition; since when these biotypes coexist not present modifications of these parameters.