Interaction of Imazapyr and a Brassinosteroid Analogue in Seedlings of Eucalyptus grandis

The application of brassinosteroids has been used to protect plants from environmental stresses. An experiment was carried out for the purpose of evaluating the interaction of the spirostanic analogue of castasterone (BB16) and the imazapyr herbicide by making use of seedlings clones of Eucalyptus grandis. It was used manual sprayers for the application of BB16, and for the herbicide application was used a CO2 pressurized backpack sprayer. The experiment was composed of six treatments: control; imazapyr (I) (0.750 kg ha-1 of active ingredient); BB16 in the concentrations of 0.08 (BB16(-)) and 0.16 mg L-1 (BB16(+)) applied immediately after the herbicide (I+BB16(-) and I+BB16(+), respectively) and, imazapyr applied immediately after the BB16 (BB16(-)+I and BB16(+)+I, respectively). At 18 days after the treatment application (DAT) it was verified that in the treatments I, BB16(-)+I and BB16(+)+I occurred total necrosis in terminal leaves of the apical branches. After 21 DAT, the treatment control, I+BB16(-) and I+BB16(+) expressed significative increments in height and stem diameter, in relation to other treatments. Similar behavior was verified to dry matter of the shoot and roots, at 35 DAT. When BB16 was applied before imazapyr, the deleterious effects on the variables dry matter of shoot, as well as in height and diameter of the seedlings, had been more significant than the isolated herbicide application. We found out that the application of analogue castasterona could act as a safener in seedlings of E. grandis submitted to the imazapyr action, when applied immediately after the herbicide, because these seedlings have not exhibited toxicity symptoms under this condition.