Glyphosate is the herbicide most applied on eucalyptus plantations for weed control, acting directly on the shikimic acid pathway, the main via for the formation of compounds connected with the natural defenses of the plant, such as lignin, salicytic acid and phytoalexins. Thus, glyphosate contact with the leaves of the plant through drift may have important consequences for disease resistance. The aim of our research was to evaluate glyphosate drift involvement with severity of rust caused by Puccinia psidii in genotypes with different levels of resistance to the pathogen, after inoculation in a controlled environment. Seedlings of four clones, two heterozygote clones resistant to rust (UFV01 and UFV02) and two homozygote clones susceptible to rust (UFV03 and UFV04) were submitted to sub-doses of 0 (control); 28.8, 57.6, 86.4 and 115.2 g ha-1 of glyphosate simulating drift. Three days after glyphosate application, the plants were inoculated with UFV01 isolated from P. psidii obtained from Eucalyptus grandis in the Itapetininga region. On day 21 after inoculation, the following parameters were evaluated: rust intensity, by means of a diagrammatic scale with four classes of severity (SO and S2 resistant to rust and S2 and S3 susceptible to rust), number of pustules per leaf area, area affected by rust, average number of urediniospores cm-2, glyphosate percentage intoxication, and average number of urediniospores/pustule. Clone UFV04 was found to be the most susceptible while UFV01 was the most tolerant to the herbicide. Drift did not change the level of resistance to rust with respect to the resistant genotypes (UFV01 and UFV02) which presented no pustule both in plants exposed to drift and control plants. Susceptibility was maintained for the other clones, with a higher pustule density and higher percentage of affected area becoming evident for clone UFV03. For some clones susceptible to rust, rust severity decreased with glyphosate dosage increase. It was concluded that glyphosate did not affect eucalyptus resistance to Puccinia psidii and that there is differential tolerance to the herbicide among the clones.
Puccinia psidii; herbicide; plant disease; Eucalyptus spp
