Adjuvant concentrations and uredospore densities on Phakopsora pachyrhizi infection efficiency in soybean

experiments were carried out in a growth chamber to evaluate the effect of spreader and uredospore concentrations on the efficiency of infection by phakopsora pachyrhizi, the causal agent of asian soybean rust. cd 214 rr soybean cultivar was inoculated with the following polyoxyethylene sorbitane monolaurate concentrations: 0, 30, 60, 120, 240, 480 and 960 μl.l-1 water, as well as a fixed uredospore concentration of 2 x 104 spores.ml-1. in a second phase, the inoculum concentrations of 0, 5 x 103, 1 x 104, 2 x 104, 4 x 104, 8 x 104 and 16 x 104 uredospores.ml-1 were evaluated, and the spreader concentration of 240 μl.l-1, selected in the previous experiment, was fixed. the spreader concentration of 240 μl.l-1 can be used in artificial inoculation studies, as well as up to 4 x 104 uredospores.ml-1. in this work, there was a correlation between uredia and lesion density. thus, the use of lesion density is recommended to assess disease intensity for its accuracy and less time consuming. there was also a positive correlation between uredia and lesion density.