Preconditioning Cattleya seeds to improve the efficacy of the tetrazolium test for viability

The tetrazolium test is one of the most reliable techniques used to estimate seed viability. Its utilization with orchid seeds has become important in the evaluation of seed batches for propagation and conservation. The aim of this work was to study the tetrazolium test to verify the efficiency of pre-conditioning, time of exposure and the concentration of tetrazolium solutions in the evaluation of seeds of tropical orchids. Seeds were pre-conditioned in a 10% sucrose solution at room temperature for 24 h followed by immersion in 0.1, 0.25, 0.5 and 1% tetrazolium solutions for 3, 6, 12 and 24 hours at 40°C in a water bath in the dark. The results obtained in the tetrazolium test were compared with germination on Knudson C medium, while evaluation of colour development was performed using a table scanner. Germination was tracked using digital photography. Pre-conditioning in 10% sucrose improved the seed staining, making the differences in seed viability easy to distinguish. Use of tetrazolium solution concentrations greater than 0.25%, and periods of exposure greater than six hours are recommended when the objective is economy and fast execution, even if the seeds have not been conditioned in 10% of sucrose.