Adaptation of the tetrazolium method for testing the seed viability, and scanning electron microscopy study of some Western European orchids

A modified tetrazolium method was formulated for use with seeds of Western European orchids. The sequence of treatments which gave the highest percentage of coloured (i.e. viable) embryos was: (1) pretreatment in a solution of 5% (w/v) Ca(OCl) 2 + 1% (v/v) Tween‐80, (2) soaking for 1 day in sterile water, (3) the classical tetrazolium test. The optimal duration of the pretreatment in Ca(OCl) 2 + Tween‐80 depends upon the species, and to investigate the effect a scanning electron microscopy study was performed on the testa of 3 species. For a given species, the optimal pretreatment period was not affected by the year of harvest or the source of the seed lots.