The most important factor which determines stability of seed is

The most important factor which determines the stability of the seed is Moisture.
Seeds attain a specific and characteristic moisture content when subjected to given levels of atmospheric humidity. This characteristic moisture content is called equilibrium moisture content.
A small change in seed moisture content has a large effect on the storage life of the seeds.
Therefore it is important to know the moisture content to make a reasonably accurate prediction of the possible storage life of each accession.