A number of distinct but interacting determinants are known to influence seed vigor and viability (Heydecker, 1972).
These are (1) genetic factors; (2) preharvest and maturational effects; (3) mechanical factors (at harvest and in handling); (4) the storage environment (particularly temperature and moisture); (5) intrinsic factors (changes to macromolecules and essential metabolites, and accumulation of toxic substances); and (6) pathological factors.
The discussion that follows does not explore each of these factors in detail: the first four are well documented in the literature of the past 20 years and are touched on only briefly here, while critical aspects of seed-associated mycoflora are discussed elsewhere in this volume.
We have chosen, therefore, to consider the intrinsic factors in some depth.