Hydrotime is a way to describe the relationship between water potential
(ψ) and seed germination rates and percentages. The minimum ψ that allows
germination to be completed is called the base water potential (ψb). The germination
rate (inverse of time to radicle emergence) increases linearly as the
seed ψ increases above ψb to its maximum rate in water (ψ = 0 MPa). As ψb
values vary among individual seeds, germination rates also vary, resulting in
lack of uniformity that can be quantified by the standard deviation in ψb values
(σψb ). The hydrotime constant (θH) indicates the inherent speed of germination
in a seed lot. Thus, hydrotime analysis quantifies the speed of germination
(θH), the stress tolerance of germination (ψb) and the uniformity
of germination for a seed lot (σψb ), which are all useful indicators of seed
vigor. Hydrotime analysis of seed lots under diverse conditions allows them
to be ranked according to their potential for successful emergence. It is also
a valuable tool for developing and assessing seed enhancement treatments
such as pelleting and priming. Hydrotime analysis can be simplified into an
endpoint test that could be useful for ranking seed lots according to vigor
and for diagnosing seed lot potential under stressful conditions.