Relationship between accumulated hydrothermal time during seed priming and subsequent seed germination rates

Abstract

AbstractSeed germination rates are sensitive to both temperature (T) and water potential (ψ). The times to germination of seeds imbibed at suboptimalTand/or reduced ψ are inversely proportional to the amounts by whichTexceeds a base temperature (Tb) and ψ exceeds a base water potential (ψb). Germination rates across a range of suboptimalTand ψ can be normalized on the basis of the hydrothermal time accumulated in excess of these thresholds. However, seeds can also progress metabolically toward germination even atTor ψ too low to allow radicle emergence to occur. Seeds preimbibed at low ψ and dried back, or primed, germinate more rapidly upon subsequent reimbibition. We show here that the increase in germination rates of tomato (Lycopersicon esculentumMill.) seeds resulting from seed priming is linearly related to the hydrothermal time accumulated during the priming treatment. The threshold temperature (Tmin= 7.05°C) and water potential (ψmin= −2.50 MPa) for metabolic advancement were considerably lower than the corresponding thresholds for radicle emergence of the same seed lot (Tb= 11°C; ψb= −0.71 MPa), allowing the accumulation of hydrothermal priming time that is subsequently expressed as more rapid germination whenTor ψ increase. The hydrothermal time model can now be applied to quantify and analyse germination rates of seeds across the entire range of suboptimalTand ψ at which metabolic progress toward radicle emergence is possible.