Temperature sensitivity of the low-moisture-content limit to negative seed longevity-moisture content relationships in hermetic storage

Abstract

• Background and Aims: The negative logarithmic relationship between orthodox seed longevity and moisture content in hermetic storage is subject to a low-moisture-content limit (mc), but is mc affected by temperature? • Methods: Red clover (Trifolium pratense) and alfalfa (Medicago sativa) seeds were stored hermetically at 12 moisture contents (2-15 %) and five temperatures (-20, 30, 40, 50 and 65°C) for up to 14.5 years, and loss in viability was estimated. • Key Results: Viability did not change during 14.5 years hermetic storage at -20°C with moisture contents from 2.2 to 14.9 % for red clover, or 2.0 to 12.0 % for alfalfa. Negative logarithmic relationships between longevity and moisture contents >mc were detected at 30-65°C, with discontinuities at low moisture contents; mc varied between 4.0 and 5.4 % (red clover) or 4.2 and 5.5 % (alfalfa), depending upon storage temperature. Within the ranges investigated, a reduction in moisture content below mc at any one temperature had no effect on longevity. Estimates of mc were greater the cooler the temperature, the relationship (P < 0.01) being curvilinear. Above mc, the estimates of CH and CQ (i.e. the temperature term of the seed viability equation) did not differ (P > 0.10) between species, whereas those of KE and CW did (P < 0.001). • Conclusions: The low-moisture-content limit to negative logarithmic relationships between seed longevity and moisture content in hermetic storage increased the cooler the storage temperature, by approx. 1.5 % over 35°C (4.0-4.2 % at 65°C to 5.4-5.5 % at 30-40°C) in these species. Further reduction in moisture content was not damaging. The variation in mc implies greater sensitivity of longevity to temperature above, compared with below, mc. This was confirmed (P < 0.005). © The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved.