Thermodynamic Characterisation of Seed Deterioration during Storage under Accelerated Ageing Conditions

Temperature and moisture play a significant and fundamental role in determining the storage longevity of seeds. Thermodynamic properties of seed water determine the reaction kinetics during seed deterioration. The relationship between seed deterioration and dependence of the thermodynamic properties of seed water namely water potential, water activity, differential enthalpy, entropy and free energy were examined in two different seed species (sensitive soya bean, tolerant wheat) differing in their sensitivity to storage under accelerated ageing conditions [high relative humidity (RH) ∼100% and high temperature: 45 and 35 °C]. A comparison of seed deterioration based on germination percentage, seed leachate conductivity and the various thermodynamic properties of water indicated that evidently, seed germination decreased faster at 45 °C than at 35 °C. The thermodynamic properties showed a critical upper limit with tolerant species having higher values than the susceptible species. In general, the values of critical limits of the thermodynamic parameters decreased with increase in temperature. In both the crop seeds the differential enthalpy and entropy increased with increase in period of storage and became asymptotic as the seeds lost their viability. Loss of viability and increase in seed leachate conductivity indicate that the changes in thermodynamic properties of seed water reflect the seed deterioration during storage under accelerated ageing conditions.