Different Assessments of the Effect of Drying Rates on Recalcitrant Seed Material

The results of the germination and tetrazolium (TZ) tests of axes of Pisum sativum, Quercus robur and Trichilia dregeana were in agreement during both drying and wet storage. The TZ test overestimated viability of Avicennia marina, Trichilia emetica and Strychnos madagascariensis axes in comparison to the germination test during dehydration. Thus, the germination test is a method of choice during desiccation and the TZ test may be a better indicator of viability during hydrated storage than drying. The survival of axes of Q. robur during slow dehydration and moist storage was unexpectedly poor possibly as a result of an unfavourable temperature during treatments. Hence, rapid desiccation is recommended for determinations of minimum ‘critical water contents’. The relationship between electrolyte leakage and water content during drying and wet storage of axes of T. dregeana harvested in 2001 and S. madagascariensis showed a ‘classic pattern’ as dehydration and hydrated storage proceeded. Consequently, the conductivity test is a poor measure of the ‘critical water contents’ but may be an indicator of differences in vigour among harvests of the same species along with the germination and TZ tests during slow desiccation. Less leakage occurred during rapid than slow drying in all species. Desiccation-sensitive seeds can be divided into three categories on the basis of the predominant mechanism of loss of viability during dehydration: minimally, moderately and highly desiccation-sensitive in which desiccation, metabolic and physical damage predominate, respectively. Irrespective of the mode of dying, the effect of rate drying of was always apparent.