Storage of cork oak (Quercus suber L., 1753) acorns and effect of storage duration on seedlings vigour : artificial regeneration implications.

Abstract

To palliate the irregular periodicity of Quercus suber acorn production and to sow in the appropriate time, the safe storage of seed of the species is unavoidable. Thus, the aim of this work was to find out a storage method that allows to preserve as long as possible the viability of cork oak acorns, already known as recalcitrant seeds. Thus, the storability of cork oak seeds harvested from two seed sources have been followed through a period of 21 months. After a vigorous cleaning, apparently healthy and intact acorns were subjected to three drying periods and stored under low temperature (0-2° C) within four storage containers. Five hundred acorns from each storage combination were sampled at three-month intervals for moisture content determination, germination tests and acorn losses. Additionally, a nursery experiment was carried out with fifteen-month well preserved acorns to evaluate whether or not they were able to develop further into normal seedlings. The results obtained show that cork oak acorns can be safely stored up to twenty-one months without substantial reduction in germinability. Moreover, storage life span seems influenced by seed origin and drying prior to storage. Sealed drums are better for long storage as compared to unsealed drums and sealed bags here tested. An initial moisture content ranging between 37 and 40 % would be suitable for storage success. Furthermore, results got from nursery trials showed that acorns kept inside sealed drums even ones after one-year storage produce more vigorous seedlings and that sowing of acorns in April seems optimal for containerized seedling production. Certainly, this long safe storage period known for this species is of considerable practical implication to its regeneration, set a solid base for longer seed storage and to carry out further investigations to explain viability loss in these recalcitrant seeds.