Morphological and physiological maturation of acorns of cork oak (Quercus suber L.)

In order to improve the long-term storage of cork oak (Quercus suber L) acorns, it is important to define the period of maturity. Changes in the morphological, physiological and biochemical characteristics were examined during acorn development until shedding. The complete acorn maturation was attained between November 8 and November 22. The reduction in moisture content differed greatly between acorn tissues with the pericarp and the embryo losing less water than cotyledons during the maturation process. Acorns were shed at high moisture content, the level could vary slightly among parental trees due to the variability in pericarp moisture content. At time of acorn shedding the cotyledon moisture content was about 46% (% fresh weight), the embryonic axis 63% and the pericarp ranged between 59 and 65%. The moisture content of cotyledons was found to be a good index of morphological maturity. Physiological maturity was more precocious than morphological maturity. The acorns aquired the ability to germinate early during maturation and reached their maximum capacity when the acorn moisture content decreased from 72% to 67% and the embryonic soluble sugars reached a steady state of about 238 mg. g⁻¹ dry weight.