Morphological and physiological markers of juvenility and maturity in shoot cultures of oak (Quercus robur and Q. petraea).
Evaluation of potential techniques for rejuvenating oak shoots requires robust quantitative markers for juvenile and mature plants. To identify suitable in vitro markers, shoot cultures of Quercus species of juvenile, adolescent and mature origin were screened for a range of morphological and physiological markers of juvenility and maturity. Criteria examined included angle of the shoot to the horizontal, stem length, stem diameter (tip, mid, base), leaf number, scale leaf number and shoot number. Image analysis was also carried out to determine leaf area, size, perimeter and breadth and length of leaves. Mature Q. robur L. clones had a larger mid-stem and tip diameter than juvenile clones, whereas mature Q. petraea ex Liebl. clones were characterized by plagiotropic growth and larger mid-stem and tip diameters compared with juvenile clones. Based on discriminant analysis of the data, we propose the following formulae for discrimination of juvenile and mature shoots, where a negative value for the discriminant score (D) indicates juvenility. For Q. petraea: D = -1.308 - 0.0351 SA + 2.206 TD + 1.435 MSD, where SA is stem angle ( degrees ), TD is tip diameter (mm) and MSD is mid-stem diameter (mm). For Q. robur: D = -3.546 + 2.418 TD + 2.202 MSD. Quercus robur clones derived from stump sprouts and designated as juvenile had a negative D value suggesting a juvenile status for these clones. Clones sourced from a hedged, grafted Q. robur tree of mature origin had a positive D value indicating a mature status. Clones initiated from a 20-25-year-old Q. petraea tree displayed morphology in vitro consistent with a mature status and had a positive D value; however, these clones displayed other traits such as vigor suggesting that vestiges of juvenility remain. Multiplication rate and leaf size and shape were variable among clones and did not provide suitable markers for juvenility or maturity for these Quercus species.
McGowran
E.
E
School of Biological Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland.
Douglas
G. C.
GC
Parkinson
M.
M