Radicle length and container size effects on root deformities in the Mediterranean oak Quercus suber L.

The aim of this study was to assess the effects on root deformations in Mediterranean cork oaks Quercus suber L. of container size and radicle length at the time of sowing. Acorns at five sowing methods – intact acorns, acorns that had germinated during storage, acorns that had germinated after moist stratification and acorns with radicles (R) less than 5 mm in length, 7 mm to 12 mm in length and more than 15 mm length – were planted individually in WM type containers of 400 cm3, 800 cm3 and 1,200 cm3. At the end of the nursery growth period, the roots of the 1,080 sampled seedlings were examined for root deformities. The experiment results showed that root deformation affected almost half (49%) of the container-grown cork oak seedlings and that the germination status of acorns at the time of planting had a significant effect on root deformations, whereas container volume had no clear effect. The largest number of deformed roots (91%) was observed in seedlings grown from germinated acorns, as compared to 9% of seedlings grown from intact acorns. Planting germinated acorns with radicles 15 < R < 20 mm and 7 < R < 12 mm in length produced the highest percentages of detrimental deformations. Irrespective of size, the bottomless WM container type was shown to be highly effective against the root spiralling frequently observed in closed cylindrical polyethylene bags. The results of this study could help to improve cork oak seedling quality for more successful reforestation programs.