Increase of flowering in Norway spruce ( Picea abies) by known rootstocks and planting grafts in Southern sites

Abstract

We can distinguish essentially two methods to stimulate flower induction: firstly, methods that stimulate flowering as a consequence of each treatment; and secondly, methods with persistent effect, where a treatment increases flowering in the long run. Certain rootstocks and the movement of grafts southward show such persistent effects upon various provenanances of Norway spruce. Results presented here indicate, on the hand, a higher number of flowering grafts in wine-growing regions of southern Germany than in northern Germany. On the other hand, at least one clonal rootstock, a dwarf-growing ornamental Picea glauca ‘Conica’ increased the number of flowering grafts considerably. This increase is greater under warmer conditions. Other rootstocks seem to have a similar effect and show broad variation in normal growing and dwarf stocks. It is hoped that early, abundant and continuous flower-stimulating rootstocks such as clonal material of P. abies ‘Acrocona Hesse’ might increase flower formation further.