Rates and Times at Which Needles are Initiated in Buds on Differing Provenances of Pinuscontorta and Piceasitchensis in Scotland

Abstract

During 1973, bud formation was monitored by sampling terminal buds from the topmost branches on four provenances plus one interprovenance hybrid of 10-year-old Pinuscontorta, and five provenances of 8-year-old Piceasitchensis, all growing in forest trials in Scotland. On both species, extension growth occurred between late May and mid-July. On pine, buds began forming in April; about a third of next year's needles (axillary bud primordia) were formed before mid-July and all were formed by mid-September. On spruce, bud formation occurred from May to October.Northerly and inland montane provenances began producing primordia earlier in spring than southerly provenances, suggesting differences in temperature sensitivity. The dates when bud development ceased were more closely related to latitude of seed origin, suggesting differences in photoperiod sensitivity. Differences among pine provenances in total numbers of primordia formed were related to differences in maximum rates of initiation during the summer, whereas in spruce they were due to differences in seasonal duration. In all cases, rates of initiation were closely correlated with apical dome diameters. Implications are noted regarding conifer breeding and environment–genotype interactions.