Shoot apical growth and cataphyll initiation rates in provenances of Pinusconforta in Scotland

Abstract

The dynamics of terminal bud development on seven 3-year-old nursery-grown provenances of Pinuscontorta Dougl. were monitored by sampling buds at 1- to 3-weekly intervals during one growing season. Differences in rates of cataphyll initiation occurred which were analysed in terms of (a) the projected areas of the apical domes, which changed over the season, (b) the relative rates at which the apical domes expanded radially during a plastochrone (square millimetres per square millimetre), as shown by the extent to which the new cataphyll primordia receded away from the domes, and (c) the projected areas of the tissues used to form new cataphyll primordia. Component a was a measure of the size of the apical dome meristems and b was a measure of their rates of 'activity.' A model-matching method is described to measure b.Those provenances which produced most cataphylls during the growing season developed and maintained large apical domes (component a above). There were unexpectedly small provenance differences in the apical dome 'activity' in midsummer (component b defined above), although differences occurred in spring and autumn. Differences in the projected areas of the new cataphyll primordia (component c) were inversely related to cataphyll initiation rates. Apical dome tissue doubling times in midsummer were estimated to be less than 120 h, irrespective of provenance.Inland provenances had small but relatively 'active' apical domes in spring, but they produced cataphyll primordia as products of this growth rather than reinvesting in apical dome 'capital.' Consequently, their apical domes remained small. Coastal Alaskan provenances, on the other hand, developed large apical domes, but these domes ceased to be very 'active' after the end of August. The apical domes on south coastal provenances did not become 'active' until early summer, but their domes were relatively large even in spring, became much larger by late summer, and they remained 'active' until mid-September.Implications are noted regarding cross-breeding of complementary genotypes to increase needle production and height growth.