Vegetative and sexual phenology, reproductive dynamics and bud differentiation in a clonal seed orchard of white and black spruce

Abstract

To evaluate the importance of phenology and strobilus production in a clonal seed orchard of white and black spruce, 14 clones of each species represented by 4 ramets each, were selected from the Mattawin seed orchard. Thunder Bay District, Ontario. The times of flushing of the terminal buds of the leaders and 4 lateral branches were determined using an index of vegetative bud and shoot development. Dates of growth cessation were determined at 95 percent of shoot elongation. An index was used to score stages of pollen release and female receptivity of black spruce. Counts were made of male and female strobilus production per ramet in black spruce. The time of reproductive bud differentiation, in two clones of black spruce, was estimated to be mid-July after viewing dissected buds under a dissecting microscope and epimicroscope. Analyses of variance showed significant differences among clones in times of flushing and growth cessation of the leaders and lateral branches of white and black spruce, and significant differences in times of pollen release and female receptivity in black spruce but not white spruce. However, few clones were significantly different from each other using Duncan's NMR test. Generally there was a small range in clonal mean dates for these characteristics, perhaps because the clone ortets all originated from the same northern seed zone. Early-flushing black spruce clones produced the greatest leader extension. Peak pollen release and female receptivity coincided in most clones, thus increasing the probability of selfing. An analysis of variance of the number of female strobili per ramet and an analysis of covariance of the number of male strobili per ramet, using ramet height as covariant, showed significant clone differences. A few clones produced the largest number of strobili, especially in male strobilus production. Heavy male strobilus producing clones were not necessarily heavy female strobilus producers. The genetic composition of the progeny was estimated from: 1) the daily stages of pollen release and female receptivity, and 2) the number of male and female strobili per clone. A few clones were the largest contributors to the genetic composition of the progeny; the timing of pollen release and female receptivity had little effect on these estimates. The total percentage of selfed-crosses was estimated at 1 1 percent, although the individual clone rates of selfing varied from 1 to 25 percent.