Morphometric, allometric, and developmentally adaptive traits in red spruce and black spruce. II. Seedling and mature tree assessment of controlled intra- and inter-specific hybrids

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Abstract
The objective of this study was to investigate the genetic nature of morphometric, allometric, and developmental traits in controlled intra- and inter-specific hybrid crosses of red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) BSP). We examined 1-year-old greenhouse-grown seedlings and 22-year-old mature trees that were part of the same set of controlled crosses performed in the early 1970s. Seed weight had a strong female species effect. Mean cotyledon number and germination time had a very strong hybrid index effect. F1 interspecific hybrids showed negative heterosis in mature tree height, whereas hybrid index 25, a black spruce backcross, produced positive heterosis for seedling and mature tree height growth. Correlations of mean height of seedlings with mean height of mature trees on two sites were remarkably high (r = 0.918 and r = 0.968) when tested by hybrid index. Any cross having black spruce as the female or male parent had significantly higher height growth than those with red spruce as either female or male parent. Of the five hybrid indices, hybrid index 0 (black spruce) had the highest biomass allocation to stem wood and hybrid index 100 (red spruce) had the highest allocation to roots.