Family selection of birch tetraploid half-sibling based on seed vigor and seedling growth traits.

In this experiment, we compared tetraploid-and diploid-families of birch in seed and seedling quality. Seeds of 23 half-sib families (18 tetraploid-and 5 diploid-families) were collected from a seed orchard and their seedlings were grown in a nursery. The measured traits included thousand-seed weight, germination potential, germination rate,vigor index, seedling height and ground diameter. The results showed that: there were significant (P 0.01) family effects for all studied traits. On average, the thousand-seed weight of triploid-families was 22.42% higher than that of diploid-families. While the tetraploid Q53 half-sibling family showed the highest germination potential (56.67%) and vigor index (37.62), all other tetraploid-families displayed lower values than diploid ones. For seedling height, the diploid-families were taller than the tetraploid ones; the top three families were all diploid-families and the tallest one, the diploid-family CK1, was 31.04% higher than other families. The ground diameter growth, however, showed a reversal pattern, with most of the top-ranking families being tetraploid-families. Based on the results of principal component analysis, tetraploid-families Q53, Q65, Q13 and Q27 were identified as the superior families. We recommend the seed trees of these families as preferred seed trees in the future establishment of triploid seed production gardens.