Progeny test of tetraploid Betula platyphylla and preliminary selection of hybrid parents
Estimating genetic parameters of parental lines through progeny testing and choosing good hybrid parents are important for genetically improving seed orchard trees. In this study, 24 tetraploid progeny seedlings were used as experimental materials, which came from test cross design: six tetraploid Betula platyphylla lines (Q33, Q13, Q103, Q19, Q83 and Q14) as female parents and four individual B. platyphylla diploid lines (F3, F4, F9 and F11) as male parents were crossed. Variance analysis of height, diameter, height-to-diameter ratio, and internodal distance showed that the differences between hybrid combinations reached highly significant levels. Using multi-objective decisionmaking, we performed a comprehensive assessment of the various hybrid combinations. Using a selection rate of 20 % of the standard, five hybrids were selected; their genetic gains in average height, diameter, height-to-diameter ratio, and internodal distance were 20.95, 6.07, 13.07 and 8.96 %, respectively. We also analyzed the combining ability and genetic parameter effect values of parents and hybrid combinations. The combined analysis revealed that Q13, Q103, Q33 and Q83 were superior females; F3, F4, and F9 were superior males; and F3 × Q13, F4 × Q83 and F9 × Q33 were superior hybrid combinations. The heights and diameters of these progenies were 22.49 and 11.48 % greater than average, respectively.
Stem taper functions for Betula platyphylla in the Daxing’an Mountains, northeast China
Accurate prediction of stem diameter is an important prerequisite of forest management. In this study, an appropriate stem taper function was developed for upper stem diameter estimation of white birch (Betula platyphylla Sukaczev) in ten sub-regions of the Daxing’an Mountains, northeast China. Three commonly used taper functions were assessed using a diameter and height dataset comprising 1344 trees. A first-order continuous-time error structure accounted for the inherent autocorrelation. The segmented model of Max and Burkhart (For Sci 22:283–289, 1976. 10.1093/forestscience/22.3.283) and the variable exponent taper function of Kozak (For Chron 80:507–515, 2004. 10.5558/tfc80507-4) described the data accurately. Owing to its lower multicollinearity, the Max and Burkhart (1976) model is recommended for diameter estimation at specific heights along the stem for the ten sub-regions. After comparison, the Max and Burkhart (1976) model was refitted using nonlinear mixed-effects techniques. Mixed-effects models would be used only when additional upper stem diameter measurements are available for calibration. Differences in region-specific taper functions were indicated by the method of the non-linear extra sum of squares. Therefore, the particular taper function should be adjusted accordingly for each sub-region in the Daxing’an Mountains.
Preferential Outcrossing in Eucalyptus regnans F. Muell
Seed production characteristics of Eucalyptus regnans following self (S), outcross (0), (S + 0) and open pollination were investigated as a contribution to understanding of breeding system control in this species. All five trees tested produced seed after self-pollination, although yield was reduced relative to outcrossing. Isozyme analysis was used to determine paternity of individual seeds produced by pollination with a 1 : 1 mixture of S and 0 pollens. Preferential outcrossing was demonstrated, with an average of 81% of seeds being outcrosses. S and 0 seeds were also found within the same openpollinated capsules, confirming the experimental observation that receipt of outcross pollen does not per se preclude self-fertilisation. The independent probabilities of survival of S and 0 embryos, as determined from seed yield per 100 flowers after separate S and 0 pollination, accounted for much of the preferential outcrossing effect. However, some trees produced more outcrosses than expected and competitive interaction of embryo genotypes within a capsule cannot be discounted. Following open pollination, samples from 15 trees averaged 16.7 ovules and 1.48 full seeds per capsule, giving a mean seed : ovule ratio of 9.0%. The modal number of seeds per capsule was 1 and the maximum 9, while 21% of capsules yielded no full seeds. These observations and experiments suggest post-fertilisation control of the breeding system, dependent upon both embryo genotype and maternal resource allocation.