The Genetic And Cultural Basis For High Genetic Quality And Ample Yield Of Pinus Tabulaeformis Carr. Seed Orchard

The high genetic quality and ample yield are the key to seed orchard management, and also a urgent problem awaiting solution at present. Therefore, during 1985-1995 in seed orchards of Pinus tabulaeformis Carr., located in Lushi county, Henan province and Ningcheng county, Inner Mongolia autonomous region, continuous observations on the patterns of female and male strobilus distribution in crowns, female and male strobilus production, pollen amount and viability, pollen grains reaching micropyles and ovules, flowering phenology were carried out. The cone characteristics and the efficiencies of different pollination modes were analyzed. In addition, the female and male strobilus buds and ovules were observed under the microscope.The vertical distribution of female and male strobili in crowns varied with clones and years, the most of female strobili were borne in the middle part of a crown, while male strobili in the lower part, there was a tendency to distribute upward for both female and male strobilus in the crowns with ages. The female strobili bearing in the upper part of a crown were nearly equal in amount for all directions. There were much more female strobilus production on the shoots facing south than the other three directions in the middle and lower parts of the crown, while no male strobili nearly bearing in the upper part of the crown. About 90.4% of female strobili were concentrated outside the crown on 1-5 year-old branches of the first order, while male ones were mainly on weak branches inside the crown. Female and male strobili were terminally borne on the shoots .Vertically, the cone with filled seeds was mainly borne in the middle part of a crown, while less in the lower part. Horizontally, the cones facing the dominant wind directions during flowering produced more filled seeds. There were remarkable differences in cone characteristics for various clones in Lushi seed orchard, while no differences in Helihe. The variations among ramets within clone had no significance in the two seed orchards.There was a fluctuation in female and male strobilus production with about 4-year-cycle in Lushi seed orchard, and the fluctuations of cones with filled seeds among years coincided with male strobilus production. The variations of the cones with filled and emptied seeds did not tended to stable until abundant cone production. There were significant differences for the female and male strobilus production between clones, greater differences for strobilus production in a seed year than a lean year, and in abundant cone period than initial period, and the smaller differences between ramets within clone. The interactive effects of clone and year for the female and male strobilus production were significant. The 20 clones stable in production for female strobilus and 22 for male were selected from 31 clones.The first pollen grain arriving at the integument arms was preferentially engulfed over pollen approaching later during conelet receptive period. Controlled pollination carried out within 2-3 days after flowering gave the greatest efficiency with 54% of filled seeds. The repeated pollination during receptive period could not significantly increase seed numbers over single pollination. The 45-50% of filled seeds in cone could be produced when 0.2-0.4 ml of pollen was applied to one pollination bag. The mixtures of fresh pollen with dead pollen or talcum powder at the ratio of 1 : 1 could produce the same percentage of filled seeds as pure fresh pollen applied.The differences of flowering phenologies among clones, among ramets within a clone, at different positions within a crown were described, the relationship of flowering phenologyof the same clones in different years were analyzed. There were great differences in the average flowering synchronization indexes, and unbalanced contributions of female and male gametes for different clones in seed orchards were detected. The average synchronization indexes within a clone were larger than those among clones. The influences of flowering phenology on the indexes were as following order: for the mating pairs > mothers > fathers. There was a small fluctuation for unifonnity indexes estimated by female gamete production, while a great fluctuation by male gamete production among years, the uniformity of gamete contribution was improved in abundant flowering years than the initial period. The unifonnity of female gametes was more preferable to male ones. There was close relationship between the genotypic values of progenies and those of the pollen-clones.In general, the genotypic values of progenies were smaller than those of their mother-clones in initial years. The gamete contribution tended to equilibrate in abundant cone period, therefore, the average genotypic values of progenies were increased. Since the influence of gamete production on gamete contribution was greater than flowering phenology, the unifonnity of gamete contribution in seed orchard could be more effectively improved by adjustment of clonal female and male gamete production.The male strobilus differentiated in late June, while the female strobilus in middle July. The microsporogenesis occurred in late April of the next year. The mature pollen, which was pollinated from late April to middle May, was composed of 4 cells. The megasporocyte was formed in late April and early May of the next year and undertook meiosis to form megaspore in early and middle May. A female gametophyte developed from free nuclei, cell and archegonia phase to a mature egg cell. Fertilization took place in late May. The interval between pollination and fertilization was about 13 months. There were great differences in differentiation time of female and male strolibi and development process of microsporocyte and megasporocyte between clones. The optimal time for promotion of female and male strobilus was about a half month and one and a na'f month after the cessation of shoot growth, respectively.In addition, factors affecting seed production and quality and relationship among factors were discussed, among them, the genetic, nutrition, pollen amount, mating compatibility, selfing and insect pests were major factors causing conelet and ovule abortions. The close of canopy and overlap of branches between grafts hampered strobilus distribution and production. Selfing was main factor causing emptied seeds, decreased the gennination rate of seeds, survival and growth rate of seedlings. The degree of flowering synchronization, gamete numbers, mating incompatibility between parents and selfing affected gamete contribution;The clonal re-selection, supplemental mass pollination, nutrition management, roguing and pruning were effective measures increasing seed yield and quality.