Abstract:
In this paper, the strategic purpose and significance of introducing Eucalyptus grandis into Hunan province were elaborated from many aspects such as climate, forest resources and the characteristic of species structure etc. After ten year experiments on the introduction of Eucalyptus , species and provenance of Eucalyptus , and families of Eucalyptus in Hunan, the purpose of Eucalyptus grandis' breeding became more clear and definite. Therefore, the strategies for breeding Eucalyptus grandis were put forward and an optimal proposal was raised for carrying out the studies on breeding of Eucalyptus grandis in Hunan.Cite
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Conventionally, Eucalyptus grandis × E. urophylla (GU) hybrid material is first tested as seedlings in progeny trials for at least four years before ortets are selected and ramets of the selected ortets are propagated to test in clonal trials. The primary constraint with this 'conventional hybrid breeding strategy' (CHBS) is the time required to first test the hybrid material as seedlings. In order to address this, an 'accelerated hybrid breeding strategy' (AHBS) was investigated to reduce the time spent on testing GU hybrid material as seedlings. However, it is of utmost importance to quantify the impact the AHBS might have on genetic gains and genetic information. With this in mind, two clonal populations have been established with genetic material that derived from the CHBS and the AHBS. The main purpose of this study was to do a comparative study between the CHBS and AHBS, firstly to quantify the genetic gains per unit time for GU hybrid clonal populations that have been derived from the CHBS and AHBS respectively, and secondly to obtain genetic parameters such as heritabilities, the ratio of dominance, clonal within family variance, and the proportion of additive and non-additive genetic variance. The results indicated that the percentage realised volume gains per year was higher for the AHBS (3.7%) than for the CHBS (1.9%) when compared with the GU commercial clone. Thus, shortening the testing time of GU seedlings had a positive impact on volume gains per year. With regard to genetic parameters, both the AHBS and CHBS clonal populations indicated that non-additive genetic variation explained the majority (88% and 71%, respectively) of the genetic variation. Due to the pre-eminence of non-additive genetic variation, the narrow-sense heritabilties for the female and male effects were negligible for both clonal populations. Overall, the majority of the non-additive genetic variation was explained by the proportion of dominance variance, and less by the clone within family effect. These results suggest that, firstly, the time spent on testing GU hybrid material as seedlings should be minimised and, secondly, a hybrid breeding strategy to capture non-additive genetic variation should be adopted.
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Orchard
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As a theoretical basis for improvement of Eucalyptus urophylla in China, the genetic diversity and structure for advanced generation breeding populations were evaluated, and the changes of genetic diversity between improved generation and their parental generation were compared.The genotyping was performed on families sampled from advanced generation with 16 neutral microsatellite loci.The testing of Hardy-Weinberg equilibrium showed significant heterozygote deficits in two improved generation breeding populations.The expected heterozygosity of the 3 rd generation was very close to that of the 2 nd generation breeding population, indicating no heterozygosity had been lost, and the genetic diversity was consistent in two improved populations supported by Shannon's information index.Wright's fixed index of two advanced generations also indicated significant heterozygote in advanced generation breeding populations, compared with their parental generation.Most of the molecular variation was explained by the source of the families, both in two advanced generations, using analysis of molecular variances (AMOVA).The advanced generation breeding population of E. urophylla had a high level of genetic diversity after heavy artificial selection, consistently, and with no significant difference among generations.
Tree breeding
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Eucalyptus nitens
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Investigating the growth status of Eucalyptus dunnii in central Hunan Province,this paper demonstrates that it grows at a rate of about 1.5 to 2 meters per year with its diameter around 2 to 3 centimeters,and has a great ability for infertile-resistance,cold-resistance and rapid growth.Concisely summarizing the breeding techniques of Eucalyptus dunnii seedlings,the paper also puts forward some solution to the existing problems.
Adaptability
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Plant Physiology
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