Genectic Analysis And F₁ Selection Of Eucalyptus Urophylla Intraspecific And Interspecific Crossing Combinations

Eucalyptus urophylla S.T.Blake has become the main species in Eucalypts plantation and as an important industry rough materials forestry species in southern China. In this thesis, E.urophylla was researched by complete diallel crossing of intraspecific and interspecific factorial crossing with E.camaldulensis, E.grandis, E.pellita of Eucalyptus. The research in order to analyse genectis effect of the main traits of crossing progeny, estimate the family and individual heritability and then provide a theoretical basis for high-generation breeding and heterosis utilization, evaluate and select excellent parents for next stage of the breeding programs, select good crossing combinations with both high-yielding and good wind resistance for application. By the way, long-term strategy for hybridization breeding was concluded on the basement of forest genetics and breeding theory and conclusions of genetic analysis appeared in this paper. The main conclusions were as follows:(1) Genetic analysis of 6×6 full diallel mating was conducted on 34 crossing combinations of E.urophylla. The results showed that there were significant differences between combinations, male parents and female parents on seedling traits, field growth traits and form quality traits. The results of genetic analysis of mating showed that the progeny traits of E.urophylla were mainly affected by dominant gene and additive effect, whereas additive effect played a leading role. Selfing progeny of E.urophylla showed depression in general, but some other combinations showed self-advantage. The growth traits of U64 and U1 had a high general combining ability effects and maternal effects, and more heterosis would be obtained if they were taken for parents in breeding. There were 21 crossing combinations which volume on per tree was greater than the optimal parent of U22. The crossing combinations of U22×U56, U21×U64 and U21×U56 had higher specific combining ability.(2)Genetic analysis of interspecific factorial mating design was conducted between E. urophylla and E. camaldulensis, E.grandis and E.pellita. The results showed that there were significant differences between combinations, male parents and female parents on growth traits of 108 factorial crossing combinations. There was greater heterosis on interspecific of eucalyptus urophylla. And more heterosis would be obtained if excellent combination were taken for parents in breeding. TH05107, TH05108 and TH05094 were selected as excellent combinations due to their higher growth performance. U21 and U15 were selected as excellent female parents by general hybrid ability, and G10, G8 (E.grandis), RT01 (E. camaldulensis) and P5 (E.pellita) were excellent male parents.The mating effect of E.urophylla×E.grandis was better than E.urophylla×E.camaldulensis. The genectic variation on growth traits of interspecies combinations were controlled by additive gene and dominant gene, but dominant gene played a leading role. Male effect was greater than female effect on E.urophylla interspecific mating trials. Family heritability on growth traits of interspecific combinations, which were mainly controlled by gene were ranged from 0.363 87 to 0.771 28 as medium to high intensity heredity. More genetic gain was expected to obtain form selection of full sibs and half-sib.(3) Genetic analysis of reciprocal crosses combinations was conducted between E.urophylla and E.camaldulensis. The results showed that there were significant differences between combinations, male parents and female parents on growth traits of 72 reciprocal crosses combinations. All E.urophylla parents had consistent performance on SHA values of growth traits without distinction of female tree and male tree. The GHA of U21 and U55 were positive not only as male parents but also as female parents. The GHA values of was different with all six E.camaldulensis parents as an female or an male tree except RT09. The growth and heterosis of direct cross combinations were higher than reciprocal cross. The volume and heterosis of crossing combinations like U21×RT01, U2×RT09, RT07×U2, and RT07×U15 were higher, as they can be defined as a combination with excellent growth traits, which volume heterosis were 41.84%, 25.75%, 32.30% and 19.80% compared to top parents, respectively. The variation on growth traits of reciprocal crosses combinations were controlled by additive gene and dominant gene, and female efect of reciprocal cross were higher than direct cross. Family heritability of all traits with reciprocal crosses combinations was medium to high intensity.(4) The results of multi-trait selection on Eucalyptus crossing combinations showed that there were significant differences on growth traits, quality traits and wind resistance. There were 17 and 3 combinations on multi-site tests which volume was higher than U22 and CK2 (DH201-2), respectively. TH04092 (E.urophylla×E.grandis) had the best growth performance, and its heterosis was 16.61% which compare to the top parent. Six crossing combinations were selected as high-yield stability combinations by non-parametric and Eco-valence methods of genectis stability analysis. There were 29 combinations which volume was higher than optimal parent RT01 in Expt.07H02. E. camaldulensis (open-pollinated families and as parents) had the best wind resistance, and the combinations of E.camaldulensis×E.urophylla had better performance. By correlation analysis, characters of wind resistance had the relative independence. Two excellent both growth and wind resistance combinations were selected by independent culling method, and percent selection rate was 2.5%.(5) The status of Eucalypts hybridization breeding and its shortcomings in our country were discussed. The development of the cross breeding programs for high-yield and stress tolerance on E. urophylla and E.camaldulensis were discussed as an example to clarify the fact that interspecies improvement and parent matching were critical steps. At the same time, more attention should be paid on F2 and male-sterile individuals for self-cross and backcross breeding. The breeding process would be accelerated by broadening the genetic basis of parent groups and applying of enhanced breeding technology. The organic combination of cross hybredization breeding, molecular biology and ploidy breeding would be an mainly important development direction on the long term research work of Eucalypts genectic and breeding in the future.