Genotvpic Variation And Selection In Eucalyptus Urophvlla And Hybrid Clones With E. Urophvlla

In this thesis, Eucalyptus urophylla families and hybrids clones with E.urophylla S.T.Blake were researched for genetic improvement and multiple-traits selection in order toanalyze genetic gain between generations, evaluate parents and cross combinations, estimategeneral combining ability, specific combining ability, heterosis and inbreeding depression,select best clones with fast growth, high wood properties and good stem-branch traits,investigate the effectiveness of nondestructive methods to predict wood properties standingtree traits in eucalypt hybrids clones, analyze age trends and correlations of growth and woodproperties in clone of Eucalyptus urophylla×E. grandis, and make a academic base foreucalypts breeding strategy and upgrade in industries. The major conclusions were to:(1) Growth traits, wood properties, stem-branch characteristics and bark percentage wereassessed for E. urophylla clones measured at age21,52,71and96months. Analysis ofvariance showed that there were significant differences on growth traits, wood properties andindividual tree wood weight at0.01and0.05levels among clones. Different traits had differentcoefficients of variation, while individual tree wood weight had biggest variation value.Repeatability ranged from0.36to0.53for growth traits,0.35to0.51for wood properties,0.21to0.24for stem-branch characteristics,0.07for bark percentage and0.31for individual treewood weight. The strongly negative genotypic correlations suggesting that selection ondiameter at breast height at21months can not be effective to predict diameter at breast heightat96months whereas it could be used to predict diameter at breast height at52and71months.The selection gain on diameter at breast height over bark by different selection proportions at21,52,71and96months old expressed that selection gain at71months was some what higherthan that at other ages during10%to30%selection proportion, while selection gain at52months was some what higher than that at other ages during60%to90%selection proportion.Genetic gain ranged from-2.11%to8.10%, and this value of branch and bark percentage werenegative. (2) Genetic analysis of6×6full diallel mating showed that different traits showeddifferent general combining ability and specific combining ability even for same parents. Crosscombinations with high general combining ability for growth traits always had high specificcombining ability. Cross combinations with high general combining ability for wood basicdensity always showed low specific combining ability. Inbreeding depression rangeddifferently for different parents with different traits in different sites. Different crosscombinations at different sites showed different heterosis. The heterosis of tree height hadsimilar value range of diameter at breast height. Same parents always had similar original andreciprocal heterosis. Genetic gain ranged from-13.19%to25.47%and this value of studiedtraits were positive except for wood basic density and bark percentage. The genetic gains ofgrowth traits were higher than other traits. The genetic gain of full diallel families wasgenerally higher than clones.(3) Growth traits, wood properties and bark percentage were assessed for19hybrideucalypt clones sampled at age51months. Analysis of variance showed that there weresignificant differences in growth traits and wood properties between clones and sites, and thatthe clone×site interactions were also significant except for basic density. Coefficients ofvariation ranged from8.4%to27.9%for growth traits,2.7%to11.1%for wood properties and14.0%to23.3%for bark percentage. Repeatability ranged from0.73to0.96for growth traits,0.32to0.93for wood properties and0.77to0.88for bark percentage. Strong genotypiccorrelations between the same traits in clones at pairs of sites indicated that the traits wererather stable across sites. The correlations between growth traits and Pilodyn pin penetrationwere positive, ranging from0.28to0.65and therefore unfavorable as lower wood density willbe associated with higher values of Pilodyn pin penetration and improved growth rate. Thegenotypic correlations between growth traits and basic density ranged from-0.67to0.43, andgenerally favorable negative genotypic correlations between growth traits and bark percentagewere also found. Differences among hybrid eucalypt clones indicated that more care should betaken regarding selection for wood basic density in cross of E. urophylla×E. grandis andgrowth in crosses of E. urophylla with E. tereticornis and E. camaldulensis. (4) Wood basic density, outer wood density, heartwood density, modulus of elasticityand pilodyn penetration were analyzed at22eucalyptus clones in Guangxi, at which time thetrial was aged56months. The results indicated that there were significant differences (1%level)in pilodyn penetration between different treatments, different directions and among the clones.Generally strongly negative correlations were found between pilodyn penetration and woodproperties, and the coefficients ranged from-0.433to-0.755, suggesting that the use of pilodynfor assessing wood density and modulus of elasticity was confirmed as a possibility. Woodproperties and nondestructive methods were assessed for23eucalypt clones in Guangdongsampled at age51months. Correlations between three traits assessed using nondestructivemethods and basic density measured on increment cores showed that genotypic correlationbetween Pilodyn penetration and basic density was significantly and negative (r=-0.83). Thecorrelation between basic density and modulus of elasticity was significantly positive (r=0.74).Stress wave velocity was found to be relatively strongly correlated with basic density (r=0.52)and modulus of elasticity (r=0.96). Results indicated that the average basic density andmodulus of elasticity can be predicted by using Pilodyn and Fakopp microsecond timer.(5) Growth traits and stem-branch traits were assessed for20hybrid eucalypt clonessampled at age44months. Analysis of results showed that there were10clones with highergrowth than general mean. The growth of No.3(DH32-28) was fastest, whereas the growth ofNo.17(U6) was lowest. Repeatability of growth traits, crown range, branch height, stem andbranch were0.86,0.80,0.80,0.54,0.85,0.77and0.44respectively. Coefficients of variation ofgrowth traits, crown range, branch height, stem and branch were9.84%,9.91%,28.54%,18.26%,11.73%,12.03%and17.28%respectively. Correlations results showed that cloneswith higher growth generally had bigger crown range, better stem and smaller branch.(6) Growth traits and wood properties were assessed for DH32-29, a clone of E. urophylla×E. grandis, at age of two to six years in Guangdong Xinhui. Analysis of variance of studiedtraits showed that there were significant differences (1%level) on all studied traits among agesexcept for wood basic density. Analysis of age trends of growth traits and wood propertiesrevealed that rotation length of DH32-29should be more than six years or longer. Phenotypic correlations among traits at individual ages indicated that correlations among growth traitswere strongly positive. There was significant change in relationship between growth and woodbasic density with increasing age, ranging from-0.03to-0.54at2and5year and0.003to0.3at3,4and6year. Correlations between Pilodyn pin penetration and basic density measured onincrement cores showed that Pilodyn could rank or group genotypes or sites into densityclasses, but failure to predict individual tree and individual clone.