Selection Of Superior Larix Kaempferi Families For Pulpwood Purpose And Family-based Growth Simulation

Larix kaempferi(Japanese larch)is one ofthe most important coniferous speciesfor pulpwood in China．Direct application of clonal propagation and hybridutilization of controlled pollination based on selected superior families isessential for improved breeding and intensive silviculture of thepulpwood-oriented Larix kaempferi．This study Was carried out in a 15一year-oldprogeny test of open-pollinated families in Jianshi County,Hubei Province．With pulpwood as a cultivated target,the genetic variation of its growth traits,stem-form and pulpwood qualities of families was comprehensively and systematically studied,and the growth variations and prediction of genetic gains of these families were explored as the first time from both quantitative genetics and biological mathematics．Height-age models for each family were established,and the age trends in genetic parameters for growth traits were analysed．Furthermore,according to its growth trait,stem-form and pulpwood qualities,a number of superior families and plus trees were selected in the subtropical region of China．Main conclusions from the study were as follows:Genetic variations among growth,stem-form and wood traitsVariance analysis revealed that DBH,height and individual tree volume weresignificantly differed from 5 yr to 15 yr among Larix kaempferi families,and SOwere among individuals within a family,which mean that there was big potential either for individual selection or families selection and they were the maj or sources for its genetic improvement．Among families,there were very significant differences in the main-branch length,bark thic;ss,andholo-celouse；there were significant differences in the main-branch diameter,crown width,fresh-branch diameter,fresh．branch number,wood basic densitNfiber length of early and late wood,wall／lumina of early and late wood；andthere were significant differences in the 1％NaOH extract at 1 0％level as well．This showed that these traits had great potential for family selection,and thenshould be mainly considered when conducting such selection．However,therewere insignificant differences among families in the taper,flesh．branch length,branch angle and under-branch height,which mean that family selection fromthese traits were not necessary．Heritabilities and genetic correlations for growth,wood qualities and stem．formwere estimated for open-pollinated families of Larix kaempferi．Most traits,whose family heritabilities were over 0．5,were moderately or stronglycontrolled by genetics,while those for taper,branch angle and under branchheight were low,only with 0．29．The age-age phenotypic and geneticcorrelations for DBHs,heights and volumes were very high,indicating thatthese relationships were mainly controlled by genetic factors．Six years was themost proper age for early selection in the half-sib families,and DBH was abetter indicator than height due to its genetic stability．Phenotypic and genetic correlation among traitsThe phenotypic and genetic correlation among traits of Larix kaempferi familiesindicated that the relationships among traits were complicated,i．e．,positive andnegative correlations coexisted．It was important to take a comprehensiveselection SO as to optimise all the traits according to the breeding target．It wasquite possible to pick out the right families with better performance in fastgrowth,high wood density,holo celouse,and long fiber,and low 1％NaOHextract and wall／lumina through rational selection and silvicultural measures．Path analysis of nine traits,which were highly correlated with tree volume,showed that the direct contribution of DBH and height on the variations of treevolume took up about 63％of the total variations．On the other hand,those traits,such as tree crown and wall／lumina,affected the volume strongly by indirectway of the geneti...