Genetic Testing And Genetic Design Of Breeding And Production Populations For Platycladus Orientalis

Platycladus orientalis is an important ecological and timber tree species for afforestation in mountainous areas of northern China.Seed orchards are established to provide genetically improved seeds for increased production gain.The current seed orchard for this species in China is in the first cycle of primary orchard that needs transformation to the advanced stage.Scientific development of breeding strategy at this stage will lay an important foundation for sustainable improvement of tree species.This thesis analyzed the genetic variation of the plus trees and open pollination families on growth and morphological traits in the breeding station in Jiaxian County,Henan Province.The genetic variation of reproductive traits and gamete contribution among clones were assessed from multi-year data.With timber production and ecological forestation as breeding targets,the thesis suggests the construction of corresponding breeding and production populations for the second cycle of improvement.The design for an advanced seed orchard is also laid out together with suggestions for modification of existing seed orchards.Main research results of this thesis are:(1)There were significant differences in tree height,DBH,volume,branch angle,branch height and crown width among 166 clones of P.orientalis in the studied seed orchard.The repeatability of the above traits among clones are 0.193,0.265,0.162,0.224,0.201,and 0.353,respectively,and 0.520,0.910,0.871,0.851,0.904,and 0.861,respectively among provenances.The relative leaf density was also significantly different among clones.The growth and morphological traits have great selection potential among the clones.(2)There were significant differences in male and female cone production among 166 clones of P.orientalis over years.The mean yield of male and female cone ranged from 1.667-4.778 to 2.000-5.000,and the variation coefficient of these traits ranged from 0.349 to 0.606.There were significant genetic variations in seed cone yield among provenances,among nested clones within provenances,and among sexes(P < 0.001),and the reproductive output of male strobili was higher than that of female.This suggests good selection potential for reproductive traits among the clones.(3)There was a significant correlation between the number of effective parents(Np)and genetic diversity(GD)in seed orchard crops.When Np was 30,GD maintained above 95%.Monitoring fertility changes in the clones is important to increase seed production and maintain the balance of genetic diversity.(4)The progeny testing showed significant differences in growth traits between families.A few families maintained growth superiority over years.Two families65 and 147 appeared outstanding in 2008 and 2021.(5)Based on pedigree reconstruction in seed orchard progeny,we found the contribution of gametes among parents was very uneven,and a few parents contributed the majority of male gametes.The number of offspring in the seed crop ranged from 1 to 46.Four fathers contributed significantly more than other parents,resulting in 5.7% of the parents in orchard sired 30% of the progeny.The pattern conforms to the "20:80 rule" of conifer seed orchard reproductive output.(6)This study found that growth traits and morphological traits are significantly correlated.The breeding value,genetic gain and genetic value of growth traits are also significantly correlated,but no correlation between growth traits and reproductive traits,and no correlation between reproductive output of strobili and actual gamete contribution.The selection of clones and progeny should be screened for these traits accordingly.(7)This study constructed the breeding and production populations for the second improvement cycle.Based on parental growth,morphology,reproduction,progeny growth,actual gamete contribution,genetic relatedness or geographical distance,18 clones and 18 progeny genotypes were selected as breeding populations with wood production as the breeding target.24 clones were selected as breeding population for ecological breeding.With high reproductive yield as the breeding goal,18 clones were selected as the production population.Both breeding population and production population could achieve high genetic gain.(8)This study developed fingerprinting marker systems for identification of the 166 clones.In order to effectively control inbreeding,increase heterozygosity in progeny,and expand the genetic diversity of seed orchard,we suggest to adopt the clonal arrangement design of grouping,unbalanced,complete,fixed block and disordered in the construction of new seed orchard in the second improvement cycle.At the same time,the site selection and stock transplanting should be considered.(9)Based on the results of parental evaluation,we suggest to carry out thinning and tree pruning in the primary seed orchards to increase light transmission.While maintaining the basic level of seed yield,the efficiency of harvest should be improved as much as possible and reduce the difficulty of harvest operation and the cost of manpower.Our study provides reference for the genetic improvement process of seed orchards.This study evaluated the genetic variation in parents and progeny of the primary seed orchard of P.orientalis,and selected good parents and progeny for the next cycle of breeding.This study provided important guidelines for the reconstruction of the exciting primary seed orchards and the construction of the second round of seed orchards,and will thus facilitate genetic improvement of P.orientalis and other conifers.