Genetic Structure And Pretreatment For Seed Germination Of Sorbus Pohuashanensis

Genetic diversity and variation patterns of Sorbus pohuashanensis were studied throughanalysis of mating system and genetic structure of different populations using allozymemarkers and morphological traits, aimed to lay a theoretical basis for germplasm collection,conservation and utilization of the species. Bioassay of inhibitors in different parts of the fruitwas carried out and endogenous hormones were measured to understand the factors leading toseed dormancy. Treatments with differet concentration of endogenous hormones combinedwith low temperature stratification were used to promote germination. The results are asfollows:1. Morphological diversity was studied among 80 individuals of S. pohuashanensis. Variationanalysis of all characteristics were significantly different among populations and amongindividuals within population. CV was varied from 5.2% to 14.51%, markably differentamong phenotypic characteristics. The variations in leaf traits were greater than those offruit traits. Average of the phenotypic differentiation coefficient (Vst) was 0.4820,indicating that the genetic variation within population was the main sources of geneticdiversity in S. pohuashanensis.2. Genetic Variation of 4 allozymes was studied by using horizontal starch-gel electrophoresisamong 60 families of S. pohuashanensis. A total of 7 loci were assayed, and 4 loci werepolymorphic. The percentage of polymorphic loci (P) was 57.14%. The average number ofeffective alleles (ne) per locus was 1.6790. The expected heterozygosity (He) was 0.2443,which was higher than the average of woody perennials angiosperms (ne=1.20, He=0.143).Gene differentiation coefficient of S. pohuashanensis was so low as 0.0574; showing thatthere was high similarity among different populations. The estimated Multi-locusoutcrossing rates were from 0.826 to 1.000. All the above parameters showed that S.pohuashanensis was great in its genetic diversity with strong adaptive potentials toenvironment.3. The analysis of seed dormancy mechanism of S. pohuashanensis showed that seeddormancy was due to embryo, not the seed coat. The existence of inhibitors in the embryo,including ABA induced embryo dormancy. Seed pretreatment with 1500ppm GA₃ for 1.5day combined with cold stratification for 45 days, could be used to break seed dormancy.It could meet the need of seedlings production. Fine management was one of the keymeasures to raise robust seedlings.4. The rich genetic diversity at morphology and molecular level of S. pohuashanensis provided a basis for selection and breeding for the genetic improvement of the species.Selection of superior individuals within population was an important step of geneticimprovement of S. pohuashanensis due to its greater variation within populations. In situconservation should be considered in order to better maintain genetic diversity of S.pohuashanensis.