Fraxinus Velutina Introduction And Interspecific Hybridization Breedings Of Fraxinus

In China the tree species resource of Fraxinus is abundant.Fraxinus velutina Torr.is one of the successful introduction of exotics.Due to its charactefistcs of good salt-resistance,good watchfulness and wide distributions,it has been introduced by many regions in China.It has also become the excellent tree species of foresting and greening by part of the coastal cities and saline and alkaline areas.Unfortunately F.velutina has not been introduced to Heilongjiang province yet.In this thesis the F.velutina introduction was taken as the major clue.The related techniques,such as seedling introduction,seed seedling,experiments of salt resistance and the grafting techniques were systematically investigated,which were expected to provide research basis.In order to improve the quality of the tree species of Fraxinus and also to integrate the excellent gene resources,the interspecific crossbreedings for Fraxinus were mainly focused in this thesis.The main research contents are as follows:Seedling Introduction The F.velutina introduction,cultivation and the regional experiments have been carried out in the areas of Daqing,Maoershan and Harbin of Heilongjiang province.The cold-resistance has been gradually enhanced after three years of introduction and domestication for F.velutina.The species can grow up and overwinter normally with good growth vigor.Compared to the local species of Fraxinus mandshurica Rupr,the introduced species exhibited faster growth,bigger crown width as well as better watchfullness.In addition,the more powerful saline-alkali tolerant capability was exposed for the seedling in Daqing and Zhaozhou experimental areas.Seed planting Seed planting experiments were conducted in the areas of Harbin, Zhaozhou and Binxi of Heilongjiang province.The germination rates of the seeds were relatively high,and the seedling vagors were good in all experimental areas.The seedling can overwinter without any extra cold-proof measures.Compared to the introduced seedlings before,the cold-resistance capability for the seeds was gradually enhanced during the course of germinating and growth.It is easier to adapt to the new environment.So the seed introduction of F.velutina in Heilongjiang is more appropriate.Experiments of salt resistance To simulate the ion,concentration and pH value of salinity of the alkaline soil in Daqing area,five neutral salts of NaCl,Na₂SO₄,MgCl₂,KCl, CaCl₂ and two alkaline salts of NaHCO₃ and Na₂CO₃ were blended into mixed-salts solutions. Three concentrations which were equivalent-to one time,two times and three times concentration of the alkaline soil were used to stress the introduced species of Fraxinus velutina Torr.A comparison was presented between the growth and the physiological indices of SPAS,SOD,POD,MDA as well as the Proline for the species.The analysis results showed that the species could survive under the stress with concentration by one time mainly due to the growth in harmony to the changes of the physiological indices.Grafting techniques As the strong affinity of F.mandshurica,it could be successfully grafted with the scion of F.velutina by both methods of chip budding and cleft grafting.In comparison,the grafting efficiency was high for the chip budding method because it can save scions effectively and the survival rate of chip budding can reach above 80%.The seedling growth and the overwinter ability were so good that the cold-resistance can be enhanced greatly, which Verifies that it is feasible to introduce to Heilongjiang by grafting.Crossbreeding techniques The interspecific crossbreeding between F.manchurica and Fraxinus velutina,,Fraxinus sogdiana and F.arnericana with different provenances and clones were studied in details as follows:Based on the preliminary single-factor experiments and the orthogonal arrays the culture medium condition for pollen germinating in vitro has been determined,the culture medium ingredients of pollen germination in vitro for Fraxinus were optimized by employing the BBD(Box-Benkhen Design) based response surface methodology so that the pollen germination rate had been greatly enhanced,which provided effective method for crossing parents selection.In addition,this is as well a new way to apply the optimum theory into the study of plant pollen in the research fields of botany.The crossing parents exhibited significant biological difference,and were complementary in advantages and disadvantages as well as the obvious heterosis.By interspecific crossing a total of 16361 seeds with 140 crossing combinations were obtained.This research will provide a basis for the cultivating of valuable hybrid F1 gene and future new crossing species.The pollen of F.velutina is treated by the proper intensity of high-pressure electrostatic field,the high pollen germination rate and high setting percentage of crossing are enhanced, which overcome the difficulty of interspecific incompatibility of Fraxinus and provide effective way for interspecific crossing of forest.Based on the conventional paraffin sectioning method,the development process of the hybrid embryos between F.mandshurian and F.velutina was observed at the optical level,which reveals the following processes:the development process of proembryo,globular embryo, heart-shape embryo,fish-torpedo-shape embryo and cotyledon embryo.The endosperm is developed firstly after fertilization.The nuclear endosperm is gradually developed into cellular shape endosperm in the course of the development.This work provides proof of morphology for the interspecific crossbreedings of Fraxinus. The embryo abortion of interspecific crossbreeding of Fraxinus can be overcomed by in vitro culture of immature hybrid embryos.The tissue culture seedling for all crossing combinations can be obtained,and the hybrid plants can be obtained in early stage by acclimatization and transplants.It takes only 3 months from embryo culture to seedling formation.This method can reduce nearly one year comparing to the traditional breeding methods.The technical platform of tissue culture and regeneration of hybrid are set up based on the culture of immature hybrid embryos,the hormone combinations and rooting conditions for culture medium for stem reproduction of hybrid canbe obtained.These can provide significant technical supports for the asexual breeding of valuable hybrids.