Studies On The Heterosis Of Interspecific Hybrid In Liriodendron

Using cross-breeding as main thread and moleculer markers technique as main means, the heterosis of interspecific hybrid in liriodendron was studied in this dissertation, included choice of parents, Cross-breeding technique, Hybrid identification, physiological foundation and utilization of heterosis, and so on. The main results are as follows: 1. The pollen quality is quite different among L. chinense, L. tulipifera and their interspecific hybrid and individual trees within a species ( or hybrid), and the cross-compatibility is different obviously among mating systems and crosses within mating systems. For the height and ground line diameter (GLD) traits after the first growing season, the general combining ability (GCA) and the maternal effects were significant, while the male effects and the specific reciprocal effects seem to be negligible. These results suggested that besides significant additive variance, there exist significant cytoplasm inheritance phenomenon. Therefore, the pollen quality, cross-compatibility and general combining ability (GCA) should be considered in parent selection of cross-breeding. The height and GLD increment of families after the first growing season showed a significant curvilinear correlation with genetic distances based on RAPD markers of parents (r=0.8235 for height and 0.5090 for GLD, respectively). So, the genetic distance could be used for the choice of parents and for the heterosis prediction in cross breeding of Liriodendron. 2. The pollen quality is changing during the flowering period, and reach the highest level in the middle time. If the pollen is stored in 4℃condition, the survival rate will dropped quickly. So, it is better to use fresh pollen of middle time of flowering period in cross-breeding. The filled samara rate of artificial pollination is changing during the flowering period and in a day. It is highest in the middle 10 dayes of flowering period and about 1PM of a day. In the early and late time of flowering period, pollination bags can improve the filled samara rate of controlled pollination. Theirfore, in this period, the artificial pollination shoud be carried out at 1PM and baged. While ,in the middle 10 dayes of flowering period, the artificial pollination can be done at any time of a day and non baged. The filled samara rate of open pollinated will be reduced to less than 1% if the petals and stamens are removed (i.e., emasculation). The pollen contamination rate of emasculated, non-bagged pollination technique, for the first time, was detected by means of RAPD markers in this paper. The results revealed that the 93 progenies decected, derived from this pollination technique, were all the progenies of the purpose male tree of the cross. No pollen contamination was found. So, the contamination of seed lots produced by controlled pollination of emasculated, non-bagged flowers will be negligible, and the emasculated, non-bagged pollination technique is viable in Liriodendron. 3. Of the 13 floral and fruit quantitative traits, the length of perianth segment and 8 other traits are different significantly among L. chinense, L. tulipifera and their interspecific hybrid, which were successfully used in group-discrimination by means of the methods of cluster analysis and principal components analysis. Of the total 136 fragments amplified with 25 10-mer primers, 3 (OPK15-1150/1,OPO12-550/3,OPAU16-1200/3) presented in all the 5 L. chinense sample trees, but absented in all the 5 L. Tulipifera sample trees, 8 (OPK09-600/1,OPO05-2500/2,OPP03-950/1,OPP05-500/2,OPY20-450/1,OPAG12-1400/1,OPAU05-600/1,OPAU19-1400/1), on the contrary, presented in all the 5 L. Tulipifera sample trees, but absented in all the 5 L. chinense sample trees. All the 11 fragments could be detected In all the 6 hybrids sample trees, and, therefore, could be used as markers in the hybrid identification. The range of genetic distance among the 5 L. chinense sample trees is 0.0606~0.1763. The range of genetic distance among the sample trees between L. chinense and L. tulipifera is 0.3909~0.5432 and between L. chinense and the hybrid is 0.2031~0.3694. Because the 3 ranges are not overlapped, therefor, the genetic distance between an unidentified tree and a L. chinense tree could also be used in the hybrid identification. All the 16 sample trees were grouped correctly according to the RAPD based genetic distance. So, the UPGMA (unweighted pair group methods of arithmetic(average))cluster analysis method is useful in the hybrid identification as well. 4. Compared with the mating system of C×C, the mating system of C×T can produce the seeds with 70.78% more higher germination efficiency, one day lesser time of average germination period and three days earlier of germination fastigium. These can consider as heterosis in seed traits. For height and GLD traits after the second growing season, the 4 matting systems of direct cross, reciprocal cross, back cross and cross among F1 individuals did not have significant difference, while the families within matting systems differed significantly (P<0.01). And the mean CV within families in height and GLD traits were 29.16% and 31.87%, respectively. Therefore, the 4 matting systems all could be used. But for obtaining higher heterosis and gain, family selection and within family selection should be carried out. 5. Of the total 57 fragments amplified with fourteen 10-mer primers across a fullsib family, including 2 parents and 18 sibs of L. chinense×L. tulipifera, 20 (35.09%) were polymorphic between the 2 parents, indicating a lower level genetic diversity between the two species. Fingerprints of 31 Liriodendron interspecific hybrid clones were constructed with RAPD markers.The 23 primers screened could result in 128 loci, of which 76 (59.38%) loci were polymorphic. The genetic distance between clones ranged 0.0813~0.3522 and averdged 0.2069. This indicated that the genetic diversity within the clones is reletively lower. Therefor, the genetic basis of parents should be broadened in aftertime cross breeding. 6. The heterosis for height growth of the interspecific hybrid mainly had been caused by the reletively great elongation of internodes. Althought the uppermost 3 internodes had the potential of elongation, the first one which had the greatest elongation amount brout about the heterosis of the height growth. The concentrations of endogenous GA1/3, IAA and iPA were different greatly among L. chinense, L. tulipifera and their interspecific hybrid. All of the 3 interspecific hybrid families stuied contained significantly higher concentrations of endogenous GA1/3 and iPA in the uppermost 1 internode than their parental species. Thus, a correlation was observed between the concentrations of endogenous GA1/3 and iPA and hybrid vigor for height growth in Liriodendron. the rankings for the concentrations of endogenous GA1/3 and iPA in the uppermost 1 internode of the 3 hybrid families were not similar to the ranking for height growth of 3-years-old trees. So, the concentrations of endogenous GA1/3 and iPA in the uppermost 1 internode could not be used in forecasting of hybrid vigor.