|其他摘要||There are some 50 species in genus Michelia L. in the world. China has about 41 species in the genus, and Yunnan province occupies over 60% of the China’s total. Both species of M. crassipes and M. calcicola are valuable ornamentals. In order to probe into the biological traits and inheritance in cross-breeding of genus Michelia and to direct the breedings of new Michelia cultivars in the future, the morphology (plant shape, leaf shape, flower color and conformation, pollen micromorphology, leaf anatomy and epidermal micromorphology), cytology and pollen vitality of M. crassipes, M. calcicola (♂) and their F1 hybrids were comparatively studied.
The F1 hybrids varied from each other in plant shape, leaf shape, flower color and conformation, pollen morphology, leaf anatomy and epidermal micromorphology. The phenotype of the F1 hybrids showed continuous variation, and inherited the characters of both parents. Most of individual plants had the characters between the parents, and a few of them beyond the parents.
The androecium color showed matrilinear inheritance or dominant inheritance. The subpolar side of pollen with a bulge in the middle may be qualitative inheritance. Besides the two characters, all the other characters showed quantitative inheritance.
Some 57.7% of the F1 hybrids had a higher stoma density than the parents. This character might be related to the F1 hybrids’ week cold-resistance as we observed in the field. The dwarf hybrids individuals had low stoma density, and they might have stronger cold-resistance than that of the normal ones. It’s expected that the dwarf ornamental cultivars of Michelia hybrids for pots can be bred.
2. Anthesis biology and pollen vitality
The amount of flowers on the F1 hybrids individuals was very variable from each other, and its amount of flowers is alternative between years. The dwarf hybrids were not yet abloom. The flowers of parents and the F1 hybrids were all protogyny to avoid self-fertilization. Duration of single flower blooming can be affected by the environmental temperature, and the longest ones can last 14 days and the shortest ones only last only 4-5 days.
Most of the F1 hybrids’ fresh pollen could well germinate in the sucrose concentration of 100g/L and 150 g/L. The germination percentage was stable after 8 hours. Pollen with -20 ℃ condition for one year have very different germination percentage in 100 g/L、150 g/L sucrose concentration. So storage pollens should be chosen for the optimum sucrose concentration, but not the fresh ones. Temperature of 25 ℃ was optimum for pollen germination and the higher temperature could prevent the tube elongation and induce the top of the tube burst. M. crassipes and M. calcicola had higher pollen germination percentage of more than 90%. But pollen of the F1 hybrids were lower vigorous than their parents, and the germination percent varied from 38% to 79%, with the average of 57.7%. The difference of pollen germination percent among the F1 hybrids individuals and between the F1 hybrids and the parents were significant.
The chromosome numbers of M. crassipes, M. calcicola and the tested F1 hybrids (normal ones) all are 38 (2n=2x=38), and the polyploidy and aneuploid were not found in the normal F1 hybrids.
In conclusion, the results would be the valuable data for further understanding the biology and heredity in cross-breedng of genus Michelia. The significant difference of morphologis and anthesis biology among the F1 hybrids provides the scientifical basis for the new cultivar selection through the successfully vegetative propagation of centain individual plants. As stated above, the normal F1 hybrids had a stable chromosome number of 38 (2n=38); polyploidy and aneuploid did not exist, and most of the pollens were fertile and vigorous. Thus, it has a great possibility for new cultivar breeding through crosses among the F1 hybrids individuals. The cytological habits of the extremely dwarf F1 hybrids and its value for further breeding need to be studied in detail.|