Abstract:

Although the natural triploids, the giant forms of poplar in volume growth have been found in a few species of genus Populus in many countries in the world, the work of natural triploids of indigenous tree of poplar species in China has not been done until the national program of poplar breeding was established since 1983.The national program selection and breeding of triploids of Populus tomentosa has being conducted by group of professors in Beijing Forestry University for over 15 years (1983-1997). As the breeding strategy of triploids of Populus tomentosa, the Populus tremula and Populus tremuloides were firstly followed. Research started with natural triploid selection from stands, observation of larger 2n pollen, and the artificial induction of triploids of Populus tomentosa by colchicine treatment. So far the results of these three mentioned aspects were obtained. In this paper the observation of 2n pollen and selection of natural triploids of Populus tomentosa were summarized.By pollen observation and chromosome accounting of Populus tomentosa, the results indicate: (1)There are larger pollen grains in the natural spectrum of pollen of Populus tomentosa the diameter of larger pollen varies from 35~45μm, they cover 3.9% of total pollen with 38 chromosomes (1n=2x=38), which proves the larger pollen grains to be unreduced 2n pollen, and the smaller pollen wth 19 chromosomes (1n=1x=19), are normal haploid pollen; (2)The natural triploids (2n=3x=57) of Populus tomentosa are existed in the distribution area of P.tomentosa. So far 5 clones of natural triploids of Populus tomentosa have been found, which distribute in northern, western, and southern parts of its distribution area, and they separated very far each from other. It shows, the existence of natural triploids of Populus tomentosa has universality; (3)The volume growth, fiber length, stem pattern and resistance to pest of natural triploids of Populus tomentosa are much better than the productive colony. The average genetic gain for volume growth of 5 natural triploids exceed 56.4% over the control; the best clone among the natural triploids, the B383 exceed 154% over the control. The discovery the selection and utilization of these natural triploids of Populus tomentosa is very important for both pulp and timber production and also for academic research of forest tree breeding. Today a large scale of cultivation of these best natural triploids of Populus tomentosa has been spread up through the north part of China.

Key words: Populus tomentosa, Unreduced pollen, Natural triploid, Selection