Fig. 1. 2n pollen production induced with colchicine in Populus tomentosa clone 5088 (Bar = 200 μm). (a) 2n pollen induced with colchicine in P. tomentosa clone 5088 (arrow). (b) Natural 2n pollen occurred in P. tomentosa clone 5088 (arrow).

Fig. 2. 2n pollen production induced by colchicine in Populus tomentosa clone 5088. The values indicated by the different letters were significantly different within the phase at α = 0.05 according to the LSD test.

Fig. 3. Pollen production per bud after different numbers of colchicine injections were given in Populus tomentosa clone 5088. The values indicated by the different letters were significantly different at α = 0.05 in LSD test.

Fig. 4. Scanning electron micrographs of pollen grains of male flower buds in Populus tomentosa clone 5088 after receiving three or seven colchicine injections at diakinesis and from male flower buds cultured in tap water at 25 ℃ as control. (a) Morphology of pollen grains derived from the control group. (b) Morphology of colchicine-induced pollen grains after three colchicine injections were given and 2n pollen grains. (c) Morphology of colchicine-induced pollen grains after seven colchicine injections were given and 2n pollen grains. (d) Details of ectexine structure of natural 2n pollen. (e) Details of ectexine structure of colchicine-induced 2n pollen after three colchicine injections. (f) Details of ectexine structure of colchicine-induced 2n pollen after seven colchicine injections. (g) Details of ectexine structure of haploid pollen from the control group. (h) Details of ectexine structure of haploid pollen after three injections. (i) Details of ectexine structure of haploid pollen after seven injections. Scale bar = 100 µm (a, b, and c) and 10 µm (d, e, f, g, h, and i).

Fig. 5. Colchicine-induced 2n pollen from Populus tomentosa clone 5088 after the germination test in pollen germination medium. (a) Germination of pollen grains treated with colchicine. (b) Germination of natural 2n pollen grains. (c) Germination of colchicine-induced 2n pollen grains.

Fig. 6. 2n pollen viability in flower buds treated with 5000 ppm colchicine solution in Populus tomentosa clone 5088. Control corresponds to 25 ℃, i.e. standard culture conditions. The values indicated by the same letters were not significantly different at α = 0.05 in LSD test.

Fig. 7. Ploidy level determination by flow cytometric analysis and chromosome counting in progeny came from the cross combinations with colchicine-induced 2n pollen (Bar = 10 μm). (a) Histogram of flow cytometric analysis of young leaves derived from diploid and triploid plants. (b) Chromosome with 2n = 3x = 57 from triploid seedlings.