Ploidy level and contrast analysis of the traits for superior trees of Populus tomentosa Carr. in gene pool

We used the flow cytometry to determine the ploidy level of 469 clones of Populus tomentosa in a gene pool located at Guan County of Shandong Province and analyzed the variations in growth, form quality and stomatal traits for identified natural triploid clones and their neighboring diploid clones of P. tomentosa from the same provenance. Twenty-eight natural triploid clones of P. tomentosa (24 female and 4 male clones) were determined, accounting for 6.0% of the total clones in the pool. Among those triploid clones, 2 were derived from Beijing, 12 from Hebei, 1 from Shandong, 2 from Shanxi and 11 from Shaanxi, which accounted for 0.4%, 2.6%, 0.2%, 0.4% and 2.3% of the total clones in the pool, respectively. There were similar characteristics such as growth, form quality and stomatal traits among natural triploid clones of P. tomentosa. Compared with diploid clones, triploid clones had characteristics of faster growth, thicker branch diameter, and bigger and sparser stomas. There were extremely significant differences between natural triploid and diploid control clones of P. tomentosa in diameter at breast height (DBH), volume of timber, branch diameter, stomatal length, stomatal width and stomatal density, and significant differences in height. Extremely significant differences in stomatal traits among all identified natural triploid clones were also observed. However, some of natural triploid clones of P. tomentosa had similar characteristics with diploid clones; some of them had worse growth traits. Our results indicated that not each of the natural triploid clones of P. tomentosa was superior. Therefore selection is still necessary while applying natural triploid clones of P. tomentosa.