Karyotype Studies On Nine Species Of Pinus

The plants of Pinus in Pinoideae of Pinaceae are well-known gymnosperm which have great economic and ecological value. The seeds of nine species of Pinus were taken as the experimental materials in this paper, P. taeda and P. thunbergii are exotic tree species, P. densata、P. kesiya var. langbianensis、P. yunnanensis、P. armandii、P. massoniana、P. densiflora and P. tabulaeformis are indigenous tree species. In this study, the conventional squashed method was improved, the root tips germinated by seeds were taken as the experimental materials, analyses and research were carried out on the karyotypic features and the evolution trend of the somatic-cell-chromosomes of these nine plants, and with the method of cluster analysis, a preliminary study was taken on their interspecific genetic relationships. The main results were as follows:1. The parameters of chromosome squashing method for Pinus species had been optimized, for example the reagent and time for pretreatment and the reagent and time for dissociation, and a technique of chromosome preparation for Pinus species had been established:seeds were cultivated in the growth cabinet of25℃, and the root tips were taken as experimental materials at9-11clock in the morning when they growed to0.5-1.0cm; then they were pretreated in the solution of0.15%colchicin under25℃for5-6h; next fixed in Camoy’s liquid for20-24h at4℃; after fixation, the root tips were treated in lmol/L hydrochloric acid for10-16min at60℃; finally,the root tips were stained with the improved carbol fuchsin solution.2. The results showed that all the chromosomes of nine species of Pinus were diploid and the number is24; they all had the same karyotype formula what was2n=2x=24=24m, and all constitute of metacentric chromosomes (m); all of the karyotype of them belonged to1A type, which is the most symmetrical karyotype in the classification standard of karyotype by Stebbins.3. The results showed that the karyotype asymmetry index of these nine species ranged from52.37%to53.16%, mean arm ratio varied from1.114to1.150, ratio of the longest chromosome to the shortest varied from1.491to1.742, mean of centromere index ranged from46.64%to47.42%. P. densata、P. kesiya var. langbianensis、P. yunnanensis、 P. massoniana、P. taeda、P. densiflora and P. tabulaeformis had the same composition of relative length that was2n=24=14M2+8M1+2S; P. thunbergii was2n=24=16M2+6M1+2S; P. armandii was2n=24=14M2+10M1.4. According to the comparison of karyotypic features and the analysis of scatter diagram which based on the degree of karyotype asymmetry on nine species of Pinus, the degree of karyotype asymmety of P. armandii of Subgen Strobus was the the lowest, P. kesiya var. langbianensis was the most hightest, the second was P. densata; P. yunnanensis and P. tabulaeformis were similar, P. massoniana and P. thunbergii were also similar; then P. densiflora should be more asymmetical than P. taeda, they had least degree of karyotype asymmety in the eight species of Subgen Pinus.5. Nine species of Pinus were finally divided into3groups by cluster analysis with chromosome karyotype parameters, as follows:the first group include P. thunbergii、P. massoniana、P. densiflora and P. taeda; the second group include P. tabulaeformis、P. yunnanensis、P. densata and P. kesiya var. langbianensis; the third group include P. armandii only. The interspecific gap between P. thunbergii and P. Massoniana、P. tabulaeformis and P. Yunnanensis was relatively samll, the next was; the genetic relationships of species clustered in the same group was approach relatively, while the genetic relationships between P. armandii and other species was much further relatively.