Morphological And Cytological Research On Species In Sorbus L.

The Sorbus L.,genus of Maloideae(Rosaceae),contains about 100 species all over the word,which are famous landscape plant, widely distributed in Asia, Europe, North America. A lot of polyploid hybrid origins exist in Sorbus, classification and species definition of genus are controversial for a long time. The morphological classification, system evolution and the genetic relationship of Sorbus were explored in this paper, which provide morphological and cytological basis for phylogenetic classification of Sorbus by the measurement of morphology and chromosome karyotype analysis. The main results were as follows:1 The shape of seeds are obovoid or ovoid, length ranged from 2.91 mm to 5.99 mm, width ranged from1.48 mm to 3.42 mm, length-width ratio ranged from 1.44 to 2.25, which belong to large seeds. The external color of seeds change between yellow brown and dark brown. The shape and size of the leaves are different. The shape ovoid and nearly broadly linear,the maximum of leaves of Sorbus is 13.99cm× 6.78 cm, and the most small is 1.68 cm×0.44 cm,in general, the leaves of the simple leaves Sorbus are bigger. The color of petioles and blade back are white or brown, but the density varies. The number of lateral veins ranged from 4 to 18, the distance of the most wide to the base of the leaves is markedly different. The angle of leaf base and the leaf tip between the compound leaves and simple leaves are not different significantly. Fruit sepals persistent or fall off, fruit white? pink?orange and red, fruit oblong?ovoid or elliptic, the surface of them is smooth or small lenticels and spots. The characteristics of leaf ?lateral veins?leaflet?bud and fruit are obviously different, which can be used as classification basis for the Sorbus.2 The results showed that chromosome number of 11 species and varieties of So rbus were 34 and diploid, without polyploidy. The actual length of chromosomes rang ed from 1.00?m to 3.73?m,relative length of chromosomes ranged from 2.92% to 9.94%,belonging to small chromosomes. The karyotype formula of S.alnifolia was 2n=2x=34=20m+2m(SAT)+12sm?The karyotype formula of S. alnifolia var. lobulata was 2n=2x=34=20m+2m(SAT)+2sm?The karyotype formula of S. alnifolia var. angulata was 2n=2x=34=30m+2m(SAT)+2sm?The karyotype formula of S.hemsleyi was 2n=2x=34=28m+2m(SAT)+4sm?The karyotype formula of S. ochracea was 2n=2x=34=26m+2m(SAT)+6s m?The karyotype formula of S.xanthoneura was 2n=2x=34=24m+2m(SAT)+8sm?The k aryotype formula of S.scalaris was 2n=2x=34=24m +2m(SAT) +8sm?The karyotype for mula of S.multijuga was 2n=2x=34=22m+2m(SAT)+10sm?The karyotype formula of S.microphylla was 2n=2x=34=20m+12sm+2sm(SAT)?The karyotype formula of S.amabilis was 2n=2x=34=18m+14sm+2sm(SAT) ?The karyotype formula of S. hupehensis var. pa ucijuga was 2n=2x=34=22m+10sm+2sm(SAT).The chromosomes of 11 species of Sorbus were mainly composed by median region chromosome(m) and submetacentric chromosome(sm), but different species with different number. Along with 2 satellites, they are in the different position.Their average arm ratio changed from 1.36 to 1.72.The variation of asymmetric coefficient is small ranged from 57.08% to 62.45%,the centromere index ranked from 24.17% to 49.56%, were not distinctively different. According to Stebbins' category, S.alnifolia, S.alnifolia var. lobulata, S.alnifolia var. angulata, S.hemsley a and S. ochracea belonged to type “2A”, which was very symmetrial and a primitive type. S.hupehensis var. paucijuga, S.amabilis, S.scalaris, S. multijuga and S.microphylla belonged to type “2B”,which were more advanced than the other plants.The result from cluster analysis showed that the 11 species of Sorbus could be divided two groups.The first type included S.alnifolia, S.alnifolia var. lobulata, S. alnifolia var. angulata, S. xanthoneura, S. hemsleyi, S. ochracea;The second type included S. hupehensis var. paucijuga, S. amabilis, S. scalaris, S. multijuga, S.microphylla.3 The asymmetrical karyotype coefficient and scatter diagram showing, the evolut ional trend of 11 species of Sorbus was S. ochracea(57.08%)?S. yuana(57.53%)?S.alni folia(57.67%)?S. alnifolia var. lobulata ?S. alnifolia var.angulata(58.91%)?S.hemsleyi(59.71%)?S.multijuga(60.52%)?S.scalaris(60.78%)?S.microphylla(61.86%)?S.amabili(62.08%)?S. hupehensis var. paucijugain(62.45%)?The compound leaves Sorbus are more advanced than the simple leaves Sorbus.