Analysis On Karyotype And Genetic Relationship Of Stylosanthes

As an excellent legume forage,Stylosanthes is distributed widely in tropical and subtropical regions.Since the beginning of 1980s,a large number of Stylosanthes germplasm were introduced into China.Stylosanthes germplasm have been used widely in soil improvement,soil and water conservation as well as inter-cultivation of forest and herbage.In this paper the number of chromosome and karyotype,the genetic relationship of 25 species of Stylosanthes were studied with method of karyotype analysis,SSR technology,the research is for the purpose of providing scientific basis to classification of Stylosanthes at the perspective of cytology and genomic level.Related research results are as follows:The results of Karyotype analysis showed that the 25 species of Stylosanthes had stable chromosome number,2n=6x=60,2n=4x=40 and 2n=2x=20.The basic chromosome number was 10,S.erecta was hexaploid,S.capitata、S.scabra、S.fruticosa、S.subsericea、S.sympodialis and S.sericeiceps were tetraploid,the others were all diploid.Chromosomes were mainly composed by median region chromosome(m)and submetacentric region chromosome(sm),the average arm ratio changed from 1.31 to 1.68,the karyotypes was classified "2A"."1B" and "2B".The karyotype evolutional level of twelve materials ranged from high to low as follows:(S.subsericea、S.acuminata、S.montevidensis、S.gracilis、S.grandifolia、S.hippocampoides、S.guianensis、S.humilis、S.hamata、S.angustifolia、S.macrocephala、S.capitata、S.pilosa、S.falconensis、S.calcicola、S.mexicana、S.sympodialis、S.sericeiceps、S.ingrata and S.erecta)2B>(S.viscosa、S.fruticosa、S.Seabrana and S.leiocarpa)2A>(S.scabra)1B.According to the distance of genetic relationship,25 species of Stylosanthes can be divided into 6 categories:S.erecta has a long-distance relationship with other Stylosanthes,so it is clustered into one group;the second category includes S.acuminata、S.grandifolia、S.hippocampoides、S.gracilis、S.montevidensis、S.ingrata and S.guianensis;the third category includes S.hunmilis、S.hamata and S.subsericea;the fourth category includes S.macrocephala、S.pilosa、S.falconensis andS.leiocarpa;the fifth category includes S.viscosa、S.Seabrana、S.scabra、S.fruticosa and S.angustifolia;the sixth category includes S.capitata、S.sympodialis、S.sericeiceps、S.mexicana and S.calcicola.The clustering analysis by method of the karyotype parameters can reflect the genetic relationship of Stylosanthes at level of karyotype.And which is partly in line with morphological characteristics.Using 25 pairs of SSR Markers to analyze the genetic relationship of 25 Species of Stylosanthes,the results show:the 25 species of Stylosanthes can be divided into six categories,the first category includes S.scabra.S.fruticosa,S.viscosa and S.Seabrana;the second category includes S.macrocephala、S.angustifolia.S.leiocarpa、S.mexicanca、S.sympodialis、S.sericeiceps、S.calcicola、S.gracilis、S.falconensis;the third category includes S.humilis、S.subsericea、S.hamata;the fourth category includes S.guianensis、S.grandifolia、S.ingrata、S.hippocampoides、S.montevidensis、S.acuminata;the fifth category includes S.capitata and S.pilosa;the sixth category is S.erecta.And the clustering of Stylosanthes with genetic identity in SSR analysis is consistent with morphological characteristics.The results of SSR analysis and karyotype analysis of 25 species of Stylosanthes showed little difference,there are two main areas of difference:(1)In the clustering of karyotype parameters,the genetic relationship between S.capitata and S.pilosa are relatively distant,in SSR marker clustering,S.capitata and S.pilosa are closely related.(2)In the clustering of karyotype parameters,S.gracilis and S.hippocampoides are closely related,the genetic relationship between S.gracilis and S.hippocampoides are relatively distant.The combination of the two methods were more conducive to the analysis of genetic relationships.