Chromosome Ploidy Identification And Genomic In Situ Hybridization Analysis Of Genomic Composition In Setaria Species

The genus Setaria belongs to Gramineae of the grass family. There are about 125 species widely distributed in the warm and temperate regions of the world. Observations drawn from karyological studies and interspecific hybridization suggest that the genus Setaria is organized into three gene pools. S. italica and its putative wild ancestor S. viridis, the green foxtail, belong to the primary gene pool, which includes the diploid species with the A genome (2n = 2x = 18). The secondary gene pool corresponds to the species carrying the B genome. It includes the diploid S. adhaerans (2n = 2x = 18) and the tetraploid species like S. verticillata (2n = 4x = 36) and S. faberii (2n = 4x = 36).The third gene pool contains S. pumila (4x, 6x, and 8x,) in addition to many other wild species with unidentified genomic composition. In 2001, it is reported that S. verticillata, S. faberii are both allotetraploid with AABB genome. Except those a few known genomic composition, the genetic relationships among the Setaria species are still poorly understood, and the genomic constitution of the polyploids needs to be reliably established.In this study ,Chromosome number and polyploidy level identification were made on 50 accessions of wild Setaria species including S.viridis, S. faberii, S.verticillata, S.glauca, S.palmifolia, S.pumila, S.grisebachii, S.queenslandica. All the S.viridis samples were found to be diploid, S.glauca samples had tetraploid and octoploid types, S.verticillata samples had diploid and tetraploid and all samples of S. faberii were tetraploid. One S.pumila sample was found to be diploid and other samples of the same species were tetraploid, and S.queenslandica was a tetraploid species.Among the two species, which were the first time ploidy level identification reported, S.grisebachii and S.leucopila were diploid.Genomic in situ hybridization (GISH) was used to investigate genomic relationship among different Setaria species of 4 diploid species (S.verticillata,S.grisebachii,S.leucopila,S.pumila) and a tetraploid species S.queenslandica .The main results are as follows:1. The labeled total DNA of S.viridis was hybridized to the metaphase chromosome of diploid S.verticillata. No signal was detected in each chromosome of diploid S.verticillata. In situ hybridization of diploid S.verticillata genome with the genomic DNA of S.adhaerans confirmed that diploid S.verticillata bears B genome.2. GISH (genomic in situ hybridization) applied to diploid S.leucopila, S.pumila and demonstrated that they are all carrying A genome. Strong signals were through out all chromosome of S.leucopila and S.pumila when using total DNA probe from S.viridis or S.italica and no signal was detected when using total DNA probe from S.adhaerans.3. Diploid species, S.grisebachii, was shown to bear an unknown genomic composition that is not closely related either to genome A or to genome B.4. We found tetraploid species, S.queenslandica, was an autotetroploid species with genome AAAA by genomic in situ hybridization.In coclusion, we have observed the chromosome numbers of 50 accessions belonging 9 Setaria species,two species are reported for the first time and we identified the genomic constrction of S.leucopila,S.grisebachii,S.verticillata and S.queenslandica by genomic in situ hybridization to analysis the evolutional relationship among Setaria species.