Cytogenetical Studies on Sorghum (S. bicolor), Sudangrass (S. sudanense), and Their Hybrid

Sudangrass (Sorghum sudanense) and sorghum (S. bicolor) are two members of the genus Sorghum (Gramineae). Their hybrids have exhibited favorable forage yields and overall improved quality and disease resistance. They are widely used in aquaculture, production of livestock food and environmental protection, but some disagreements exist as to whether they actually belong to the same species. The Karyotypes of two sudangrass varieties, two sorghum varieties, three sorghum-sudangrass F1 hybrids were analyzed by the method of cell wall degradation and hypotonic treatment for chromosome preparations, and the meiosis behavior of three F1 hybrids and the chromosome numbers of two F2 hybrids were observed. The result showed that the karyotypic types of sorghum and sudangrass were 1A, and the karyotype formula was 2n=18 m+2 sm (sat) for Sa, 2n=20m for 3042A and 3042A×Sa F1, and 2n=20m(sat) for the others. The difference of chromosomes among three groups (i.e. sudangrass, sorghum, and sorghum-sudangrass hybrid F1) were not significant in terms of absolute long arm, absolute short arm, absolute total length, arm ratio (l/s), relative total length (P＞0.05); the change of chromosome length was not obvious in sorghum and sudangrass. The paired chromosome configuration of sorghum-sudangrass hybrid F1 in pollen mother cells at diakinesis and metaphaselwas 2n=2x=20(10II) and the chromosome pairing behavior was regular, but the frequencies of rod bivalent of Tx623A×S722 F1, 3042A×Sa F1, and Tx623A×Sa F1 were 4.887, 5.710, and 5.126, respectively; those of ring bivalent were 5.113, 4.290, and 4.874, respectively. At anaphase I, the paired chromosomes of sorghum-sudangrass hybrid F1 could separate from each other. The chromosome numbers of F2 hybrid were 20 (2n=20). Therefore, the sudangrass/sorghum relationship is sufficiently close.