| Abstract: | The cytotaxonomic investigation of various species in the Cenchrus-Pennisetum Complex was conducted to provide information for taxonomic classification and as a basis for a breeding program. These species (x = 9) are similar to Cenchrus and Pennisetum in floral morphology and tend to form an intergradation between the two genera. The interrelationships among species of this Complex and their relationship to other species of Cenchrus and Pennisetum were also considered. The following accessions were included in this study: C. setigerus Vahl. (PI 226051), P. alopecuroides (L.) Spreng., P. flaccidum Griseb., P. orientale (Ness.) Stapf. (PI 271593, 271595, 271595, 271596, and 215600), P. repustre Chase, and a sexual buffelgrass [C. ciliaris (L.) Link.]. Embryo sac analysis and chromosome studies of these species showed that, with the exception of the sexual buffelgrass and P. alopecuroides, these grasses were obligate apomicts with aposporic embryo sac development and had a basic chromosome number of x = 9. P. alopecuroides is a sexual diploid (2n = 18) and accession of P. orientale (PI 215600) was aneuploidy (2n = 38). The remaining accessions were tetraploid (2n = 36). The primary differences observed in the karyotypes of these species were predominantly the presence or absence of B chromosomes and differences in chromosome size. The representative, species of Cenchrus and Pennisetum are base 17 and 7 respectively, and are all sexual diploids. Hybridization attempts between these two base groups and base 9 species were totally unsuccessful. The base 9 tetraploids exhibited varying degrees of cross compatibility with sexual buffelgrass (2n = 36, x = 9) and other base 9 species. The hybrids obtained in these crosses formed an array of floral characters between the parents and included features unrelated to either parent yet recognizable in other species in this Complex. Evidence from hybridization studies indicates that the same mechanism for control of method of reproduction is present in all apomictic accessions. Characteristics of the hybrids indicated a closer relationship within this base 9 tetraploid Complex than between this group and representative types of Cenchrus and Pennisetum. |
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