The cytology of Eragrostis with special reference to E. tef and its relatives
Thirty-seven species of the genus Eragrostis (Poaceae: Eragrostoideae) have been examined cytologically. Somatic chromosome numbers are reported for the first time for seven species. New chromosome numbers are reported for a furtherseven species. Counts confirming those obtained by previousauthors were obtained for twenty-six species. An annotatedlist of all published counts for species of Eraarostis was compiled. The base number for the genus is x=10. Many of the speciescontain two or more chromosome races. The frequency ofpolyploidy is high (76%,). This is notable for a tropical genus. Aneuploids are relatively frequent (14%) and possible explanations are provided. The karyotypes of fifteen species were studied. Most of themshowed a gradation in the size of chromosomes whose centipmeres were mostly median and submedian. Three species had karyotypes which were distinctly different, having shorter, fatter and less symmetrical chromosomes respectively. All the varieties of the Ethiopian cereal Eragrostis tef examined were tetraploid, with regular meiosis. Hybrids between t'ef varieties of very different appearance were fertile and formed only bivalents in meiosis, but hybrids between tetraploid cilianensis and tetraploid minor were sterile, having abnormal meiosis with many univalents. Pollen diameter was found not to be a reliable indicator of chromosome number.