Cytological Studies of some Species and Hybrids in the Eu-Sorghums

Cytological analysis of chromosome association at metaphase I was made in the parents and the hybrids of Sorghum vulgare x S. halepense, S. vulgare x S. almum, S. almum x S. halepense, S vulgare x S. arundinaceum, and S. vulgare x S. verticilliflorum. S. halepense and S. almum have 2n = 40, and the others have 2n = 20. 2. Heterosis was apparent in all hybrids with the exception of S. almum x S. halepense, which showed very little hybrid vigor. The chromosome number was determined for eleven of the seventeen hybrids of S. vulgare x S. halepense; one hybrid had 2n = 30, and ten had 2n = 40. Association of chromosomes at metaphase I was studied in three of these hybrids, and it was concluded from the type of pairing in the hybrids and the parents that one genome in S. halepense is similar to the genome in S. vulgare. Data also indicate that S. halepense arose as a segmental allopolyploid with only two genomes and that its chromosomal complement now consists predominantly of one genome, which is similar to that of S. vulgare. 3. The chromosome number of twelve hybrids of S. vulgare x S. almum showed that one had 2n = 30, two had 39, and nine had 40. One hybrid of S. almum x S. halepense had 2n = 39, and two had 2n = 40. Pairing of chromosomes in the analyzed hybrids supports the assumption of other workers that S. almum is a segregate from a cross between S. vulgare and S. halepense. The data further show that most of the genetic complement of S. almum is composed of chromosome segments of S. vulgare. It is concluded that a grain sorghum type crossed with S. halepense to produce S. almum. Bridges and fragments were observed in anaphase I in the two 40 -chromosome species and in all hybrids. 4. Cytological studies of hybrids between the 20-chromosome species revealed only bivalent pairing and normal meiosis, except for an infrequent bridge and fragment at anaphase I of two of the hybrids.