Contributions to the Cytology of Genus <i>Saccharum</i>

Abstract

1) Studies of chromosomes were made in F1 progenies of the sugar cane variety 2725 POJ crossed with Sorghum vulgare.2) In 2725 POJ, the chromosome number was 2n=107. Since, in the meiosis of its PMC, univalent chromosomes were observed together with bivalents, and occasionally multivalents, in the polar view of the heterotypic metaphase, we counted usually more chromosome elements than the haploid number corresponding to its somatic one. The pollen grains were completely sterile. The number of chromosomes of Sorghum vulgate was n=10.3) The F1 plants were classified by their external characterss into three types. The first type resembled sugar cane (normal or sugar cane type), the second was a dwarf (dwarf or terato-type), and the third an intermediate between the above two (intermediate type).4) The chromosome number of the normal type of F1 was, 2n=118. This number arose probably by doubling of the maternal chromosomes, so that its chromosome constitution should be given as 2C+1S. Here, C represents a haploid set of chromosomes (not genom) of sugar cane and S that of sorghum. Both the dwarf and the intermediate types of F1 showed 2n=64, their chromosome constitutions being regarded as 1C+1S. As the result of genetic inequalities, the two last-named types exhibited considerable morphological differences between them and also between different individuals of a type.5) In the normal type of F1, about 10 univalents were found in meiosis. which may be recognized to have come from sorghum.6) In the intermediate type of F1, usually 37 chromosome elements, including uni-, bi-, and sometimes multivalents, were counted in its meiosis. Of these, the number of univalents exceeded. 10, which may be owing to the fact that many chromosomes of the haploid set of sugar cane conjugated autosyndedically to form bior multivalents, and the sorghum chromosomes remained univalents. Whence, it may be concluded that 2725 POJ is, at least partially, of an autopolyploid nature.7) The doubling of chromosomes in the F1 of normal type, resulting in chromosome constitution 2C+1S, is probably the result of splitting of the maternal chromosomes, as pointed out by Bremer (1923, 1928).