Problems in breeding and cytology of sugar cane

Abstract

In connection with the increase of chromosome number found in species hybrids of Saccharum the author studied embryo-sac development within several Saccharum froms from early stages of meiosis in the embryo-sac mother cells to stages where fertilization already had taken place.

Normally by meiosis within E M C's a row of four haploid megaspores is formed from which the innermost, the chalazal megaspore, develops into an embryo-sac and the other three degenerate.

Haploid embryo-sacs, thus formed, may occur in Saccharum. Frequently however, in Saccharum endo-duplication takes place, that is splitting of the chromosomes within the nucleus of the chalazal megaspore, through which the chromosome number is increased.

It is described how within Saccharum by this phenomenon embryo-sacs may be formed with diploid and tetraploid chromosome numbers and with numbers between haploid and diploid.

The increase of chromosome number, observed in the young megaspore after meiosis, could be confirmed by counting the chromosomes of dividing nuclei within young embryo-sacs.

Chromosome numbers found in dividing zygotes and endosperm nuclei within fertilised embryo-sacs also pointed to the occurrence of egg-cells and polar nuclei that must be haploid, diploid and tetraploid.

The significance of this research in relation to plant breeding will be discussed in Part V.