Chromosome studies in a diploid potato (Solanum mochicense Ochoa).

Abstract

The haploid number of chromosomes in S. mochicense Ochoa is found to be 12. The diploid number is determined from tapetal cell and is found to be 24 (2n=24). Endoreduplication with a degree of ploidy was observed in tapetal cells. Chromosomal reduplication was so marked that normal diploid chromosome number reached 48. All chromosomes have either metacentric or submetacentric centromeres. Four satellite chromosomes are seen among them. Frequencies of chiasmata at diakinesis are analysed. The chiasma frequency per bivalent is 1.2.Association of chromosomes in three and four are seen. The frequency is 13.10%. The occurrence of multivalents seemed to indicate the presence of translocation heterozygote in S. mochicense Ochoa.The frequency of univalents varied from 1.19 to 10.17%. Structural changes and gene mutation are probably responsible for failure of pairing among pairable chromosomes. The univalents behave in different ways, they either pass to the poles or lag in between separating groups of chromosomes or divide. The division and elimination of univalents cause unequal distribution of chromosomes on second metaphase plates. Univalents and fragments which failed to be included in the daughter nuclei formed micronuclei (7.21%).Chromatid bridge formation is 3.60%. There is some correlation between the percentage of chromosome irregularities 18.58 and abortion of pollen 11.54.The meiotic irregularities and partial sterility indicate that the diploid S. mochicense Ochoa is presumably of hybrid origin.