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Cytology and Molecular Cytogenetics of Cucumeropsis mannii Naudin: Implications for Breeding and Germplasm Characterization

Keywords: Cucumeropsis mannii Naudin , cultivars , somatic chromosome number , chromosome size , ribosomal RNA genes

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Cytological and molecular cytogenetic studies were conducted on the two accessions of Cucumeropsis mannii Naudin to establish the true somatic chromosome count, investigate the occurrence and number of ribosomal RNA genes in its genome as well as investigate any cytological and cytogenetic variation in the two cultivars of the monospecific taxon. Chromosomal counts from squashed root tips stained with FLP orcein and DAPI stained mitotic chromosomes showed a somatic count 2n = 24 for this species. The chromosomes were small in size measuring 3-4.5 μm long and mostly varied from submetacentric to subacrocentric in shape. Both 18S-5.8S-25S and 5S rRNA genes were observed in the genome. Four sites, comprising two major and two minor, of 18S-5.8S-25S rRNA genes were present on four of the largest chromosomes (4.5 μm long) while two sites of the 5S rRNA genes were observed on two other individuals of the largest chromosomes. This report establishes the correct somatic chromosome count as well as the ribosomal rRNA features of this taxon. It also shows no cytological variation between the two cultivars of this species.


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