Cytotaxonomic studies of three species of the genus Annona
Abstract
Background: Karyotype analysis is a vital technique in plant cytogenetics, offering insights into chromosomal structures, species differentiation, and evolutionary relationships. This study focused on three Annona species L. (Annona muricata L., Annona squamosa L. and Annona senegalensis Pers.) collected from Abia State, Nigeria, with the goal of characterizing their chromosomal features and assessing cytogenetic variation. Methods: Root tip cells were prepared using squashing and staining techniques, and chromosomes were analyzed under an Amscope microscope with a 1000MA (milliamp) camera. Results: species were found to be diploid (2n) with a somatic chromosome number of 2n = 2x = 14. Chromosome measurements revealed slight variations among the species: total chromosome lengths ranged from 3.066µm (microns) in A. squamosa to 3.142µm in A. senegalensis, short arm lengths varied between 1.234µm in A. squamosa to 1.344µm in A. muricata, and long arm lengths varied between 1.789µm in A. muricata to 1.834µm in A. squamosa. The centromeric index ranged between 1.906µm in A. squamosa and 2.095µm in A. muricata, while the arm ratio was highest in A. squamosa (1.486µm) and lowest in A. muricata (1.331µm). R-values varied from 0.672µm to 0.751µm. Conclusion: These karyotypic differences, although subtle, are significant for species delimitation and may inform strategies for genetic improvement and conservation. The study highlights the potential of cytogenetic markers in supporting the taxonomy and sustainable use of underutilized tropical fruit crops like Annona.