Exploring the potentials of polyploidization, cytology, and histology of soursop (Annona muricata L.) genotypes

This study explored the potential applications of polyploidization, cytology, and histology in different soursop (Annona muricata L.), by means of colchine treatments and characterized resultant genotypes via flow cytometric DNA content analysis, chromosomal counts and leaf histology. Polyploidization was initiated ex vitro, soursop seeds were imbibed in four different colchicine levels (0, 0.5, 1, and 1.5%) and exposed to six exposure durations (0, 6, 12, 18, 24, and 30 hours). Fresh soursop leaf samples collected from the treated seedlings were used for flow cytometric analysis, direct chromosome count, and histology. Direct somatic chromosome count revealed that soursop genotypes had a consistent diploid chromosome number of 2n=13 and 2n=14 across treatments, with no unequivocal polyploidy cells. Additionally, Flow cytometry studies confirmed the ploidy status of colchicine-induced soursop genotypes as diploids and triploids. Histology assay showed activities of cell proliferation with an increased stratification of epithelial cells in the epidermis, and hyperplasia of the palisade and spongy mesophyll layers and increased chlorophyll pigment signals at 12, 18, 24, and 30 hours of exposure. For ex vitro polyploidization of soursop, higher percentage of colchicine concentration (2% to 4%) and longer exposure durations (24, 48 and 72 hours) are recommended, as well as the use of primordial tissues or newly sprouted seedlings. Based on these findings, optimization of colchicine concentration, exposure time and selection of regenerants is recommended to achieve stable polyploidy lines in soursop, and historical markers may provide early screening tools.