Cytological analysis reveals intraspecific genetic diversity of Begonia handelii (Begoniaceae, sect. Platycentrum)

Begonia L. is an ideal model for studying plant diversity due to its high species richness and diversity. In this study, we performed detailed cytological analysis for plants collected from 13 wild populations of Begonia handelii, a highly diverse species classified into three varieties. We first determined the chromosome number of these plants and identified diploid, tetraploid, and hexaploid individuals with 2n=22, 44, and 66 chromosomes, respectively. Surprisingly, three plants were found to have 2n=24 chromosomes. The number and position of both 5S and 45S rDNA in these B. handelii plants were determined using fluorescence in situ hybridization (FISH). The rDNA-FISH analysis revealed that the number of loci for both rDNA types was consistent within each ploidy level, with tetraploid and hexaploid individuals having two and three times the number of loci observed in diploid individuals, respectively. In addition, genomic in situ hybridization (GISH) was used to analyze the genomic relationships among the three varieties and to determine the auto- or allopolyploidy of the polyploid plants. The results suggest that the individuals with 2n=24 chromosomes may be hybrids, the tetraploid individuals may be allopolyploids, while hexaploid individuals may be autohexaploids.