Comparative Chromosomal Localization of 45S and 5S rDNA Sites in 76 Purple-Fleshed Sweet Potato Cultivars

In recent years, the purple-fleshed sweet potato has attracted more attention because of its high nutritional value. The cytogenetics of this crop is relatively unexplored, limiting our knowledge on its genetic diversity. Therefore, we conducted cytogenetic analysis of 76 purple-fleshed sweet potato cultivars to analyze the chromosome structure and distribution of 45S and 5S rDNA. We noted that only 62 cultivars had 90 chromosomes, and the others were aneuploid with 88, 89, 91, or 92 chromosomes. The number of 45S rDNA in the 76 cultivars varied from 16 to 21; these sites showed different signal sizes and intensities and were localized at the chromosomal termini or satellite. The number of 5S rDNA was relatively stable; 74 cultivars showed six sites located at the chromosomal sub-terminal or near the centromere. Only the 'Quanzishu 96' and 'Yuzixiang 10' showed seven and five 5S rDNA sites, respectively. Additionally, both parent cultivars of 'Quanzishu 96' showed 18 45S and six 5S rDNA sites. Overall, our results indicate a moderate diversity in the distribution pattern of rDNAs. Our findings provide comprehensive cytogenetic information for the identification of sweet potato chromosomes, which can be useful for developing a high-quality germplasm resource.