Genome size variation among sex types in dioecious and trioecious Caricaceae species

Caricaceae is a small family consisting of 35 species of varying sexual systems and includes economically important fruit crop, Carica papaya, and other species of “highland papayas”. Flow cytometry was used to obtain genome sizes for 11 species in three genera of Caricaceae to determine if genome size differences can be detected between sexes. Genome sizes ranged from 442.5 to 625.9 megabases (Mb) likely due to variation in the accumulation of retrotransposons in the genomes. The C. papaya genome size was estimated to be 442.5 Mb, larger than previously reported. Significant differences were detected between male and female samples in Jacaratia spinosa, Vasconcellea horovitziana, and V. stipulata, and between male and hermaphrodite samples of V. cundinamarcensis, suggesting the presence of sex chromosomes for these species. The small size differences between genomes of the papaya sexes were not detected using flow cytometry. Vasconcellea horovitziana was discovered to have a larger female genome size than male, suggesting the possibility of a ZW sex chromosome system in the family. The estimated genome sizes of these 11 species will be used in sequencing their genomes and in sex chromosome research for this family.