Karyotype characterization of endosperm-derived plants of Passiflora cristalina Vanderplank and Zappi, a wild amazonian passionfruit species

We assessed the efficacy of regenerating triploid plants from endosperm cultures of Passiflora cristalina Vanderplank and Zappi, a wild Amazonian passionfruit species. The ploidy and karyotype features of endosperm-derived plants were determined. P. cristalina endosperms were cultured for 30 d in MS medium supplemented with 6.65 µM 6-benzyladenine to stimulate shoot regeneration. The triploid nature of endosperm-derived plants was confirmed by flow cytometry and chromosomal analysis. Pisum sativum internal standard (2C DNA 9.09 pg) and diploid control seed-derived P. cristalina plants (2n = 2x = 18; 2C DNA 3.42 pg). Conversely, endosperm-derived plants contained on average 2C-value = 4.72 pg DNA and 27 chromosomes (2n = 3x = 27), mirroring the triple ploidy of the endosperm. Chromosomal morphometry revealed an identical karyotype formula (KF = 8 m + 1sm) in diploid (2x) and triploid (3x) plants. Finally, both seed-derived plants (2x) and endosperm-derived plants (3x) exhibited two terminal sites of CG-rich heterochromatin (chromosomes V and VIII) in the monoploid set of P. cristalina (x = 9), indicating a stable karyotype. These findings pave the way for new opportunities in passionfruit breeding, particularly for wild Amazonian species with ornamental potential such as P. cristalina.