Endosperm culture: a facile and efficient biotechnological tool to generate passion fruit (Passiflora cincinnata Mast.) triploid plants

Triploid plants represent an important resource for the breeding of fruit and ornamental plants. Here, we report a facile and robust system for regenerating passion fruit triploid plants (Passiflora cincinnata Mast.) through in vitro endosperm culture. We describe the histological and biochemical aspects associated with the de novo shoot organogenesis. Endosperms were cultured on Murashige and Skoog medium supplemented with 1.5, 2.0, and 3.0 mg L−1 of 6-benzyladenine or thidiazuron, while a cytokinin-free medium was used as control. The highest percentage of organogenic calli (56%) was estimated at 1.7 mg L−1 6-benzyladenine, whereas the highest average number of shoots (24.85) per explant was estimated at 1.6 mg L−1 6-benzyladenine. Flow cytometry and chromosomal analysis confirmed that endosperm-derived plants were triploid, with a chromosome count of 27 (2n = 3x = 27) as well as a DNA amount similar to that of endosperm and 1.5 times greater than in diploid counterparts (2n = 2x = 18). The regeneration of adventitious shoots was evident 30 days after culture and occurred from the reprogramming of edge cells of the endosperm. During this process, lipids and proteins were quickly mobilized in the early stages of shoot organogenesis, whereas carbohydrates were synthesized throughout the development of adventitious shoots. This observation illustrates the mobilization dynamics of endosperm reserves during de novo shoot organogenesis in P. cincinnata. Adventitious shoots induced by reprogramming of the outer cell layers of the endosperm generate true-to-type triploid passion fruit plants.