Optimization of culture medium for the in vitro germination and histochemical analysis of Passiflora spp. pollen grains

•We optimized the culture medium for in vitro pollen germination and assessed the pollen viability of Passiflora species with use of staining.•The pollen germination and pollen tube growth were influenced by the culture medium, sucrose concentration and species.•In general, 30–35% sucrose added to the SM medium stimulated the greatest pollen germination rates.•P. edmundoi showed the highest percentage germination and pollen tube development in SM medium with 30% sucrose.•Pollen viability, detected by staining with Alexander's solution, was above 80%. Pollen viability studies are essential for high production of fruits and seeds, as well as for genetic improvement and conservation strategies. The objective of this work was to investigate the most suitable culture medium for in vitro germination of pollen grains and pollen tube growth of 11 wild Passiflora species and to examine the viability by means of histochemical testing with 2% Alexander's solution. This is the first study to provide data on the pollen tube growth of passion fruit. For in vitro germination, two culture media were used, BK and SM, both supplemented with different concentrations of sucrose (5, 10, 15, 20, 25, 30 and 35%). The experimental design was completely randomized in an 11×7 × 2 factorial scheme (species x sucrose concentrations x culture media). Sucrose influenced the germination of pollen grains and the pollen tube growth. P. edmundoi had the highest germination rate (89%) and pollen tube length (2.6 mm) in SM culture medium supplemented with 30% and 15% sucrose, respectively. Regarding the histochemical analysis, all the Passiflora species presented high percentage of viable pollen grains (above 79%). The information obtained in this study allowed identifying the most suitable culture medium for each Passiflora species, helping in the choice of male parents with high potential for fertility, to maximize the potential success of controlled crosses in genetic improvement programs. The results can also support studies of the conservation of pollen grains.