Micropropagation of Apple Cultivars ‘Golden Delicious’ and ‘Royal Gala’ in Bioreactors

This study aimed to investigate culture conditions for the efficient micropropagation of apple cultivars ‘Golden Delicious’ and ‘Royal Gala’ in liquid medium by temporary immersion. RITA^® bioreactors were used for the multiplication stage whereas RITA^® or Plantform™ were used for the rooting stage. Murashige and Skoog media (MS) with N⁶-benzyladenine (BA) was used for shoot multiplication and indole-3-butyric acid (IBA) for root induction. During the multiplication phase, we evaluated the mineral medium, BA concentration, immersion frequency, silver nitrate and activated charcoal supplementation and the use of physical supports to hold explants in an upright position. The results demonstrated that longer incubation periods (10 weeks) were better than shorter periods (6 weeks) for decreasing hyperhydricity and increasing the multiplication coefficient (MC). For ‘Golden Delicious’, the highest MC were obtained either with explants placed directly on the bioreactor basket and immersed six times per day for 60 s in MS with 2.2 µM BA or explants placed between rockwool cubes cultivated with 4.4 µM BA (both yielding MC of 8.9 and 5–10% hyperhydricity). These results were superior to ‘Royal Gala’, which showed a MC of 7.3 and 23% of hyperhydricity when cultivated in MS with half nitrates, 1.55 µM BA and rockwool cubes. Both varieties rooted efficiently (96–100%), and resulting plantlets were successfully acclimated. This is the first report in the micropropagation of these two commercial fruiting cultivars in temporary immersion, demonstrating the potential of this technology to enhance large-scale plant production for the apple nursery industry.