Effects of nanoparticles on shoot formation of cherimoya (Annona cherimola Mill.) from hypocotyl explants

Cherimoya (Annona cherimola Mill.) is a subtropical fruit tree growing in southern Spain, world’s leading producer, with Fino de Jete as the main cultivar. In this cultivar, shoot regeneration from hypocotyl explants was investigated. Split explants (1 cm) and cross sections (0.3 cm), different culture media, and antioxidant treatments were evaluated. For split explants, a modified Murashige and Skoog medium supplemented with 0.3 mg L⁻¹ 6-benzyladenine, resulting in shoot formation in 66% of explants with an average shoot length of 1.2 cm. In cross sections, using the same medium supplemented with 100 mg L⁻¹ casein hydrolysate, 33% shoot regeneration and an average shoot length of 0.9 cm was achieved. This medium was also effective for hypocotyl cross section regeneration of Campas and Alboran cultivars. Additionally, the effect of carbon-dots nanoparticles (CDs; 0 to 0.8 mg L-1) and silver nanoparticles (AgNPs; 0 to 0.3 mg L-1), on shoot production using cross sections was evaluated. Treatment with CDs at 0.6 mg L⁻¹ significantly reduced explant necrosis and promoted earlier shoot formation after 8 weeks of culture. Meanwhile, AgNPs markedly enhanced bud regeneration, shoot proliferation, and shoot elongation. These effects were most pronounced at 0.2 mg L⁻¹ after 12 weeks of culture. Although rooting was achieved in control shoots (up to 40%), the efficiency of the rooting process in this material needs to be improved. Auxins and nanoparticles are currently being investigated to enhance this process. Completing a plant regeneration protocol from cherimoya hypocotyl explants would allow us to address the genetic transformation of this species in the future.