Micropropagation of Vanilla planifolia Jacks. RH₃₃₀ genotypes resistant to Fusarium oxysporum f. sp. vanillae in double-phase culture

A highly valuable species, Vanilla planifolia Jacks., is threatened with extinction due to its extreme susceptibility to Fusarium oxysporum f. sp. vanillae (Fov). It is therefore essential to propagate genetic material such as the RH₃₃₀ genotype, selected for its in vitro resistance to 30% of the pathogenic strain H₃ of Fov fungal filtrates. For this reason, this work was developed with the aim of evaluating the effect of a double-phase culture (DPC) system in relation to a semi-solid medium (SSM) culture system, as well as different concentrations of GA₃ on hypocotyl elongation and rooting of shoots of V. planifolia RH₃₃₀. A total of 8 treatments of 15 shoots each: T₀-T₃ semi-solid MS medium cultures with four concentrations of GA₃ (0, 0.5, 1, and 1.5 mg L^− 1), and T₄-T₇ double-phase cultures with four concentrations of GA₃ (0, 0.5, 1, and 1.5 mg L^− 1), in their liquid phase, were evaluated in a completely randomized design. After eight weeks, hypocotyl elongation, the number of leaves and roots, and root length were evaluated. The treatment of the DPC system without the addition of GA₃ (T₄) showed the greatest hypocotyl elongation (0.36 cm), while the treatment of the DPC system with the addition of 1.5 mg L^− 1 GA₃ in the liquid phase (T₇) produced the greatest number of leaves (1.05 cm). The highest number and length of roots (1.91 and 2.67 cm, respectively) were obtained in the control treatment. Compared to the traditional method of propagation in semi-solid culture medium (SSC), the DPC system without GA₃ was the most successful in producing seedlings with the desired characteristics, such as longer hypocotyl length and the presence of longer roots.