Ex Vitro Simultaneous Acclimatization and Rooting of In Vitro Propagated Tamarillo Plants (Solanum betaceum Cav.): Effect of the Substrate and Mineral Nutrition

Abstract

Plants propagated by seed do not ensure genetic uniformity and are sometimes infected with diseases. In Vitro micropropagation techniques are an alternative method to traditional cloning approaches for producing true-to-type and pathogen-free plants. However, due to the particularities of the in vitro environment, these plants face many challenges, often critical to their survival, to adapt to ex vitro conditions. In this context, four substrates and two types of mineral nutrition (quick-release (QRF) and controlled-release (CRF) fertilizers), as well as their absence were evaluated in the process of acclimatization of Solanum betaceum plants. Stomatal conductance (gs), chlorophyll content index (CCI), and dry biomass of roots, shoots, and entire plants were the parameters analyzed during the acclimatization. The best crop performance (gs, CCI, and dry biomass) were observed in substrates consisting of vermiculite plus the application of mineral nutrients through a CRF, proving that mineral nutrition has the greatest positive impact on the acclimatization process. In these conditions, plants were obtained with a total dry biomass being significantly higher (515.0 mg (QRF) and 635.9 mg (CRF) when compared to the total dry biomass of untreated plants (119.9 mg). The best conditions for this first experiment were replicated in a second test in order to assess the best fertilizer amount suited for plantlet growth. In this case, the best results were obtained with 0.4 g of CRF, in which plants showed a dry biomass of roots (542.7 mg) and a total dry biomass (594.5 mg), which was significantly higher than in the control (183.2 mg and 165.9 mg, respectively) or with other concentrations of CRF (0.8 and 1.6 g). A similar trend was found concerning the CCI (5.3) and gs (72.5 mmol m−2 s−1) in which 0.4 g CRF gave also the best results when compared with the control (without CRF) or with 0.8 g (4.7 and 56.2 mmol m−2 s−1) and 1.6 g (4.7 and 52.2 mmol m−2 s−1) treatments. In general, it was found that tamarillo plantlets acclimatized to 0.4 g of CRF had a faster initial growth and better performance (CCI and gs), with plants ready to go to the greenhouse/field more quickly, thus reducing the time to obtain suitable plants for the market and shortening the production cycle.