The objectives of this study were to test the effects of melatonin (N-acetyl-5-methoxytryptamine), a natural compound of edible plants on the rooting of certain commercial sweet cherry rootstocks. Shoot tip explants from previous in vitro cultures of the cherry rootstocks CAB-6P (Prunus cerasus L.), Gisela 6 (P. cerasus × P. canescens), and M × M 60 (P. avium × P. mahaleb) were included in the experiment. The effect of indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA) alone or in combination with melatonin was tested concerning their rooting potential. Seven concentrations of melatonin (0, 0.05, 0.1, 0.5, 1, 5, and 10 μM) alone or in combination with 5.71 μM of IAA or 4.92 μM of IBA were tested. For each rootstock, 21 treatments were included. The explants were grown in glass tubes containing 10 mL of substrate. The parameters measured include rooting percentage, number of roots per rooted explant, root length, and callus formation. The data presented in this study show that melatonin has a rooting promoting effect at a low concentration but a growth inhibitory effect at high concentrations. In the absence of auxin, 1 μM melatonin had auxinic response concerning the number and length of roots, but 10 μM melatonin was inhibitory to rooting in all the tested rootstocks. The final conclusion of this experiment is that exogenously applied melatonin acted as a rooting promoter and its action was similar to that of IAA.

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Conservation and sustainable exploitation of threatened endemic plants with medicinal and/or horticultural/ornamental value can be achieved through the development of effective propagation protocols. After unveiling the bioclimatic preferences of Carlina diae (Asteraceae) with geographic information systems (GIS), four propagation trials were conducted using seeds of this endangered local Cretan endemic for in vivo and in vitro germination, as well as seasonal vegetative propagation trials (softwood cuttings) and micropropagation (nodal explants). Seed germination was accomplished at a level of 77–90% in vivo (30 days) and 96% in vitro (10 days) using an MS medium with 2.9 μM gibberellic acid (GA3). The optimum treatments for cuttings’ rooting were 1000 and 2000 ppm indole-3-butyric acid (IBA) (11–16 roots, 2–3 cm long, 100% rooting) within 40 days in mist. In vitro shoot propagation exhibited a 2.8 proliferation rate after six successive subcultures on an MS medium with 2.9 μM GA3. Both ex vitro rooting and acclimatization were successful in 40 days, with 96% microshoot rooting and an equal survival rate. The GIS-facilitated effective species-specific propagation protocols developed in this study can consolidate the perspective of successful re-introduction of ex situ-raised material of C. diae into wild habitats and may serve its sustainable exploitation for high-added value ornamental products.

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In the present study, the effects of three ethylene inhibitors, silver nitrate (AgNO 3 ), silver sulfate (Ag 2 SO 4 ), and cobalt chloride (CoCl 2 ), on the morphogenic and biochemical responses in CAB-6P and Gisela 6 cherry rootstocks were investigated. In both rootstocks, AgNO 3 and Ag 2 SO 4 promoted shoot regeneration while CoCl 2 had such an effect only in Gisela 6. The rooting percentage of CAB-6P and Gisela 6 explants was diminished with AgNO 3 , Ag 2 SO 4 , and CoCl 2 . AgNO 3 increased root number (40 µM) and root length (50 µM) in the CAB-6P rootstock while it had an inhibitory effect in Gisela 6. Ag 2 SO 4 and CoCl 2 enhanced root length of Gisela 6 explants whereas Ag 2 SO 4 decreased root number and root length of CAB-6P explants. CoCl 2 at 10 µM in both rootstocks augmented root number whereas 20 µM CoCl 2 increased root length of CAB-6P microshoots. AgNO 3 , Ag 2 SO 4 , and CoCl 2 decreased leaf chlorophyll and carbohydrate content in CAB-6P rootstock. On the other hand, in Gisela 6, 10 µM AgNO 3 gave elevated chlorophyll levels and 20 µM AgNO 3 or 10-50 µM CoCl 2 raised leaf carbohydrate content. The three ethylene inhibitors led to elevated leaf proline levels in the CAB-6P rootstock, whereas in Gisela 6 the increase or decrease in leaf proline content was dependent on both type and concentration of ethylene inhibitor. An efficient micropropagation protocol was established for the CAB-6P and Gisela 6 cherry rootstocks using ethylene inhibitors.

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