This article presents a new acclimatization method, ex vitro acclimatization in float hydroculture. This protocol ensures the ex vitro acclimatization of the plantlets obtained in vitro in the rooting stage or the ex vitro rooting and acclimatization of the shoots obtained in the multiplication stage. Our hydroculture method is different from the techniques of flotation hydroculture because no fertilizers or plant growth regulators or other biostimulators are used and water oxygenation by bubbling is not provided. Ex vitro rooting and acclimatization in one stage without an in vitro rooting stage in floating cell trays was successfully carried out in Rubus fruticosus and Rosa hybrida cultivars, whereas ex vitro acclimatization of in vitro-rooted plantlets was successfully carried out in Rubus idaeus, Ribes nigrum, Prunus cerasus × P. canescens, Lycium barbarum (Goji berry), Amelanchier canadensis, Drosera rotundifolia, Drosera capillaris, and Nephrolepis sp. In another set of experiments, the floating cell trays were replaced with layers of floating perlite and the latter method was also tested for non-rooted shoots obtained in vitro in the multiplication stage or rooted plantlets obtained in the rooting stage. Direct ex vitro rooting in floating perlite was successful in ‘Tayberry’ (Rubus fruticosus × Rubus idaeus) (78.12% rooting); Amelanchier canadensis, Rubus fruticosus ‘Chester’, Rubus idaeus ‘Erntesegen’, Vaccinium macrocarpon, and Vaccinium corymbosum with rooting percentages above 80%; and Rubus idaeus ‘Willamette’ and Rosa hybrida ‘Cristiana’ with rooting percentages above 80%.

Apple cultivar 'Royal Gala' was multiplied in vitro on starch-gelled MS media supplemented with 0.7 mg/l BAP, which provided intense proliferation of axillary shoots. In order to test the influence of gelling agents upon proliferation rate in this apple cultivar, modified MS media were used, supplemented with 0.7 mg/l BAP and five types gelling agents: fibrous agar, 6.8 g/l; Phytagel + starch, respectively 0.5 + 50 g/l; guar gum, 20 g/l; Psyllium husk, 15 g/l; Phytagel at 2.2 g/l. The highest proliferation rate, 13.44 ± 1.22 was obtained when the media was gelling with the mixture of Phytagel + starch. By using ex vitro rooting and acclimatization in floating perlite, the rooting percentages were between 99.45% and 93.92%, depending on the culture media used in the multiplication stage, from which the axillary shoots were harvested.

The current research was carried out to investigate the effects of iron source in the culture media for Vaccinium corymbosum L. ʻBluerayʼ, ʻDukeʼ, and ʻPatriotʼ cultivars grown on five different types of medium (Woody Plant Medium supplemented with 1.0 mg·L−1 zeatin and 0, 25, 50, 75, and 100 mg·L−1 Sequestrene 138). After 10 weeks of culture, seven physiological parameters were measured, such as the number and length of axillary shoots, rooting and acclimatization percentage, as well as chlorophyll (a, b, a/b) and carotenoid content of the leaves. Adding Sequestrene 138 to the culture media led to a slight decrease of the proliferation rate but increased the length of the shoots. The chlorophyll and carotenoid content in all of the three cultivars was considerably increased as the iron concentration of the media increased. The shoots developed on the Sequestrene 138–free medium were chlorotic and short, whereas at different concentrations of iron in the culture medium the shoots were dark green and vigorous, providing a greater acclimatization success than those grown in iron-free medium.

In vitro shoot multiplication responses of Amelanchier canadensis ‘Rainbow Pillar’ were studied on media solidifi ed with different gelling agents. The media were gelled either with 6.8 g l-1 fi brous agar-agar, or 50.0 g l-1 wheat starch, or 20.0 g l-1 Guar gum, or 15 g l-1 Isubgol or 50.0 g l-1 wheat starch mixed with 0.5 g l-1 Phytagel. Shoot cultures were grown for two months, thereafter the multiplication rates (number of newly developed shoots per explant) were counted and the length of shoots were measured. We found that the highest shoot multiplication of Amelanchier canadensis ‘Rainbow Pillar’ occurred on media gelled with Guar gum, while the longest shoots developed on media with Starch. About four-fold shoot number were obtained on media with Guar gum compared to the weakest results found on media gelled with Isubgol. Finally, considering all factors (shoot growth parameters, costs) the most economical gelling agent for Amelanchier canadensis ‘Rainbow Pillar’ was proved to be wheat starch among the tested alternatives which allows a 75.6% cost reduction.

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The apple rootstock varieties 'MM 106/4', 'MM 106/6', 'D 18', 'D 20', 'JTE-H' and 'MR 09/4' were multiplied in vitro on modified Murashige and Skoog media gelled with wheat starch (MSs) and supplemented with 0.7 mg/l BA, which provided intense axillary shoot proliferation. Among the studied genotypes, 'MR 09/4' had the highest multiplication rate (19.56), followed by 'D18' (15.36). The lowest multiplication rates were recorded in 'MM 106/6' (5.36) and in 'MM 106/4' (3.32). The use of the technique of direct ex vitro rooting and acclimatization in floating perlite provided rooting percentages of more than 90 %.

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