Vujović T., Ružić Dj., Cerović R., 2012. In vitro shoot multiplication as influenced by repeated subculturing of shoots of contemporary fruit rootstocks. Hort. Sci. (Prague), 39: 101-107.In vitro shoots of vegetative rootstocks for cherry (Gisela 5 and Gisela 6), plum (Fereley Jaspi) and pear (Pyrodwarf ) were repeatedly subcultured for 10 subcultures on Murashige and Skoog medium of unchanged hormonal composition. Shoot formation capacity decreased over repeated subculturing in all genotypes. The first significant decrease in multiplication index was observed after first subculture in Gisela 6 and Fereley Jaspi, while in Gisela 5 the decline occurred after second subculture, and remained at that level. As for Gisela 6 and Fereley Jaspi, multiplication index was mainly stable from second to forth subculture, whereupon the second decline in shoot formation was observed. Although Pyrodwarf showed very low multiplication capacity, shoot multiplication slightly increased over the first three subcultures and then declined. This irreversible decline could be due to residual effects of hormones. However, no visible morphological variations or aberrations of shoots were found in successive subcultures in any genotype. Quality of shoots in terms of shoot length varied during subculturing, but the highest quality was observed in later subcultures (from fifth subculture onwards). After subculturing, several media were evaluated for induction of rhizogenesis in order to achieve high rooting rates in tested rootstocks. The highest rooting ability (100%) among genotypes was observed in Fereley Jaspi, followed by Pyrodwarf and Gisela 6 (the best rooting percentage being 90% in both) and Gisela 5 (70%). Rooted shoots were successfully acclimatized under the mist system in greenhouse.

Murashige and Skoog medium (MS) and modified Anderson's Rhododendron medium (mAN) were compared for in vitro shoot multiplication of three highbush blueberries 'Berkeley', 'Bluecrop' and 'Goldtraube'. All media contained 0.5 mg l −1 zeatin applied either alone or combined with 0.1, 1 and 5 mg l −1 IBA. In vitro rooting was induced using mAN medium supplemented with 0.8 mg l −1 IBA and 4 g l −1 activated charcoal. The results obtained showed that mAN medium is more suitable for in vitro multiplication of the selected highbush blueberry cultivars than MS medium. Low concentration of IBA (≤1 mg l −1) added in zeatinsupplemented mAN medium increases shoot multiplication efficiency of highbush blueberries in vitro and can be recommended for large-scale propagation of high-quality plants. MS medium induced partial or full necrosis of stems and leaves, which was more pronounced on media containing zeatin combined with increasing concentration of IBA. Rooting capacity of shoots varied widely among the tested blueberry cultivars. The highest rooting and acclimatization rates were achieved in 'Goldtraube' (82.8% and 91.8% respectively), and the lowest (10% and 66.7% respectively) were in 'Berkeley'.

Determination of the most optimal types and concentrations of plant growth regulators as medium constituents is one of the most important aspects of successful micropropagation, among other in vitro factors. With the aim of optimization of in vitro multiplication of sweet cherry cv. Lapins the effect of following cytokinins has been studied: benzyladenine (BA), isopentenyl adenine (2iP), kinetin (KIN) and thidiazuron (TDZ) at concentrations of 1, 2, 5, 10 and 15μM, combined with auxine, indole-3-butyric acid (IBA) at concentrations of 0, 0.5, 2.5 and 5μM. Murashige and Skoog (1962) was the basic medium used in all the combinations. The following multiplication parameters were monitored: multiplication index, length of axial and lateral shoots. Fresh and dry shoot weight (callus, stem and leaves -S + L) were determined. Some specific issues, such as colour, leaf and callus size, leaf roll, incidence of chlorosis or necrosis along with occurrence of rhizogenesis, i.e. roots unusual for this phase of micropropagation, were also monitored. The highest multiplication index as well as length of axial and lateral shoots was obtained on media with BA. Very poor multiplication, with large sized shoots and big leaves, was achieved on media with 2iP, TDZ and KIN, whereas in many combinations with 2iP, and particularly in those with KIN, rhizogenesis was induced. Obtained results suggest that the choice of cytokinins for the phase of multiplication of sweet cherry is limited to BA. For more rapid micropropagation, through joining rooting and multiplication phases, KIN and 2iP may be applied. The latter two may be also used to obtain sturdy shoots (elongation phase, prior to rooting).

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