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  • Author or Editor: J. Dobránszki x
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The effects of environmental factors (photoperiod and light intensity) on in vitro tuberization were analysed on five potato cultivars of different genetic origin representing various maturity groups. No growth regulators were added to the culture media to avoid the potential effect(s) of growth regulators on the response to environmental stimuli. An 8% sucrose treatment was used for tuber initiation. Light (short-day treatment) applied after the induction phase delayed or inhibited tuber initiation. By contrast, darkness applied after the tuber induction stage accelerated and synchronized tuber initiation after high light intensity. No relationship was observed between the maturity groups of the tested cultivars and their tuber initiation response. The tuber number (.2 mm) per shoot varied from 1.19 to 1.52 depending on the cultivar in the best treatments. Consequently, the manipulation of light alone gave reliable tuberization.

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The dormancy of potato microtubers produced under different photoperiodic treatments and light intensities was investigated in the varieties Desiree and Gülbaba. The dormant period was defined as the period between harvest or tuber initiation and the end of dormancy. The effects of environmental factors could be detected due to the use of a hormone-free tuber-producing system. Combined treatments had a slight effect on dormancy, while different light intensities influenced it considerably. The lower the light intensity the longer the dormant period for both cultivars. The effects of light intensities depended on the photoperiodic treatments applied for tuber induction.

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In vitro plantlets of four varieties of potato (Solanum tuberosum L.) were grown at different plant densities to study their effects on growth and microtuber yield. The responses of the cultivars to plant density, as expressed by changes in development characteristics, especially stem length and leaf area, were different. The time of tuber initiation was earlier at higher plantlet densities for all cultivars. The microtuber number per plantlet was not affected by the plantlet density. The highest number of well-sized (≯4 mm) microtubers per jar could be harvested from the higher plantlet densities (30–40 plantlets per jar). In addition to good yield, the microtubers were uniform in these treatments, so they appear to be economical.

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The effects of a new type of aromatic cytokinin, meta-topolin, on the morphology and histology of apple leaves and its post-effects on the subsequent shoot regeneration from in vitro leaves were studied in cv. Royal Gala. The media applied for pre-treatment differed from each other in their cytokinin composition: medium No. 1 contained no cytokinin, No. 2 was supplemented with 0.5 mg l-1 benzyladenine, while Nos. 3-6 contained meta-topolin, the new type of cytokinin, in four concentrations (0.5-1.0-1.5-2.0 mg l-1). After a 3-week pre-treatment on these media shoot regeneration was induced on two test regeneration media containing thidiazuron (0.2 mg l-1) or benzyladenine (5.0 mg l-1). Irrespective of the pre-treatments, high regeneration (97-100%) was observed on all the regeneration media. however, the conditioning of apple shoots for three weeks on medium supplemented with meta-topolin in a concentration range between 0.5 and 1.5 mg l-1 caused a significant decrease in the rate of vitrified shoots (down to 13.4%) and increased the number of regenerated shoots per leaf segment significantly (up to 15.1). There was a positive correlation between the histological status and regeneration capacity of in vitro leaves. According to these results, meta-topolin, as a new source of cytokinin, could increase the morphogenic potential of apple leaves.

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The in vitro shoot multiplication of apple cv. Jonagold was tested on media containing benzyladenine, benzyladenine riboside or meta-topolin in different concentrations (from 0.0 to 5.0 mg l-1). The optimal concentration for the best multiplication varied according to the type of cytokinin. The highest multiplication rate (on average 6.9 and 5.9 new shoots per explant) was achieved using 5.0 mg l-1 meta-topolin or 2.0 mg l-1 benzyladenine riboside. The longest shoots were formed on media containing benzyladenine riboside at a concentration of 0.5 mg l-1. The length of newly developed shoots was strongly suppressed by high concentrations of different cytokinins, but the suppression effect of a high concentration of meta-topolin on shoot length was less than that of benzyladenine or benzyladenine riboside. In this study meta-topolin and benzyladenine riboside proved to be effective cytokinins to induce adequate shoot proliferation, while benzyladenine was the least active cytokinin

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