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Rhododendrons in gardens in the city of Szczecin

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Rhododendrons in the cities are relatively rare planted shrubs. Climatical requirements in Szczecin allowed for good growth of those plants. There are grown old specimens planted before many years. In the last time there are often meet in gardens of Szczecin (plants 6-10 years old).
Grafting plays an important role in rhododendron propagation. Successful graft union depends on selection of a suitable stock, grafting season, and method. In this study, three methods (whip, cleft, and side grafting) were compared in two seasons. The stocks were mainly cuttings of R. catawbiense-Hybridum, R. ‘Cunningham's White', but also R. pachytrichum and R. brachycarpum. Scions were taken from several cultivars deriving from R. catawbiense. To shorten the production period, scions were grafted on unrooted stocks, and the results are encouraging. The best stock was R. ‘Cunningham's White', especially when side grafting was applied in spring.
The purpose of the present study was to determine whether water deficit affects cold hardiness of rhododendron ‘Catawbiense Boursault’, ‘Lee’s Dark Purple’, ‘Prinz Karneval’ and ‘Old Port’ shrubs. Plants were grown in unheated greenhouse and for 14 weeks from June to mid-September were subjected to six irrigation treatments. In the end of September shrubs were left in an unheated greenhouse or planted into the ground and at the beginning of each month from December to March freezing tolerance tests were performed. The results showed that in all rhododendron cultivars the highest cold hardiness was noted in January and February, lower in March but the lowest in December. Application of four-week water deficit period during summer especially between the first and the second vegetative growth may improve the frost resistance of Rhododendron shrubs.
We examined whether peroxidase activity in cutting bases and leaves and starch content in cutting bases can be used as rooting phase markers in the elepidote rhododendron cv. 'Babites Baltais' (Rhododendron L.). Changes in peroxidase activity in cutting leaves and bases, as well as starch content in cutting bases, were determined in relation to anatomical stages of rhizogenesis in leaf bud cuttings treated with 1% indole-3-butyric acid (IBA+) or without IBA (IBA–). The pattern of change of peroxidase activity was similar in cutting bases and leaves of IBAleaf bud cuttings. Three phases of adventitious root formation were identified: induction, initiation and expression. During the induction phase peroxidase activity decreased, but no anatomical changes were observed in the cuttings. Peroxidase activity increased in the initiation phase when adventitious root initials were formed. Peroxidase activity decreased during the expression phase when adventitious root primordia developed. The starch content of IBA– leaf bud cuttings decreased during the first few days and then gradually rose to maximum, followed by a sharp reduction and another increase at the end of the experiment. The changes of starch content did not coincide with rooting phases as peroxidase activity did, and cannot be used as a rooting phase marker in rhododendrons. Adventitious root formation did not occur in IBA+ leaf bud cuttings, so distinct rooting phases could not be observed. There was a significant correlation between peroxidase activity in cutting bases and leaves of IBA- leaf bud cuttings. Peroxidase activity in leaves of rhododendron leaf bud cuttings are potentially useful as a marker for rooting phases, but that requires further anatomical and physiological study of rooting in leaf bud cuttings.
Among the numerous protocols that describe the extraction of DNA, those relating to the isolation of DNA from infected plants, are rare. This study describes a rapid and reliable method of extracting a high quality and quantity of DNA from rhododendron leaves artificially infected with Phytophthora cactorum, P. cambivora, P. cinnamomi, P. citrophthora, and P. plurivora. The use of the modified Doyle and Doyle protocol (1987) allowed us to obtain high quantity and quality DNA (18.26 μg from 100 mg of the fresh weight of infected leaves at the ratios of A260/280 and A260/230 – 1.83 and 1.72, respectively), suitable for conventional polymerase chain reaction (PCR) and real-time PCR amplifications.
Plants of ‘Catawbiense Boursault’ and ‘Eskimo’ rhododendrons or ‘Cannon’s Double’ and ‘Kilian’ azalea grown in 4 l containers were treated twice with chlormequat (2000, 4000 and 8000 mg · dm-3), trinexapac-ethyl (50, 100, 200, 400 mg · dm-3), daminozide (2500, 5000, 7500 mg · dm-3), proxeadione calcium (75, 150, 300 mg · dm-1) and once with paclobutrazol (50, 100, 200, 400 mg · dm-3). Shoot length of the subsequent growth flush following the treatments decreased with increasing rates of the growth retardants. The number of flower buds per plant increased with increasing rates of pacloburazol, chlormequat and daminozide. Prohexadione calcium was less effective in flower bud initiation and the worst results were obtained with trinexapac-ethyl.
For proper growth and development, rhododendrons need acidic soils, whereas calcium carbonate (CaCO3) in the substrate markedly limits their growth. In this study, we analysed the reactions of rhododendrons to high concentrations of calcium salts and pH in the substrate. We used 4-month-old seedlings of Rhododendron ‘Cunningham’s White’ and 1.5-year-old seedlings and rooted cuttings of R. ‘Cunningham’s White’ and R. ‘Catawbiense Grandiflorum’. Their reactions depended mostly on calcium salt type added to the substrate (sulphate or carbonate). An increase in concentrations of phenolic compounds was detected mostly in roots of the plants grown in a substrate with a high calcium carbonate content. Addition of calcium salts to the substrate caused a significant rise in total nonstructural carbohydrates in leaves and roots of the studied plants. As compared to the control, an increase in substrate pH in the variant with calcium carbonate limited the activity of acid phosphatase, while lowering of substrate pH in the variant with calcium sulphate, significantly increased its activity. Along with the rise in substrate pH, a remarkable increase was observed in the activity of nonspecific dehydrogenase (DHA) in the substrate with CaCO3, as compared to the control. Unfavourable soil conditions (high calcium content and alkaline pH) caused a decrease in assimilation of minerals by the studied plants (mostly phosphorus and manganese). Our results show that the major factor limiting rhododendron growth is an increase in substrate pH, rather than an increase in the concentration of calcium ions.
The spontaneous seedlings of Rhododendron luteum Sweet and Rhododendron calendulaceum (Michx.) Torr., Rhododendron maximum L., and Rhododendron japonicum Suringer were documented in Kaunas Botanical Garden of Vytautas Magnus University in 2006. More seedlings of these four rhododendron species were observed in 2007, 2008 and 2009. In 2010, altogether with aforementioned species, seedlings of Rhododendron dauricum L., Rhododendron schlippenbachii Maxim. and Rhododendron minus Michx were observed. The assessment of climatic conditions suggests that the self-regeneration of rhododendron genus plants was possibly provoked by global climate change – warmer winters and increased amount of precipitation in summers.
High content of calcium compounds in soil limits cultivation possibilities of the majority of cultivars of rhododendron. In the research presented an attempt was made to determine the influence of a high level of calcium salts CaCl2, CaSO4, Ca(NO3)2 and CaCO3, pH and an increased level of auxins in a medium, on the development of microcuttings of R. ‘Catawbiense Grandiflorum'. On the basis of the results of the research it is justifiable to state that it was the anions of some salts used that had an adverse effect on the development of rhododendron cultures, not calcium cations. Significant differences were noted in the uptake of calcium, magnesium and sodium ions by the microcuttings depending on salts used in the media. The pH value of the medium higher than optimum significantly affected the degree of chlorosis of the microcuttings analyzed. Supplementing the media with additional auxin - IBA was stimulating for the plant growth especially in the medium containing CaCO3.
Biological activity of6 fungicides in the inhibition of Phytophthora ramorum sporulation and development ofblight on rhododendron leaves and stems were evaluated. All tested compounds at dose 8 µg ofa.i./cm3 already inhibited zoosporangia formation at least in 73%. On leafpetioles and leafdisks, taken from rhododendron one week after treatment with fungicides, formation of chlamydospores was especially suppressed by fenamidone + phosetyl Al and oxadixyl + mancozeb whereas development ofspores was not inhibited by cymoxanil + famoxate. All tested compounds significantly inhibited the development and spread oftwig blight on rhododendron. However, furalaxyl, applied as spraying of plants 48 hrs before or after inoculation of leaves and stems by P. ramorum was the most effective
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