In recent years, light emitting diodes (LEDs), due to their low energy consumption, low heat emission and specific wavelength irradiation, have become an alternative to fluorescent lamps (FLs) in plant tissue culture. The aim of this study was to investigate the effects of various LED light sources on the in vitro growth and rooting of plum rootstock Saint Julien (Prunus domestica subsp. insititia). The test plantlets were cultivated under a Philips GreenPower LEDs research module illumination system with four spectral regions: white (W), red (R), blue (B) and mixed (W:R:B:far-red = 1:1:1:1). The control plantlets were cultivated under fluorescent lamps (FL) and the photosynthetic photon flux density (PPFD) of all treatments was set at 87 ± 7.5 μmol m⁻² s⁻¹. The effect of light source on the selected physiological, biochemical and growth parameters of plantlets was monitored. Additionally, microscopic observations of leaf anatomy, leaf morphometric parameters and stomata characteristics were carried out. The results showed that the multiplication index (MI) varied from 8.3 (B) to 16.3 (R). The MI of plantlets grown under mixed light (WBR) was 9, lower compared to the control (FL) and white light (W), being 12.7 and 10.7, respectively. In addition, a mixed light (WBR) favored plantlets’ stem growth and biomass accumulation at the multiplication stage. Considering these three indicators, we could conclude that under the mixed light, the microplants were of better quality and therefore mixed light (WBR) was more suitable during the multiplication phase. A reduction in both net photosynthesis rate and stomatal conductance in the leaves of plants grown under B were observed. The quantum yield (Yield = F_V/F_M), which represents the potential photochemical activity of PS II, ranged from 0.805 to 0.831 and corresponded to the typical photochemical activity (0.750–0.830) in the leaves of unstressed healthy plants. The red light had a beneficial effect on the rooting of plum plants; the rooting was over 98%, significantly higher than for the control (FL, 68%) and the mixed light (WBR, 19%). In conclusion, the mixed light (WBR) turned out to be the best choice during the multiplication phase and the red LED light was more suitable during the rooting stage.

ISHS I International Symposium on Biotechnology of Fruit Species: BIOTECHFRUIT2008 EFFICIENT SHOOT REGENERATION SYSTEM OF PEAR ROOTSTOCK OHF 333 (PYRUS COMMUNIS L.) LEAVES

Pear rootstock OHF 333 (Pyrus communisL.), which is included in the US ‘Old Home’ × ‘Farmingdale’ series, is characterized by good compatibility with most other varieties, high yields, and a moderate degree of resistance to fire blight. Micropropagation in vitro has shown promise for rapid, large-scale cloning of disease-free plant material throughout the year. However, pear shoots are often recalcitrant to rooting, and this process is highly genotype-dependent. This study aimed to improve the micropropagation protocol by ex vitro rooting of pear rootstock OHF 333 (Pyrus communisL. ‘Old Home’ × ‘Farmingdale’). Charkor, a new plant growth regulator of natural origin was used, which contains metabolism products of symbiotic fungus-endophytes of ginseng roots, as an alternative to synthetically produced plant growth regulators (PGRs). Microcuttings were obtained from in vitro cultured shoots and subjected to four different treatments for ex vitro rooting: 1 g L⁻¹1-naphthaleneacetic acid (NAA) (as a powder), 0.5 mL L⁻¹Charkor for 3 hr or 6 hr, or the same concentration of Charkor prepared as a powder. Microshoots dipped in sterile distilled water with no additional hormonal treatments served as controls. Cultures were kept in a growth chamber under a 16-hr photoperiod, with air humidity maintained close to 100% (above 96%) for 2 weeks and then gradually reduced to 60%. Data on final acclimatization rate (survival rate; %), mean number of roots per plant, stem and root length, mean number of leaves per plant, and final acclimatization rate were collected 90 days after transplanting to ex vitro conditions. All treatments induced a successful acclimatization rate of more than 31%. The highest survival rate (86%) and longest stems were achieved by treatment with 0.5 mL L⁻¹Charkor for 6 hr. The greatest mean number of roots per plant, root length, and number of leaves was achieved in the variant treated with 1 g L⁻¹powdered NAA.

The present study aimed to evaluate the effects of new meta-topolin derivatives meta-topolin riboside (mTR) and meta-methoxy topolin riboside (memTR) on the ultiplication and subsequent rooting and ex vitro acclimatization of Pyrus communis L. (‘OHF 333’). The cytokinins mTR and memTR were included in the nutrient medium (0 μM, 3 μM, 6 μM, 9 μM, 12 μM). In plants from three passages of three-week-old cultures grown on different nutrient media, the following parameters were evaluated: multiplication coefficient, fresh (FW) and dry (DW) weight (mg), average length of shoots (mm), average number of leaves, leaf length and width (mm). At the rooting stage, data on the rooting frequency, number of roots per rooted micro-cutting and the length of roots were recorded 18 days after the start of the experiment. In the acclimatized plants, leaf area, FW and DW, and the content of photosynthetic pigments were determined 40 days after the transfer to ex vitro conditions. Gas exchange rate and chlorophyll fluorescence were also evaluated for the control and the variants with 6 and 9 μM mTR and memTR. The plantlets grown on cytokinin-supplemented media showed a higher number of leaves than the control. Plantlets grown on nutrient media with 6 and 12 μM mTR were distinguished by the highest FW and DW. In these variants, the shoots were of the greatest length. The plants grown on medium with 6 μM mTR had the highest number of leaves. Control plants had larger leaves. Тhe highest rooting percentage (70%) was achieved in plantlets grown with 9 μM mTR. A higher ex vitro acclimatization survival rate (76–100%) was found in all plants cultured with mTR or memTR compared to control plants (65%).

Plasma technology, relatively new in the fields of biomedicine, agriculture, and ecology, is the subject of intensive research as a prospective means of decontamination of various microorganisms (bacteria, viruses, and fungi). The objectives of the present study were to follow the effect of cold atmospheric plasma (CAP) treatment on in vitro grown plum plants (Prunus domestica L. ‘Kyustendilska sinya’ cv.) and the possibility of eradicating or inactivating plum pox virus (PPV) causing Sharka disease by CAP. The source tree is naturally co-infected by PPV (both M and D strains). In the experiments, two different plasma sources were used. First, a surface-wave-sustained Argon plasma torch and second, an underwater diaphragm discharge. For the treatments, nodal segments (10 mm in length) from in vitro cultured plum plants with or without one leaf were prepared. Apical shoots from treated plants (PPV-positive and negative clones as well non-treated controls) were cultivated in vitro for four passages. Then they were rooted and acclimatized to ex vitro conditions, and their virus status was observed periodically for more than 3 years after treatment for the appearance of Sharka symptoms. All plants, acclimatized to ex vitro conditions, were tested for PPV by immune capture–reverse transcription–polymerase chain reaction (IC-RT-PCR). As a first step in understanding the plasma treatment of living plants, a plasma treatment variant causing no damage must be established; this has been done in our previous works. Treatment of plants by plasma with parameters that have been carefully selected leads to better development than the non-treated plants. In the treated in vitro plants, no significant differences were found in the number and length of shoots compared to the control plantlets. In ex vitro acclimated plants, greater stem length was reported, but no differences in leaf number were observed. No significant differences in growth were recorded between the control and plants that were treated twice or three times. At this stage, 3 years after ex vitro cultivation in a greenhouse, Sharka symptoms were not registered on treated in vitro negative PPV plants, and the virus was not detected by IC-RT-PCR. Very mild symptoms were showing in CAP-treated PPV-positive plants. Development of typical Sharka symptoms on non-treated controls were observed.

In vitro micropropagation of plants is highly useful for obtaining large quantities of planting material with valuable economic qualities. However, plantlets grow in vitro in a specific environment and the adaptation after the transfer to ex vitro conditions is difficult. Therefore, the acclimatization is a key step, which mostly determines the success of micropropagation. The aim of this investigation was to study the effect of the biofertlizer Lumbrical on ex vitro acclimatization of micropropagated pear rootstock OHF 333 (Pyrus communis L.). Micropropagated and rooted plantlets were potted in peat and perlite (2:1) mixture with or without Lumbrical. They were grown in a growth chamber at a temperature of 22±2 °C and photoperiod of 16/8 hours supplied by cool-white fluorescent lamps (150 µmol m-2 s-1 Photosynthetic Photon Flux Density, PPFD). The plants were covered with transparent foil to maintain the high humidity, and ten days later, the humidity was gradually decreased. Biometric parameters, anatomic-morphological analyses, net photosynthetic rate and chlorophyll a fluorescence (JIP test) were measured 21 days after transplanting the plants to ex vitro conditions. The obtained results showed that the plants, acclimatized ex vitro in the substrate with Lumbrical, presented better growth (stem length, number of leaves, leaf area and fresh mass) and photosynthetic characteristics as compared to the control plants. This biostimulator could also be used to improve acclimatization in other woody species