Effects of plant growth promoting bacteria (PGPB) on yield,growth and nutrient contents of organically grown strawberry

The effects of plant growth promoting bacteria (PGPB) on the fruit yield, growth and nutrient element content of strawberry cv. Fern were investigated under organic growing conditions between 2006 and 2008. The experimental plot was a completely randomized design with 3 replicates. Three PGPB strains (Pseudomonas BA-8, Bacillus OSU-142 and Bacillus M-3) were used alone or in combination as bio-fertilizer agent in the experiment. Data through 3 years showed that the use of PGPB significantly increased fruit yield, plant growth and leaf P and Zn contents. Root inoculation of M3 and floral and foliar spraying of OSU-142 and BA-8 bacteria stimulated plant growth resulting in significant yield increases. M3 + BA-8, BA-8 + OSU-142, M3, M3 + OSU-142 and BA-8 applications increased cumulative yield by 33.2%, 18.4%, 18.2%, 15.3% and 10.5%, respectively. Number of fruits per plant significantly increased by the applications of M3 + BA-8 (91.73) and M3 (81.58) compared with the control (68.66). In addition, P and Zn contents of strawberry leaves with bacterial inoculation significantly increased under organic growing conditions. Available P contents in soil were increased from 0.35 kg P₂O₅/da at the beginning of the study to 2.00, 1.97 and 1.82 kg P₂O₅/da by M3 + OSU-142, M3 + BA-8 and M3 + BA-8 + OSU-142 applications, respectively. Overall, the results of this study suggest that root inoculation of Bacillus M3 alone or in combination with spraying Bacillus OSU-142 or Pseudomonas BA-8 have the potential to increase the yield, growth and nutrition content of strawberry plant under organic growing conditions.     

Ethylene influences development and flowering of Ptilotus spp. in vitro and ex vitro

The genus Ptilotus has immense potential for ornamental horticulture but its commercial development has been hindered by propagation limitations. Poor seed quality and germination are reported. Cutting propagation is limited by cutting supply as the juvenile phase of Ptilotus is short. Micropropagation has been used in an attempt to overcome these difficulties but explants become floral in vitro and this causes plantlets to elongate. Ethephon has been used to control flowering of stock plants of many ornamental species. This study investigated the effect of ethephon applied to young (3-week-old, deflasked from tissue culture) and mature (1-year-old) Ptilotus plants in a greenhouse. A system of applying gaseous ethylene at 0, 100, 200 and 300 mg l⁻¹ to the headspace of in vitro plantlets in glass jars was developed and the response of in vitro plantlets to ethylene studied. One-year-old Ptilotus plants were treated with 500 mg l⁻¹ ethephon 2 days before pruning or 1 or 2 weeks after pruning. Ethephon application 2 days before pruning decreased the number of inflorescences and increased the number of shoots (compared to the control) but was phytotoxic. Ethephon applications of 150 or 300 mg l⁻¹ applied weekly or fortnightly to 3-week-old plants deflasked from tissue culture reduced plant height and number of inflorescences and at low concentrations increased the number of new shoots. A fortnightly application at 150 mg l⁻¹ is recommended. Previous reports on the effects of ethylene on inflorescence production on plantlets in vitro are limited. Our study showed that exposure of in vitro plantlets of P. nobilis to ethylene gas at 100 mg l⁻¹ for 1 h significantly increased the number of shoots and plant height but this did not occur for plantlets of P. spicatus. Plantlets of P. spicatus exposed to transient ethylene at 200 and 300 mg l⁻¹ showed significantly greater rooting (52.4%) than the control (13.6%).     

Modeling plant morphology and development of petunia in response to temperature and photosynthetic daily light integral

The effects of mean daily temperature (MDT) and mean photosynthetic daily light integral (MDLI) on flowering during the finish stage of two petunia (Petunia × hybrida) cultivars were quantified. Petunia ‘Easy Wave Coral Reef’ and ‘Wave Purple’ were grown in glass-glazed greenhouses at 14–23 °C or 14–26 °C and under 4–19 mol m⁻² d⁻¹ with a 16-h photoperiod. The flower developmental rate was predicted using a model that included a linear MDT function with a base temperature multiplied by an exponential MDLI saturation function. The flower developmental rate increased and time to flower decreased as MDT increased within the temperature range studied. For example, under a MDLI of 12 mol m⁻² d⁻¹, as MDT increased from 14 to 23 °C, time to flower of ‘Easy Wave Coral Reef’ and ‘Wave Purple’ decreased from 51 to 22 d and 62 to 30 d, respectively. Flower developmental rate increased as MDLI increased until saturation at 14.1–14.4 mol m⁻² d⁻¹. Nonlinear models were generated for effects of MDT and MDLI on flower bud number and plant height at flowering. The number of flower buds at flowering increased as MDT decreased and MDLI increased. For example, at an MDT of 14 °C with 18 mol m⁻² d⁻¹, plants had 2.5–2.9 times more flower buds than those grown at 23 °C and 4 mol m⁻² d⁻¹. Models were validated with an independent data set, and the predicted time to flower, flower bud number, and plant height were within ±7 d, ±20 flowers, and ±4 cm, respectively, for 96–100%, 62–87%, and 93–100% of the observations, respectively. The models could be used during greenhouse crop production to improve scheduling and predict plant quality of these petunia cultivars.     

The influence of irrigation system and nutrient solution concentration on potted geranium production under various conditions of radiation and temperature

Zonal geranium (Pelargonium × hortorum ‘Real Mintaka’) were grown in closed soilless systems to evaluate the effects of irrigation system (drip and subirrigation) and nutrient solution concentration (half and full) under various conditions of radiation and temperature (winter and summer) in terms of substrate electrical conductivity (EC_s), growth, quality, crop evapotranspiration (ET_c) and growth index water use efficiency (WUE_GI) and nutrient uptake. At he end of the cultural cycle the highest EC_s in the upper and lower layers were recorded in the spring season on plants grown in subirrigation using a full nutrient solution concentration. The highest shoot biomass, leaf area, plant growth index, and quality index were recorded in the winter season on plants grown in both drip-irrigation and subirrigation using half and full nutrient solution concentration, whereas the lowest value was observed in the spring season on plants grown with subirrigation using the full nutrient solution concentration. The highest maximum air temperature recorded during the first 20 days after transplanting in the spring growing season was presumably responsible for the reduction in shoot biomass production, growth and quality index, and in time of geranium flowering compared to the plants grown in the winter season. The ET_c was 44% higher in spring than in winter season treatment, while the effect of the irrigation system was less pronounced with an increase in 11% in the subirrigation treatment compared with the drip-irrigation system. WUE_GI was not stable and showed a seasonal variability. Solar radiaton (R_s), air temperature (T_a) and vapour pressure deficit (VPD) were greatly higher in the spring season, which influenced WUE_GI negatively. The WUE_GI improved especially when R_s, T_a and VPD were below 12 MJ m², 20 °C and 0.6 kPa, respectively. The highest N, and Mg uptake were recorded in the winter season, especially on plants grown with subirrigation at 2 dS m⁻¹. The highest P, K, and Ca uptake values were measured during winter season using subirrigation system, and on plants grown under full strength nutrient solution. The variation of the nitrate concentration and EC in the nutrient solution during the spring growing cycle was less pronounced in the subirrigation than with a drip-irrigation system which represents an important aspect for the simplification of the closed loop management of the nutrient solution.     

Pollination with laser-irradiated pollens breaks cross-incompatibility between zicaitai (Brassica campestris var. purpurea) and ornamental kale (Brassica oleracea var. acephala) to produce hybrids with the aid of ovule culture

The objective of this study was to produce interspecific hybrids between an Ogura-cytoplasmic male sterile (CMS) line of zicaitai (Brassica campestris var. purupurea, 2n = 20) and cultivars of ornamental kale (Brassica oleracea var. acephala, 2n = 18) to develop a CMS system for hybrid seed production. Pollination with pollen grains of ornamental kales irradiated at a power output of 9.0 mW with a He–Ne laser for 3 min could overcome the cross-incompatibility between the species concerned. Intact hybrids could be efficiently produced from ovules cultured on Murashige and Skoog media supplemented by 0.2 mg l⁻¹ 6-benzyladenine. Chromosome number of hybrids was confirmed to be 2n = 19. Hybrids resembled ornamental kales in leaf morphology and in vernalization response. Pollens of hybrids had a sterile appearance. Moreover the hybridity of the putative hybrids was confirmed by RAPD data on a DNA fragment of 820 bp.     

High frequency early flowering from in vitro seedlings of Dendrobium nobile

Dendrobium nobile Lindl. is a popular temperate Chinese orchid commonly marketed as a traditional medicinal plant. Seedlings of Dendrobium nobile Lindl. produced floral buds (33.3–34.8%) precociously on a defined basal medium (1/2 MS) containing paclobutrazol (PP₃₃₃) at 0.5 mg L⁻¹ or thidiazuron (TDZ) at 0.1 mg L⁻¹ within 4 months of culturing. The frequency of floral buds formation can be further increased to 95.6% by growing seedlings in a PN (PP₃₃₃ 0.3 mg L⁻¹ + NAA 0.5 mg L⁻¹)-containing medium followed by transfer onto 1/2 MS medium with PP₃₃₃ and TDZ (PP₃₃₃ + TDZ). However, flower developed was deformed under 25 °C but it developed fully when grown in a lower temperature regime (23 °C/18 °C, light/dark) for 45 days. Under optimal condition, in vitro flowering was observed about 6 months after seed sowing.     

Aneuploid strawberry (2n = 8x + 2 = 58) was developed from homozygous unreduced gamete (8x) produced by second division restitution in pollen

Unreduced gamete formation is significant in the evolutionary development of complex polyploidy series found in wild strawberry, genus Fragaria (Rosaceae). Also, it is important for genetics and breeding in strawberry plants to elucidate the mechanism of unreduced gamete formation. The objective of this study was to search for ploidy anomalies resulting from artificial diploid × octoploid crosses, and examine the mechanism through which these unreduced gametes were produced. Five everbearing cultivars of Fragaria vesca L. diploid (2n = 2x = 14) were crossed with pollen from six June-bearing cultivars of Fragaria × ananassa Duch., octoploid (2n = 8x = 56). A total of 3000 mature seeds, 100 from each of the 30 parental combinations were sown at 23 °C/20 °C (day/night) under artificial lighting with a 16 h day. The seedlings were transplanted to pots and grown in a greenhouse. Reproductive and morphological observations, flow cytometry analyses, chromosome counts and DNA analyses using CAPS markers were performed to identify the genetic background of the offspring. Most of the seed (79%) did not germinate or died soon after germination. Of the seedlings produced, 7% seemed to be pure F. vesca based on morphological characteristics, flow cytometry analyses and chromosome counts; 14% were pentaploids (2n = 5x = 35), 0.1% were hexaploids (2n = 6x = 42), and 0.03% (one individual) was aneuploid (2n = 8x + 2 = 58). Electrophoresis banding patterns obtained by CAPS marker analysis were heterozygotic in the 8x pollen parent but homozygotic in the aneuploid progeny. Judging from the chromosome counts and the CAPS marker analysis, the aneuploid was the result of a homozygous unreduced pollen grain (8x) crossed with an incomplete chromosome compliment from the egg. Because of the homozygosity, the unreduced male gamete must have been derived from second division restitution (SDR) in the octoploid pollen parent.     

Effect of phosphite fertilization on growth,yield and fruit composition of strawberries

Traditionally, phosphates (Pi, salts of phosphoric acid, H₃PO₄) have been used for plant fertilization, and phosphites (Phi, salts of phosphorous acid, H₃PO₃) have been used as fungicides. Nowadays several Phi fertilizers are available in the EU market despite the fact that in research trials Phi has often had a negative influence on plant growth. The objective of this study was to elucidate the effect of a Phi fertilizer on plant growth, yield and fruit composition of strawberries (Fragaria × ananassa Duch.). Experiments were carried out with ‘Polka’ frigo plants in South Estonia in 2005 and 2006. The number of leaves per plant, total and marketable yields, fruit size, fruit ascorbic acid content (AAC), soluble solids content (SSC), titratable acidity (TA), anthocyanins (ACY) and total antioxidant activity (TAA) were recorded.     

Improvement of staining method for observation of mitotic chromosomes in octoploid strawberry plants

An important strategy to conduct intentional breeding of octoploid strawberry plants is to recognize the functions of every chromosome. To do so, a methodology must be developed to distinguish chromosomes one by one. We reported the possibility of distinguishing chromosomes using light microscopy when somatic cells of octoploid strawberry plants were stained using ordinary methods with lacto-propionic orcein (LPO). However, karyotype analysis of octoploid strawberry plants required clearer chromosome images. This study obtained clearer chromosome images of octoploid Fragaria × ananassa and F. chiloensis plants. Three staining methods were examined: 60% acetic acid (AA) alone, 1.5% LPO alone, and two-step treatments with 60% AA and 1.5% LPO. Collected root tips of the plants were placed in 2 mM 8-hydroxyquinoline solution for 1 h and were subsequently stored at 4 °C for 15 h. The samples were then fixed in a 3:1 absolute alcohol: glacial acetic acid solution for 40 min, followed by mixture with 1N HCl solutions at room temperature for 2 h and then at 60 °C for 10 min. For separate staining using 60% AA and 1.5% LPO, the root tip was expelled on the glass slide with a drop of each solution for a few minutes to stain the chromosomes. For the two-step staining method, the samples stained with 60% AA were frozen at −80 °C for at least 5 min. The cover slip was removed using a razor blade. Subsequently, the specimens were air-dried and stained with the 1.5% LPO for 3 min. Digital images of chromosomes were obtained using light microscopy. Samples of the two-step staining method produced the clearest chromosome images in both F. × ananassa and F. chiloensis. Furthermore, the greatest color difference between the chromosomes and the cytoplasm was obtained from images of the two-step staining method among the three staining methods. These results demonstrate that the two-step staining method is useful for chromosome counting and karyotype analysis in strawberry plants.     

6-Benzylamino purine stimulates in vitro shoot organogenesis in Eucalyptus erythronema, E. stricklandii and their interspecific hybrids

In vitro bud and shoot organogenesis was investigated for the ornamental plants Eucalyptus erythronema var. erythronema, E. stricklandii and their interspecific hybrids cv. ‘Urrbrae Gem’ and ‘Hybrid 2.5’ by using 0.0, 0.1, 0.25, 0.5 or 1.0 μM BAP on apex and leaf explants. Callus developed on all explants and increased with all concentrations of BAP without significant differences between BAP concentrations. Buds formed on apex and leaf explants of E. erythronema and E. cv. ‘Urrbrae Gem’ especially with 1.0 μM BAP, but these buds rarely developed into shoots. Bud clusters formed on E. erythronema and E. cv. ‘Urrbrae Gem’ apex and leaf explants whereas E. stricklandii and ‘Hybrid 2.5’ produced fewer, individual buds on the explant. Shoots regenerated from apex explants of all genotypes with all levels of BAP, whereas few shoots of any genotype regenerated from leaf explants regardless of the number of buds formed. Shoots from apex explants could be multiplied successfully. Light microscopy showed meristems developed within the callus, and at the callus and bud surfaces. However, few shoots developed considering the level of bud and meristem formation. This report is the first for successful shoot organogenesis and multiplication in an ornamental eucalypt.     

Effects of plant growth promoting rhizobacteria (PGPR) on yield,growth and nutrient contents in organically growing raspberry

During 2003 and 2005, plant growth promoting effects of two Bacillus strains OSU-142 (N₂-fixing) and M3 (N₂-fixing and phosphate solubilizing) were tested alone or in combinations on organically grown primocane fruiting raspberry (cv. Heritage) plants in terms of yield, growth, nutrient composition of leaves and variation of soil nutrient element composition in the province of Erzurum, Turkey. The results showed that Bacillus M3 treatment stimulated plant growth and resulted in significant yield increase. Inoculation of raspberry plant roots and rhizosphere with M3 and/or OSU-142 + M3, significantly increased yield (33.9% and 74.9%), cane length (13.6% and 15.0%), number of cluster per cane (25.4% and 28.7%) and number of berries per cane (25.1% and 36.0%) compared with the control, respectively. In addition, N, P and Ca contents of raspberry leaves with OSU-142 + M3 treatment, and Fe and Mn contents of the leaves of raspberry with M3 and OSU-142 + M3 applications significantly improved under organic growing conditions. Bacterial applications also significantly effected soil total N, available P, K, Ca, Mg, Fe, Mn, Zn contents and pH. Available P contents in soil was determined to be increased from 1.55 kg P₂O₅/da at the beginning of the study to 2.83 kg P₂O₅/da by OSU-142, to 5.36 kg P₂O₅/da by M3 and to 4.71 kg P₂O₅/da by OSU-142 + M3 treatments. The results of this study suggest that Bacillus M3 alone or in combination with Bacillus OSU-142 have the potential to increase the yield, growth and nutrition of raspberry plant under organic growing conditions.     

Direct regeneration of plants derived from in vitro cultured shoot tips and leaves of three Lysimachia species

The regenerability of three ornamental species—Lysimachia christinae, Lysimachia rubinervis and Lysimachia nummularia ‘Aurea’, were investigated using in vitro leaves and shoot tips. 6-Benzylaminopurine (BAP) and α-naphthalene acetic acid (NAA) added to Murashige and Skoog (MS) medium were tested for their effect on organogenesis. On the medium, shoot regeneration occurred directly without callus formation. In these species, L. christinae developed the highest regeneration rate and numbers of shoots/explant from shoot tips (100%, 12.25) and leaf bases (100%, 13.01) on the MS medium containing 3.0 mg l⁻¹ BAP and 0.1 mg l⁻¹ NAA. For L. rubinervis, the highest shoot induction rate and number of shoots/explant were obtained from shoot tip (100%, 16.87–17.20) on the MS medium with 0.1 mg l⁻¹ NAA and 3.0–5.0 mg l⁻¹ BAP. L. nummularia ‘Aurea’, however, showed the highest regeneration rate and number of shoots/explant (100%, 12.73) from leaf bases on MS medium supplemented with 1.0 mg l⁻¹ BAP and 0.1 mg l⁻¹ NAA. All in vitro shoots rooted well on half macronutrient MS medium containing 0.1 mg l⁻¹ NAA. After acclimatization, transplanted plantlets grew normally and flowered in the field.     

Planting density for grafted melon as an alternative to methyl bromide use in Mexico

One of the major challenges of melon (Cucumis melo L.) yield is the decrease of fruit yield and quality caused by soil diseases. Soil disinfection with methyl bromide (MB) has been used to prevent soil-borne diseases damage; however, use of MB is being restricted because this substance damages the ozone layer. Searching for new MB alternatives, field experiments were carried out in open fields in soils infested with Fusarium oxysporum f. sp. melonis, Olpidium bornovanus, and Melon Necrotic Spot Virus (MNSV) in Colima, Mexico, where melons had only been grown previously using soil fumigation with MB. Yield and quality of melon cultivar Cruiser F1 (Harris Moran seed company) grafted on two rootstocks of Cucurbita maxima Duchesne × Cucurbita moschata Duchesne (“RS841”; Séminis seed company and “Shintosa Camelforce”; Nunhens seed company) were evaluated during two consecutive years. Each experiment had five treatments, two of which with non-grafted plants at a density of 18,519 plants/ha, with and without MB fumigation. The other three treatments consisted of grafted plants in non-fumigated soil with plant densities of 14,815, 11,111, and 9260 plants/ha. The use of melon grafted on “RS841” and “Shintosa Camelforce” rootstocks significantly increased the average fruit weight and the total yield of melons in soil without the need for MB. Grafting may be considered an alternative to MB fumigation. With the use of grafted melon plants, planting density may be reduced by 60%, obtaining higher yields than those obtained from non-grafted plants grown on fumigated land. Fruits harvested from grafted plants had equal firmness than those harvested from non-grafted plants, without affecting the content of soluble solids.     

Effects of simple and double grafting melon plants on mineral absorption,photosynthesis, biomass and yield

The Spanish type cultivar ‘Piel de Sapo’ (Cucumis melo L. var. saccharinus), has a limited compatibility with the Cucurbita maxima × Cucurbita moschata hybrids currently used as rootstocks. Double grafting can be used to improve compatibility between rootstock and scion by means of an intermediate rootstock compatible with both. Non-grafted, single, and double grafted melon plants of the cultivar Piel de Sapo were evaluated for water, nutrient absorption, photosynthesis activity, biomass production in early phases, as well as for yields and fruit quality in a long term trial. The hybrid ‘Shintoza’ (C. maxima × C. moschata) was used as rootstock, and the cantaloupe type melon cultivar ‘Sienne’ as an intermediate scion. Grafting did not affect net photosynthetic values, yet increased water use efficiency (35%). Double grafted plants increased aerial dry weights (66% and 31% with respect to non-grafted and simple graft plants, respectively), and also increased capacity for uptaking beneficial minerals (between 61% and 13% and particularly for NO₃⁻, P, K, Ca, Mn, and Zn) with respect to non-grafted and single grafted plants. The quantum efficiency PSII photochemistry values increased in double grafted plants (12%) with respect to the control plants. Consequently, double grafting on a vigorous rootstock such as ‘Shintoza’, with an intermediate scion, results in improved mineral and water absorption and achieves an increase in ion influx to the scion – so enabling an increase in light photosynthetic reaction and biomass. Double grafted plants increased fruit yield when compared to simple grafted and non-grafted plants (12% and 56%, respectively) and did not affect fruit quality in terms of °Brix and colour. In conclusion, double grafting presents several beneficial aspects that are counter-balanced by the extra cost of the technique. The difference in yields reflects compatibility problems.     

Seed inoculation with Azospirillum mitigates NaCl effects on lettuce

Data on the growth-promoting effects of Azospirillum on lettuce exposed to either normal or saline conditions, is scarce. Lactuca sativa L., cv Mantecosa seeds were colonized with A. brasilense Sp245 cells during imbibition. Germination percentages were determined after 7 d treatments with 0, 30, 50 or 80 mol m⁻³ NaCl. In another experiment, seeds germinated in Hoagland were irrigated for 30 d with 0, 30, 50 or 80 mol m⁻³ NaCl supplemented media. Vegetative growth proceeded in a growth chamber with a 13–11 h day–night cycle. Buffer-imbibed seeds were considered non-inoculated controls. Plant samples were taken at 0, 14, 20, and 30 d after the onset of NaCl treatments and dissected in aerial and root portions. The weights of both tissues were measured. Azospirillum-inoculated seeds had significantly higher germination percentages than controls in all treatments. Inoculated dried seeds stored up to 30 d maintained such characteristic in most of the treatments, particularly at 80 mol m⁻³ NaCl. Plants grown from inoculated seeds and irrigated with saline media displayed higher total fresh and dry weights and biomass partition to the aerial portion, than non-inoculated controls. Azospirillum-inoculated lettuce seeds had better germination and vegetative growth than non-inoculated controls after being exposed to NaCl.     

Effect of plant growth temperature on membrane lipids in strawberry (Fragaria × ananassa Duch.)

Changes in membrane lipid composition are important in the acclimation of plants. The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, and 30/22 °C) on membrane lipids of ‘Earliglow’ and ‘Kent’ strawberry (Fragaria × ananassa Duch.) were studied. The monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) were the major galactolipids in the strawberry leaves. ‘Earliglow’ contained a higher amount of galactolipids in the leaves than ‘Kent’. The major phospholipids in the strawberry leaves, roots, and fruit were phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). PC and PE were the two predominant phospholipids in the strawberry. The leaves and fruit of ‘Earliglow’ contained higher amounts of phospholipids compared to those of ‘Kent’, whereas ‘Kent’ strawberry roots had higher phospholipids. Palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and α-linolenic (C18:3) acids were major fatty acids in galacto- and phospholipids of the ‘Earliglow’ and ‘Kent’ strawberry. PC is very rich in linolenic acid in leaves compared to the fruit and root tissues. PC had the highest ratio of unsaturated to saturated fatty acids among all phospholipids. There was a significant increase in the content of galactolipids (MGDG, DGDG) and phospholipids (PC, PI, PG and PE) and unsaturation of their fatty acids in the cool day/night growth temperature. Increasing day/night growth temperatures decreased MGDG/DGDG ratios. The shifts in saturation and composition of fatty acids observed with strawberry may be an adaptation response of plants to the temperature changes.     

Flowering and changes in respiration in Asiatic hybrid lilies as influenced by bulb vernalization

Asiatic hybrid lilies, Lilium × elegans Thunb., ‘Red Carpet’ and ‘Sunray’ were used to investigate the effect of bulb vernalization at 2.5 °C on plant growth, flowering, and CO₂ production (respiration), and to use the CO₂ production pattern to monitor the time of flower bud initiation and development. Lily shoot emergence and flowering were accelerated when bulbs received 2.5 °C bulb vernalization; however, flowering was delayed when bulbs were stored at 20 °C before treatment at 2.5 °C; this indicated that bulbs were de-vernalized. The maximum CO₂ level, and the minimum level, reached in 78 h in non-vernalized bulbs and in 110 h in 6 weeks of 2.5 °C (6 weeks/2.5 °C) treated bulbs, was increased as the 2.5 °C duration was increased; this indicated that CO₂ level can be an useful parameter to measure the cold stimulus (i) accumulated in bulbs following bulb vernalization. The respiration rate higher than the predicted values of the best-fit curves derived from the quadratic equations was designated as Blip A and this was correlated to the time of flower bud initiation and development. Shoot elongation may follow the rise in carbon dioxide levels after reaching the minimum level. It is proposed that increased carbon dioxide levels higher than the predicted levels (Blip A), was correlated to the time of flower bud initiation and development. Measurement of carbon dioxide production upon receipt of bulbs may be a useful technique to provide important information for optimum vernalization treatments for bulbs that have accumulated different levels of low temperature stimulus after bulb vernalization.     

Production of inter-section hybrids between Primula filchnerae and P. sinensis through ovule culture

Inter-section hybrids were obtained in the reciprocal crosses between Primula filchnerae (2n = 2x = 24) of Sect. Pinnatae and P. sinensis ‘Fanfare’ (2n = 2x = 24) of Sect. Auganthus by rescuing ovules on half-strength (1/2) Murashige and Skoog's (MS) medium supplemented with 50 g l⁻¹ sucrose, 2.5 g l⁻¹ gellan gum, 0.1 mg l⁻¹ α-naphthaleneacetic acid (NAA), 0.1 mg l⁻¹ 6-benzyladenine (BA) and 50 mg l⁻¹ gibberellic acid (GA₃). In ovule culture, germination occurred with radicle elongation but no plumule was observed. The radicle kept on the initial medium showed root proliferation with callus formation. When the calluses were transferred to (1/2)MS media containing 30 g l⁻¹ sucrose and 3 g l⁻¹ gellan gum, without plant growth regulators (PGRs) or with 1 mg l⁻¹ zeatin and 0.1 mg l⁻¹ NAA, plantlets were regenerated. The plants thus obtained were confirmed to be hybrids through flow cytometry (FCM) and random amplified polymorphic DNA (RAPD) analyses. The hybrid obtained when P. filchnerae was used as the maternal parent was diploid, whereas hexaploid hybrid was obtained when using P. sinensis as the maternal parent. The hexaploid hybrid might be produced through chromosome doubling of a triploid originated from the fertilization of P. sinensis with unreduced pollen of P. filchnerae.     

Relationships between yield components in first cropping year and average yield of short-day strawberries over two main seasons

Fruit productivity of the garden strawberry, Fragaria × ananassa Duch., is a result of interrelationship of yield components contributing to it directly or indirectly. The main aim of the investigation was to find out whether there exists any general regularity, connecting relationships between main yield components in first cropping year to average yield of two main seasons. Two successive studies which primarily included 23 genotypes, differing in yield components and productivity, each, were planted in field conditions in spring 1999 and in spring 2000, respectively, and used for data collection to explore the material obtained in them. Four key yield components and average yields were measured in both cropping years, after which all possible ratios between the components were calculated to find out: first, the relationships to be influential on average yield of the two main seasons; second, type of the probable yield dependence upon the ratios; and, third, their values leading to high yields. Two ratios between the key yield components in first season, i.e.: inflorescence number per plant to branch crown number per plant, named ratio 1, and fruit weight (g) to flower count per inflorescence, named ratio 2, have been found to be related to average yield. An irregular surface, with a single peak falling approximately in its centre, describes average yield dependence upon the ratios. Values of the two ratios falling in the range of 1.0–1.6 each, provided that they are close, have enabled plants to produce high yields cumulatively over two first years. The paper highlights the most important differences in plant behaviour and yield dynamics of strawberry genotypes, depending on combinations of the ratios in first year, discerning those, which have been particularly advantageous to obtain very high yields, and are influenced by negative environmental factors least of all. Based on the findings, a method of predicting of average yield has been developed. Following this, usefulness of the method and possibilities of its using in strawberry breeding and variety trial are discussed.     

Indicators of nitrogen status for ornamental woody plants based on optical measurements of leaf epidermal polyphenol and chlorophyll contents

Indicators of plant nitrogen (N) status adapted to woody ornamental plants are essential for the adjustment of fertilization practices in nurseries. The objective of this study was to investigate whether optical measurements of leaf epidermal polyphenol (EPhen) and chlorophyll (Chl) contents could be used as N status indicators for woody deciduous and evergreen ornamental plants. One-year-old plants of Lagerstroemia indica, Callicarpa bodinieri and Viburnum tinus were grown outdoors in containers. They received low (TN₁, 4 mg L⁻¹) or high (TN₂, 105 mg L⁻¹) levels of N during 2 months in spring and summer. TN₁ treatment limited shoot growth from 28 to 37 days after treatment initiation in Lagerstroemia and Callicarpa, respectively. Shoot growth was unaffected until day 176 in Viburnum. The mass-based leaf N content (N_M) of a sample of young expanded leaves exposed to direct sunlight was tightly correlated with shoot N content and differentiated treatments several weeks before shoot growth reduction for the three species. N_M was therefore used as an index of plant N status. EPhen and Chl contents were recorded with Dualex™ and SPAD-502 leaf-clip meters, respectively. Dualex values were strongly and negatively correlated with N_M, and differentiated the treatments early in the experiment, in all three species. SPAD values were positively correlated with N_M for Lagerstroemia and Callicarpa, but not for Viburnum, because large variations in leaf mass per area (LMA) in this species compensated for variations in leaf dry mass invested in Chl. The SPAD/Dualex ratio was used to assess changes in the proportion of leaf dry mass allocated to proteins and polyphenols in response to fertilization. It differentiated between the treatments early in the experiment and was correlated with N_M in all three species.