Physiological response of onion plants to foliar application of putrescine and glutamine

Two field experiments were carried out in Egypt during two successive seasons (2007/2008 and 2008/2009). This study aimed to investigate the response of growth, yield quality and some metabolic constituents of onion (Allium cepa L. cv. ‘Giza 20’) to foliar application of putrescine (Put; 25, 50 and 100 mg L⁻¹) and glutamine (Glut; 50, 100 and 200 mg L⁻¹), the former a diamine and the latter an amino acid, either alone, or in combination. Foliar application of Put and Glut, either alone or in combination, significantly increased plant height, number of leaves, fresh weight of leaves/plant, fresh and dry weight/plant, leaf area, leaf area/plant, bulb length, bulb diameter and weight, as well as yield of onion and quality of bulbs. Total soluble sugars, sulfur compounds, total soluble phenols, total free amino acids and total photosynthetic pigment content in leaves were increased by increasing Put and/or Glut concentrations up to 100 and 200 mg L⁻¹, respectively. Generally, foliar application of Put at 100 mg L⁻¹ and Glut at 200 mg L⁻¹ singly, or combined, effectively increased bulb yield and quality. In conclusion, the yield-contributing characters and quality of onion could be improved by application of Put and/or Glut.     

Response of four olive (Olea europaea L.) cultivars to six B concentrations: Growth performance,nutrient status and gas exchange parameters

A greenhouse experiment was conducted to study the effects of boron (B) on growth, nutrient status, B distribution and gas exchange parameters of olive plants (Olea europaea L.). One-year-old own-rooted olive plants of the Greek cultivars Megaritiki, Chondrolia Chalkidikis, Amfissis and Kalamon were grown in a sand–perlite medium and irrigated with nutrient solutions containing: 0.27, 0.5, 1, 2.5, 5 and 10 mg L⁻¹ B (0.27 and 10 mg L⁻¹ were considered as control and excess B treatment, respectively). After culturing for 185 days, leaves and stems (from basal and apical part of the shoots) and roots were separately sampled. Our results showed that the final number of leaves per plant was negatively correlated with B concentration in the nutrient solution. Furthermore, in B10.0 treatment, ‘Megaritiki’ had decreased length and number of lateral stems, ‘Chondrolia Chalkidikis’ and ‘Amfissis’ showed decreased length of lateral stems and ‘Kalamon’ decreased length of lateral stems and plant height. In general, dry weight of stems and leaves was not significantly correlated with B concentration in the nutrient solution. B concentration in leaves and stems was linearly correlated with B supply. A linear correlation existed between B concentration of the nutrient solution and that of leaves and stems. At the end of the experiment, B levels in the leaves and stems of B0.27 and B0.5 treatments did not differ significantly. In general, the increase of B concentration in the nutrient solution, negatively affected the nitrogen (N) concentration of leaves and stems while phosphorus (P) and iron (Fe) concentrations were not affected. Furthermore, potassium (K) and calcium (Ca) concentration in stems of plants supplied with 10 mg L⁻¹ B was decreased. In addition, high B supply resulted in increased magnesium (Mg) and manganese (Mn) concentrations in ‘Chondrolia Chalkidikis’ and ‘Amfissis’ and in the decrease of zinc (Zn) concentrations, in all plants. A significant decline in photosynthetic rate at the end of the experiment was observed in the B5.0 treatment regardless of cultivar.     

In vitro shoot proliferation and enhancement of rooting for the large-scale propagation of yellow bamboo (Bambusa vulgaris ‘Striata’)

Continuous and rapidly proliferating axillary shoots were raised from axillary buds in secondary branches of adult field culms and nursery grown 1-year-old tissue culture-raised plants of Bambusa vulgaris ‘Striata’. Shoots continuously proliferated in a MS medium containing 4 mg L⁻¹ 6-benzyladenine (BA). The effects of indole butyric acid (IBA) levels, a pretreatment with thidiazuron (TDZ) (1-phenyl-1-([1,2,3-thidiazol-5-yl])urea) and illumination on rooting, were investigated after 6 months of shoot proliferation. A rooting medium with IBA at 3 mg L⁻¹ was optimum for root induction. Shoots of adult field culms that were proliferated in the presence of BA when induced to root in this medium resulted in 40% rooting in 27 days. In vitro shoots raised from 1-year-old tissue cultured plants showed 92% rooting under the same conditions. Rooting was enhanced when the relatively difficult-to-root in vitro shoots from adult field culms were pretreated with 0.5 mg L⁻¹ TDZ for two to three subcultures before placing in the root induction medium. Continuously illuminated shoots pretreated with TDZ for three subcultures showed 100% rooting compared to 83% rooting of shoots that were exposed to a 12 h photoperiod. These findings have been applied in the large-scale propagation of this species.     

Spray pollination as a labor-saving pollination system in Japanese pear (Pyrus pyrifolia (Burm.f.) Nakai): Development of the suspension medium

Effects of suspension media used for spray pollination on pollen grain viability were investigated in Japanese pear (Pyrus pyrifolia (Burm.f.) Nakai ‘Kosui’). The suspension media tested in this study consisted of pectin methylesterase (PME) and polygalacturonase (PG) combined with either 0.1% agar or 0.04% xanthangum (XG). We also evaluated the influences of spray pollination on fruit set and fruit quality. Pollen grain viability, as measured by germination and pollen tube growth rates, was maintained in media supplemented with 0.1 mg L⁻¹ PME or 0.1 mg L⁻¹ PG. The level of fruit set after spray pollination using media containing PME or PG in combination with either 0.1% agar or 0.04% XG was almost the same as the level after artificial pollination by hand (hand pollination). The media containing XG combined with either PME or PG seemed to show better results for pollen grain viability and fruit set, although the results were variable from year to year. With regard to fruit size, shape and other parameters for fruit quality, spray pollination and hand pollination gave comparable results, irrespective of the medium composition. The time required for spray pollination was less than half of that required for hand pollination, and the amount of pollen grain required for spray pollination was one-third or less than the amount required for hand pollination. Thus, spray pollination may be a time- and labor-saving pollination system for the cultivation of Japanese pear.     

Abscisic acid drenches can reduce water use and extend shelf life of Salvia splendens

Inadequate watering of potted ornamental plants during retail can cause a decline in quality as well as plant death. Abscisic acid (ABA) is the main phytohormone controlling plant responses to drought stress, including regulation of stomatal opening and closure. ABA may become available for the greenhouse industry in 2010. The objective of this study was to determine whether exogenous ABA applications can be used to induce stomatal closure and reduce water loss from the substrate. We drenched salvia (Salvia splendens F. Sellow. ex Roem & Shult.) ‘Bonfire Red’ with 50 mL of ABA solutions at concentrations of 0, 250, 500, 1000, and 2000 mg L⁻¹, after which plants were no longer irrigated. ABA drenches slowed down substrate water loss by reducing transpiration in a dose-dependent manner. Stomata closed within 3 h after ABA treatment, decreasing transpirational water loss. However, ABA drenches also caused abscission of lower leaves, resulting in approximately 60% leaf loss with 2000 mg L⁻¹ ABA. ABA drenches with 250 mg L⁻¹ and 500 mg L⁻¹ increased the shelf life of salvia ‘Bonfire Red’ by 3 days, without excessive leaf abscission. ABA can be used to increase the shelf life of salvia, but the lowest effective concentration should be used to minimize leaf abscission.     

Growth and flowering of black iris (Iris nigricans Dinsm.) following treatment with plant growth regulators

The effects of application method and concentration of gibberellic acid (GA₃), paclobutrazol and chlormequat on black iris performance were assessed. Plants (10 cm high, 4 ± 1 leaves) were sprayed with 125, 250, 375 or 500 mg L⁻¹ or drenched with 0.25, 0.5, 1 or 2 mg L⁻¹ GA₃. In a second experiment, the plants were sprayed with 100, 250, 500 or 1000 mg L⁻¹ or drenched with 0.25, 0.5, 1 or 2 mg L⁻¹ paclobutrazol. Other plants were sprayed with 250, 500, 1000 or 1500 mg L⁻¹ or drenched with 100, 250, 375 or 550 mg L⁻¹ chlormequat. In each experiment, the control treatment consisted of untreated plants. Results indicated that the tallest plants (37.3 cm) in the GA₃ experiment were those sprayed with 250 mg L⁻¹. The most rapid flowering (160 days after planting) occurred when a 375 mg L⁻¹ GA₃ spray was used, whereas flowering was delayed to 200 days using 1 mg L⁻¹ GA₃ drench. Drenching with 1 mg L⁻¹ GA₃ increased height of the flower stalk by 7 cm compared to the control. Though relatively slow to flower, plants drenched with 1 mg L⁻¹ GA₃ had long and rigid stalks, which were suitable as cut flowers. Number and characteristics of the sprouts were not affected by GA₃. All paclobutrazol sprays resulted in leaf falcation. A 500 or 1000 mg L⁻¹ paclobutrazol spray resulted in severe and undesirable control of plant height, drastic reduction in stalk height and weight, and delayed flowering. Plants drenched with 0.25 or 1 mg L⁻¹ paclobutrazol were suitable as pot plants. Chlormequat reduced plant height only at the highest drench concentration, which also reduced flowering to 70%. No leaf falcation was observed with GA₃ or chlormequat. Chemical names: ( ± )-(R*,R*)-beta-((4-chlorophenyl)methyl)-alpha-(1,1,-dimethylethyl)-1H-1,2,4,-triazol-1-ethanol (paclobutrazol); (2-chloroethyl) trimethylammonium chloride (chlormequat).     

Plant regeneration of Carica papaya L. through somatic embryogenesis in response to light quality,gelling agent and phloridzin

Difficulties to develop an easy and reproducible protocol to get healthy and well formed plants from somatic embryos of papaya (Carica papaya L.) had included low germination, callus production at the base of the embryo radicle and the occurrence of hyperhydric plantlets among others, and by consequence unsuccessful transfer to the field. With the aim of improving a propagation method, the effects of light quality, gelling agent and phloridzin concentration on the germination of somatic embryos of hermaphrodite C. papaya L. var. Maradol were studied. Somatic embryos were grown on half strength MS medium, with the addition of Chen vitamins [Chen, M.H., Wang, P.J., Maeda, E., 1987. Somatic embryogenesis and plant regeneration in Carica papaya L. tissue culture derived from root explants. Plant Cell Rep. 6, 348–351], solidified with three distinct gelling agents: Sigma^® Agar–Agar, Difco^® Bacto agar and Phytagel^®; supplemented with phloridzin and exposed to different light qualities: blue (54 μmol m⁻² s⁻¹), red (65 μmol m⁻² s⁻¹), gro-lux (68 μmol m⁻² s⁻¹), red + blue, white (32 μmol m⁻² s⁻¹) and wide spectrum (49 μmol m⁻² s⁻¹) during a period of 4 weeks. Results show that light quality and gelling agent had important effects on germination and plant growth, while 3.0 mg L⁻¹ phloridzin had an important role on germination as well as in root development. Somatic embryos exposed to white light, culture medium solidified with 3.0 mg L⁻¹ phytagel and 3.0 mg L⁻¹ phloridzin showed longer roots. Meanwhile, germination and plant length were promoted on an improved culture medium solidified with 7.5 g L⁻¹ Difco^® Bacto agar, 3.0 mg L⁻¹ phloridzin and exposed to gro-lux lamps. Under these conditions, 70% of somatic embryos germinated and developed normal roots without hyperhydricity. The regenerated plantlets with well developed roots and shoots were successfully transferred to a greenhouse with a survival rate of 95%.     

In vitro proliferation from axillary buds and ex vitro protocol for effective propagation of Syringa × hyacinthiflora ‘Luo Lan Zi’

As a precondition for lilac mass propagation, the optimal shoot-multiplication medium for Syringa × hyacinthiflora ‘Luo Lan Zi’ was ascertained mainly based on clustered microshoot inducement and large leaf area establishment in 6-benzyladenine (BAP) (1.00 mg L⁻¹) and zeatin (Z) (0.10 mg L⁻¹) combination. Medium supplied with lower level of BAP (0.50 mg L⁻¹) and auxin (IAA) (0.25 mg L⁻¹) was not suitable for lilac shoot proliferation, but it could be competent for long-term preservation of the un-rooted shoots so that subsequent proliferation culture could be carried out at anytime. In addition, excess height growth which resulted in low transplanting survival rate was effectively controlled by decrease in node number when paclobutrazol (PBZ) was applied in rooting medium at a concentration of 1.00 mg L⁻¹ after taking into account the effects on shoot height, rooting, persistent leaf area and PBZ carry-over. An important overwintering treatment was to use a plastic chamber covering for plants in the greenhouse prior to field planting to ensure adequate biomass of stem and underground parts not only in the current growing season but also in the subsequent years.     

Effect of ABA and sucrose on germination of encapsulated somatic embryos of guava (Psidium guajava L.)

Present study demonstrates the effect of sucrose and ABA on germination of encapsulated somatic embryos of guava (Psidium guajava L.). Sucrose and ABA at different concentrations were also evaluated for their effects on maturation and germination of somatic embryos. Mature somatic embryos developed on MS medium containing high concentration of sucrose (10%) or ABA (1.0 mg l⁻¹) showed inhibition in germination if they continued to be in same medium for 4 weeks. With increasing concentrations of sucrose (3–9%) or ABA (0.01–1.0 mg l⁻¹) in medium, percent germination of encapsulated somatic embryos decreased significantly. Encapsulated somatic embryos after storage on MS medium supplemented with 9% sucrose or 1 mg l⁻¹ ABA for different duration (0–60 days) germinated when they were transferred to medium containing 3% sucrose. About 20.8% and 37.5% encapsulated somatic embryos germinated after storage on ABA (1 mg l⁻¹) or sucrose (9%) for 60 days, respectively. Temporarily suppression in germination of encapsulated somatic embryos by high concentration of sucrose or ABA may be important for short-term conservation of elite genotype of guava.     

An upper limit for elevated root zone dissolved oxygen concentration for tomato

It is well understood that insufficient oxygen within plant root zones can greatly diminish plant productivity. However, little is known about the effect of elevated root zone oxygen concentrations. Tomato (Lycopersicon lycopersicum Mill., cv. Trust) seedlings were grown in nutrient solutions containing dissolved oxygen (DO) concentration ranging from 5.3 to 40 mg L⁻¹ for 4 weeks. There were no visible symptoms observed on the leaves or stems in any of the treatments. Leaf chlorophyll content was higher in the 40 mg L⁻¹ treatment than with 20 and 30 mg L⁻¹ DO treatments. Two weeks from the start of the experiment, roots in the 40 mg L⁻¹ treatment exhibited stunted growth, became thicker, and had fewer side and fine roots compared to roots in the lower levels of DO treatment. Almost all the measured growth parameters (fresh and dry weights of root, stem, and leaf, leaf area, stem diameter) were significantly reduced in plants grown in the 40 mg L⁻¹ treatment compared to plants in the lower level of DO treatments, except that the plant height increased with the increasing DO concentration. Root respiration increased linearly with increasing DO concentration; however, there was no effect on leaf net CO₂ exchange rate. It is suggested that it was safe to enrich root zone DO to as high as 30 mg L⁻¹, although the growth benefit was minor by increasing DO from ambient air saturated level (∼8.5 mg L⁻¹) to 30 mg L⁻¹. Higher than 30 mg L⁻¹ could cause reduction in tomato plant growth.     

Effect of high temperatures in the pre-blooming and blooming periods on ovule formation,pollen grains and yield of ‘Granada’ peach

The aim of this work was to evaluate the effects of high temperatures in the pre-blooming and blooming periods on the growth of sexual gametes and yield of ‘Granada’ peach. The experiment was carried out in the commercial orchard of Charqueadas, under the subtropical conditions of the Central Depression at Rio Grande do Sul State, Brazil (28°57′S; 51°37′W; 30 m alt.). Two treatments were tested: (1) trees in the greenhouse with partial ventilation and (2) trees in the orchard. The phenology, morphologic constitutions of the pollen grains, ovule growth, yield and germination (%) of pollen grains and fruit set were evaluated. High temperatures in the pre-blooming and blooming periods anticipated the break of dormancy and blooming. These conditions also delayed the female gametophytes (embryo sac) and promoted anomalies in the formation of male gametophytes. Those factors promoted low pollen viability and a lack of synchrony in fertilization, thereby generating low fruit set percentages and yield.     

Comparison of S-RNase,RNase T1, T2, and A effects on growth inhibition and RNA degradation of in vitro-cultured pear pollen

To obtain the basic information on fruit set regulation, effects of several RNases including S-RNase on pollen tube growth and RNA degradation in the tube were studied in the pear. Purified S-RNase from the Japanese pear ‘Kosui’ (S₄S₅) predominantly inhibited the growth of ‘Kosui’ pollen tubes (self) in vitro at 0.28 unit μL⁻¹, but it inhibited ‘Chojuro’ (S₂S₃) pollen (cross) only slightly. The same unit of RNase T₁ (EC 3.1.27.3) clearly inhibited the pollen tube growth, but the action was significantly weaker than that of the S-RNase against the self-pollen. Inhibitory effect of RNase T₂ (EC 3.1.27.1) and RNase A (EC 3.1.27.5) was only slight. The proteins other than the S-RNase extracted from pear style did not have any inhibitory action, though they possessed RNase activity 3.8 times higher than S-RNase. Thus, RNases tested here could not substitute for the S-RNase in specific inhibition against the self-pollen tube growth. Total RNA degradation by each RNase occurred in the pollen tubes as following order; S-RNase (self) ≥T₁ > T₂ ≥ A > S-RNase (cross). Degradation degree of 28S and 18S rRNA was as follows; S-RNase (self) > A > T₁ > T₂ > S-RNase (cross). The degradation of 5.8S and 5S rRNA was; S-RNase (self) > S-RNase (cross) > A > T₂ > T_1. The degree of rRNA degradation was, thus, not always in parallel with the degree of pollen growth inhibition. The S-RNase may degrade not only rRNA but also mRNA essential for pollen tube growth, and may be specifically adapted to inhibit the growth of self-pollen tubes. Therefore, controlling S-RNase amount in the style will produce self-thinning cultivars efficiently, which are unnecessary not only for hand-pollination but fruit-thinning practices in the pear. Practically, cultivar with weak self-incompatibility and small amount of S-RNase, such as ‘Okusankichi’, may be an expecting candidate for breeding self-thinning cultivars.     

Amelioration of chilling stress by paclobutrazol in watermelon seedlings

Paclobutrazol (PBZ) is a member of the triazole plant-growth inhibitor group that is responsible for inducing tolerance to number of biotic and abiotic stresses. An experiment was, therefore, conducted to test whether PBZ application at various concentrations (0, 25, 50 and 75 mg L⁻¹) through seed soaking or foliar spray would protect watermelon (Citrullus lanatus) seedlings, subjected to chilling stress. Thirty-five-day old plants were exposed to chilling 5 h/day at 4 °C for 5 days. PBZ improved growth rate of watermelon seedling subjected to chilling stress and increased relative leaf chlorophyll content (RLCC) and chlorophyll fluorescence ratio (Fv/Fm) compared with the control at the end of chilling stress. PBZ ameliorated the injury caused by chilling stress by inhibiting increases in proline and leaf electrolyte leakage, which suggested that PBZ ameliorated the negative effect of chilling stress. PBZ was most effective in increased chilling tolerance of watermelon seedling when applied using the seed soak method than as a foliar spray. The best protection appeared to be obtained from seedlings seed soaked with PBZ at 50 and 75 mg L⁻¹.     

硼、钙和农药对草莓花粉萌发和花粉管生长的影响

采用花粉液体培养法研究温度、硼、钙及农药对草莓花粉萌发和花粉管生长的影响。结果表明,(1)草莓花粉萌发和花粉管生长适宜的温度为25～30℃。(2)外源硼酸为草莓花粉萌发必需物质,适宜质量浓度为0.3g/L,低质量浓度促进花粉萌发和花粉管生长,而高于0.3g/L则起抑制作用。(3)外源钙为非必需物质,但适量的外源钙离子有利于花粉萌发,适宜质量浓度为0.3g/L,高钙抑制花粉萌发。(4)在培养液中分别加入常规浓度的7种农药,每处理几乎无花粉萌发,加入1/10常规体积分数的7种农药中,只有一遍净、速克灵、奥美特等3种农药处理有少量花粉萌发,说明农药对花粉萌发和花粉管生长有强烈抑制作用。     

精胺对梨花粉原位萌发及花粉管生长的影响

为进一步研究活体条件下精胺对梨花粉萌发及花粉管生长的影响,以幸水、新雪、长-二十世纪为材料,采用荧光显微镜观测了不同浓度精胺处理的花粉萌发及花粉管生长情况。试验结果表明:较低浓度的精胺能促进花粉萌发,而超过一定浓度时则表现抑制作用,适宜于花粉萌发的精胺浓度是0-0.025mmol/L。精胺对花粉管生长的促进作用因品种而异,0-0.05mmol/L,精胺促进幸水、新雪花粉管生长的作用主要表现在花柱中上部;而到达基部的花粉管仍较少,与对照间差异不显著。在0-0.025mmol/L的适宜浓度下,精胺可促进长-二十世纪花粉管生长并到达花柱基部。不同浓度的精胺对幸水、新雪坐果影响不大;而适宜浓度的精胺可促进长-二十世纪坐果。     

Putting back what we take out,but how much?: Phosphorus and nitrogen additions to farmed Leucadendron ‘Safari Sunset’ and Leucospermum ‘Succession’ (Proteaceae)

Proteaceae are adapted to low-nutrient soils in the various regions where they occur. However, harvesting of flowering stems for the cut-flower industry must eventually cause soil nutrient depletion sufficient to reduce yields. Different N forms, and N and P concentrations were supplied to two Proteaceae cultivars (Leucadendron ‘Safari Sunset’ and Leucospermum ‘Succession’) in a controlled fertigation experiment, and appropriate concentrations for maximum growth with minimum nutrient accumulation or loss were determined. Small additions of N (0.025–0.1 mM) significantly improved growth of both cultivars growing on Strandveld sandy soil. Larger additions of N (up to 2 mM N) resulted in poor growth (both cultivars) and N accumulation in the soil (Safari Sunset). Small additions of P (<10 μM) significantly improved growth of both cultivars and resulted in no accumulation or loss of P in the soil. Larger additions of P (up to 500 μM) resulted in poor growth, P toxicity symptoms and P leaching from the upper soil layers. Best N forms in descending order of both plant visual appearance and vegetative yield were: urea ≥ ammonium nitrate > ammonium sulphate > calcium nitrate. Phosphorus toxicity symptoms were associated with increased concentrations of leaf P, Ca and Fe. Under conditions of maximum growth (10 μM P and 0.1 mM N) Safari Sunset removed 18 ± 0.6 g N, 1.5 ± 0.1 g P, 5.3 ± 0.6 g K and Succession removed 5.5 ± 0.2 g N, 0.3 ± 0.02 g P, 3.1 ± 0.5 g K over 6 months. At maximum growth, plants acquired more N and P amounts than were supplied, but supplying higher N and P concentrations adversely affected growth. Thus, a more complex or slow-release form of N and P than urea and soluble phosphate, respectively, may provide enough N and P to replace losses from the farm soil at the low concentrations required for proteas.     

Seed germination and tissue culture of Cymbidium giganteum Wall. ex Lindl.

Efficient protocols were established for in vitro seed germination, neo-formation of secondary (2°) protocorms from primary (1°) protocorms and multiple shoot buds and protocorm-like body (PLB) induction from pseudo-stem segments of in vitro-raised seedlings of Cymbidium giganteum. Four nutrient media, namely Murashige and Skoog (MS), Phytamax (PM), Mitra et al. (M), and Knudson ‘C’ (KC) were evaluated for seed germination and early protocorm development. In addition, the effects of peptone, activated charcoal (AC) and two plant growth regulators [6-benzylaminopurine (BAP) and 2,4-dichlorophenoxyacetic acid (2,4-D)] were also studied. Both M and PM supplemented with 2.0 g l⁻¹ peptone or 1.0 mg l⁻¹ BAP resulted in ∼100% seed germination. Media supplemented with 2.0 g l⁻¹ AC could effectively induce large protocorms (1.6 ± 0.1 mm in diameter). Neo-formation of 2° protocorms from 1° protocorms was achieved in liquid and agar-solidified PM medium fortified with different concentrations and combinations of auxins (α-naphthalene acetic acid (NAA) and 2,4-D) and cytokinins [BAP and kinetin (KN)]. The highest number of 2° protocorms was obtained in liquid medium (10.7 ± 0.9/1° protocorm) supplemented with 2.0 mg l⁻¹ BAP + 1.0 mg l⁻¹ NAA. Although protocorms proliferated profusely in liquid medium, these did not develop further unless transferred to agar-solidified medium within 6–8 weeks. Multiple shoot buds and PLBs were induced from pseudo-stem segments on agar-solidified PM medium fortified with different concentrations and combinations of BAP and NAA and the maximum number of PLBs (6.00 ± 0.20) was recorded when BAP and NAA were applied at 2.0 mg l⁻¹ each. A solid root system was induced from PLBs and shoot buds when these were transferred to half-strength PM or M media fortified with 0.5 mg l⁻¹ indole-3-acetic acid. Well-rooted plants were transferred to the greenhouse with 95% survival.     

Nutritional quality of greenhouse lettuce at harvest and after storage in relation to N application and cultivation season

The effect of five levels of nitrogen fertilization on the growth and nutritional quality of Cos lettuce (Lactuca sativa L. cv. Parris Island) at harvest and after storage was studied during autumn and winter in South-West Greece. Plants were cultivated hydroponically in a greenhouse and the nitrate, chlorophyll and ascorbic acid (vitamin C) concentrations within the plant tissues were measured at harvest and following storage at 5 or 10 °C for 10 days. Nitrate accumulated in the leaves with increasing amounts of N within the nutrient solution and was higher in the winter than in the autumn. At the lowest N level (20 mg L⁻¹), the inner leaves accumulated more nitrate than the outer leaves, whereas at higher N levels (140, 200 or 260 mg L⁻¹) nitrate accumulation was higher in the outer leaves. Overall, the highest nitrate concentrations were detected in the petiole and the proximal end of the leaf, but at the lowest N application rate (20 mg L⁻¹) nitrate accumulated in the distal region of the leaf too. Although the nitrate concentrations within the leaves did not change significantly during 10 days storage at 5 or 10 °C, the chlorophyll and vitamin C concentrations decreased. Chlorophyll loss was higher in lettuce that was grown under low N levels and was higher at 10 °C than at 5 °C, but was reduced by enclosure of the lettuce in polyethylene film. It is concluded that the optimum N application rate for Cos lettuce grown hydroponically under cover during autumn and winter in South-West Greece, and in other areas with a similar climate, is 200 mg N L⁻¹ because at this N rate yield is satisfactory and leaf nitrate concentrations are below the maximum acceptable level for human consumption. Nutritional value (vitamin C concentration) and market quality (chlorophyll content) are highest at harvest and decrease during storage, but quality in terms of nitrate concentration does not change.     

Rooting response of shoot cuttings from three peach growth habits

Current year shoot cuttings were collected in October and August from three growth habits of peach (Compact, Pillar, and Standard) and treated with one of four concentrations of indole butyric acid (0, 250, 1250, and 2500 mg L⁻¹ IBA). Rooting response was measured after 5 weeks in the greenhouse. Little or no rooting occurred with cuttings from any growth habit that was collected in October or in August when treated with 0 and 2500 mg L⁻¹ IBA. In August, the number of shoots that rooted was greater in cuttings from Pillar (79 and 45%) than Compact (13 and 3%) treated with 250 and 1250 mg L⁻¹ IBA, respectively. Cuttings from Standard trees had intermediate rooting of 56 and 6% at 250 and 1250 mg L⁻¹ IBA, respectively. Pillar trees consistently grew more roots with greater root length per cutting than the other growth habits. It is proposed that differences in rooting response among the growth habits may be associated with differences in endogenous auxin concentration that had been found in previous studies. Within peach and possibly other fruit trees, the capacity of shoot cuttings to develop adventitious roots can vary by cultivar and successful root induction with exogenous plant growth regulators may depend, in part, on endogenous hormone levels.     

Response of apple trees to boron fertilization under conditions of low soil boron availability

The aim of the study was to examine the effect of boron (B) fertilization on the vegetative and the reproductive responses of apple (Malus domestica Borkh.) trees grown at low soil B availability. The experiment was carried out in 2005 under a greenhouse on 5-year-old ‘Jonagold’ apple trees/M.9 EMLA planted singly in 50-L containers filled with a sandy loam soil with hot water-soluble B concentration of 0.32 mg kg⁻¹. The trees were fertilized with B as foliar or soil application. Foliar B sprays were applied at the stage of pink bud, beginning of flowering, petal fall, and 10 days after flowering, at a solution concentration of 0.03%. Soil B fertilization was done at the bud break stage at a rate of 2 g per tree (27 mg B kg⁻¹ soil). The trees untreated with B served as the control. The results showed that soil B fertilization improved root development and tree vigor. Leaves of trees supplied with B to the soil had higher B concentration and chlorophyll, net photosynthetic rate, stomatal conductance, and activity of catalase and glutathione reductase than those of the control plants. Boron fertilization, regardless of application mode, increased fruit yield; the efficiency of foliar B sprays was higher than soil B application. Apple fruits of trees fertilized with B to the soil were bigger, more colored, richer in B, and had higher soluble solids concentration, and titratable acidity compared to those of the control trees.