Inoculation of growing media with the rhizobacterium Variovorax paradoxus 5C-2 reduces unwanted stress responses in hardy ornamental species

Inoculation of growing media with plant growth promoting rhizobacteria (PGPR) has a number of potential benefits for the production of ornamental plants. Certain rhizobacteria synthesise the enzyme ACC deaminase, which cleaves ACC, the precursor of the plant hormone ethylene. Bacterial metabolism is now known to lead to a reduction in [ACC] in the plant transpiration stream and bacteria are hypothesised to act on ACC exuded from roots. This in turn reduces the ethylene generated in plants growing in growing media inoculated with these bacteria. Here we tested if applications of the ACC deaminase containing rhizobacteria Variovorax paradoxus⁵C–²could be of benefit to ornamental growers by reducing ethylene generation in stressed plants. Ethylene is produced at levels that are inhibitory to growth and development under a number of abiotic stresses. The propagation and production of hardy ornamentals is deleteriously affected by abiotic stresses that involve ethylene signalling, including drought and physical wounding. Inoculation of growing media with V. paradoxus 5C-2 lowered ethylene emission from mature leaves of Cytisus × praecox experiencing drought stress. In addition, bacterial inoculation of the growing media resulted in significantly reduced abscission of the mature leaves under drought treatment. Beneficial effects of inoculation where also found in the wounding response of Fargesia murielae following divisional propagation and late season senescence in Aquilegia × hybrida in response to drought stress. Together these results demonstrate that V. paradoxus⁵C–²has real potential for use on ornamental nurseries in situations where plant stresses are unavoidable.     

The effects of low boron on growth,gas exchange,boron concentration and distribution of ‘Newhall’ navel orange (Citrus sinensis Osb.) plants grafted on two rootstocks

The effects of low boron (B) on plant growth, photosynthesis, B concentration and distribution of ‘Newhall’ orange (Citrus sinensis Osb.) plants grafted on either Trifoliate orange (Poncirus trifoliata (L.) Raf.) or Carrizo citrange [C. sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.] rootstocks were investigated. One-year-old plants of the two scion-rootstock combinations were grown for 183 days in sand:perlite (1:1, v/v) medium under greenhouse conditions. The plants were irrigated with half-strength Hoagland's nutrient solutions containing four B concentrations (0.01, 0.05, 0.10 and 0.25 mg l⁻¹). The growth of root, stem of scion and leaves was less affected by low B treatments when ‘Newhall’ scion was grafted on Carrizo citrange than on Trifoliate orange. Thus, the growth of scions under low B conditions was mainly depended on the rootstock used, i.e., Carrizo citrange-grafted plants were more tolerant to low B compared to the plants grafted on Trifoliate orange. Boron concentrations in all plant parts decreased significantly by decreasing the B supply in the nutrient solution. Leaves were the dominant sites of B accumulation and showed the greatest reduction in B concentration compared to the other plant parts, as B concentration in the nutrient solution decreased. Irrespective of the rootstock, B levels in the upper–younger leaves were substantially higher than in basal-older leaves when plants were exposed to low B concentrations (≤0.05 mg l⁻¹), suggesting that under such conditions B was preferentially translocated to upper–younger leaves to support their growth. Furthermore, B distribution in different plant parts indicated that there was a restriction in translocation of B from root to scion tissues (stems and leaves of scion) under conditions of limited B availability. In addition, low B treatments decreased leaf photosynthetic rate, stomatal conductance and transpiration rate but increased intercellular CO₂ concentration in the leaves of ‘Newhall’ plants, irrespective of the rootstock used.     

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.     

Differential effect of transpiration and Ca supply on growth and Ca concentration of tomato plants

To determine the extent to which transpiration and Ca concentration in the nutrient solution affect the regulation of growth, two independent experiments with young tomato plants were carried out under fully controlled climate conditions and grown hydroponically. The first experiment consisted of the regulation of transpiration by three levels of relative air humidity (RH): 50%, 70% (control) and 95% (corresponding to 1.32, 0.79 and 0.13 kPa, respectively) during 7 days. The second experiment involved four periods of 1, 3, 7 or 14 days of low-calcium (0.5 meq L⁻¹) compared with the nutrient standard solution (9 meq L⁻¹). The results show that plant growth was affected more by RH than by the reduction of Ca in the nutrient solution. High humidity reduced the total plant dry matter and total leaf area, increasing the dry matter partitioning into the stems and reducing it into the leaves. However, the low-Ca supply did not affect those parameters. Plant Ca concentration was significantly reduced by low-Ca supply as well as by high RH, but to a much greater extent by the Ca supply than by high RH. Ca concentrations in leaves, stem, and roots were quickly reduced already after 1 day of low-Ca. After 14 days, Ca concentration in all plant organs (leaves, stems and roots) was reduced by approximately 70% compared to control plants. Our data show that calcium supply, and consequently Ca concentration in the tomato plant can be reduced drastically for short-term periods during the vegetative growth stage without any adverse effect on growth whilst higher humidity reduce both growth and Ca concentration in young vegetative tomato plants. Consequently, reduced Ca uptake at high air humidity is not the cause for the reduction in growth.     

Effects of oxygen-enriched nutrient solution on greenhouse cucumber and pepper production

A series of experiments were conducted with greenhouse cucumber and pepper plants to determine the effects of oxygen enrichment of the irrigation water on yield and fruit shelf-life. The experiments were carried out in soilless culture in research greenhouses. Depending on the experiment, treatments included sub-ambient (2 mg L⁻¹), ambient (5–6 mg L⁻¹), medium (16 mg L⁻¹) and high (30–40 mg L⁻¹) levels of oxygen in the supply tank. Cucumber plants were grown in yellow cedar sawdust and pepper plants in either sawdust or perlite. Oxygen enrichment resulted in a promotion of cucumber yield in only one experiment; in two other experiments, none of the oxygen treatments, including those at sub-ambient levels, had an effect. There were no effects of oxygen enrichment on pepper yield. However, in both cucumber and pepper, fruit shelf-life was extended in oxygen-enriched treatments. In terms of system efficacy, oxygen levels in the irrigation water were measured at the dripper and found to decrease by 20–67% of initial values compared to the supply tank values, depending on the initial oxygen concentration and on the experiment. Oxygen concentrations decreased even further to virtually ambient levels when measured in the drain water or in the substrate reservoir. Cucumber plant growth was promoted under conditions which facilitated consistently high oxygen in the root zone, achieved through heavy irrigation (1 min in two) with oxygen-enriched nutrient solution of plants grown in saturated substrate (pumice). However, those extreme irrigation rates would not be practical for commercial cucumber or pepper production. Overall, this study demonstrates that oxygen enrichment of porous substrates under typical hydroponic conditions is difficult and possibly because of this, effects on yield are infrequent. However, fruit shelf-life may be improved.     

A novel in vitro hydroponic culture system for potato (Solanum tuberosum L.) microtuber production

An innovative in vitro hydroponic culture system used in potato (Solanum tuberosum L.) microtuber production is described in this paper. In vitro potato plantlets, 6–8 cm in height, derived from meristems of potato tubers cultured on 1/2 Murashige and Skoog (MS) nutrient medium after 30 days culture were cut into 1.5 cm stem node segments and used as explants. These stem nodes were cultured in a novel system called in vitro hydroponic culture system containing 1/2 MS medium supplemented with 0.5 μM naphthaleneacetic acid (NAA), 0.3 μM gibberellic acid (GA₃), 3.7 μM adenine sulfate, 10% coconut water, 0.5 g/l activated charcoal, 80 g/l sucrose with or without 8 g l⁻¹ agar. Liquid medium was distributed to the carrier substrates in each storey of the system with the aid of capillary robes. In the present paper, the effects of porous material used as substrate carrier and the number of storeys involved in the culture system on microtuber formation and their morphological characteristics are reported. Cotton layer substrate is more stable for organogenesis of potato microtubers. Microtubers, 3.19 mm in diameter and 49.82 mg in weight, could be harvested from a one-storey in vitro hydroponic culture system containing filter paper as substrate. However, microtubers cropped from three-storey in vitro hydroponic culture system with cotton layer were bigger and weightier than those from three-storey system containing filter paper. The above results of the in vitro hydroponic system examined in this study might open up a new approach in producing potato and other hygrophilous microtuber.     

Effect of iron supply and nitrogen form on growth,nutritional status and ferric reducing activity of spinach in nutrient solution culture

This study was carried out in order to give some information that could improve spinach nutritional status and productivity. In this paper, the effect of two N forms (N was added either as 100% nitrate or as 80% nitrate and 20% ammonium) and three Fe levels (0 μM Fe; 20 μM FeEDDHA; 3 μM FeEDDHA + 10 mM NaHCO₃) on the growth, chlorosis symptoms and shoot nutrient element accumulation was studied in spinach plants (var. Viroflay), grown in hydroponics; six treatments and three harvests (at about 20 days interval each, until plants reached their commercial size) were applied in total. The results indicated that under conditions of Fe sufficiency (20 μM Fe), mixed N nutrition induced higher production of dry matter as well as improved Fe, Mn and Zn plant nutritional status. In plants grown under Fe deprivation (0 μM Fe), shoot Fe concentration was not significantly affected by the N form until the end of the experiment despite mixed N nutrition induced higher dry matter production up to harvest 2; plants grown under Fe deprivation and with mixed N nutrition presented also higher shoot Mn and Zn concentration. Under conditions of high concentration of bicarbonates and low level of Fe (3 μM Fe + 10 mM NaHCO₃), the N form had not a significant influence on total dry matter production whereas shoot Fe and Mn accumulation in 100% NO₃-fed plants was found to be significantly reduced compared to mixed N nutrition; regardless of the N form, those plants presented the least dry matter production, highest intensity of leaf chlorosis as well as highest root ferric reducing activity compared to plants grown under Fe deprivation.     

Leaf pruning intensities at flowering of banana (Musa AAA,cv. Grande Naine) did not influence fruit green and yellow life and quality

This study examined the effects of leaf pruning intensities at flowering on the green and yellow life and fruit quality of bananas (Musa AAA, cv. Grande Naine). The fruit from banana plants that retained 7, 9, 11 and 13 leaves after pruning were packed in carton boxes of 13.7 kg and stored in a cold room at 14 °C for 21 days to simulate transportation conditions. During this period, eight visual evaluations of fruit peel colour were made. Next, fruits were induced to commercial ripening using ethylene at 100 μl/ml. Four evaluations (every 2 days) on fruit firmness, soluble solids, titratable acidity, fruit weight and peel colour were made to assess fruit yellow life. No interaction between evaluations and number of leaves retained was found for pulp firmness, soluble solid percentage, fruit acidity, fruit weight and maturation grade. The fruit green life and peel colour was similar for plants retaining different number of leaves. After the application of ethylene, there were no differences in fruit firmness (P > 0.62), percentage of soluble solids (P > 0.24) nor in the percentage of acidity (P > 0.32). No difference in fruit weight (P > 0.07) and ripening grade (P > 0.17) were observed among plants retaining different number of leaves. The results suggest that in tropical commercial banana plantations, producing for international markets, it is possible to defoliate the banana plants to seven leaves at flowering without causing a reduction on the green and yellow life and quality of fruit.     

Effects of NaCl application to hydroponic nutrient solution on fruit characteristics of tomato (Lycopersicon esculentum Mill.)

NaCl was applied to nutrient solution (5 dS m⁻¹ versus 1.4 dS m⁻¹ in the control) of hydroponically-grown tomato and its effects on taste grading and chemical composition of fruit were investigated. Taste panels indicated NaCl treatment increased sweetness, acidity, umami (i.e. the taste of deliciousness) and overall preference. Hexose concentration of the fruit grown on NaCl treated plants significantly increased; and at the same time, chloric ion, organic and amino acids in general had higher concentrations in NaCl treated plants than the control. Our results showed that (1) consumer grading of the tomato fruit was influenced not only by sugar content but also by the organic and amino acids; (2) increased concentration of soluble solids in the fruit of NaCl treated plants was not the result of simple overall condensation due to the reduction of water transport. The relation of diversified consumer preference, fruit chemical composition, and appropriate evaluation of tomato fruit are also discussed.     

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.     

Effects of plastic mulches on root zone temperature and on the manifestation of tomato spotted wilt symptoms and yield of tomato

Tomato spotted wilt (TSW) disease is a serious constraint to tomato production in various regions of the world. The effect of TSW on tomato yield is largely influenced by time of infection. Early infection usually results in severe stunting of the seedling and even death of the plant. Plastic film mulches affect both the incidence of TSW, and plant growth and yield of tomato. The objective of the present study was to determine the effect of root zone temperature (RZT) as affected by plastic film mulch on the manifestation of symptoms of TSW, and growth and yield of tomato plants either artificially inoculated with tomato spotted wilt virus (TSWV) or under natural TSW infection. In artificially inoculated plants as well as in plants under natural TSW infection, vegetative top fresh weight (FW) and fruit FW both increased with the length of time after transplanting that the plants remained free from TSW symptoms. The root zone temperature was highest under black mulch (seasonal mean = 27.5 °C), followed by gray (27.0 °C), silver (25.8 °C), and white (24.8 °C) mulches. The plants grown on black mulch showed the earliest appearance of TSW symptoms, and had significantly reduced vegetative growth and fruit yields compared to plants on the other mulches. In conclusion, utilization of plastic mulches that created conditions of high RZT stress resulted in reduced plant growth and yield and predisposed the plants to earlier expression of TSW symptoms compared to plants grown at RZTs more favorable to tomato plant growth (optimal RZT = 26.1 °C [Díaz-Pérez, J.C., Batal, K.D., Granberry, D., Bertrand, D., Giddings, D., Pappu, H., 2003. Vegetative top growth and yield of tomato grown on plastic film mulches as affected by the appearance of symptoms of Tomato spotted wilt virus. HortScience 38, 395–399]). Since these plant responses to TSW under heat stress occurred in artificially inoculated plants as well as in plants under natural TSW infection, high RZTs probably affected the plants directly, independently of any possible effects on the thrips vectors.     

Changes in carbohydrate contents in shoot tips,leaves and roots of strawberry (Fragaria × ananassa Duch.) during flower-bud differentiation

Flowering is an important step in crop production. Under flower-inducing conditions, biochemical or physiological changes can be recognized. Changes in carbohydrates have an important role in flower development in plants; however, carbohydrate changes during flower bud differentiation in strawberry have not been thoroughly investigated. In this study, runner plants potted in 18 cm diameter pots and grown under non-inducing conditions (28 ± 3/22 ± 3 °C day/night; 16 h day length). When the plants were established, half of the plants then were put under inducing conditions (23 ± 3/13 ± 3 °C day/night; 8 h day length). After the induction period of 21 short-day cycles, plants were brought to non-inductive conditions again. In order to evaluate the carbohydrate changes during flower differentiation, shoot tips, leaves and roots were sampled from four replicated plants collected weekly for the period of 7 weeks. Sucrose, glucose and fructose contents were determined by HPLC, and starch by the anthrone method. The results obtained indicated that the most abundant soluble sugar in all organs tested was sucrose. Sucrose in the shoot tips of induced plants at 42, 56 and 70 days after the start of the short-day treatment were significantly higher than corresponding time in non-induced plants. However, the glucose, fructose and starch contents in shoot tips, leaves and roots of non-induced plants in most sampling dates were greater than those of induced plants. In other words, the shoot tips (bud) of induced plants acted as strong ‘utilizing sink’ and preferentially metabolized carbohydrates rather than storing them. It seems that non-structural carbohydrate contents in shoot tips, leaves and roots of strawberry may have an important role in flower-bud differentiation.     

Photoperiodic reaction of sexual and asexual reproduction in Fragaria chiloensis L. CHI-24-1 plants grown at various temperatures

Floral initiation of a wild strawberry strain, Fragaria chiloensis CHI-24-1, is strongly induced by a 24 h day-length (DL) treatment for 40 days consisting of natural daylight and continuous lighting at night by an incandescent lamp. To use the characteristics of floral initiation in CHI-24-1 as a genetic resource for breeding of cultivated strawberries, the photoperiodic reactions of sexual and asexual reproductive growth under various temperature conditions should be clarified. For that purpose, we examined: (1) floral initiation, inflorescence emergence and runner production seasons of CHI-24-1 plants grown under natural climatic conditions in an open field at the Faculty of Agriculture, Kagawa University and (2) the effects of various DLs and temperatures on floral initiation and runner production of CHI-24-1 plants. When the CHI-24-1 plants were grown under natural conditions, the floral initiation, inflorescence emergence and runner production were observed, respectively, in late autumn, spring, and from spring to autumn. Floral initiation of CHI-24-1 plants was induced strongly by 24 h DL at mean temperatures greater than 20 °C. The maximum floral initiation rates were 90% in the parent plant and 94% in the daughter plants, which were linked by runners to the parent plant. The floral initiation of the daughter plants occurred under 20, 22, and 23 h DL at mean temperatures greater than 20 °C, but not for the parent plants. Floral initiation was induced in 100% of the parent plants by the 8 h DL and the lowest mean-temperature conditions. Results of those experiments indicated that CHI-24-1 was an absolute long day plant having critical DL of about 20 h at mean temperatures greater than 20 °C, even though it was a June-bearing strawberry plant. In addition, CHI-24-1 was a facultative short-day plant at mean temperatures of less than 15 °C.     

Growth and nutrient partitioning of containerized Cercis siliquastrum L. under two fertilizer regimes

Lebanon's native flora is threatened by loss of natural habitat to rural and urban development and the increased demand of plant materials for landscaping. Despite Lebanon's floristic richness, most taxa used for landscaping are non-native. This study was done to determine if Cercis siliquastrum (L.) is amenable to container production. Therefore, six open pollinated seeds sources native to Lebanon were grown under two fertilizer rates to study growth, N, P, K uptake efficiency, and partitioning. Two-year-old seedlings were planted in 11 L containers in a 3:1 pine bark:compost substrate. Seedlings within each seed source or mother tree were grown at either 25 or 100 mg N L⁻¹ from 21N–3.1P–5.9K water-soluble fertilizer. Seedlings of all sources grown under 25 mg N L⁻¹ had greater dry weight than those grown at 100 mg. Nutrient loading occurred in plants under the high fertilizer rate, although total plant N, P, and K content were not affected by fertilizer rate. There were significant differences in mineral nutrient uptake and nutrient use efficiencies among the seed sources. The results show that C. siliquastrum is amenable to container production. The great variation in growth rate and nutrient use efficiency among the limited number of seed sources studied suggest that significant improvement can be made through mother tree selection and/or clonal propagation of superior individual plants within a source.     

Effects of foliar application of some macro- and micro-nutrients on tomato plants in aquaponic and hydroponic systems

An aquaponic system was designed to investigate effects of foliar applications of some micro- and macro-nutrients on tomato growth and yield in comparison with a hydroponic system. Common carp, grass carp and silver carp were stocked in the rearing tanks at 15, 20 and 15 fish m⁻³, respectively. The fish were fed three times daily with a pellet diet containing 46% protein. Fourteen days old tomatoes seedlings were transplanted on to growth bed units of aquaponic and hydroponic systems after stocking of carp fish for 2.5 months in the rearing tanks. Foliar nutrients application began 30 days after transplantation. Eight treatments were used, untreated control, foliar application at the rate of 250 mL plant⁻¹ with 0.5 g L⁻¹ K₂SO₄, MgSO₄·7H₂O, Fe-EDDHA, MnSO₄·H₂O, H₃BO₃, ZnCl₂, and CuSO₄·5H₂O. Plants were sprayed twice a month. The results showed that biomass gains of tomatoes were higher in hydroponics as compared to aquaponics. Foliar application of K, Mg, Fe, Mn, and B increased vegetative growth of plants in the aquaponics. In the hydroponics, only Fe and B had positive effects on plant growth. Cluster number per plant in aquaponics was lower than in hydroponics treatments, but it increased with foliar application of elements. There was no difference in fruit number and yield between aquaponics and hydroponics grown plants in the control treatments. Except Cu, foliar spray of all elements significantly increased plant fruit number and yield in the aquaponics in order of: K > Fe > Mn > Zn > Mg > B. In the hydroponics, foliar application of K, Mg and Zn increased fruit number and yield of plants compared to control. These results indicated that foliar application of some elements can effectively alleviate nutrient deficiencies in tomatoes grown on aquaponics.     

Supplementary phosphorus can alleviate boron toxicity in tomato

The effect of supplementary phosphorus on growth and yield of tomato (Lycopersicon esculentum cv. Target F1) plants grown at high boron was investigated. The results showed that high B reduced dry matter, fruit yield and chlorophyll content. High B plus 0.5 or 1 mM P increased plant dry matter, fruit yield and chlorophyll concentrations as compared to high B treatments only. Membrane permeability was not increased significantly due to high B application. In the leaves of plants grown at high boron treatments, superoxide dismutase (SOD), peroxidase (POD) and polyphenol oxidase (PPO) levels were increased. However, supplementary P to nutrient solution containing high B reduced the activities of the earlier mentioned enzymes in leaves but their levels were still higher than those at the control treatments. The study revealed that B status affects the activities of some antioxidant enzymes examined. Boron (B) concentrations increased in leaves and roots in the highest external B treatment as compared to the control treatment. Concentrations of Ca, P and K were significantly lower in the leaves of plants grown at high B than those in the control plants. Supplemented nutrient solution containing high B with 0.5 or 1 mM P increased the tissue concentrations of nutrients. These results indicate that supplementary P can mitigate the adverse effects of high B on fruit yield and growth in tomato plants.     

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%).     

Nickel supplementation effect on the growth,urease activity and urea and nitrate concentrations in lettuce supplied with different nitrogen sources

Effect of nickel (Ni) in the nutrient solution on yield, N metabolism, and nitrate content of leafy vegetables is poorly understood. The aim of this nutrient solution culture experiment was to investigate the effects of Ni supplementation on the nitrogen (N) metabolism and growth of lettuce (Lactuca sativa L. cv. Baker) with either urea or nitrate as the N source. Nickel supplement at 0.04 μM reduced urea toxicity to the urea-fed plants. Addition of Ni to the nutrient solution significantly increased the leaves and root growth of the urea-fed lettuce plants while it increased the growth of lettuce plants fed with nitrate only at N level of 20 mM. At N level of 20 mM, the leaves fresh weight of the urea-fed plants promoted by Ni supplement was comparable with the nitrate-fed plants untreated with Ni. Nickel supplementation increased the leaf total N concentrations in the urea-fed plants, although the nitrate-fed plants accumulated greater N in their leaves compared with urea treated plants at without Ni treatment. Nickel addition decreased the concentrations of leaf urea-N in the urea-fed plants and NO₃-N in the nitrate-fed plants. Nickel addition enhanced urease activity in the leaves of urea-fed plants. The results indicated Ni supplementation enhances the growth of the urea-fed lettuce plants while it has role in decreasing leaf nitrate concentration and thus, improving the health quality of the nitrate-fed plants.     

Vernalization promotes flowering of a heat tolerant Calandrinia while long days replace vernalization for early flowering of Brunonia

The flowering responses of Brunonia australis (blue pincushion) and Calandrinia sp. to vernalization, photoperiod, temperature and plant age were investigated to provide a foundation for manipulating flowering in these potential potted plants. Plants were vernalized at 4.8 °C for 0, 3 or 6 weeks at the plant age of 1–4 or 8–14 leaves. Following vernalization, plants were grown at 25/10 or 35/20 °C (day/night) under short days (11 h, ambient daylight averaged 380 ± 44 μmol m⁻² s⁻¹) or long days (16 h) provided by an additional 5 h night break (21:00–2:00 h at <4.5 μmol m⁻² s⁻¹ from incandescent lamps), for 85 days. This is the first work to investigate flowering of these ornamental species. Both species showed enhanced flowering following vernalization and a quantitative requirement for long days. The reduction of the time until the first visible inflorescence (Brunonia) or flower (Calandrinia) buds by 8–13 days was affected by vernalization for 3 or 6 weeks, respectively. Long days were effective for reducing the time to first visible floral bud and increasing the number of inflorescence or flowers per plant for both species. For Brunonia, LDs replaced vernalization when applied to plants with 1–4 leaves. Raising temperature from 25/10 to 35/20 °C increased the number of flowers per plant of Calandrinia by 2–2.5-fold for plants with 1–4 or 8–14 leaves respectively.     

Yield,blossom-end rot incidence,and fruit quality in pepper plants under moderate salinity are affected by K and Ca fertilization

One of the most important factors limiting agricultural expansion and production is the restricted supply of good quality water. The present study examines the effects of K⁺ and Ca²⁺ fertilization on sweet pepper production, blossom-end rot (BER) incidence and fruit quality of pepper plants (Capsicum annuum L.) grown under moderate saline conditions. Pepper plants were grown in a controlled-environment greenhouse under hydroponic conditions with different nutrient solutions obtained by modifying the Hoagland solution. The experiment consisted on four K⁺ treatments (0.2, 2, 7 and 14 mM) +30 mM NaCl, and four Ca²⁺ treatments (0.2, 2, 4 and 8 mM) +30 mM NaCl, having in common a control without salt with 7 mM K⁺/4 mM Ca²⁺. Salinity decreased total fruit yield and marketable fruit yield by 23% and 37%, respectively. The marketable fruit yield reduction by salt treatment was mainly due to the increase in the number of fruit affected by BER. This typical physiopathy of the pepper fruits occurred between 18 and 25 days after anthesis (DAA), when the highest fruit growth rate was reached. Fruit quality parameters were also affected by salt treatment where the fruit pulp thickness and firmness were decreased, and fructose, glucose and myo-inositol fruit concentrations increased with salinity relative to fruits from control treatment. Under saline conditions an increased supply of K⁺ reduced the fruit fresh weight, the percentage of BER and the marketable yield although promoted the vegetative growth. However, increasing Ca²⁺ concentration in the nutrient solution increased the fruit production, and the marketable yield as consequence of decreasing the percentage of fruit affected with BER. Fruit quality parameters also were affected by the K⁺ and Ca²⁺ treatments.