Transpiration,photosynthetic responses,tissue water relations and dry mass partitioning in Callistemon plants during drought conditions

Callistemon is an Australian species used as ornamental plant in Mediterranean regions. The objective of this research was to analyse the ability of Callistemon to overcome water deficit in terms of adjusting its physiology and morphology. Potted Callistemon laevis Anon plants were grown in controlled environment and subjected to drought stress by reducing irrigation water by 40% compared to the control (irrigated to container capacity). The drought stress produced the smallest plants throughout the experiment. After three months of drought, the leaf area, number of leaves and root volume decreased, while root/shoot ratio and root density increased. The higher root hydraulic resistance in stressed plants caused decreases in leaf and stem water potentials resulting in lower stomatal conductance and indicating that water flow through the roots is a factor that strongly influences shoot water relations. The water stress affected transpiration (63% reduction compared with the control). The consistent decrease in g_s suggested an adaptative efficient stomatal control of transpiration by this species, resulting in a higher intrinsic water use efficiency (P_n/g_s) in drought conditions, increasing as the experimental time progressed. This was accompanied by an improvement in water use efficiency of production to maintain the leaf water status. In addition, water stress induced an active osmotic adjustment and led to decreases in leaf tissue elasticity in order to maintain turgor. Therefore, the water deficit produced changes in plant water relations, gas exchange and growth in an adaptation process which could promote the faster establishment of this species in gardens or landscaping projects in Mediterranean conditions.     

Response of Vitis vinifera L. plants inoculated with Phaeoacremonium angustius and Phaeomoniella chlamydospora to thiabendazole,resveratrol and sodium arsenite

The effect of some pesticides (sodium arsenite, thiabendazole and ziram) and the natural phytoalexin (resveratrol) on mycelial growth of Phaeomoniella chlamydospora and Phaeoacremonium angustius was studied. Several strains of these species were grown on malt extract agar (MEA) plates containing different concentrations of inhibitory compounds and colony diameters were measured. While sodium arsenite and ziram had little effect on the growth of both species, thiabendazole inhibited colony growth, at minimum concentrations of 6 μM for Ph. chlamydospora and 15 μM for P. angustius. Resveratrol at concentrations equal to or grater than 867 μM also inhibited colony growth of both species. To assay the effect of these substances on plant response to infection, in vitro grapevines were inoculated with Ph. chlamydospora or P. angustius spores and were grown in the presence of sodium arsenite (0–30 μM), thiabendazole (0–30 μM) or resveratrol (0–876 μM). Infected untreated plants and sodium arsenite-treated plants developed symptoms of senescence (reduced growth, increased membrane lipid peroxidation, and decreased chlorophyll content and fluorescence). In contrast, infected plants treated with thiabendazole (30 μM) or with resveratrol (876 μM) showed similar characteristics of fresh weight, malondialdehyde accumulation and chlorophyll fluorescence to those of uninfected plants. These results are promising with respect to the use of thiabendazole-containing pesticides as alternatives to currently used pesticides for control of esca in vines. Results also suggest that the presence of resveratrol in grapevines may be useful to induce resistance to these fungi.     

Application of chlorophyll fluorescence for the diagnosis of salt stress in tomato “Solanum lycopersicum (variety Rio Grande)”

To study the response of tomato (Solanum lycopersicum cv. Rio Grande) to salinity, the effect on plant growth, water relations, stomatal conductance and Chlorophyll fluorescence was investigated. Tomato plants were grown in peat culture under controlled conditions and submitted during 28 days to saline stress ranging from 0 to 25, 50, 100, 150 and 200 mM of NaCl. At the end of the experiment period, plant growth was significantly decreased with increasing salinity.     

Photosynthesis of field-grown Arracacha (Arracacia xanthorriza Bancroft) cultivars in relation to root-yield

There has been limited research on measuring potential differences in leaf gas exchange of Arracacha (Peruvian parsnip, Arracacia xanthorriza Bancroft) cultivars, as affected by different environments, as well as its relation to storage root-yield. The present paper reports field measurements of leaf CO₂ assimilation rates (A) for five contrasting cultivars grown at two different high-altitude locations. Using a design of plots chosen at random with three repetitions, commercial root production was determined in the two locations at different altitude (1580 and 1930 m). Daily leaf gas exchange was repeatedly monitored with a portable open-mode infrared gas analyzer at different times in both locations during the growth cycle. Root-yield, leaf area and dry weight were measured. Significant differences in leaf photosynthetic rate and in specific leaf area (SLA) were observed among cultivars. Cultivars with high SLA, had high CO₂ assimilation. Mean (A_n) and total (A_tot) of CO₂ assimilation and SLA were significantly correlated with storage root-yield across cultivars and locations. The three cultivars with the greatest commercial root production also had the highest maximum values for A and the highest specific leaf area, indicating that these two parameters can be used to select for highly productive cultivars of A. xanthorriza.     

Sennoside content and yield attributes of Cassia angustifolia Vahl. as affected by NaCl and CaCl2

Pot culture experiments were conducted to assess the extent of growth, photosynthetic capacity, sennoside concentration and yield attributes of Senna plant under the individual as well as combined influence of NaCl and CaCl₂. Six treatments, i.e. NaCl (80 and 160 mM), CaCl₂ (5 and 10 mM) alone and a combination of NaCl + CaCl₂ (80 + 10 and 160 + 10 mM) were given to the growing Senna plants at pre-flowering (45 DAS), flowering (75 DAS) and post-flowering (90 DAS) stages. Significant reductions were observed in pod biomass, leaf area, stomatal conductance, photosynthetic rate and sennoside concentration and yield, with each NaCl treatment. On the contrary, individual CaCl₂ treatments had a favourable effect. Under the effect of combination treatments, although these parameters were reduced, the extent of reduction was much less than one caused by NaCl treatments. The combined treatments thus mitigated the adverse effects caused by NaCl.     

Rootstocks influence fruit oleocellosis in ‘Hamlin’ sweet orange (Citrus sinensis L. Osbeck)

Oil spotting or oleocellosis, is a major problem in citrus crops. As the rootstock and fertilization play important roles in citrus growth and fruit development, we investigated the influence of different rootstocks on the growth, mineral nutrition metabolism, water relations, and fruit oleocellosis of eight-year-old field ‘Hamlin’ sweet orange trees. Trees grafted onto Lichi16-6 trifoliata (Poncircus trifoliate) had the greatest rate of oleocellosis (RO), and trees grafted onto Goutou orange (Citrus aurantium) had the greatest degree of oleocellosis (DO). In contrast, trees grafted onto Rangpur lime (Citrus limonia Osbeck) had the lowest RO and DO. Trees were the most vigorous on Rangpur lime rootstocks, followed by Lichi16-6 trifoliata, and then Goutou orange. In addition, because the scion/stock girth ratio showed significant correlations with the RO and DO, oleocellosis parameters can be a good indicator of scion/stock affinity. The total N, total P, Ca²⁺, and Mg²⁺ in leaves from trees on Rangpur lime were significantly lower than in leaves from trees on Goutou orange or Lichi16-6 trifoliata. In addition, the RO showed a significant correlation with the leaf Ca²⁺ and S concentrations and with the peel Mg²⁺ concentration. The DO was significantly correlated with the total peel N and S concentrations. In addition, the RO showed a significant correlation with the net assimilation of CO₂ (ACO₂), stomatal conductance (GS), transpiration rate (ET), and water-use efficiency (WUE). However, the DO showed a significant correlation with the GS, ACO₂, and WUE. Taken together, these results indicate that rootstocks affect the development of oleocellosis in ‘Hamlin’ sweet orange due to their effects on the mineral nutrition balance and water relations.     

Root restriction-induced limitation to photosynthesis in tomato (Lycopersicon esculentum Mill.) leaves

Root restriction often depresses photosynthetic capacity and the mechanism for this reduction, however, remains unclear. To identify the mechanism by which root restriction affects the photosynthetic characteristics, tomato (Lycopersicon esculentum Mill.) seedlings were subjected to root restriction stress with or without supplemental aeration to the nutrient solution. With the development of the root restriction stress, CO₂ assimilation rate was decreased only in confined plants without supplemental aeration. There were also significant decreases in leaf water potential, stomatal conductance (g_s), intercellular CO₂ concentration (C_i), and increases in the stomatal limitation (l) and the xylem sap ABA concentration. Meanwhile, the maximum carboxylation rate of Rubisco (V_cmax) and the capacity for ribulose-1,5-bisphosphate regeneration (J_max) also decreased, followed by substantial reductions in the quantum yield of PSII electron transport (Φ_PSII). Additionally, root restriction resulted in accumulation of carbohydrates in various plant tissues irrespective of aeration conditions. It is likely that root restriction-induced depression of photosynthesis was mimicked by water stress.     

Sap flow measurements in young olive trees (Olea europaea L.) cv. Chétoui under Tunisian conditions

Measurements of sap flux were carried out from May 2003 to March 2004 on 6 year-old irrigated olive trees of cultivar Chétoui cultivated at 6 m × 6 m spacing in Mornag (36.5°N, 10.2°E), Northern Tunisia. The aim of the research is to evaluate the sap flux technique for its applicability with young olive trees and to estimate their water consumption under field conditions. Three thermal sensors were implanted in the trunk of three olive trees following to North (N), South-East (SE) and South-West (SW) directions. Data were analyzed following to the procedure of Do and Rocheteau (2002b) that derives from Granier (1985). In this paper, data on probe calibration, wood conductive section estimation and sap flux spatial-variability are presented and discussed. Relationships between sap flux measurements, climate and soil water status have been investigated. Results show that sap flux values vary with sensor position, soil water content and climate demand. Good agreements between sap fluxes and global radiation and reference evapotranspiration measurements were observed. Some variations were recorded under water shortage conditions. Maximum and minimum daily fluxes of 4.5 l and 41.0 l per tree were found in February 2003 and in August 2003, respectively. Maximum transpiration represented only 53% of the crop evapotranspiration as determined by the F.A.O. method.     

Response to drought and salt stress of lemon ‘Fino 49’ under field conditions: Water relations,osmotic adjustment and gas exchange

Drought and salinity are two of the most important factors limiting the lemon yield in south-eastern Spain. The effects of drought and salt stress, applied independently, on water relations, osmotic adjustment and gas exchange in the highest evapotranspiration period were studied to compare the tolerance and adaptive mechanisms of 13-year-old ‘Fino 49’ lemon trees, in immature and mature leaves. The study was carried out in an experimental orchard located in Torre Pacheco (Murcia). Three treatments were applied: Control, well-irrigated; drought-stress (DS), non-irrigated from 15th May to 7th July and salinity, irrigated with 30 mM NaCl from 1st March to 7th July. At the end of the experiment, only DS trees showed a decreased leaf stem water potential (Ψ_md). Under DS conditions, both types of leaf lost turgor and did not show any osmotic or elastic mechanism to maintain leaf turgor. Osmotic adjustment was the main tolerance mechanism for maintenance of turgor under salt stress, and was achieved by the uptake of Cl⁻ ions. Gas-exchange parameters were reduced by DS but not by salinity, stomatal closure being the main adaptive mechanism for avoidance of water loss and maintenance of leaf turgor. Salinity gave rise to greater Cl⁻ accumulation in mature than in immature leaves. The increase of proline in immature leaves due to DS indicates greater damage than in mature leaves.     

Effects of greenhouse cooling method on growth,fruit yield and quality of tomato (Solanum lycopersicum L.) in a tropical climate

A tomato (Solanum lycopersicum L.) crop was grown in four greenhouses during the dry season 2005/06 in Central Thailand. Sidewalls and roof vents of two greenhouses were covered with nets and these greenhouses were mechanically ventilated when air temperature exceeded 30 °C (NET). The other two greenhouses were covered with polyethylene film and equipped with a fan and pad cooling system (EVAP). Overall mean air temperature was significantly reduced by 2.6 and 3.2 °C (day) and 1.2 and 2.3 °C (night) in EVAP as compared to NET and outside air, respectively. Temperature maxima in EVAP averaged about 4 °C lower than in NET and outside. The relative humidity was around 20 and 30% (day) and 10 and 15% (night) higher in EVAP than in NET or outside, respectively. Vapour pressure deficit averaged 0.25 kPa in EVAP, 1.03 kPa in NET and 1.48 kPa outside. The crop water-consumption was significantly lower in EVAP (1.2) than in NET (1.8 L plant⁻¹ day⁻¹), which is ascribed to reduced transpiration in EVAP. Total fruit yield was similar in NET (6.4 kg plant⁻¹) and EVAP (6.3 kg plant⁻¹). The quantity of undersized (mostly parthenocarpic) and blossom-end rot (BER)-affected fruits was reduced in EVAP. However, the proportion of marketable yield was significantly higher in NET (4.5 kg plant⁻¹) than in EVAP (3.8 kg plant⁻¹), owing largely to an increased incidence of fruit cracking (FC) in EVAP. Higher FC but lower BER incidence coincided with higher fresh weight and Ca concentration in the fruits in EVAP. It is concluded that in regions with high atmospheric relative humidity evaporative cooling without technical modifications allowing dehumidification will not improve protected tomato production.     

Effects of diurnal temperature alternations and light quality on growth,morphogenesis and carbohydrate content of Cucumis sativus L.

The effects of the difference (DIF) between day/night temperature (DT/NT) and end-of-day (EOD) light quality on growth, morphology, dry matter (DM) content and carbohydrate status in cucumber (Cucumis sativus L.) were examined. Plants were grown under a 12 h high light intensity period and DT/NT of 25/19 °C (positive DIF) or 19/25 °C (negative DIF) in combination with an exposure of 30 min EOD-red (EOD-R) or far-red (EOD-FR) light. A significant interaction between DIF and EOD light quality was found on morphology, DM and carbohydrate content in axial plant organs like stems and petioles, but not in leaf blades and roots. Positive DIF induced taller stems, and higher DM and carbohydrate content than negative DIF when the plants were grown under EOD-R. The stems developed under EOD-FR were tall and accumulated the highest content of DM and carbohydrates and only small differences were found between positive DIF and negative DIF. Under EOD-R a higher content of glucose and fructose was found under positive than negative DIF, while EOD-FR light resulted in a high glucose and fructose content under both positive and negative DIF and thereby equalized the effect of the two temperature treatments. The results show that positive DIF can induce similar responses in elongation growth, DM and carbohydrate accumulation as EOD-FR, and further that phytochrome status interact with the responses to alternating DT and NT.