Water status indicators of lemon trees in response to flooding and recovery

Potted 2-year-old lemon trees [Citrus limon (L.) Burm. fil, cv. Verna] grafted on sour orange (C. aurantium L.) rootstock were subjected to flooding for 3 d. Control plants were irrigated daily to field capacity. Continuously (sap flow, trunk diameter fluctuations) and discretely (predawn and midday leaf water potential, leaf conductance) measured plant-based water status indicators were compared. The sensitivity of the maximum daily trunk shrinkage signal intensity to flooding and its behaviour during the recovery period demonstrated that this indicator is more feasible than the others for use in automatic irrigation. The responses to flooding of continuously and discretely measured plant-based water status indicators were very similar to those observed in response to drought stress indicating that it necessary to use soil water measurement automatic sensors to detect the cause of the stress. The results underlined the robustness of the compensation heat-pulse technique for estimating instantaneous and daily transpiration rates on flooding stress and recovery.     

Rearing of Prays citri on callus derived from lemon stigma and style culture

A new method for rearing the citrus flower moth (Prays citri Mill.) (Lepidoptera, Yponomeutidae) on lemon [Citrus limon (L.) Burm.] callus is reported. In the present research callus (an undifferentiated mass of plant cells that can be grown under sterile conditions on an artificial medium in vitro) was induced from lemon stigma and style explants cultured on Murashige and Skoog (MS) medium supplemented with 500 mg l^–1 malt extract, 13.3 M 6-benzylaminopurine, and 146 mM sucrose. Also somatic embryogenesis and plant regeneration were obtained from the cultures of styles and stigmas of lemon. Adults were obtained from larvae on infested flowers collected in the field. Different oviposition substrates were used: white oval pearls (WOP), black oval pearls (BOP), rooted shoots (RS) of lemon obtained in vitro, and artificial flowers containing lemon callus (AF). Larvae were reared on lemon callus. Adults oviposited on RS, on WOP, and on AF. BOP were rejected as oviposition substrates. The flower moth reared on callus oviposited fertile eggs. In our tests P. citri completed three generations on callus or on callus plus shoots. In the latter case the larvae preferred callus and fed on shoots only after callus was completely eaten. The life cycle on callus at 23 ± 1 °C lasted about 21 days. There were significant differences between oviposition substrates for what concerns the number of eggs laid. It was observed that females generally preferred WOP (about 25 eggs/female) to AF (about 20 eggs/female) or RS (about 12 eggs/female) as oviposition substrate. Nevertheless the percentage of eggs that developed into adults was higher when AF sealed with stretched Parafilm were used (about 70% of eggs developed into adults). The method of rearing P. citri with AF was labour-saving and the feeding substrate (callus) had less tendency to become mouldy or decompose than when WOP and RS were used. Since such a diet is available for the insect all year round and callus can be produced in unlimited quantity, it could be possible to obtain a mass production of this moth.     

Irrigation effects on daily and seasonal variations of trunk sap flow and leaf water relations in olive trees

Irrigation effects on whole-plant sap flow and leaf-level water relations were characterised throughout a growing season in an experimental olive (Olea europaea L.) orchard. Atmospheric evaporative demand and soil moisture conditions for irrigated and non-irrigated olive trees were also monitored. Whole-plant water use in field-grown irrigated and rain fed olive trees was determined using a xylem sap flow method (compensation heat-pulse velocity). Foliage gas exchange and water potentials were determined throughout the experimental period. Physiological parameters responded diurnally and seasonally to variations in tree water status, soil moisture conditions and atmospheric evaporative demand. There was a considerable degree of agreement between daily transpiration deduced from heat-pulse velocity and that determined by calibration using the Penman–Monteith equation in the field. Summer drought caused decreasing leaf gas exchange and water potentials, and a progressive increase in hydraulic conductance (stronger in non-irrigated than irrigated trees), probably attributable to modifications in hydraulic properties at the soil-root interface. Negligible hysteresis, attributable to low plant capacitance, was observed in the relationship between leaf water potential and sap flow. A proportional decrease in maximum daily leaf conductance with increasing vapour pressure deficit was observed, while mean daytime canopy stomatal conductance decreased with the season. As a result, plant water use was limited and excessive drought stress prevented. Non-irrigated olive trees recovered after the summer drought, showing a physiological behaviour similar to that of irrigated trees. In addition to physiological and environmental factors, there are endogenous keys (chemical signals) influencing leaf level parameters. Olive trees are confirmed to be economical and sparing users of soil water, with an efficient xylem sap transport, maintenance of significant gas exchange and transpiration, even during drought stress.     

HPLC法测定不同产地和品种柠檬果皮中柠檬苦素和诺米林含量

该研究建立了同时测定檬苦素和诺米林含量的高效液相色谱法,并采用该方法对8种不同柠檬样品中柠檬苦素和诺米林含量进行了测定。色谱条件如下:安捷伦Eclipse XDB-C18(250 mm×4.6 mm,5μm)色谱柱,流动相为0.1%磷酸水溶液(A)-乙腈(B),梯度洗脱,流速为1.0 mL·min^-1,柱温为30℃,波长为210 nm。结果表明:3个产地尤力克果皮中柠檬苦素含量依次为云南瑞丽(EUR_D)、四川安岳(EUR_C)和广东河源(EUR_Y),诺米林含量依次为EUR_D、EUR_C和EUR_Y;不同品种柠檬果皮中柠檬苦素含量依次为北京柠檬(M_NM)、粗柠檬(R_NM)、无核柠檬(S_NM)、热那亚(RNY)、里斯本(LSB),诺米林含量依次为S_NM、R_NM、LSB、RNY和M_NM。综上结果表明,不同产地和品种柠...     

Saturated and mono-unsaturated long-chain hydrocarbons from lemon juice sacs

Three varieties of lemon—Lisbon, Malta and Kusner—were examined for their content of juice sac saturated and mono-unsaturated long-chain hydrocarbons. The saturated fractions were 20 times the concentrations of the monoene fractions. The dominant linear hydrocarbon in the saturated fraction was C₂₅ while C₂₉ predominated in the monoene fraction. The saturated hydrocarbon profiles for Lisbon and Kusner were very similar to the profiles previously reported for Eureka lemon and Persian lime. The mono-unsaturated profiles were distinct for each of the three lemon varieties. In addition the lemon mono-unsaturated profiles were quite distinct from the hydrocarbon profiles previously reported for several other citrus species. In general the data support the elongation-decarboxylation mechanism for hydrocarbon synthesis proposed by Kolattukudy.     

Effect of Salt Stress on the Superoxide Dismutase Activity in Leaves of Citrus limonum in Different Rootstock-Scion Combinations

The effect of salinity on leaf superoxide dismutase (SOD) activity of lemon trees of different rootstock-scion combinations was studied. In leaves from Citrus limonum cv.Verna scions on Citrus macrophylla and C. reticulata rootstocks, salinity treatment clearly caused a significant depression in both Fe-SOD and Mn-SOD activities and an increase in Cu,Zn-SOD activity. However, in leaves from Citrus limonum on Citrus aurantium rootstook, the reduction observed in the activity values of Fe-SODs and Mn-SODs was not statistically significant. Salt stress also produced a decrease in the content of soluble proteins and chlorophylls. However, this drop was greater in C. limonum leaves on C. macrophylla than for other combinations.     

Effects of soil phosphorus and Glomus intraradices on growth,nonstructural carbohydrates,and photosynthetic activity of Citrus aurantium

Sour orange (Citrus aurantium L.) grown in low-P (9–12 ppm) and high-P (420 ppm) soil inoculated with or without Glomus intraradices (G.i.), were evaluated for biomass, carbohydrates, ribulose bisphosphate carboxylase (RuBPCase), phosphoenolpyruvate carboxylase (PEPCase) activity, leaf ¹⁴CO₂ incorporation, and other physiological parameters. Growth of plants in the low-P, noninoculated soil was lowest, with total dry biomass reduced up to half of the low-P, inoculum treatment. Total nonstructural carbohydrates were 40% lower in leaves of plants in the low-P, noninoculated soil, compared with the other treatments. Inoculation of the low-P soil enhanced leaf ¹⁴CO₂ incorporation by 67%, total chlorophyll content by 28%, and RuBPCase activity by 42%, compared with low-P, noninoculated treatment. Improved P-use efficiency by G.i. in low-P soil was comparable to high-P nutrition in improving leaf ¹⁴CO₂ incorporation and concentration of major leaf photosynthetic products that include starch and sucrose. Leaf PEPCase activity in the low-P, noninoculated treatment, however, was at least threefold higher than the other treatments, suggesting a possible alteration in organic acid metabolism in sour orange leaves as a result of P deficiency.     

Postharvest Imaging of Chlorophyll Fluorescence from Lemons Can Be Used to Predict Fruit Quality

We demonstrate the feasibility of assaying and predicting post-harvest damage in lemons by monitoring chlorophyll (Chl) fluorescence. Fruit quality was assayed using a commercial instrument that determines photosynthetic performance by imaging Chl fluorescence parameters under different irradiances. Images of Chl fluorescence from individual lemons reveal that photosynthesis is active throughout the post-harvest ripening process. Because photosynthesis is highly sensitive to biotic and abiotic stress, variations in Chl fluorescence parameters over the surface of a lemon fruit can be used to predict areas that will eventually exhibit visible damage. The technique is able to distinguish between mould-infected areas that eventually spread over the surface of the fruit, and damaged areas that do not increase in size during ripening. This study demonstrates the potential for using rapid imaging of Chl fluorescence in post-harvest fruit to develop an automated device that can identify and remove poor quality fruit long before visible damage appears.     

Root-pressure driven xylem sap flow in greenhouse melon (Cucumis melo L.): diurnal change and the effects of shading, growth stage, rootstock and fruit number

Grafted and ungrafted greenhouse melon were used to investigate the effect of diurnal change, shading, growth stage, rootstock and fruit numbers on melon xylem sap flow rate. A clear diurnal change was observed in xylem sap flow rate. Shading of the plant on the previous day decreased the sap flow rate. An increase in the number of fruit on a plant decreased the sap flow rate, but, grafting to squash plant lessened the effect of fruit number. Consideration of timing and environmental factors is necessary when the xylem sap is collected for root study.     

Selection and breeding for salinity tolerancein vitro

Summary Selection for tolerance to NaCl inCitrus sinensis andC. aurantium has been carried out in agar and suspension cultures. Callus was subjected to culture media containing up to 0.17M NaCl for ten passages. Selected cell lines were grown for three passages on media without salt before further tests on saline media. Four stable tolerant cell lines, differing in degree of tolerance, have been selected fromC. sinensis. Four lines of similar tolerance have been selected fromC. aurantium. The stability of most lines was very satisfactory. MostC. sinensis lines grew well in media containing up to 0.2M NaCl, andC. aurantium lines in media of up to 0.15M NaCl.Embryos were regenerated in most selected cell lines fromC. sinensis and, more sporadically, fromC. aurantium. Addition of 0.5–0.6% NaCl to the media often enhanced embryogenesis. Embryos from a selected line ofC. sinensis showed higher tolerance to NaCl in the medium than comparable embryos from an unselected line.Single embryos derived from both selected and unselected cell lines ofC. sinensis were successfully cloned. A limited comparison of plantlets from one tolerant line (R14) with plantlets from unselected control lines showed better adaptation of the former to salt (0.085 to 0.12M NaCl in the medium), and a lesser degree of leaf burn symptoms.Contribution No. 1045-E, 1984 series.     

Sap flow as an indicator of transpiration and the water status of young apricot trees

The relationship between water loss via transpiration and stem sap flow in young apricot trees was studied under different environmental conditions and different levels of soil water status. The experiment was carried out in a greenhouse over a 2-week period (November 2–14, 1997) using three-year-old apricot trees (Prunus armeniaca cv. Búlida) growing in pots. Diurnal courses of leaf water potential, leaf conductance and leaf turgor potential also were recorded throughout the experiment. Data from four days of different enviromental conditions and soil water availability have been selected for analysis. On each of the selected days the leaf water potential and the mean transpiration rates were well correlated. The slope of the linear regression of this correlation, taken to indicate the total hydraulic resistance of the tree, confirmed an increasing hydraulic resistance under drought conditions. When the trees were not drought stressed the diurnal courses of sap flow and transpiration were very similar. However, when the trees were droughted, measured of sap flow slightly underestimated actual transpiration. Our heat-pulse measurements suggest the amount of readily available water stored in the stem and leaf tissues of young apricot trees is sufficient to sustain the peak transpiration rates for about 1 hour. This revised version was published online in June 2006 with corrections to the Cover Date.     

Evaluation of various heat-pulse methods for estimation of sap flow in orchard trees: comparison with micrometeorological estimates of evaporation

Summary A microcomputer-controlled heat-pulse system for the measurement of sap velocity in trees is described. Several published methods for determining sap velocity from the temperature rise measured either above or below a heater inserted into the stem were compared and evaluated. All methods could be improved by the use of curve-fitting procedures, with a particularly useful approach involving direct estimation of the parameters of the diffusion equation using the non-linear curve-fitting package maximum likelihood programme. An alternative approach that was based on measurement of the value of the maximum temperature was proposed and tested. This was found to be particularly robust and sensitive to changes in flow rate. Although sap-flow velocity varied markedly with depth in the stem (as shown by the rate of dye movement), the maximum temperature at any given flow rate was found to be relatively insensitive to sensor depth. Estimated sap-flow velocities were compared with evaporation rates estimated either by weighing (for potted trees) or by the Penman-Monteith equation. Several independent methods were used for estimating the values of boundary layer resistance and net radiation that were required for application of the Penman-Monteith equation. There was a close relationship between flow and evaporation with some evidence for hysteresis. Although absolute calibration of the sap-flow estimates is difficult, the methods described are all useful for relative studies and all responded rapidly to altered flow rates caused by changing weather conditions.     

Improvement of the heat pulse method for determining sap flow in trees

Abstract. The heat pulse method for determining sap flux in large woody sterns was modified for easier field operation. It uses the measurement of the time elapsed between heat pulse release by a line heater radially inserted in the stem, and the occurrence of maximum temperature 15 mm downstream of the heater. This spacing between heater and thermometer is critical to the reliability of the measurement. Calculations using uncorrected theory provide estimates of the sap flux density in stems with both uniform and non-uniform cross-sectional distribution of conducting tissues which are about 55% of the actual sap flux density. This factor results from insufficient thermal homogeneity between tissues where sap flow occurs and tissues where sap flow has been interrupted.
Sap flow in trunks of citrus trees was inferred from measurements of the cross-sectional distribution of sap flux density. Variability of sap flux density is specific to each trunk and is time-dependent and imposes multiple radial and angular measurements. The method was checked in a citrus trunk ramified into three branches. Instantaneous determinations of the flow in the trunk and in the branches differed by less than 5.7%. The daily values agreed within 2.8%.     

Inter-simple sequence repeat markers and flow cytometry for the characterization of closely related Citrus limon germplasms

The genetic relationship among commercial cultivars of Citrus limon (lemon) was analysed by inter-simple sequence repeats (ISSR) and flow cytometry techniques. Two cultivars with a close germplasm were distinguished by screening 10 SSR primers and by measuring DNA content of prestained nuclei.     

Gas-exchange and sap flow measurements of Salix viminalis trees in short-rotation forest

Simultaneous field measurements of transpiration and sap flow were performed on short-rotation Salix viminalis trees ranging in diameter from 1.5 to 3.5 cm (2-year-old shoots on 8-year-old stumps). Transpiration was measured using an open-top ventilated chamber enclosing the whole foliage of a tree. Sap flow was measured using a tree-trunk heat balance (THB) technique with a constant temperature difference and variable heat input. Both the instantaneous and daily values of water flux measured by the two absolute techniques agreed well with a difference of up to about 5%. In July, the hourly transpiration reached a maximum of about 0.2 kg m^–2 (leaf area) or 0.45 kg tree^–1, whereas maximum daily integrals reached 4 kg tree^–1. The response of sap flow rate to abrupt flux change when inducing emboli by cutting-off the stem was very rapid: the registered signal dropped by 85% within 10 min for a specimen with a projected leaf area of 2 m². For S. viminalis trees, transpiration was linearly correlated with stem cross-sectional area and with leaf area.     

Stem and leaf water potentials, gas exchange, sap flow, and trunk diameter fluctuations for detecting water stress in lemon trees

The sensitivity of continuous (on a whole-day basis) and discretely (at midday) measured indicators of the plant water status in adult lemon trees in response to a cycle of water deprivation and recovery, and the feasibility of obtaining baselines for tree water status indicators was investigated in 30-year-old Fino lemon trees (Citrus limon (L.) Burm. fil.) grafted on sour orange (C. aurantium L.) rootstocks. Control plants (T0) were irrigated daily above their crop water requirements in order to obtain non-limiting soil water conditions, while T1 plants were subjected to water stress by withholding irrigation for 50 days, after which time irrigation was restored and plant recovery was studied for 16 days. In T0 plants the water relations and the plant symptoms confirmed that they had not suffered waterlogging. In contrast, T1 plants showed a substantial degree of water stress, which developed very slowly. Maximum daily trunk shrinkage (MDS) increased in response to water stress during the first 15 days of the experiment, but when the stem water potential (Ψ_stem) fell below −1.8 MPa, the MDS signal intensity decreased. However, Ψ_stem and sap flow (SF) signal intensities progressively increased during the water stress period. The results showed that MDS is a very suitable plant-based indicator for precise irrigation scheduling in adult lemon trees. Reference or baseline relationships for MDS, Ψ_stem, and SF measurements as a function of several parameters related to the evaporative demand of the atmosphere were obtained. This fact open up the possibility of considering a plant-based indicator measurement at a given time relative to the expected value under non-limiting water conditions, which can be calculated from the reference relationships.     

Comparison of continuously recorded plant-based water stress indicators for young lemon trees

Continuously recorded plant-based water stress indicators (sap flow and parameters derived from trunk diameter fluctuations) were compared in potted young lemon trees (Citrus limon (L.) Burm. fil, cv. Verna) grafted on sour orange (C. aurantium L.) rootstock submitted to deficit irrigation. Daily maximum (MXTD) and minimum (MNTD) trunk diameters and daily trunk diameter shrinkage (MDS) were directly influenced by the water supply to the trees from the soil. The continuously recorded plant-based water stress indicators presented different degrees of sensitivity when used to estimate the water status of the plants. Sap flow (SF) and MDS were more immediate and sensitive than MXTD and MNTD. However, the higher signal intensity: noise for SF and the fact that its signal intensities remained clearly above unity during the stress period, indicating that the soil water was depleted, point to the greater reliability of this indicator. Also, the possibility of developing further baseline relationships between SF and air vapour pressure deficit in fully irrigated trees in field conditions increases the feasibility of using this parameter in automatic irrigation systems.     

Diurnal changes in the radius of a subalpine Norway spruce stem: their relation to the sap flow and their use to estimate transpiration

Diurnal changes in the stem radius of a subalpine mature Norway spruce were measured simultaneously with the flow of sap in xylem. Matric potentials in the soil were > -35 kPa. The kinetics of the flow were closely related to the changes in the radius of the stem resulting from depletion of its extensible tissues. The radius of the stem oscillated daily and, fairly independently of this, fluctuated over several days. The daily shrinkage (_d) was correlated with the daily flow through its base (Q_d). When the crown transpired little and was nearly saturated during rainy days, ASd tended to increase relative to Q_d. Using a linear relation, the estimates of flow by _d deviated less than ± 10% from the values measured by heat balance, provided that the periods of calibration in their ratio of dry to rainy days were comparable to those estimated. If the two periods differed in this respect, the estimates of flow deviated up to 42%. A quadratic relation yielded estimates that depended less on weather. It reduced maximal deviations to ±22%. Since _d additionally may represent the time pattern of the daily transpiration better than Q_d, analysing changes in the radius of stems may supplement or partly replace measurements of sap flow in stems.