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The photosynthetic light response of commercial blackberry cultivars (Rubus L. subgenus Rubus Watson) is largely unexplored, although they are frequently grown in full sun. In this experiment, light response curves of floricane leaves from the cultivars Natchez, Apache, Navaho, and Von were examined throughout the following production stages: before shiny black fruit were present (before harvest, BH), during peak production of fruit (peak harvest, PH), and when most fruit had fallen from plants or any remaining were dull black (after harvest, AH). Each cultivar was evaluated between an irradiance of 2000 and 0 μmol·m–2·s–1. The estimated maximum photosynthetic rate (photosynthetic capacity, PNmax) was greater BH than AH across all cultivars, whereas ‘Natchez’ had a greater PNmax BH and PH compared with the other cultivars. During AH, all cultivars had a similar PNmax. The BH response curves declined under the highest irradiance measured, whereas the PH and AH response curves remained stable at similarly high irradiance. Of the four cultivars, Apache, Navaho, and Von appeared to be more photosynthetically limited than Natchez under increasing irradiance. Based on the cultivar-specific performance observed, blackberry response to light is a relevant trait that breeding programs should consider for improving cultivar adaptability to local and regional conditions.

Horticultural performance of eleven blackberry cultivars, including two primocane-fruiting cultivars, was evaluated over three years after fruiting began at the Musser Fruit Research Center in Sout...

The aim of this research was to assess how fruit tree age influences nutrient partitioning patterns in aboveground organs. We selected 6-year-old (mature) and 20-year-old (old) ‘Cresthaven’ peach trees and measured the macronutrient concentrations in organs removed during pruning, thinning, harvesting, and leaf fall for 3 years. Then, we calculated the total amount of nutrients removed at each event and studied the partitioning patterns between mature and old peach trees. The results showed that mature peach trees had higher phosphorus (P) and potassium (K) concentrations in fruit mesocarp and fallen leaves than old trees. When we estimated the total nutrient content, mature peach trees allocated more nitrogen (N), P, K, and calcium (Ca) to pruned wood and harvested fruit but had less N and Ca in senescing leaves compared with old peach trees. The results of this study suggest that the different proportion of organs removed through orchard management practices from trees of different ages as well as the concentration of nutrients in these organs must be considered when estimating nutrient restitution needs and tree nutritional requirements.

Maintaining shelf life and postharvest quality of blackberries (Rubus subgenus Rubus) from harvest to consumer is challenging for growers and packers due to several postharvest issues including fresh weight (FW) loss, red drupelet reversion, and fruit leakiness. The time of day blackberries are harvested, the time from harvest to cold storage, and the time in cold storage are factors that may alter the incidence and severity of these postharvest problems. In this experiment, blackberries from 10 cultivars were picked at two different times (7:00–7:30 am and 10:00–10:30 am), delivered to cold storage either immediately or following a 90-minute delay, and evaluated after 1 or 2 weeks in cold storage for FW loss, red drupelet reversion, and leakiness. The response of blackberry postharvest quality to time of harvest, delay to cold storage, and storage length was cultivar-specific. In summary, time of harvest, delay to cold storage or storage length did not affect cultivars Arapaho and Ouachita. Different harvest times did not affect FW or incidence of reddening, but increased leakiness in ‘Chester’ and ‘Triple Crown’; thus, these two cultivars should be preferably harvested early in the morning. Our recommendation for ‘Chester’, ‘Triple Crown’, ‘Osage’, ‘Prime-Ark® Traveler’, and ‘Von’ is to store the fruit of these cultivars as soon as possible. Limiting cold storage to 1 week maintained postharvest quality for at least one attribute of most cultivars (all but Arapaho and Ouachita) compared with 2 weeks of storage.

A delay of leaf senescence resulting from variable fall climate may allow for additional nutrient resorption, and storage within reserve organs. Autumn leaves and reserve organs (1 year shoots, stem above and below the graft union, the tap root, and fine roots) during dormancy of young peach trees were evaluated following warmer fall temperatures and limited soil moisture on two cultivars (‘Scarletprince’ and ‘Autumnprince’ both on GuardianTM rootstock) over two seasons. Four treatments were established for the two cultivars: (1) well-watered trees (100% ETc needs) in ambient outdoor temperatures; (2) water deficient trees (50% ETc needs) in ambient outdoor temperatures; (3) well-watered trees grown within a greenhouse; and (4) water deficient trees within a greenhouse. The greenhouse environment was on average 5°C warmer than the ambient outdoor temperature. Senescence was delayed on greenhouse-grown trees both years with leaf number and area similar in the greenhouse and outdoor environments prior to senescence. Across leaf samples, leaf nitrogen and phosphorus concentrations were lower within delayed senescence tree leaves while potassium was lower in leaves experiencing normal senescence. During dormancy, multiple reserve organs showed higher nitrogen, phosphorus, and potassium in trees with delayed senescence than normal senescence and similar increases were observed in water-deficient trees compared to well-watered trees. Phosphorus and potassium concentrations were also higher in multiple reserve organs within ‘Autumnprince’ trees compared to ‘Scarletprince’ trees. This study suggests variable climate conditions of increased temperatures or reduced soil moisture during autumn resulting in delayed senescence influence the process of nutrient resorption and increase nutrient storage within reserve organs.

Phythophthora infections in citrus trees may result in poor tree health. Infections are very common under wet conditions. However, the interaction of Phytophthora and flooding conditions has yet to be studied in citrus. In this study, Phytophthora was inoculated into the soil of potted grapefruit trees, and trees were either well-watered or flooded for six weeks; then, these trees were compared with trees without Phytophthora inoculation under the same irrigation regimes. Phytophthora reduced root hydraulic conductance in citrus even though the propagule count was very low when root hydraulic conductance was measured (at the end of the experiment). In the presence of flooding, Phytophthora significantly reduced root hydraulic conductance compared to non-flooded citrus trees inoculated with Phytophthora alone. Flooding reduced stomatal conductance and increased tree mortality more than Phytophthora, but Phytophthora decreased the number of leaves per tree and tended to decrease tree growth more than flooding.

Subtropical and tropical climates are becoming more vulnerable to drought and salinity problems. Of the crops produced in these climates, citrus is especially sensitive to increasing salinity. In times of water scarcity and periodic drought alternative water sources that may be lower in quality may be required for irrigation, leading to reduced yield unless a mechanism of increasing salinity tolerance is found. The salinity tolerance of citrus rootstocks differs depending on species and cultivar in their ability to exclude or sequester toxic ions. Identifying rootstocks that are more salt tolerant is important to citrus production in susceptible areas. ‘Olinda’ Valencia trees budded to three rootstocks (sour orange [SO], C22, and C146) and the ungrafted rootstocks were subjected to 6 months of saline irrigation. Simulated brackish water at 1, 3, 5, and 10 dS m −1 along with a 0 dS m −1 control were used to irrigate trees over the course of the study. Throughout this time period chlorophyll fluorescence, stomatal conductance, electrolyte leakage, and SPAD were measured to identify how trees responded to different levels of salinity stress. Chlorophyll fluorescence, stomatal control, and SPAD decreased with increased salinity, while electrolyte leakage increased. These responses were more pronounced in grafted trees than ungrafted trees. C22 and C146 rootstocks showed more tolerance to increases in salinity than the SO rootstocks. The ‘Olinda’ Valencia scion reduces rootstock tolerance to salinity, however, trees grafted to the C22 and C146 rootstocks showed more salinity tolerance than those grafted to SO rootstocks. This study emphasizes that both rootstock and scion should be considered when selecting trees for saline conditions.

Variable fall temperature and moisture conditions may alter leaf senescence of deciduous fruit trees, influencing carbon assimilation before dormancy and phenology the following spring. This study explored gas exchange of young peach trees (Prunus persica (L.) Batsch) when senescence proceeded normally or was delayed during the fall under two soil moisture treatments: Well-irrigated trees or water deficit. Results showed leaf carbon assimilation was similar between the senescence treatments, but whole tree assimilation was estimated to be greater in delayed senescence trees compared to normal senescence trees based on timing of defoliation and total leaf area. The effect of soil moisture on carbon assimilation was not consistent between years. Delayed sap flow and bloom time resulted as a consequence of delayed senescence the previous fall, but soil moisture did not affect spring phenology.

Exogenous application of biochemicals has been found to improve water stress tolerance in herbaceous crops but there are limited studies on deciduous fruit trees. The goal of this research was to study if ascorbic acid applications could improve physiological mechanisms associated with water stress tolerance in young fruit trees. Ascorbic acid was foliarly applied at a concentration of 250 ppm to water-stressed and well-watered peach trees (control) of two cultivars (‘Scarletprince’ and ‘CaroTiger’). Trees received either one or two applications, and one week after the second application all trees were rewatered to field capacity. Upon rewatering, CO2 assimilation and stomatal conductance of water-stressed ‘Scarletprince’ trees sprayed with ascorbic acid (one or two applications) were similar to those of well-irrigated trees, but water-stressed trees that had not received ascorbic acid did not recover photosynthetical functions. Also, water status in sprayed water-stressed ‘Scarletprince’ trees was improved to values similar to control trees. On the other hand, water-stressed ‘CaroTiger’ trees needed two applications of ascorbic acid to reach values of CO2 assimilation similar to control trees but these applications did not improve their water status. In general terms, different response mechanisms to cope with water stress in presence of ascorbic acid were found in each cultivar, with ‘Scarletprince’ trees preferentially using proline as compatible solute and ‘CaroTiger’ trees relying on stomatal regulation. The application of ascorbic acid reduced cell membrane damage and increased catalase activity in water-stressed trees of both cultivars. These results suggest that foliar applications of ascorbic acid could be used as a management practice for improving water stress tolerance of young trees under suboptimal water regimes.

The exogenous application of the plant hormone abscisic acid (ABA) may provide a new approach for preventing freeze damage to fruit tree crops. Exogenous ABA (1 mM) was foliarly applied to citrus trees under different irrigation regimes: well-irrigated trees or drought-stressed trees. Foliar applications of ABA increased the endogenous leaf ABA concentrations, and drought-stressed trees sprayed with ABA had a greater freeze tolerance than well-irrigated trees and drought-stressed trees that did not receive ABA. On the contrary, soil applications (zero, 1 nM ABA, 1 μM ABA, 1 mM ABA) did not increase the leaf ABA concentration and freeze tolerance.

As population and agricultural pressure on high quality fresh water resources increases, it becomes more important to identify rootstocks and production techniques that allow the usage of lower quality water in irrigated agriculture. Water of 0, 1, 3, 5 and 10 dS m −1 salinity was applied to grafted (with Olinda Valencia ( Citrus sinensis var. Olinda) scion) and ungrafted sour orange ( Citrus aurantium L.), C22, and C146 ( Citrus sunki Hort. Ex Tan. × Poncirus trifoliata L. Raf. ‘Swingle’) trees to evaluate the effect of grafting and rootstock variety on salinity tolerance. Grafted rootstocks had a lower survival rate at higher salinity concentration than ungrafted trees and effects were dependent upon tree variety. Height growth rate and standing leaf area of grafted citrus trees declined with increased salinity concentrations while the response of ungrafted and grafted citrus trees was variety dependent. Mortality increased and standing leaf area decreased with increasing tissue Na + and Cl − concentrations. Mortality in response to salinity was greater in grafted rootstocks than mortality of ungrafted trees. Overall, C22 and C146 rootstocks and ungrafted trees were found to be more tolerant of saline conditions than grafted SO rootstock or ungrafted SO trees.

We determined if winter drought stress could delay flowering and fruit development of immature 'Valencia' sweet oranges to avoid young fruit loss during late-season mechanical harvesting. Beginning in December over three consecutive seasons (2007-2009), Tyvek, a water-resistive barrier material, was used as a rain shield groundcover under 13- to 15-year-old trees. There were three treatments: (1) drought = no irrigation and covered soil, (2) rain only = no irrigation, no cover and (3) normal irrigation with rain and no cover. Covers were removed in February or March and normal irrigation and fertilization were resumed. The drought stress did not affect fruit yield, size, percentage juice or juice quality of the current crop harvested in May and June relative to continuously irrigated trees. Drought stress delayed flowering by 2-4 weeks so that the immature fruit for next season’s crop were smaller than on continuously irrigated trees during June, but fruit growth caught up by September. During mechanical harvesting, previously drought-stressed trees lost fewer young fruit than continuously irrigated trees. Thus, winter drought stress effectively delayed flowering and avoided young fruit loss during late-season mechanical harvesting without negative impacts on yield or fruit quality of ‘Valencia’ orange trees.

7 Pag., 5 Tabl., 1 Fig. The definitive version is available at: http://www.sciencedirect.com/science/journal/00988472, The effects of different levels of Fe-deficiency chlorosis on the fruit yield, appearance and composition of pear and peach trees grown in field orchards have been studied. The major effect of Fe deficiency in both species was a large yield reduction, even when chlorosis was moderate, associated to decreases in fruit tree load. Fruit size increased with moderate chlorosis in both species and decreased with severe chlorosis in peach. In peach, moderate or severe chlorosis affected uniformly all branches, leading to firmer fruits with higher acidity, total phenolics and carboxylates. This indicates a delayed maturity that can be attributed to a low C-availability for fruits. In Fe-deficient pear trees, the majority of fruits (98%) were on non-chlorotic or moderately chlorotic branches, and fruits were less green and firm with an increased sugars/acids ratio. This indicates an advanced fruit maturity that can be attributed to an increased C-availability for fruits. All chlorosis levels increased within-tree variation in fruit appearance., Study supported by the Spanish Ministry of Science and Innovation (projects AGL2006-1416 and AGL2009-09018 co-financed with FEDER), the European Commission (Thematic Priority 5-Food Quality and Safety, 6th Framework RTD Programme, Contract no. FP6-FOOD–CT-2006-016279) and the Aragón Government (group A03).

SUMMARYThe effects of deficit irrigation (DI) and partial rootzone drying (PRD) on the growth and mineral nutrition of citrus rootstock seedlings in the glasshouse were determined, as well as the potential of DI and PRD to trigger root-to-shoot signalling of abscisic acid (ABA) to increase the growth per amount of water used (water use efficiency (WUE)). In the DI study, 3-month-old seedlings of the important citrus rootstock Swingle citrumelo with intact roots received three irrigation treatments: control (1·00 evapotranspiration (ET)), 0·75 ET and 0·50 ET. DI clearly decreased growth, the net assimilation of CO2(ACO2), WUE and the total content of N and K in leaves, even though concentrations of leaf N and K were increased in the drought-stressed smaller plants. Root K was not affected by DI treatments. Leaf ABA concentration increased linearly with DI. For the PRD study, root systems of 6-month-old Swingle citrumelo were split into half and allowed to become established in adjacent pots. There were three irrigation treatments: control (1·00 of the total crop ET, 0·50 in each pot), PRD 50-0 (0·50 ET by weight applied to only one-half of root zone) and DI 25-25 (0·50 ET in total, with 0·25 ET applied to each root half). Although the total root length was decreased by the DI 25-25 treatment, PRD 50-0 did not affect any growth characteristics compared to control plants. The dry root zone of the PRD 50-0 treatment had a higher specific root length, longer roots per dry weight, than the wet root zone. Leaf ACO2and WUE of the DI 25-25 treatment were significantly lower than control plants after 11 weeks. Although the total contents of N and K in leaves were not affected by either PRD treatment, the concentrations of N and K in leaves were increased by DI 25-25. Root K was decreased by PRD treatments. Leaf ABA concentration was increased by PRD 50-0 but not by DI 25-25. Although all drought stress treatments increased the levels of ABA in leaves, DI and PRD treatments did not affect the whole plant WUE. Compared to well-irrigated control plants, DI reduced growth, whereas PRD 50-0 did not.

We determined if winter drought stress could delay flowering and fruit development of immature ‘Valencia’ sweet oranges to avoid young fruit loss during late-season mechanical harvesting. Beginning in December over three consecutive seasons (2007–2009), Tyvek® water-resistive barrier material was used as a rain shield groundcover under 13- to 15-year-old trees. There were three treatments: 1) drought = no irrigation and covered soil; 2) rain only = no irrigation, no cover; and 3) normal irrigation with rain and no cover. Covers were removed in February or March and normal irrigation and fertilization were resumed. The drought stress did not affect fruit yield, size, percentage juice, or juice quality of the current crop harvested in May and June relative to continuously irrigated trees. Drought stress delayed flowering by 2 to 4 weeks so that the immature fruit for next season's crop were smaller than on continuously irrigated trees during June but fruit growth caught up by September. During mechanical harvesting, previously drought-stressed trees lost fewer young fruit than continuously irrigated trees. Thus, winter drought stress effectively delayed flowering and avoided young fruit loss during late-season mechanical harvesting without negative impacts on yield or fruit quality of ‘Valencia’ orange trees.

In three separate experiments, the growth and water use of salinized citrus rootstock seedlings and grafted trees were modified using different growth substrates, elevated CO2, or 50% shade screen under field conditions. By reanalyzing previously published data, we tested the hypothesis that salinity tolerance in citrus can be characterized as the ability to maintain low levels of leaf Cl− accumulation through high plant growth and high water use efficiency (WUE) under saline conditions. Well-irrigated salinized seedlings of the relatively salt-sensitive Carrizo citrange [Carr (Citrus sinensis × Poncirus trifoliata)] were grown in sand, clay, or a peat-based soilless media. Salinity stress reduced plant growth and water use. Leaf Cl− concentration was negatively related to plant growth, but leaf Cl− increased with transpiration rate in low-saline treatments. In a second experiment using salinized seedlings of the relatively salt-tolerant Cleopatra mandarin [Cleo (Citrus reticulata)] grown along with Carr seedlings with or without elevated CO2, leaf Cl− was negatively related to growth and to shoot/root dry weight ratio, but was positively related to water use such that leaf Cl− was negatively related to leaf WUE. In a third experiment using salinized 2-year-old ‘Valencia’ orange (C. sinensis) trees grafted on Cleo or Carr rootstocks and grown with or without shadecloth, leaf Cl− was positively related to leaf transpiration as both were higher in the spring than in the fall, regardless of rootstock or shade treatment. Overall, leaf Cl− was positively related to water use and was negatively related to leaf WUE. High growth, low water use, and consequently, high WUE of salinized citrus were related to low leaf Cl−. Such relationships can be used as indicators of salinity tolerance.

Root-zone salinity stress and high solar irradiance concomitantly occurs in the Mediterranean basin, where Olea europaea is the dominating fruit-tree crop-species. Although the effect of each individual stressor on plant performance has been widely investigated, much less is known on the interaction effects of salinity stress and solar irradiance on the physiology and biochemistry of olive plants. Here we analyzed how changes in root-zone NaCl concentration and sunlight radiation affect relevant physiological and biochemical features in olive cv. Cipressino. Two-year-old plants were supplied with 0 or 125 mM NaCl and exposed to 15% (shade) or 100% sunlight (sun) over a 5-week period, starting from July 10th, 2005. Measurements were conducted of (i) gas exchange and plant growth, (ii) the concentrations of cations and chloride, (iii) the concentrations of soluble carbohydrates, violaxanthin-cycle pigments and polyphenols, and (iv) the protein oxidation and the lipid peroxidation in the leaves. Salt-induced reductions in gas exchange performance and plant growth were greater at the sun than at the shade site, mostly due to light-induced changes in leaf water relations and vapour pressure deficit (vpd), rather than in the concentration of potentially toxic ions. Light-induced increases in leaf Na + and Cl − concentrations were countered by parallel enhancements in the concentrations of K + and Ca 2+ . Sun leaves had sharply greater concentrations of mannitol and xanthophylls, irrespective of root-zone salinity. The amount of “newly assimilate carbon” allocated to polyphenols, especially to flavonoids, increased in response to salinity stress and high sunlight. Remarkably, the protein oxidation was greater in shade than in sun leaves of well-watered plants, and increased more at the shade than at the sun site because of high salinity. We suggest that heat-stress (on average maximum T exceeded 33 °C for 50% of the experimental period), which acted in concert with salinity stress and sunlight irradiance in determining plant responses in our experiment, was responsible for leaf oxidative damage in plants growing under contrasting solar radiation. Indeed, sun leaves of salt-stressed plants were equipped with an extraordinary-rich arsenal of antioxidant compounds, distributed in different cell compartments, i.e., mannitol, zeaxanthin and flavonoids, which likely countered effectively the oxidative damage driven by heat-stress, a clear example of cross-tolerance.

The effects of salinity on growth, leaf nutrient content, water relations, gas exchange parameters and chlorophyll fluorescence were studied in six-month-old seedlings of citrus (Citrus limonia Osbeck) and rooted cuttings of olive (Olea europaea L. cv. Arbequina). Citrus and olive were grown in a greenhouse and watered with half strength Hoagland’s solution plus 0 or 50 mM NaCl for citrus, or plus 0 or 100 mM NaCl for olive. Salinity increased Cl - and Na + content in leaves and roots in both species and reduced total plant dry mass, net photosynthetic rate and stomatal conductance. Decreased growth and gas exchange was apparently due to a toxic effect of Cl - and/or Na + and not due to osmotic stress since both species were able to osmotically adjust to maintain pressure potential higher than in nonsalinized leaves. Internal CO2 concentration in the mesophyll was not reduced in either species. Salinity decreased leaf chlorophyll a content only in citrus.

The responses of leaf water status, growth, and ion concentrations to water or to saline stresses were compared in olive cuttings of different Ca2+ status. Mist-rooted ‘Picual’ olive cuttings were ...

The effects of shading in combination with salinity treatments were studied in citrus trees on two rootstocks with contrasting salt tolerance to determine if shading could reduce the negative effects of salinity stress. Well-nourished 2-year-old 'Valencia' orange trees grafted on Cleopatra mandarin (Cleo, relatively salt tolerant) or Carrizo citrange (Carr, relatively salt sensitive), were grown either under a 50% shade cloth or left unshaded in full sunlight. Half the trees received no salinity treatment and half were salinized with 50 mM Cl- during two 9 week salinity periods in the spring and autumn interrupted by an 11 week rainy period. The shade treatment reduced midday leaf temperature and leaf-to-air vapour pressure deficit regardless of salinity treatments. In non-salinized trees, shade increased midday CO2 assimilation rate (A(CO2)) and stomatal conductance, but had no effect on leaf transpiration (E(lf)). Shade also increased leaf chlorophyll and photosynthetic water use efficiency (A(CO2)/E(lf)) in leaves on both rootstocks and increased total plant dry weight in Cleo. The salinity treatment reduced leaf growth and leaf gas exchange parameters. Shade decreased Cl- concentrations in leaves of salinized Carr trees, but had no effect on leaf or root Cl- of trees on Cleo. There were no significant differences in leaf gas exchange parameters of shaded and unshaded salinized plants but the growth reduction from salinity stress was actually greater for shaded than for unshaded trees. Shaded trees on both rootstocks had higher leaf Na+ than unshaded trees after the first salinity period, and this shade-induced elevated leaf Na+ persisted after the second salinity period in trees on Carr. Thus, shading did not alleviate the negative effects of salinity on growth and Na+ accumulation.

Oleocellosis or oil spotting on the peel of citrus fruit is a common post-harvest injury caused by improper handling. Mechanical injury allows phytotoxic oil to leak out of oil glands and cause injury to surrounding flavedo cells, resulting in oleocellosis. Mechanical harvesting (MH) of ‘Valencia’ sweet orange is conducted in late spring, when the next season's fruitlets are in their early stages of development. There is a concern that mechanical injury from harvesting machines can cause oleocellosis and fruit drop of young, green ‘Valencia’ sweet orange fruitlets, especially late in the harvest season when fruitlets are relatively large. We evaluated the effects of winter drought stress and subsequent late-season MH with a canopy shaker on oleocellosis of ‘Valencia’ sweet orange fruitlets. In April, mature fruit size, juice content, total soluble solids, and acidity were unaffected by previous winter drought stress treatments. Mechanical harvesting removed ≈90% to 95% of mature fruit and 20% to 50% of fruitlets depending on previous drought stress treatments and harvesting date. Beginning 1 week after the late harvest (13 June), attached fruitlets were tagged and visually evaluated approximately every other month to determine oleocellosis injury until the late-season harvest 12 months later. Only 12% of the fruitlets had oleocellosis on more than 30% of their surface area. Up to 75% of the fruitlets from the previously drought-stressed trees had less than 10% of their surface area injured after MH and 11% of these fruitlets dropped before harvest. Nonetheless, there was no significant increase in fruit drop with increased surface area injured nor was juice quality affected at harvest. Overall, fruit surface oleocellosis decreased and healed as fruit expanded, but surface blemishes did not completely disappear. Thus, fruitlet oleocellosis in late-season mechanically harvested trees was cosmetic and did not increase fruit drop nor alter internal fruit quality.

‘Picual’ olive cuttings were grown in a greenhouse under saline conditions in 2 L plastic pots containing perlite. Plants were irrigated with a nutrient solution plus 75 mM NaCl and 0, 2.5, 10 or 40 mM CaCl 2 . Vegetative growth, leaf and root Na + and Ca 2+ concentrations were measured. Na + toxicity symptoms were observed in plants non-treated with Ca 2+ . Shoot length was higher in Ca 2+ treated plants, although shoot growth was reduced at 40 mM CaCl 2 , probably due to the high total ion concentration reached in the external solution. Ca 2+ supply linearly increased leaf and root Ca 2+ concentration and decreased leaf Na + concentration. However, there were no differences in root Na + concentration. Results indicate Ca 2+ may take part in the Na + exclusion mechanism, mainly preventing Na + transport to the shoot, that may be an important ability for survival under saline conditions.

The interactive effects of root-zone salinity and sunlight on leaf biochemistry, with special emphasis on antioxidant defences, were analysed in Olea europaea L. cv. Allora, during the summer period. Plants were grown outside under 15% (shade plants) or 100% sunlight (sun plants) and supplied with 0 or 125 mM NaCl. The following measurements were performed: (1) the contribution of ions and soluble carbohydrates to osmotic potentials; (2) the photosystem II (PSII) photochemistry and the photosynthetic pigment concentration; (3) the concentration and the tissue-specific distribution of leaf flavonoids; (4) the activity of antioxidant enzymes; and (5) the leaf oxidative damage. The concentrations of Na(+) and Cl(-) were significantly greater in sun than in shade leaves, as also observed for the concentration of the 'antioxidant' sugar-alcohol mannitol. The de-epoxidation state of violaxanthin-cycle pigments increased in response to salinity stress in sun leaves. This finding agrees with a greater maximal PSII photochemistry (F(v)/F(m)) at midday, detected in salt-treated than in control plants, growing in full sunshine. By contrast, salt-treated plants in the shade suffered from midday depression in F(v)/F(m) to a greater degree than that observed in control plants. The high concentration of violaxanthin-cycle pigments in sun leaves suggests that zeaxanthin may protect the chloroplast from photo-oxidative damage, rather than dissipating excess excitation energy via non-photochemical quenching mechanisms. Dihydroxy B-ring-substituted flavonoid glycosides accumulate greatly in the mesophyll, not only in the epidermal cells, in response to high sunlight. The activity of antioxidant enzymes varied little because of sunlight irradiance, but declined sharply in response to high salinity in shade leaves. Interestingly, control and particularly salt-treated plants in the shade underwent greater oxidative damage than their sunny counterparts. These findings, which conform to the evolution of O. europaea in sunny environments, suggest that under partial shading, the antioxidant defence system may be ineffective to counter salt-induced oxidative damage.

Physiological responses of olive cuttings of `Koroneiki' and `Picual' (Olea europaea L.) to zero or high salinity (NaCl 100 mmol·L-1) and to ambient CO2 (380 ppm) or elevated (700 ppm) CO2 concentration were studied in sand culture in greenhouses. Growth parameters, net gas exchange of leaves and leaf chloride concentration were measured after two months of treatment. `Koroneiki' had significantly greater shoot growth and net assimilation of CO2 (Ac) at elevated CO2 than at ambient CO2 but this difference disappeared under salt stress. Growth and Ac of `Picual' did not respond to elevated CO2 regardless of salinity treatment. Stomatal conductance and leaf transpiration were lower at elevated CO2 such that leaf water use efficiency increased at elevated CO2 in both cultivars regardless of saline treatment. The saline treatment increased leaf chloride (Cl) concentration and reduced growth and net gas exchange responses in both cultivars. There was no difference in leaf Cl accumulation between the two varieties. At high salinity, elevated CO2 had little effect on leaf Cl implying that at least in `Koroneiki', Cl accumulation was not closely linked to water uptake.