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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.

Fruit bagging is an acceptable cultural practice for organic production that provides a physical barrier to protect fruit. It can reduce pest and pathogen injury for a variety of fruit crops, but quality attributes have been inconsistent for peach [Prunus persica (L.) Batsch] and other bagged fruit. A 2-year experiment on a U.S. Department of Agriculture (USDA) organic-certified peach orchard in central Florida was conducted to analyze the effects of a commercially available paper bag designed for fruit protection and cardinal quadrant (north, south, east, and west sides) of the tree canopy on low-chill peach ‘TropicBeauty’ fruit quality. Protective bags appeared to delay fruit maturity. Flesh firmness and chlorophyll concentration of bagged fruit were 31% and 27% greater than unbagged fruit, respectively. Bagged fruit were protected as demonstrated with a reduction in mechanical injury by 95%, fruit fly injury by 450%, and scab-like lesions by 810%. Bagging reduced fruit brown rot (Monilinia fructicola) at harvest and 7 days after harvest; unbagged fruit were 2 and 3.5 times more likely to have rot at harvest and 7 days after harvest, respectively. Fruit bags did not affect yield, fruit size, total soluble solids, titratable acidity, pH, peel lightness, peel hue angle, or flesh color. Overall, canopy cardinal quadrant location had minimal effect on fruit quality or fruit injury. These results demonstrate that bagging peach fruit protects against various pests and diseases but has minimal effects on fruit quality. Broad adoption of this technology is highly dependent on available labor, market demands, and profitability but may be suitable for producers using direct-to-consumer market channels.

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.

In this study, one-year old grapefruit trees grafted onto sour Orange (SO) and C22 rootstocks were exposed to NaCl-induced salinity (approx. 6 dS m-1) in pot culture for two months under greenhouse conditions. The experiment was laid out in a randomized block design with eight replicates. The trees were irrigated with saline solution containing 0.1% liquid fertilizer “Miracle-Gro Liqua Feed 9-4-9” (N-P2O5-K2O) enriched with micronutrients. The experimental treatments consisted of three levels (4 mM, 8 mM, 12 mM) of foliar applied proline along with control application. Distilled water served as the control. During the experiment the seedlings were sprayed totally five times with ten days intervals. At the end of the treatment physiologically mature leaves, free of damage or defects, were sampled. Dried and ground leaf samples were used for chemical (Na and Cl) and biochemical (DPPH scavenging activity, reducing power, total phenolic content, proline) analysis. Spesific leaf area, leaf water relations and leaf gas exchange of the plants were also determined. Foliar PRO application decreased Na and Cl concentrations of the leaves, and improved spesific leaf area in the final dose. Water leaf relations, photosynthetic activity and biochemical parameters were affected positively even though some differences were determined between the cultivars.

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.

Partial rootzone drying (PRD) has been reported to potentially improve crop water use efficiency (WUEcrop) compared to full irrigation in different fruit trees; however, field studies on the effect of PRD in citrus are scarce. In this field study, three irrigation strategies were tested in an orchard of mature grapefruit trees during two consecutive seasons (2013/2014 and 2014/2015): drip PRD (two drip lines, alternating irrigation between lines every month), microsprinkler irrigation, and double-line drip irrigation (control). Irrigation was applied during the fruit enlargement stage (April–August). The aims of this field study were: 1) to provide a quantitative comparison of irrigation water productivity among irrigation treatments; and 2) to study their effects on fruit quality, yield, tree growth, and flowering. Drip PRD saved 43 to 47% of irrigation water compared to control irrigation, and microsprinkler irrigation saved 12 to 18% of water compared to control irrigation PRD-irrigated trees maintained or increased yield compared to microsprinkler-irrigated and control trees, depending on the experimental season. Therefore, WUEcrop in PRD-irrigated trees was significantly higher than in control and microsprinkler-irrigated trees at the end of both seasons. Fruit and juice quality parameters were statistically similar among all treatments. PRD irrigation did not reduce the flowering potential of the trees although it delayed the onset of flowering in trees relative to the other treatments in 2013/2014. There was a similar timing of flowering among treatments in 2014/2015 and there were no differences in vegetative growth among the irrigation treatments by the end of March (86 Julian data) in both experimental seasons. Our results suggest that PRD can be economically beneficial for citrus growers who use double-line drip irrigation systems, and a strategy to sustain tree growth, tree health and yield during seasons of extreme drought or when high water restrictions are placed in citrus-producing areas.

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.

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.

The effect of partial rootzone drying (PRD) on whole plant water use efficiency (WUE wp = tree growth per water applied) and physiological responses of two-year-old split-root potted grapefruit trees was studied in a greenhouse. Four treatments were applied through above and below tree evapotranspiration (ET c ) requirements for 12 weeks: optimum PRD (100% ET c applied on one split rootzone, no water on the other side), excess PRD (200% ET c applied on one side, no water on the other side), deficit PRD (50% ET c applied on one side, no water on the other side), and control (50% ET c on both pots). Optimum PRD and deficit PRD trees used 18% and 79% less water than control trees, respectively, while excess PRD trees used 70% more water than control trees. Deficit PRD trees, imposing severe water stress by the end of the experiment, had the highest WUE wp , however, decreased efficiency of photosystem II, impaired stomatal conductance, increased concentrations of ABA in leaf tissues, and reduced tree growth. Both optimum PRD, imposing mild water stress, and excess PRD had similar physiological responses, growth, and leaf ABA concentration to control trees. Excess PRD trees did not increase growth with excess water application compared to the other treatments, resulting in drastically reduced WUE wp . On the other hand, optimum PRD trees increased growth allocation to roots over shoots without decreasing growth compared to control trees. Thus, optimum PRD resulted in water-savings without impairing growth or any physiological parameters.

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.

Improving sustainable citrus production through soil and water conservation strategies such as plastic mesh groundcovers and raised planting beds has not been thoroughly evaluated. To determine the impacts of these practices on tree growth parameters, fruit yield, and soil environmental conditions we monitored a grapefruit grove (Citrus paradisi Macf. cv.‘Rio Red’) for five years after planting. Trees were planted under four grove floor management strategies that included flat beds with no plastic mesh groundcover (traditional practice), flat beds with groundcover, raised beds with no groundcover, and raised beds with groundcover. The use of ground cover increased soil temperature and moisture content and led to higher tree growth rates and yields relative to uncovered grove floors. Raising the planting bed to approximately 45 cm higher than the surrounding field reduced soil deposition from irrigation and improved soil properties, but caused fluctuations in soil moisture due to improved water infiltration of heavy clay soils compared to the flat beds. Despite the positive effects of the use of ground cover on yields, there was a trend of alternate bearing, smaller and sweeter fruit sizes for trees under this planting design. The traditional method of planting (flat bed with no groundcover) resulted in smaller trees as measured by tree height, canopy circumference, and trunk diameter. While yields were moderate, they were fairly consistent across years and increased slightly each year of the study. These results show that adoption of plastic mesh groundcovers in citrus or other tree fruit production could potentially improve water conservation while increasing production.

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).

We determined if frequency of application of irrigation water plus fertilizer in solution (fertigation) could modify root and shoot growth along with growth per unit nitrogen (N) and water uptake of seedlings of the citrus rootstock Swingle citrumelo growing in a greenhouse. In the first experiment, all plants received the same amount of water with sufficient fertilizer N but in three irrigation frequencies applied in 10 1.5-mL pulses per day, one 15-mL application per day, or 45 mL applied every 3 days. Plants irrigated at the highest frequency grew the least total dry weight and had the highest specific root length. Plants with lowest irrigation frequency grew the most and used the least water so had the highest water use efficiency. There were no irrigation frequency effects on relative growth allocation between shoot and roots, net gas exchange of leaves, or on leaf N. A second experiment used identical biweekly irrigation volumes and fertilizer rates, but water and fertilizer were applied using four frequency combinations: 1) daily fertigation; 2) daily irrigation with fertilizer solution applied every 15 days; 3) fertigation every 3 days; or 4) irrigation every 3 days and fertilizer solution applied every 14 days. Total plant growth was unaffected by treatments, but the highest frequency using the lowest fertilizer concentration grew the greatest root dry weight in the uppermost soil depths. Roots grew less and leaf N was highest when N was applied every 15 days, implying that root N uptake efficiency was increased when fertigated with the highest fertilizer concentration. All plants had similar water use efficiencies. A third experiment was conducted with irrigation every 3 days and with four different N application frequencies: every 3, 6, 12, or 24 days using four fertilizer concentrations but resulting in similar total N amounts every 24 days. There were no differences in growth, gas exchange, or water use efficiency. Given the fact that all treatments received adequate and equal amounts of water and fertilizer, fertigation frequency had only small effects on plant growth, although very high frequency fertigation decreased N uptake efficiency.

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.

Water demand for irrigation is increasing in olive orchards due to enhanced yields and profits. Because olive trees are considered moderately tolerant to salinity, irrigation water with salt concentrations that can be harmful for many of fruit tree crops is often used without considering the possible negative effects on olive tree growth and yield. We studied salt effects in mature olive trees in a long term field experiment (1998–2006). Eighteen-year-old olive trees ( Olea europaea L.) cv. Picual were cultivated under drip irrigation with saline water composed of a mixture of NaCl and CaCl 2 . Three irrigation regimes (i. no irrigation; ii. water application considering soil water reserves, short irrigation; iii. water application without considering soil water reserves and adding a 20% more as a leaching fraction, long irrigation) and three salt concentrations (0.5, 5 or 10 dS m −1 ) were applied. Treatments were the result of the combination of three salt concentrations with two irrigation regimes, plus the non-irrigated treatment. Growth parameters, leaf and fruit nutrition, yield, oil content and fruit characteristics were annually studied. Annual leaf nutrient analyses indicate that all nutrients were within the adequate levels. After 8 years of treatment, salinity did not affect any growth measurement and leaf Na + and Cl − concentration were always below the toxicity threshold of 0.2 and 0.5%, respectively. Annual and accumulated yield, fruit size and pulp:stone ratio were also not affected by salts. However, oil content increased linearly with salinity, in most of the years studied. Soil salinity measurements showed that there was no accumulation of salts in the upper 30 cm of the soil (where most of the roots are present) because of leaching by rainfall at the end of the irrigation period. Results suggest that a proper management of saline water, supplying Ca 2+ to the irrigation water, using drip irrigation until winter rest and seasonal rainfall typical of the Mediterranean climate leach the salts from the first 0–60 cm depth, and growing a tolerant cultivar, can allow using high saline irrigation water (up to 10 dS m −1 ) for a long time without affecting growth and yield in olive trees.

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 aim of this work was to evaluate long-term effects of different irrigation regimes on mature olive trees growing under field conditions. A 9-year experiment was carried out. Three irrigation treatments were applied: no irrigation, water application considering soil water content (short irrigation), or irrigation without considering soil water reserves and applying a 20% of extra water as a leaching fraction (long irrigation). Leaf water content, leaf area, vegetative growth, yield and fruit characteristics (fruit size, pulp:stone ratio and oil content) were determined yearly. Results showed that growth parameters did not show significant differences as a consequence of applied water. Yield was increased in irrigated trees compared to non-irrigated ones, but little differences between short and long irrigation were observed, only when accumulated yield from 1998 to 2006 was considered. Irrigation did not cause significant differences in fruit size or pulp:stone ratio either. Irrigation regimes similar to those applied in this experiment, under environmental conditions with relatively high mean annual precipitation, does not increase growth, yield or fruit characteristics when compared to rain-fed treatment, and consequently, the installation of a irrigation system could be not financially profitable.

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 ...

5 páginas.-- 3 figuras.-- 5 tablas.-- 18 referencias, This experiment evaluates the potential of using parameters based on tree trunk fluctuations for detecting water deficit in citrus trees under two different water saving-irrigation strategies: sustained deficit irrigation and partial root-zone drying. Three irrigation treatments were applied: 1) Control: trees were irrigated with 100% of their evapotranspirative needs (ETc); 2) 60 sustained deficit irrigation (SDI): 60% ETc; and 3) partial root-zone drying (PRD): 100% ETc needs, applied to only one-half of root zone. Maximum daily shrinkage (MDS), trunk growth rate (TGR), and MDS ratio (ratio between MDS of stressed trees and control trees) were determined. Day-to-day MDS values varied largely and could not be used to determine tree water deficit. TGR did not show significant differences among treatments at this level of stress. Nevertheless, the MDS ratio was a reliable indicator to measure tree water status, and it was more sensitive for detecting water deficit at the onset of a water deficit in trees under SDI than in trees under PRD., The authors thank the Consejo Superiorde Investigaciones Científicas (CSIC) for funding the stay of S. Elsayed-Farag at the Texas A&M University-Kingsville Citrus Center and her JAE-predoc fellowship and Ayako Kusakabe, research associate at the Citrus Center, for her technical support.

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.