Mandarin Rootstocks Research Articles

GROWTH, YIELD, FRUIT QUALITY AND MINERAL COMPOSITION OF FIVE CITRUS ROOTSTOCKS

This study was carried out on 12 years old citrus rootstocks namely: Sour orange, Rangpur lime, Volkamer lemon, Troyer citrange and Cleopatra mandarin to evaluate their growth, yield, fruit quality and mineral composition of roots and leaves. The obtained results are summarized as follows: 1. Volkamer lemon and Rangpur lime have the largest tree size and leaf or shoot growth characters. Sour orange was moderate while, Troyer citrange and Cleopatra mandarin had the lowest values of all tested growth parameters. 2. Volkamer lemon and Rangpur lime, had the greatest weight of fibrous roots at all distances from tree trunk, but the lowest weight of fibrous roots was found for Cleopatra mandarin rootstock. 3. Volkamer lemon and Rangpur lime had significantly heavier fruit yield as (kg) per tree as compared with the other tested rootstocks. Fruits in Volkamer lemon and Sour orange was large and heavier, but in Troyer citrange, it was moderate, while fruit of Rangpur lime and Cleopatra mandarin was small. Rangpur lime gave numerous seeds per fruit, however Sour orange, Volkamer lemon and Troyer citrange were moderate, while Cleopatra mandarin gave the lowest number of seeds per fruit. 4. On the other hand, Sour orange gave the highest percentage of seed germination, followed by Cleopatra mandarin, while, troyer citrange recorded the least value. Volkamer lemon and Rangpur lime recorded moderate value of seed germination percentage. 5. Leaves of Volkamer lemon and Rangpur lime contained higher N, P, K, Ca, Mg, Fe, Mn and Cu but lower Na and Cl levels than that of the other tested rootstocks. However, macro and micronutrients in the roots of all tested rootstoc1ks were not consistent in their trend.

Differential expression of putative 9- cis-epoxycarotenoid dioxygenases and abscisic acid accumulation in water stressed vegetative and reproductive tissues of citrus

The relationship between ABA accumulation and the expression of putative carotenoid cleavage dioxygenase ( CCD) genes in water-stressed vegetative and reproductive tissues from Clemenules mandarin ( Citrus clementina) scions grafted on Cleopatra mandarin ( Citrus reshni) rootstocks was investigated. Four full-length cDNAs ( CcNCED3, CcCCD4a, CcCCD4b, and CcNCED5) closely related to the CCD group and in particular to the 9- cis-epoxycarotenoid dioxygenase ( NCED) subfamily of Arabidopsis were cloned. In citrus seedlings drought-induced progressive ABA accumulation in roots, leaves and developing ovaries while re-hydration provoked sudden reduction of its levels. In these organs expression of CcCCD and CcNCED genes in normal conditions was low and similar. During the drought/re-watering cycles expression of CcNCED3, the major drought-induced gene, paralleled the pattern of ABA accumulation. In contrast, either minor or no up-regulation changes of CcNCED5 and CcCCD4a transcripts were observed. In green fruits, transcript levels of CcNCED3 and CcNCED5 in the flavedo (coloured fruit layer) were rather similar to those observed in developing ovaries. However, CcNCED5 expression dramatically increased at colour break and remained high in ripe fruit. Consistent with this observation, in the flavedo of detached ripe fruits a 37 °C dehydration treatment increased in parallel levels of ABA and CcNCED5 transcripts. The above results showed that in Clemenules mandarin water stress induced specific up-regulation of CcNCED3 in photosynthetically active tissues such as leaves and developing ovaries. On the other hand, CcNCED5 was preferentially induced in Clemenules mandarin ripening fruits.

Effects of citrus rootstocks on fruit yield and quality of Ruby Red and Marsh grapefruit

Introduction. Generally, in Iran, citrus cultivars are grafted on Sour orange rootstocks. However, susceptibility of this rootstock to tristeza (CTV) has required a research program to replace Sour orange trees with other rootstocks. Materials and methods. Yield performance and fruit quality of Ruby Red and Marsh grapefruits were assessed for 5 years (1999 to 2003) in the Agricultural Research Station in Dezful (Southern Iran) according to the eight different rootstocks used: Carrizo citrange, Citrus amblycarpa, Cleopatra mandarin, King mandarin, Sour orange, Swingle citrumelo, Troyer citrange and Volkamer lemon. Results and discussion. For the 5 years studied, cumulative yields per tree and yield per trunk cross-section area were the highest on Cleopatra mandarin, Sour orange, Swingle citrumelo and Volkamer lemon, whereas trees on Citrus amblycarpa, Carrizo citrange, King mandarin and Troyer citrange were the least productive. The results showed that individual fruit wei- ght, size and skin thickness were significantly higher for both cultivars on Volkamer lemon, compared with the other rootstocks. Fruits on the Cleopatra mandarin rootstock had the lowest weight and fruit diameter. The rootstock type also affected the fruit juice amount and soluble solid content. Fruits from cultivars which were grafted on Sour orange rootstock had total soluble solids of 9.93% and 51% of juice content, whereas on Volkamer lemon rootstock, they had 7.81% of total soluble solids and 45.3% of juice content. Total acid of the fruits from cultivars grafted on Volkamer lemon had the significantly smallest amount (1.33%). In both cultivars of grapefruits, no significant differences were observed except in the size of the fruit, fruit juice and vitamin C contents. Interactions between rootstock and cultivar were significantly different. Conclusion. Our results indicated that the yield and fruit quality of grapefruit are strongly influenced by the rootstock used. Also, the interaction between cultivars and rootstocks may be an interesting strategy for the adaptation of cultivars to different climatic areas. Iran Islamic Republic / Citrus paradisi / rootstocks / fruits / quality / yields

Growth of Young`Minneola' Tangelo Citrus Trees Fertilized with Banded Poultry Litter Overlaid with Wood Chips

Soil incorporation of poultry litter can damage roots of citrus trees grown on shallow soils in southern Florida. Using an alternative application method, young `Minneola' tangelo trees (Citrus reticulata Blanco × C. paradisi Macf.) on Cleopatra mandarin rootstock (C. reticulata Blanco) on bedded groves in southeast Florida were fertilized for 18 months after planting with surface-banded poultry litter (PL) overlaid with wood chips (WC). PL/WC was applied at 142, 284, and 425 kg·ha-1 N in two applications/year in one 0.6-m band within the dripline of trees planted at 278 trees/ha. Other treatments with different N rates included 220 kg·ha-1 N broadcast in the middle of the bed twice a year and 116 kg·ha-1 N as controlled release fertilizer applied within the dripline of trees in three applications per year. Eighteen months after planting, growth of trees receiving PL/WC treatments of 142, 284, and 425 kg·ha-1 N per year and 116 kg·ha-1 N per year was similar and greater than growth of trees receiving PL broadcast in grove middles at 220 kg·ha-1 N per year. Soil P, Ca, and Mg levels beneath the three banded PL/WC treatments were higher than in other treatments; in all treatments leaf N levels were optimum, but leaf P, K, Ca, Mg, and Fe levels were excessive. Banded PL/WC treatments applied at 142 kg·ha-1 N per year and even lower rates may be adequate for growth of young citrus trees, especially in terms of reducing excessive soil and leaf nutrient levels.

Crescimento e composição mineral do porta-enxerto tangerineira cleópatra cultivado em substrato acrescido de polímero hidrorretentor

Os efeitos de polímero hidrorretentor acrescido ao substrato foi avaliado na fase inicial de produção do porta-enxerto tangerineira 'Cleópatra' cultivado em tubetes plásticos com substrato comercial à base de casca de Pinus compostada e parcialmente fertilizado. Foi utilizado o delineamento experimental de blocos casualizados com três repetições, sendo os tratamentos seis doses do hidrorretentor (0, 4, 8, 12, 16 e 32 mg.dm-3) incorporado ao substrato, com 60 plantas úteis por parcela. Avaliaram-se o Índice de Velocidade de Emergência (IVE), altura de planta, peso da matéria seca total e seus teores de N, P, K, Ca, Mg, S, B, Cu, Mn, Zn e Fe, e valores de pH do substrato ao final do período experimental. A incorporação do hidrorretentor ao substrato de cultivo promoveu elevação nos valores do pH do substrato, decréscimos no IVE, no crescimento e no peso da matéria seca total, não havendo alteração expressiva no estado nutricional dos porta-enxertos aos 150 dias pós-semeadura.

Rootstocks for 'Tahiti' lime

The 'Tahiti' lime (Citrus latifolia Tanaka) is an important commercial citrus cultivar in Brazil. 'Rangpur' lime has being used as its main rootstock, but it is susceptible to root rot caused by Phytophthora, reducing tree longevity. An experiment was set up in a randomized block design, with three trees per plot of each rootstock and four replicates, and run for 12 years, aiming to compare the performance of 'IAC-5 Tahiti' lime, budded on 'Rangpur' lime (Citrus limonia Osb.); 'C-13' citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.); 'African' rough lemon (Citrus jambhiri Lush.); 'Volkamer' lemon (Citrus volkameriana Ten. & Pasq.); trifoliate orange (Poncirus trifoliata (L.) Raf.); 'Sunki' mandarin (Citrus sunki Hort. ex Tan.) and 'Cleopatra' mandarin (Citrus reshni Hort. ex Tan.). Eleven years after the establishment of the orchard, trees with the greatest canopy development were budded on 'C-13' citrange and 'African' rough lemon, and both differed significantly from trees budded on trifoliate orange, 'Sunki' and 'Cleopatra' mandarins, which presented the smallest canopy development. Trees budded on 'Rangpur' lime and 'C-13' citrange had the highest cumulative yields, and were different from trees budded on trifoliate orange, 'Cleopatra' and 'Sunki' mandarins. There was no rootstock effect on mean fruit weight and on the total soluble solid/acid ratio in the juice. The 'Rangpur' lime and the 'Cleopatra' mandarin rootstocks reduced longevity of plants.

Effect of Rootstock on Stem-end Rind Breakdown and Decay of Fresh Citrus

Rootstock significantly affected the development of stem-end rind breakdown (SERB) on `Valencia' and navel oranges (Citrus sinensis), but not `Ray Ruby' grapefruit (C. paradisi) or `Oroblanco' (C. grandis × C. paradisi), and affected postharvest decay on navel orange, `Ray Ruby' grapefruit, `Oroblanco' and one of two seasons (2002) on `Valencia' orange. In `Valencia' and navel oranges, fruit from trees grown on Gou Tou (unidentified Citrus hybrid) consistently developed low SERB. `Valencia' oranges on US-952 [(C. paradisi × C. reticulata) × Poncirus trifoliata] developed high levels of SERB in both years tested. Relative SERB of fruit from other rootstocks was more variable. Navel oranges, `Ray Ruby' grapefruit, and `Oroblanco' fruit from trees on Cleopatra mandarin (C. reticulata) rootstock consistently developed relatively low levels of decay, and in navel this level was significantly lower than observed from trees on all other rootstocks. In three of five trials we observed significant differences between widely used commercial rootstocks in their effects on postharvest SERB and/or decay. Given the expanding importance of sales to distant markets, it is suggested that evaluations of quality retention during storage be included when developing citrus rootstocks and scion varieties for the fresh market.

Estimation of Nitrate Leaching in an Entisol under Optimum Citrus Production

Leaching of fertilizer nutrients and widespread NO3‐N contamination of drinking water wells in proximity to citrus growing regions of central Florida are a serious concern. We evaluated NO3‐N distribution in soil solution at various depths in the vadose zone, and N leaching below the root zone for two cropping seasons under the canopy of 21‐yr‐old Hamlin orange [Citrus sinensis (L.) Osbeck] trees on Cleopatra mandarin (Citrus reticulata Blanco) rootstock, on an entisol of central Florida. The treatments included 112, 168, 224, and 280 kg N ha−1 yr−1 as either dry granular fertilizer (DGF; broadcast, in 4 equal doses) or fertigation (FRT; 15 applications yr−1), and 56, 112, and 168 N kg ha−1 yr−1 as controlled‐release fertilizer (CRF; single application yr−1). Irrigation was scheduled using recommended tensiometer set points as guidelines, with a target wetting depth of 90 cm. The NO3‐N was measured in soil solutions bi‐weekly at 60‐, 120‐, and 240‐cm depths using suction lysimeters (SLs) installed under the tree canopy. The 240‐cm depth sample represented soil solution below the rooting depth of the trees, and the NO3‐N at this depth could contaminate groundwater. At the 60‐ or 120‐cm depths, the NO3‐N concentrations occasionally peaked at 12 to 100 mg L−1, but at 240 cm NO3‐N concentrations mostly remained below 10 mg L−1 The careful irrigation management, split fertilizer application, and timing of application contributed to the low leaching of NO3‐N below the root zone. Calculated NO3‐N leaching losses below the rooting depth increased with increasing rate of N application and the amount of water drained, and accounted for 1 to 16% of applied fertilizer N.

474 High Application Rates of Reclaimed Water Benefit Citrus Growth and Production

Citrus trees in an experimental planting responded well to high application rates of reclaimed water. Irrigation treatments included annual applications of 400 mm of well water and 400, 1250, and 2500 mm of reclaimed water. The effects of these irrigation treatments on two citrus cultivars (`Hamlin' orange and `Orlando' tangelo) combined with four rootstocks were compared. Growth and fruit production were better at the higher irrigation rates. The concentration of soluble solids in juice was diluted at the highest irrigation rate, but total soluble solids per hectare increased due to the greater fruit production. Average soluble solids/ha production was >15% higher at the 2500-mm rate than the 400-mm reclaimed water rate. While fruit soluble solids were usually lowered by higher irrigation, the reduction in fruit soluble solids observed on three of the rootstocks did not occur in trees on Carrizo citrange. Trees on Cleopatra mandarin grew similarly at the different irrigation rates, but canopy volume of trees on Swingle citrumelo was significantly smaller at the 400 mm rate than at the 2500 mm rate. Fruit peel color score was lower but juice color score was higher at the highest irrigation rate. Weed pressure increased with increasing irrigation rate, but was controllable. Both juice and fruit soluble solids were higher on Swingle citrumelo and lower on Cleopatra mandarin rootstock. Total soluble solids/ha, solids/acid ratio, and juice color were higher on Swingle rootstock. Reclaimed water, once believed to be a disposal problem in Florida, can be an acceptable source of irrigation water for citrus on well drained soils at rates up to twice the annual rainfall.

AN EVALUATION OF SOIL WATER STATUS USING TENSIOMETERS IN A SANDY SOIL PROFILE UNDER CITRUS PRODUCTION1

Redistribution and depletion of soil water in a Tavares fine sand (Typic Quartzipsamments) profile were evaluated after irrigation or rain in a commercial citrus grove with under-tree microsprinkler irrigation. Tensiometers were installed at 15-, 30-, 90-, and 150-cm depths in five clusters along the dripline of 25-year-old Hamlin orange trees on Cleopatra mandarin rootstock. Irrigation was scheduled when the soil water potential at the 15- and 30-cm depths exceeded either −10 KPa (Jan. to June) or −15 KPa (July to Dec.) to replenish the water deficit (below field capacity) in the top 90 cm of the soil profile. The tensiometers placed at 15- and 30-cm depths responded to changes in soil water regardless of irrigation or rainfall. Tensiometer readings at various depths were used to estimate the water content at corresponding depths using the van Genuchten analytical relationship equations. Total soil water contents within the rootzone (0 to 90 cm) and below the rootzone (90 to 150 cm) within the monitoring depth (0 to 150 cm) were also calculated to estimate the water available for the trees and water that drained below the rootzone. Results showed some leaching does occur during months when there is heavy rainfall. This study demonstrated that tensiometer readings can be used to calculate the soil water content at various depths within the soil profile. Therefore, duration of irrigation can be adjusted to minimize leaching below the rootzone. Because optimal irrigation management is important to minimize nutrient leaching below the rootzone, tensiometer-based irrigation scheduling is an important component of nutrient and irrigation best management practices for citrus in sandy soils.

Nitrogen Management for High Yield and Quality of Citrus in Sandy Soils

AbstractWe are in the process of developing N best management practices for citrus in sandy Entisols to increase N uptake efficiency and to minimize NO3 leaching below the rooting depth. We evaluated the effects of N sources as either dry granular form (DGF), fertigation (FRT), or controlled‐release fertilizer (CRF), and rates (56–280 kg N ha‐1 yr‐1) with optimum irrigation management on: (i) the fruit yield and quality and leaf nutrient concentrations of bearing ‘Hamlin’ orange [Citrus sinensis (L.) Osbeck] trees on ‘Cleopatra’ mandarin (Citrus reticulata Blanco) rootstock (planted in 1974) grown in a Tavares fine sand (hyperthermic, uncoated Typic Quartzipsamments) and (ii) changes in NO3‐N status in soil solution sampled from the vadose zone both within and below the root zone. For the DGF and FRT sources, 3‐yr mean fruit yield increased with an increase in N rates in the range of 112 to 224 kg ha‐1 yr‐1. For further increase in N rate, the fruit yield showed a diminishing response, which was quite marked for the DGF. The N requirements for 1 Mg of fruit, mean across all N rates, were 1.79, 2.58, and 2.75 kg N for the CRF, FRT, and DGF sources, respectively. Leaf N concentrations were maintained within the optimal range (25–27 g kg‐1) at N rates ≥168 kg ha‐1 yr‐1, regardless of source of N. Various N rates and sources did not significantly affect the fruit size, nor juice quality parameters. The improved management of irrigation and fertilizer placement and timing of application contributed to minimized leaching of NO3‐N below the root zone.

Impact of Nitrogen Management Practices on Total Nitrogen in the Fruits of High Productive Hamlin Orange Trees

For perennial crop production conditions, major portion of nutrient removal from the soil-tree system is that in harvested fruits. Nitrogen in the fruits was calculated for 22-year-old `Hamlin' orange (Citrus sinensis) trees on Cleopatra mandarin (Citrus reticulata) rootstock, grown in a Tavares fine sand (hyperthermic, uncoated, Typic Quartzipsamments) that received various N rates (112, 168, 224, and 280 kg N/ha per year) as either i) broadcast of dry granular form (DGF; four applications/year), or ii) fertigation (FRT; 15 applications/year). Total N in the fruits (mean across 4 years) varied from 82 to 110 and 89 to 111 kg N/ha per year for the DGF and FRT sources, respectively. Proportion of N in the fruits in relation to N applied decreased from 74% to 39% for the DGF and from 80% to 40% for the FRT treatments. High percentage of N removal in the fruits in relation to total N applied at low N rates indicate that trees may be depleting the tree reserve for maintaining fruit production. This was evident, to some extent, by the low leaf N concentration at the low N treatments. Furthermore, canopy density was also lower in the low N trees compared to those that received higher N rates.

Citrus Blight Found in Yucatan, Mexico.

Citrus blight, a serious tree decline problem of unknown cause in humid citrus-growing areas such as Florida and Louisiana, South America, South Africa, and the Caribbean, has never been reported from Mexico. Citrus blight has no reliable visual symptoms, and physical and chemical tests have to be used for diagnosis. We used water injection into the trunk (2), zinc and potassium analysis of the outer trunk wood (3), and an immunological test for specific blight proteins in the leaves (1). Low uptake when water is injected into the trunk, and high zinc and potassium in the wood, compared with healthy trees, are characteristic of citrus blight (3). Water injection tests and wood analysis of four healthy and four declining trees in the Dzan, Yucatan, Mexico, area in August 1995, showed highly significant differences in water uptake (healthy trees 44.3 ml/min, declining trees 1.0 ml/min), little difference in wood zinc (healthy 2.8 μg/g, declining 3.0 μg/g) and 39% more potassium in the wood (healthy 0.147%, declining 0.204%). No leaf protein tests were done at this location. Tests on eight declining and five healthy trees in Seye, Yucatan, Mexico, in June 1996, showed significant (P = 0.01 to 0.05) differences in water uptake (healthy 12.9 ml/min, declining 0.6 ml/min), in wood zinc (healthy 2.0 μg/g, declining 7.0 μg/g) and potassium in the wood (healthy 0.156%, declining 0.251%). Leaf samples from all eight declining trees were positive for blight in a specific protein test (1). The visual symptoms of all declining trees tested were the same as those of blight-affected trees in Florida and Cuba: zinc deficiency symptoms in the leaves, thin foliage, wilt, and sprouting from the trunk and the main branches. The reasons for the lack of earlier reports of citrus blight from Mexico are apparently climatic and rootstock related. Many of Mexico's citrus-producing areas are dry and blight does not occur in dry areas such as the Mediterranean countries and California. Most of Mexico's citrus is grown on sour orange (Citrus aurantium L.) rootstock that is highly resistant to citrus blight, but very susceptible to tristeza virus disease. In response to warnings that tristeza disease might appear in Yucatan, growers planted Valencia orange (C. sinensis (L.) Osbeck) on Cleopatra mandarin (C. reticulata Blanco) rootstock in Dzan and on Volkamer lemon (C. limon (L.) N. L. Burm.) in Seye, both highly susceptible to citrus blight (4). Changes in rootstock to avoid one disease led to problems with another.

Performance of `Ambersweet' Orange Trees on Cleopatra Mandarin and Swingle Citrumelo Rootstocks

Because of the many concerns about fruit quality and fruit production of `Ambersweet' cultivar, this study was conducted in Florida to evaluate the performance of this cultivar budded on two rootstocks and grown in three locations. The effects of Cleopatra mandarin (CM) rootstock on tree growth, yield, fruit quality, and leaf mineral concentration were compared to those of Swingle citrumelo (SC). Although tree shape differed with the rootstock, no consistent difference was found in tree growth between the two rootstocks. Significant differences in yield, fruit size, and fruit quality were found between the two rootstocks. Fruit produced on CM were large with a rough, thick peel and poor color. Swingle citrumelo rootstock promoted higher yield and better fruit and juice quality than CM. Earlier fruit maturity and higher soluble solids and juice content were obtained from trees grown on the Flatwoods compared to trees grown on the central ridge. With the exception of magnesium, no consistent difference in leaf mineral concentration was found between the two rootstocks.

Seedling emergence, growth, and mineral concentration of three citrus rootstocks under salt stress

Abstract Salt tolerance of Carrizo citrange (CC), sour orange (SO), and Cleopatra mandarin (CM) rootstocks during emergence and early seedling stage of development was studied under greenhouse conditions. Increasing salt concentration in the nutrient solution delayed and depressed seedling emergence (SE), increased time to 50% emergence, reduced seedling growth (SD) but did not affect emergence spread. At the first salinity level (5 mmol), emergence of the first seedling (EFS) was delayed by 2–3 days in CC and one day in SO but was not affected in CM. At the two lowest salinity levels (5 and 10 mmol), final percent emergence (FPE) was not affected in CC but was reduced in SO and CM while shoot biomass was reduced in CC but was not affected in SO and CM. This study showed a non‐consistent trend among citrus rootstocks concerning whether the delay in emergence is more sensitive to salt stress than final percent emergence. However, SG was generally more affected by salinity than SE, particularly at high sali...

Rootstock and scion effects on the leaf nutrient composition of citrus trees

Four long-term citrus rootstock trials (navel orange, mandarin, Valencia orange, and lime soil trial) established at Irymple, in the Sunraysia district of Victoria, were tested for leaf nutrient composition in each of 2 years. Scion or rootstock significantly influenced leaf nutrient composition in orange and mandarin trees in all 4 trials. Poncirus trifoliata and citrange rootstocks and Ellendale tangor scion resulted in high to moderate leaf N, P, and K concentrations, while Symons sweet orange rootstock and Dancy mandarin gave low leaf nitrogen (N), phosphorus (P), and potassium (K) concentrations. Potassium concentrations of navel and Valencia oranges on rough lemon rootstock were lower than on most of the other rootstocks tested. For all rootstocks, however, leaf N, P, and K concentrations were in the high range in the navel orange and Valencia orange trials, while leaf K concentrations were in the high range in the mandarin trial. Citrange rootstocks and Ellendale scion also had higher concentrations of leaf magnesium (Mg), while Symons sweet orange, Cox sweet orange, and Rangpur lime had lower leaf Mg concentrations than other rootstocks and scions. In the Valencia rootstock trial, rough lemon and Rangpur lime induced the highest leaf sulfur concentrations, while citrange rootstocks gave the lowest. Soil depth in the lime soil trial influenced foliar P and K levels in Valencia orange trees but these differences were small. In all trials, rootstock, but not scion, strongly influenced chloride (Cl) concentrations of citrus leaves. Poncirus trifoliata rootstock accumulated high concentrations of Cl, and the citrange rootstocks moderate, while Cleopatra mandarin rootstock showed consistently low leaf C1 concentrations in all trials. Rough lemon rootstock was not consistently good at excluding C1, and Rangpur lime showed good C1 exclusion only in the Valencia rootstock trial. There was no evidence of a negative relationship between uptake of N and C1 by citrus rootstocks. Poncirus trifoliata had a lower uptake of sodium (Na) in the Valencia rootstock trial, while Cleopatra and Emperor mandarin rootstocks showed slightly higher leaf Na levels than most other rootstocks tested. The 2 citranges, mandarin, rough lemon, and Rangpur lime rootstocks induced higher boron (B) concentrations in leaves of navel orange compared with other rootstocks but they were still in the adequate range for citrus (Reuter and Robinson 1986), while sweet orange rootstocks had lower levels. Emperor mandarin scion on all rootstocks tested had the lowest B levels. Concentrations of iron and copper were rarely influenced by scion or rootstock. Rootstock significantly influenced leaf manganese (Mn) and zinc (Zn) levels in a number of trials, but scion effects were minor. In comparison with all other rootstocks, rough lemon induced higher Mn levels in some cases; sweet orange rootstocks gave higher leaf Zn levels in other cases; while Rangpur lime induced higher Mn and Zn levels in trees grown in the lime soil trial. In the first 3 trials, concentrations of Zn and Mn were low in many of the rootstocks and scions, indicating a need for a second micronutrient spray per growing season.

SEEDLING EMERGENCE AND GROWTH OF THREE CITRUS ROOTSTOCKS UNDER SALT STRESS

Salt tolerance of Carrizo citrange (CC), sour orange (SO), and Cleopatra mandarin (CM) rootstocks during seedling emergence (SE) and early seedling growth (SG) was studied under greenhouse conditions. Increasing salt (NaCl + CaSO4) concentration delayed and emergence, reduced SG, but did not affect emergence spread. At the first salinity level (5 mmol), emergence of the first seedling (EFS) was delayed by 2 to 3 days in CC and one day in SO but was not affected in CM. At the highest salt level (80 mmol), EFS was delayed by up to 6, 7, and 5 days for CC, SO, and CM, respectively. At the two lowest salinity levels (5 and 10 mmol), final percent emergence (FPE) was not affected in CC but was reduced in SO and CM while shoot biomass was reduced in CC but was not affected in SO and CM. At the 80 mmol salt level, FPE was reduced by 23% in CC and by 33% in SO and CM while SG was reduced by 70% in CC and by 60% in SO and CM. Among the rootstocks studied, the delay in emergence was not necessarily more salt sensitive than FPE. However, SG was generally more affected by salinity than SE, particularly at high salinity levels (20, 40, and 80 mmol).

Tree Size, Yield, Fruit Quality, and Leaf Mineral Nutrient Concentration of `Fairchild' Mandarin on Six Rootstock

The influence of six rootstock on growth, yield, fruit quality, and leaf mineral nutrient concentration of `Fairchild' mandarin [`Clementine' mandarin (Citrus reticulata Blanco) × `Orlando' tangelo (C. paradisi Macf. × C. reticulata)] is reported for the arid climate of southwestern Arizona. Trees on macrophylla (Alemow) (C. macrophylla Wester) were precocious and produced high yield 4 years after planting. Six-year cumulative yields of trees on Volkamer lemon (C. limon Burro f.), Carrizo citrange [C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.], Taiwanica (C. taiwanica Tan. & shin.), and rough lemon (C. jambhiri Lush.) were similar and higher than those of trees on macrophylla and Batangas mandarin (C. reticulata). `Fairchild' mandarin tree canopies were large with Volkamer lemon and Taiwanica; intermediate with Carrizo citrange, rough lemon, and Batangas mandarin; and small with macrophylla rootstock. Fruit from trees on Carrizo citrange had the highest soluble solids concentration (SSC), while those on Volkamer lemon and rough lemon had the lowest SSC and total acids. `Fairchild' trees on macrophylla had higher levels of leaf N, Mn, and Fe but lower Ca, while trees on Batangas mandarin and Carrizo citrange had higher leaf K than those on the other rootstock. Trees on Volkamer lemon had higher leaf Zn than those on Carrizo citrange, Taiwanica, rough lemon, and Batangas mandarin rootstock. Considering yield, growth, fruit quality, and/or leaf nutrient concentration, Volkamer lemon, Carrizo citrange, Taiwanica, and rough lemon are suitable for `Fairchild' mandarin in the arid regions of southwestern Arizona. Trees on macrophylla could be advantageous for short-term planting, but would not be satisfactory for long-term planting because of gradual decline in growth and yields. Batangas mandarin is not recommended for `Fairchild' mandarin due to poor production.

Effects of peg‐induced water stress on two citrus cultivars

Abstract The effect of polyethylene glycol (PEG) 4000 on sour orange (SO) and Cleopatra mandarin (CM) rootstock seedlings grown in fine sand under greenhouse conditions was studied. The PEG treatments were initiated by adding PEG to half strength Hoagland's solution to achieve final osmotic potentials of ‐0.10, ‐0.20, and ‐0.35 MPa. The no PEG control treatment had an osmotic potential of ‐0.05 MPa. Seedlings were harvested 6 months after starting PEG treatments. No significant differences in growth, root hydaulic conductivity, water flow rate, stomatal conductance, and evapotranspiration were detected between SO and CM. However, all these variables were significantly reduced by PEG. At a relatively low PEG level (‐0.10 MPa), shoot and root dry weights, stem cross sectional area, total leaf area, and fibrous root length were reduced by more than 60%. Although SO and CM were similarly sensitive to PEG‐induced water stress, significant differences between these two rootstocks were found in leaf mineral composition, chlorophyll content, leaf succulence, and specific leaf weight. PEG reduced N, K, and Mg, increased P, Ca, Zn, Mn, and Fe leaf contents, but did not affect Cu leaf content. PEG‐treated seedlings produced heavier leaves per unit area and heavier roots per unit length than nontreated seedlings.

Effects of salinity and rootstock on lemon fruit quality

SummaryPhysical characteristics and constituents of juice were studied in ‘Verna’ lemon fruit in relation to the salinity of the irrigation water and to three rootstocks, sour orange (C. aurantium L.), Cleopatra mandarin (C. reticulata Blanco) and macrophylla (C. macro- phylla Wester). Yield reduction by salinity was not caused by changes in physical conditions or juice content, whatever the rootstock. However juice quality was affected by both salinity and rootstock. Sour orange and Cleopatra mandarin rootstocks were superior to macrophylla because their fruits were highly satisfactory in both total soluble sugars (TSS) and acidity, which are the most important components of juice quality. Most quality factors were correlated with each other within rootstocks. Differences between rootstocks are presented.