Yield,fruit quality,and tree health of ‘Allen Eureka’ lemon on seven rootstocks in Saudi Arabia

Since environmental conditions and cultural practices vary from one area to another, yield, fruit quality, and tree health measurements were conducted over 9 years to evaluate the long-term adaptability and performance to local conditions of ‘Allen Eureka’ lemon (Citrus limon Burm.f.) budded on seven rootstocks in the Najran area of Saudi Arabia. Trees on Citrus macrophylla (CM), Volkamer lemon (VL), and Cleopatra mandarin (Cleo) were the most productive, while trees on Amblycarpa (Amb), rough lemon (RL), Citrus taiwanica (CT), and sour orange (Citrus aurantium L.) (SO) had the lowest yield. Fruit from trees on CM and VL were also the largest in size and had the thickest rind, but were among those that had the lowest juice content and lowest total soluble solids. None of the trees on Cleo, VL, or RL died until the 14th year. However, there was a high mortality rate and severe tree decline on SO, CT, and Amb.     

几种砧木对哈姆林甜橙植株生长、产量及果实品质的影响

以7种不同砧木的8年生哈姆林甜橙为试材,对植株营养生长、产量和果实品质进行了比较。结果表明,不同砧木对哈姆林甜橙生长和产量有不同影响,其中以卡里佐枳橙为砧的植株树冠体积最大,以光皮酸橘、枸头橙和李齐16-6枳为砧的植株树冠体积较小,单位树冠体积产量以光皮酸橘为砧的植株最高,单株挂果数则以李齐16-6枳和卡里佐枳橙为砧的最多。不同砧木对果实品质有显著影响,其中以光皮酸橘为砧的果实体积和单果质量最大,以兰普来檬为砧的果汁含量最高,以李齐16-6枳和卡里佐枳橙为砧的果实可溶性固形物(TSS)含量最高,以李齐16-6枳为砧的果实可滴定酸含量亦最高,而李齐16-6枳和兰普来檬为砧的果实维生素C含量最高。从外观品质看,枸头橙为砧的果实油斑病发生程度最高。综合评价认为,以卡里佐枳橙、李齐16-6枳为砧的单株具产量高、果汁TSS含量高和风味浓郁等优点,是哈姆林甜橙较为理想的砧木。     

Evaluation of rootstocks for the Cyprus local lemon variety ‘Lapithkiotiki’

The effect of various rootstocks on yield, yield efficiency, tree size and fruit quality of the local lemon variety ‘Lapithkiotiki’ (Citrus limon (L.) Burm. F.) was studied under Cyprus conditions. Total cumulative yield over 13 years of production was the highest on rough lemon (C. jambhiri Lush) followed by that on Volkameriana (C. volkameriana Ten. & Pasq.), Yuma Ponderosa lemon (C. limon (L.) Burm. F.), sour orange (C. aurantium L.), Citrus macrophylla Wester, Morton citrange (C. sinensis cv. Washington navel × Poncirus trifoliata (L.) Raf.), Yuma citrange, Rangpur lime (C. limonia Obs.), Palestine sweet lime (C. limettioides Tan.), C-32 citrange and Citremon 1449 (C. limon × P. trifoliata), although no statistically significant differences were found between sour orange, the commercial rootstock used in Cyprus, and the other above mentioned rootstocks. Next in order as regards to total cumulative yield was Cleopatra mandarin (C. reticulata Blanko.) followed by Carrizo citrange, with statistically significant differences compared with sour orange. Trees on Citrumelo CPB-4475 (C. paradisi Macf. × P. trifoliata) and C-35 citrange died 3–4 years after grafting. Canopy volume was the lowest for trees on Cleopatra mandarin and Carrizo citrange. Yield efficiency A, expressed as total cumulative yield per trunk cross-sectional area, was the highest on C. macrophylla and lowest on Carrizo citrange. Rootstock significantly affected fruit size and weight, rind thickness, juice content, brix, total acids and brix:acid ratio. The results of the present study reveal that the most promising rootstocks that may replace sour orange for the local lemon variety ‘Lapithkiotiki’ under Cyprus conditions are Volkameriana, Yuma Ponderosa lemon, C. macrophylla and Citremon 1449.     

Fino lemon clones compared with the lemon varieties Eureka and Lisbon on two rootstocks in Murcia (Spain)

Six clonal selections of the autochthonous Spanish lemon tress cv. Fino, named Fino 46, Fino 47, Fino 48, Fino 49 and Fino 77, and two foreign varieties Eureka and Lisbon (Citrus limon (L.) Burm. f) grafted on sour orange (C. auramtium L.) and Citrus macrophylla (C. macrophylla Wester) rootstocks were studied in Murcia (Spain). The fruit were harvested for 6 years, and fruit quality and tree size were evaluated after the sixth harvest. Fino 49, Fino 77 and Lisbon trees produced the highest cumulative yield. However, Eureka trees on macrophylla had the highest yield efficiency (cumulative yield/trunk cross-sectional area (TCSA)) due to its small TCSA. There were few differences between Fino group and Lisbon as regards fruit quality; however, Eureka trees on macrophylla produced smaller fruit with a higher concentration of total soluble solids (TSS) and titratable citric acid (TA) than the other varieties. Macrophylla was a better rootstock than sour orange for lemon trees since lemon trees grafted on macrophylla had higher cumulative yield and yield efficiency than those on sour orange. However, sour orange induced the highest TSS and TA in all lemon varieties evaluated.     

Isotopically-labelled nitrogen uptake and partitioning in sweet cherry as influenced by timing of fertilizer application

Sweet cherry (Prunus avium L.) is a fruit of increasing economic importance though it is less significant than other stone fruit species such as peach. Cherry has received little attention concerning nitrogen (N) uptake and dynamics in mature trees. The aim of this work was to determine N uptake and partitioning as influenced by the timing of fertilizer application in 7-year-old sweet cherry trees cultivated in a cold region (Los Antiguos, Santa Cruz, Argentina; 71°38′ W, 46°32′ S). Nitrogen (95 kg ha⁻¹) was applied as ammonium nitrate to a soil with ‘Bing’ sweet cherry trees grafted onto Prunusmahaleb rootstocks. Fertilization was split into two equal applications per treatment, involving either the commercial fertilizer ammonium nitrate or the same fertilizer labelled with ¹⁵N isotope (10% atom.). Treatments consisted of one early spring (full bloom, October 2005) or one summer (late January 2006, 15 days after harvest) application of ¹⁵N ammonium nitrate to three replicate trees. Fruit were harvested in early January and leaves were collected at both full canopy and leaf fall. All trees were excavated in winter (August, 2006). Trees were partitioned into their components: trunk, branches (current-season shoots, 1-year-old and over-1-year-old branches), buds of the same age, small roots (less than 1 mm thick), large roots, leaves (sampled in February and April), and fruit (collected at harvest). Those components were dried and analysed for total N and ¹⁵N content. Total N per tree and N content derived from the fertilizer did not differ between treatments. Summer postharvest ¹⁵N application partitioned not only to structural components (trunk and roots) but also to buds and leaves. Uptake efficiency was significantly (p = 0.0113) higher in the spring than in the summer application (65.7% vs. 37.44%). Nevertheless, 52.5% of N applied in spring was lost due to harvest and summer pruning. This emphasizes the importance of the postharvest N fertilization which increases N accumulation in both reserve organs and buds though, according to our data, it is less efficiently used. The extent of nitrogen uptake, efficiency of use and partitioning in the following growing seasons are still open questions that deserve further research.     

Horticultural performance of ‘Folha Murcha’ sweet orange onto twelve rootstocks

Despite its outstanding position, the Brazilian citriculture is established on a very limited pool of varieties that limits its expansion and restricts the fruit availability throughout the year. This situation determines the urgent necessity of developing alternative scion and rootstock cultivars, with good performance under local conditions. ‘Folha Murcha’ sweet orange (Citrus sinensis (L.) Osbeck) is a late-harvest cultivar, suitable both for the juice processing industry and the fresh fruit market, being described as tolerant to citrus canker (Xanthomonas citri subsp. citri Schaad et al.), and less affected by citrus variegated chlorosis (Xylella fastidiosa Wells et al.). A study was conducted in Bebedouro, São Paulo State, Brazil, to evaluate the horticultural performance of ‘Folha Murcha’ sweet orange budded onto 12 rootstocks: the citrandarin ‘Changsha’ mandarin (Citrus reticulata Blanco) × Poncirus trifoliata ‘English Small’; the hybrid ‘Rangpur’ lime (Citrus limonia Osbeck) × ‘Swingle’ citrumelo (P. trifoliata (L.) Raf. × Citrus paradisi Macfad.); the trifoliates (P. trifoliata (L.) Raf.) ‘Rubidoux’, ‘FCAV’, and ‘Flying Dragon’ (P. trifoliata var. monstrosa); the ‘Sun Chu Sha Kat’ mandarin (C. reticulata Blanco); the ‘Sunki’ mandarin (Citrus sunki (Hayata) Hort. ex. Tanaka); the ‘Rangpur’ limes (C. limonia Osbeck) ‘Cravo Limeira’ and ‘Cravo FCAV’; ‘Carrizo’ citrange (C. sinensis × P. trifoliata), ‘Swingle’ citrumelo (P. trifoliata × C. paradisi), and ‘Orlando’ tangelo (C. paradisi × Citrus tangerina cv. ‘Dancy’). The experimental grove was planted in 2001, using a 7 m × 4 m spacing, in a randomized block design, with five replications and two plants per plot. No supplementary irrigation was applied. Fruit yield, canopy volume, tree tolerance to drought and to citrus variegated chlorosis, and fruit quality were assessed for each rootstock. Trees grafted onto the ‘Flying Dragon’ trifoliate were smaller in size, but had largest yield efficiency when compared to those grafted onto other rootstocks. Lower alternate bearing index was observed on trees budded onto ‘Cravo FCAV’ ‘Rangpur’ lime. Both ‘Rangpur’ lime rootstocks and the ‘Sunki’ mandarin induced higher tree tolerance to drought. The ‘Flying Dragon’ trifoliate induced better fruit quality and higher tolerance to citrus variegated chlorosis (CVC) to ‘Folha Murcha’ trees. A cluster multivariate analysis identified three groups of rootstocks with similar effects on ‘Folha Murcha’ tree performance. Among the 12 evaluated rootstocks, the ‘Flying Dragon’ trifoliate has a unique effect on plant growth, tolerance to drought and CVC, fruit yield and fruit quality of ‘Folha Murcha’ trees, and may be better suited for high-density plantings.     

Tree performance and fruit yield and quality of ‘Okitsu’ Satsuma mandarin grafted on 12 rootstocks

The citriculture in Brazil, as well as in other important regions in the world, is based on very few mandarin cultivars. This fact leads to a short harvest period and higher prices for off-season fruit. The ‘Okitsu’ Satsuma (Citrus unshiu Marc.) is among the earliest ripening mandarin cultivars, and it is considered to be tolerant to citrus canker (Xanthomonas citri subsp. citri Schaad et al.) and to citrus variegated chlorosis (Xylella fastidiosa Wells et al.). Despite having regular fruit quality under hot climate conditions, the early fruit maturation and absence of seeds of ‘Okitsu’ fruits are well suited for the local market in the summer (December through March), when the availability of citrus fruits for fresh consumption is limited. Yet, only a few studies have been conducted in Brazil on rootstocks for ‘Okitsu’. Consequently, a field trial was carried out in Bebedouro, São Paulo State, to evaluate the horticultural performance of ‘Okitsu’ Satsuma mandarin budded onto 12 rootstocks: the citrandarin ‘Changsha’ mandarin (Citrus reticulata Blanco) × Poncirus trifoliata ‘English Small’; the hybrid Rangpur lime (Citrus limonia Osbeck) × ‘Swingle’ citrumelo (P. trifoliata (L.) Raf. × Citrus paradisi Macfad.); the trifoliates (P. trifoliata (L.) Raf.) ‘Rubidoux’, ‘FCAV’ and ‘Flying Dragon’ (P. trifoliata var. monstrosa); the mandarins ‘Sun Chu Sha Kat’ (C. reticulata Blanco) and ‘Sunki’ (Citrus sunki (Hayata) Hort. ex. Tanaka); the Rangpur limes (C. limonia Osbeck) ‘Cravo Limeira’ and ‘Cravo FCAV’; ‘Carrizo’ citrange (Citrus sinensis × P. trifoliata), ‘Swingle’ citrumelo (P. trifoliata × C. paradisi), and ‘Orlando’ tangelo (C. paradisi × Citrus tangerina cv. ‘Dancy’). The experimental grove was planted in 2001, using a 6 m × 3 m spacing, in a randomized block design. No supplementary irrigation was applied. Fruit yield, canopy volume, and fruit quality were assessed for each rootstock. A cluster multivariate analysis identified three different rootstock pairs with similar effects on plant growth, yield and fruit quality of ‘Okitsu’ mandarin. The ‘Flying Dragon’ trifoliate had a unique effect over the ‘Okitsu’ trees performance, inducing lower canopy volume and higher yield efficiency and fruit quality, and might be suitable for high-density plantings. The ‘Cravo Limeira’ and ‘Cravo FCAV’ Rangpur limes induced early-ripening of fruits, with low fruit quality. ‘Sun Chu Sha Kat’ and ‘Sunki’ mandarins and the ‘Orlando’ tangelo conferred lower yield efficiency and less content of soluble solids for the latter rootstock.     

Additional nitrogen fertilization affects salt tolerance of lemon trees on different rootstocks

Irrigation with saline water is one of the major problems in citrus crop in arid and semi-arid regions. Because rootstock and fertilization play an important role in citrus salt tolerance, we investigated the influence of the nitrogen fertilization and rootstock on salt tolerance of 2-year-old potted Fino 49 lemon trees. For that, trees grafted on Citrus macrophylla (M) or Sour orange (SO) rootstocks were watered for 12 weeks with complete nutrient solution containing either 0 mM NaCl (control, C), 50 mM NaCl (S), 50 mM NaCl with an additional 10 mM potassium nitrate (S + N), or 50 mM NaCl with a 1% KNO₃ (S + Nf) foliar spray application. Trees on M were more vigorous than trees on SO and saline treatments reduced leaf growth similarly in trees on both rootstocks. Trees on SO had a lower leaf Cl⁻ and Na⁺ concentration than those on M. Additional soil nitrogen (S + N) decreased leaf Cl⁻ concentration and increased leaf K⁺ concentration in salinized trees on both rootstocks. However, the salinity-induced reduction leaf growth was similar in S + N and S trees. This was due to osmotic effect, beside leaf Cl⁻ and Na⁺ toxicity, played an important role in the growth response of Fino 49 lemon to the salt stress. Additional foliar nitrogen in the S + Nf treatment also reduced leaf Cl⁻ concentration relative to the S treatment but trees from S + Nf treatment had the lowest leaf growth. Net assimilation of CO₂ (ACO₂$A_{\text{C}{\text{O}}_2}$), stomatal conductance (g_s) and plant transpiration were reduced similarly in all three salt treatments, regardless rootstock. Salinity reduced leaf water and osmotic potential such that leaf turgor was increased. Thus, the salinity-induced ACO₂$A_{\text{C}{\text{O}}_2}$ reductions were not due to loss of turgor but rather due to high salt ion accumulation in leaves.     

Identification of drought-induced genes from the leaves of Rangpur lime (Citrus limon (L) Osbeck)

Water stress is one of the limiting factors for citrus production and Citrus species show great variation in their response to drought stress. Although the majority of Citrus rootstocks are sensitive to water stress, Rangpur lime (Citrus limon (L) Osbeck) (RL) shows a high degree of drought tolerance. Therefore, it has been used as a rootstock in drought-prone environments, but mechanisms of drought tolerance are not yet known. In this study, to explore the mechanisms of drought adaptation and tolerance, a subtractive cDNA library was constructed from the leaves of 14-day drought-stressed and non-stressed RL for identification of drought-induced genes. 285 cDNA sequences were obtained from randomly selected clones from the subtracted library containing the drought-induced genes. The expression analyses of 200 cDNAs in 14-day drought treated and untreated RL by macroarray hybridisation revealed that the expression of 56 cDNAs increased two to 11-fold. 30 non-redundant drought-induced genes were identified from these cDNAs and drought induction of eight selected genes was confirmed by a real-time RT-PCR assay suggesting that expressions of these genes were regulated by drought-stress. Genes identified in this study were mostly related with cell rescue and defense pathways involved in drought adaptation and tolerance of RL.     

Rootstock influence on the incidence of rind breakdown in ‘Navelate’ sweet orange

Summary

The influence of three rootstocks, Carrizo citrange (Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf.), Cleopatra mandarin (Citrus reshni Hort. ex Tanaka) and sour orange (Citrus aurantium L.) on the incidence and severity of rind breakdown in ‘Navelate’ sweet oranges was studied over seven years in four orchards. The proportion of affected fruit was greater in trees on Carrizo citrange (60% on an average) followed by Cleopatra mandarin (38%) and then on sour orange (9%). There were also significant differences in the severity of the disorder among rootstocks; more than 35% and 20% of fruit from trees on Carrizo citrange and Cleopatra mandarin, respectively, were rejected for commercialization, whereas only 4% of fruit on sour orange was rejected. Cryo-scanning electron microscopy (SEM) of fruit peduncles showed that average diameter of xylem vessel elements of peduncles of fruits on Carrizo citrange rootstock were 6% and 17% larger than those on Cleopatra mandarin and sour orange, respectively. Defoliation of fruit-bearing branches reduced water loss from fruit, maintained fruit peel water potential at a higher value than that of fruit on undefoliated branches and reduced the proportion and severity of affected fruit. It is concluded that fruit-tree water relationships are related to rind breakdown in ‘Navelate’ oranges and low fruit water content might be responsible for the disorder.     

‘Swingle’ citrumelo propagation by cuttings for citrus nursery tree production or inarching

‘Swingle’ citrumelo [Citrus paradisi MacFaden × Poncirus trifoliata (L.) Raf.] has been extensively used as a rootstock in several citrus growing regions of the World, including Southern Brazil where ‘Rangpur’ lime (Citrus limonia Osbeck) is still the predominant variety despite being affected by several important pathogens. In this case, ‘Swingle’ citrumelo is used to produce nursery trees to establish new orchards or to be inarched in adult and healthy groves in order to change the rootstock. We report herein a system to produce trees on ‘Swingle’ citrumelo more rapidly by budding onto non-rooted cuttings, as well as assessing potential to rapidly multiply ‘Swingle’ through rooting of non-budded cuttings. Therefore, two potential products are described: budded trees and rooted rootstock cuttings. ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] was budded at different heights on cuttings derived from eight-month old rootstocks. Grafted and additional non-budded cuttings were then treated with indole-3-butyric acid (500 mg L⁻¹) or left untreated before rooting. Three types of cuttings were evaluated: softwood, semi-hardwood and hardwood. The use of nursery trees derived from pre-budded hardwood cuttings of ‘Swingle’ citrumelo is an alternative grafting method on this cultivar. Softwood cuttings with one leaf pair were considered the most adequate material for rapid multiplication of ‘Swingle’ citrumelo by cutting. This could be particularly useful for inarching production or conventional budding after transplant of cutting-derived rootstocks.     

Determination of grafting compatibility of grapevine with electrophoretic methods

This study was carried out to determine the efficiency of electrophoretic methods in predicting graft incompatibility of grape cultivars with American rootstocks. Three isoenzyme systems (peroxidase, PER; esterase, EST; acid phosphatase, AcPH) and total protein profiles were obtained in 15 grape cultivars (Vitis vinifera L.) and 12 American rootstocks. Compatibility levels were determined by the band similarities. Field compatibilities were also calculated. Results showed that incompatibility exists between different cultivar–rootstock combinations. AcPH and total protein profiles of the cultivar–rootstock combinations could be suggested to use for forecasting graft incompatibility.     

Agrobacterium tumefaciens-mediated genetic transformation and plant regeneration from a complex tetraploid hybrid citrus rootstock

Agrobacterium-mediated genetic transformation of a tetraploid “tetrazyg” citrus rootstock selection ‘Orange #16’ [Nova mandarin (Citrus reticulata Blanco) + Hirado Buntan pummelo (Citrus grandis L. Osbeck)] × [Cleopatra mandarin (C. reticulata Blanco) + Argentine trifoliate orange (Poncirus trifoliata (L.) Raf.)] was performed. Juvenile epicotyl segments were transformed with a construct containing a bifunctional egfp–nptII fusion gene under the control of an enhanced double CaMV 35S promoter. Our protocol resulted in a reasonable transformation efficiency of 18%. Stable integration of the transgene was confirmed by visual observation of EGFP expression, PCR and Southern blot hybridization. The purpose of this work was to investigate the amenability of novel citrus rootstock germplasm being developed for improved tree size control, soil adaptation, and disease resistance, to existing transformation technologies. Seed trees of such transgenic tetraploids also have potential as trap plants containing potent insecticidal transgenes, due to their inedible fruit and inherent crossing barriers with conventional commercial diploid scion cultivars, and could be planted around producing citrus groves.     

Differential tolerance to iron deficiency of citrus rootstocks grown in nutrient solution

We studied the effects of Fe deficiency on physiological parameters of citrus rootstocks grown in nutrient solution. Three 4-week old rootstocks (‘Troyer’ citrange – Citrus sinensis (L.) Osb. × Poncirus trifoliata (L.) Raf., Citrus taiwanica Tan. and Shim., and ‘Swingle’ citrumelo – Poncirus trifoliata (L.) Raf. × Citrus paradisi Macf.) were grown in nutrient solutions with 0, 5, 10, 15 and 20 μmol Fe dm⁻³. Calcium carbonate (1 g dm⁻³) was added to all solutions to mimic the natural conditions in calcareous soils. For each rootstock, shoot length, number of leaves, and root and shoot dry weights were measured at the end of experiment. Chlorophyll concentration was estimated using a portable SPAD-502 meter calibrated for each rootstock. The amount of nutrients (P, K, Mg, Ca, Fe, Zn, Mn, and Cu) was determined in shoots. Chlorophyll fluorescence parameters (F₀: basal fluorescence; F_m: maximum fluorescence; F_v = F_m − F₀: variable fluorescence) were measured with a portable fluorimeter. ‘Troyer’ citrange rootstock was the most tolerant to Fe deficiency. These plants grew more and accumulated more chlorophyll and nutrients than the others in the presence of low levels of Fe (10 μmol Fe dm⁻³). ‘Swingle’ citrumelo plants needed 20 μmol Fe dm⁻³ in the nutrient solution to secure adequate growth. ‘Taiwanica’ orange rootstock had an intermediate behaviour, but could be distinguished from ‘Troyer’ citrange based on fluorescence parameters, since there was a variation in the basal fluorescence in the former, whereas in ‘Troyer’ citrange the basal fluorescence was not affected by the supply of Fe.     

Orange varieties as interstocks increase the salt tolerance of lemon trees

Summary

We investigated the ability of interstocks to increase salt tolerance in lemon trees. We compared 2-year-old ‘Verna’ lemon trees [Citrus limon (L.) Burm.; VL] grafted on Sour Orange (C. aurantium L.; SO) rootstock either without an interstock (VL/SO), or interstocked with ‘Valencia’ orange (C. sinensis Osbeck; VL/V/SO), or with ‘Castellano’ orange (C. sinensis Osbeck; VL/C/SO). Trees were grown under greenhouse conditions and supplied with nutrient solutions containing 0, 30, or 60 mM NaCl. Reductions in leaf growth caused by salt treatment were greatest in non-interstocked (VL/SO) trees, followed by VL/C/SO trees, and were the least in VL/V/SO trees. Although the levels of Cl^? and Na⁺ ions in the roots and stems were not affected by either interstock, leaf concentrations of Cl^? and Na⁺ were higher in VL/SO trees than in VL/C/SO or VL/V/SO trees, suggesting that an interstock in Citrus trees could limit the uptake and transport of such ions to the shoots. Saline-treated VL/SO trees also tended to have the lowest shoot:root (S:R) ratios; so, overall, there was a negative relationship between S:R ratio and leaf Cl- ion concentration. Leaf transpiration (E_leaf) may also be involved in the reduction in leaf Cl^? concentration, as interstocked trees had lower E_leaf values at mid-day than non-interstocked trees. Salinity increased leaf concentrations of Ca²⁺ in VL/C/SO trees and increased both leaf K⁺ and N concentrations in all trees, regardless of interstock. Salinity reduced leaf water potentials and osmotic potentials, such that leaf turgor was increased in all trees.     

Long-term performance of ‘Ellendale’ mandarin on seven commercial rootstocks in sub-tropical Australia

‘Ellendale’ mandarin (Citrus reticulata Blanco) on seven commercially important rootstocks was assessed over a 26-year period on a site not previously planted to citrus. Tree yield data collected each season from 1969 to 1991 showed that yields were highest on ‘Lockyer’ rough lemon (C. jambhiri Lush) and lowest on ‘Emperor’ mandarin. Yields for the two citranges (C. sinensis (L.) Osbeck × Poncirus trifoliata (L.) Raf.), ‘Troyer’ and ‘Carrizo’, were intermediate, and somewhat higher than those for two selections of sweet orange (C. sinensis (L.) Osbeck), ‘Parramatta’ and ‘Joppa’. Linear regression was used to examine changes in yielding pattern across the 23 seasons of fruit production. This revealed that ‘Troyer’ was comparable with the rough lemon selections throughout most of the experiment and significantly higher than ‘Carrizo’ during certain periods in the middle of the experiment. Similarly, while ‘Joppa’ and ‘Parramatta’ produced near-identical results during most of the experiment, ‘Joppa’ out-performed ‘Parramatta’ toward the end of the experiment. ‘Emperor’ showed a low yield trend throughout the experiment, often more than 50 kg per tree per year less than the rough lemon and citrange selections. Detailed assessment of biennial bearing showed a significant pattern commencing when trees were approximately 15 years old and intensifying until the end of the experiment. However, rootstock had no effect on the biennial bearing behaviour of ‘Ellendale’ mandarin. Correlations of cumulative yields at each harvest date with the final cumulative yield (for 23 seasons of cropping) showed instability up until approximately the eighth year of cropping after which it increased steadily, suggesting that in similar experiments there may be only marginal value in assessing yields beyond about the 10th season. Fruit quality assessments made in two consecutive seasons showed expected trends, with rough lemon (both ‘Lockyer’ and ‘Mazoe’) producing the largest and heaviest fruit, with thicker rinds, lower juice content, and lower Brix. The citrange selections (‘Troyer’ and ‘Carrizo’) resulted in fruit quality comparable to the sweet oranges (‘Parramatta’ and ‘Joppa’), with ‘Troyer’ producing significantly higher Brix levels than any other rootstock. All rootstocks produced leaf nutrient levels close to the desirable range, with significant differences for the elements P, Mg, Ca, Mn, and B. These differences separated the seven rootstocks into categories consistent with their genetic relatedness.     

The effect of grafting on nitrogen use in determinate field-grown tomatoes

Grafting tomato (Solanum lycopersicum L.) onto disease resistant rootstocks has grown in use in North America over the past two decades. Rootstocks have traditionally been bred and used for their resistance packages to numerous soil-borne diseases but some rootstocks appear to improve scion yield and vigour in comparison to non-grafted plants in conditions lacking disease challenge. In this study, the tomato rootstocks ‘Maxifort’ or ‘RST-106’ were used to determine if vigour improved ‘Tribute’ scion traits, especially yield, and if marketable yield could be maintained in grafted plants at reduced nitrogen fertiliser inputs. Plants were grown in an open-field plasticulture production system at five rates of nitrogen from 0 kg ha^?1 to 224 kg ha^?1 applied via drip irrigation. Marketable yield was significantly affected by nitrogen rate and rootstock in both years. ‘Tribute’ grafted onto ‘Maxifort’ rootstock had the greatest, most consistent impact and increased marketable yield 15% and 30% in 2013 and 2014, respectively, compared to the non-grafted ‘Tribute’. Our findings suggest that some rootstocks can increase scion growth and yield but do not differentially respond to decreased nitrogen rates.     

Influence of no-tillage and organic mulching on tomato (Solanum Lycopersicum L.) production and nitrogen use in the mediterranean environment of central Italy

In conservation tillage systems based on legume mulches it is important to optimize N management strategies. The present study evaluated the effect of some winter legume cover crops converted into mulches on the following no-tillage tomato (Solanum Lycopersicum L.) yield, tomato nitrogen uptake, tomato use efficiency (NUE), soil nitrate and the apparent N remaining in the soil (ARNS) in a Mediterranean environment. Field experiments were carried out from 2002 to 2004 in a tomato crop transplanted into: four different types of mulches coming from winter cover crops [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterranem L.), snail medic (Medicago scutellata L. Miller), and Italian ryegrass (Lolium multiflorum Lam.)]; a conventional tilled soil (CT); and a no-tilled bare soil (NT). All treatments were fertilized with three different levels of nitrogen (N) fertilizer (0, 75, and 150 kg N ha⁻¹). Cover crop above-ground biomass at cover crop suppression ranged from 4.0 to 6.7 t ha⁻¹ of DM and accumulated from 54 to 189 kg N ha⁻¹, hairy vetch showed the highest values followed by subclover, snail medic and ryegrass. The marketable tomato yield was higher in no-tilled legume mulched soil compared to no-tilled ryegrass mulched soil, CT, and NT (on average 84.8 vs 68.7 t ha⁻¹ of FM, respectively) and it tended to rise with the increase of the N fertilization level. A similar trend was observed on tomato N uptake. Hairy vetch mulch released the highest amount of N during tomato cultivation followed by subclover, snail medic, and ryegrass (on average 141, 96, 90 and 33 kg N ha⁻¹). The tomato NUE tended to decrease with the increase of the N fertilization rates, it ranged from 39 to 60% in no-tilled legume mulched soil and from −59 to 30% in no-tilled ryegrass mulched soil when compared to the CT. The soil NO₃-N content and the ARNS was always higher in the soil mulched with legumes compared to the soil mulched with ryegrass and in NT and CT. This study shows that direct transplanting into mulches coming from winter legume cover crops could be useful for improving the yield and the N-uptake in a no-tillage tomato crop. Furthermore, considering the high N content in the upper soil layer and the remaining N content in the organic mulch residues after tomato harvesting, there is a large amount of N potentially available which could be immediately used by an autumn–winter cash crop.     

The effect of sprinkler and drip irrigation on lime-induced chlorosis of citrus

Trials were carried out on grapefruit (Citrus paradisi Macf.) ‘Marsh Seedless’ and orange (C. sinensis L.) ‘Valencia’, both on Sour orange (C. aurantium L.) rootstock. Shortening the interval between sprinkler irrigations increased the occurrence of lime-induced chlorosis (LIC), as indicated by reduced leaf chlorophyll and peroxidase enzyme activity. Drip irrigation, on the other hand, corrected LIC and increased leaf chlorophyll, peroxidase activity and photosynthesis.     

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

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