Mandarin Rootstocks Research Articles

Metabolic profiling of drought tolerance: Revealing how citrus rootstocks modulate plant metabolism under varying water availability

Water stress is a major environmental factor affecting Citrus spp. and Rangpur lime is a drought-tolerant rootstock used to enhance orange yield in rainfed orchards. Here, we combined morpho-physiological analyses with metabolic profiling of roots and leaves of Valencia orange scions grafted onto Rangpur lime, Swingle citrumelo or Sunki mandarin rootstocks under water deficit. Our aim was to present a comprehensive spatio-temporal evaluation of citrus responses to drought and highlight the metabolic adjustments associated with drought tolerance induced by Rangpur lime. Plant responses were evaluated during the initial phase of reduction in water availability, when water deficit was maximum and also after rehydration. Fifty-eight primary metabolites were modulated by water deficit, mainly amino acids, organic acids and sugars. Metabolic changes indicated adjustments related to osmotic, energetic and redox processes under low water availability, which were dependent on rootstock and varied between roots and leaves and along the experimental period. Rangpur lime prioritized root growth in the initial phase of water deficit, which was linked to less sugar accumulation, changes in nucleotide metabolism and downregulation in Shikimic acid pathway. After rehydration, the resume of shoot growth was associated with high accumulation of arginine and asparagine. The better performance of Rangpur lime seems to be associated with its high sensitivity of roots to changes in water availability and possible signaling compounds, such as auxin and nitric oxide, have been suggested.

Comparative Transcriptome Profiling of Salinity-Induced Genes in Citrus Rootstocks with Contrasted Salt Tolerance

Salinity is one of the most destructive environmental challenges for citriculture worldwide, and all climate change scenarios are predicting an increased impact of salinity on citrus orchards. Citrus cultivars are grown as grafts on various rootstocks to provide specific adaptation to abiotic stress and tolerance to major diseases such as citrus tristeza virus. To understand rootstock–scion interactions with regard to salinity, transcriptome profiling of mRNA expression was analyzed for 12 candidate genes in leaves, shoots, and roots of five Hernandina clementine scions grafted on Rangpur lime (LR), Volkamer lemon (CV), Carrizo citrange (CC), sour orange (Big), and Cleopatra mandarin (MC) rootstocks in response to moderate and severe salinity. qRT-PCR analysis revealed differential gene expression that varied by rootstock, salinity level, and tissue. The majority of induced genes were those involved in ion transporter proteins (mainly NHX1 and HKT1 genes), Cl− homeostasis (CCC1 gene), biosynthesis and accumulation of compatible osmolytes, proline (P5CS gene) and glycine betaine (CMO gene), accumulation of proteins (LEA2 gene), and ROS scavenging antioxidant activity (mainly APX). We show that these expression patterns could explain the relative tolerance of the used rootstocks and report new insights on the main salt tolerance mechanisms activated by these rootstocks.

Vegetative shoot flush dynamics of ‘Pera’ sweet orange on three rootstock cultivars

The dynamics and intensity of new shoot flushes of ‘Pera’ sweet orange scions [Citrus × sinensis (L.) Osbeck] grafted onto ‘Rough’ lemon (Citrus × limonia var. jambhiri Lush.), ‘Swingle’ citrumelo [Citrus × aurantium var. paradisi x Poncirus trifoliata (L.) Raf.] and ‘Sunki’ mandarin (Citrus reticulata ‘Sunki’) rootstocks were evaluated in the field at a citrus farm located in a northern region of the state of Sao Paulo, Brazil. Every 20 days for 16 months, new shoots were counted within a square frame of 0.25 m2 set on the central portion of the canopy and classified based on their phenological stages. Trees on ‘Swingle’ rootstock produced a lower area under the flush shoot dynamics curve (AUFSD) and mean number of new shoots than trees on ‘Rough’ lemon or ‘Sunki’ mandarin. For trees on all three rootstocks, new shoot intensities varied significantly over time with the greatest number of new shoots developing during late spring and early summer. Increases in minimum air temperature and available soil water were important indicators of overall emergence of new shoots. 

IMPACT OF GIBBERELLIC ACID TREATMENTS ON GERMINATION OF CLEOPATRA MANDARIN SEEDS

This study was carried out throughout two successive seasons (2021 and 2022) for investigating GA3 pre-sowing soak solutions influence on Cleopatra mandarin seeds (Citrus reshni L.). It was aimed to enhance the Cleopatra mandarin seeds germination process, as well as seedlings vigor. Thus, seeds of Cleopatra mandarin rootstock were subjected to soaking for 24 hours in GA3 solutions at 200, 250, and 300 ppm as well as soaking in tap water (control treatment), for investigating their effect on some germination and growth parameters. Data obtained during both experimental seasons revealed obviously that all GA3 treatments increased significantly both germination measurements (total germinated seeds & germination %) and some growth parameters as compared to control (soak for 24 hours in tap water). However, soaking in GA3 at 250 and 300 ppm concentrated solutions particularly were statistically the most effective in this study.

Rootstocks and planting types on root architecture and vegetative vigor of ‘Pera’ sweet orange trees

ABSTRACT Root architecture affects plant growth and agricultural productions. Although it is related to genetic factors, soil physical limitations can affect the root system and volume of explored soil, compromising plant growth and fruit production. Considering the need to mitigate these restrictions, the objective of the present study was to evaluate two planting types (planting of protected seedlings and planting of seeds in definitive place) and two scion-rootstock combinations (‘Pera’ sweet orange, CNPMF D-6 selection, combined with ‘Santa Cruz Rangpur’ lime and ‘Sunki Tropical’ mandarin rootstocks). The experiment was conducted at the Lagoa do Coco Farm, Rio Real, BA, Brazil, in a Oxisol under rainfed conditions. Biometric, physiological, and soil water content evaluations were made during the experiment. Soil mechanical resistance to root penetration and root system characteristics were also evaluated. Roots were concentrated on the soil surface layers (0-0.40 m), extending horizontally up to 1.50 m from the plant, regardless of the management practices used. The total root length in each root diameter classes studied, root length density, and total root mean diameter were higher for planting of protected seedling, resulting in greater root development. Plants from ‘Pera’ sweet orange scion grafted on ‘Santa Cruz Rangpur’ lime rootstock had earlier production and were more vigorous. Soil structure affects root growth, and the root distribution up to 0.40 m depth is correlated with plant vigor, yield, and water status under rainfed conditions.

Sunki mandarin and Swingle citrumelo as rootstocks for rain-fed cultivation of late-season sweet orange selections in northern São Paulo state, Brazil

ABSTRACT In Brazilian regions affected by the citrus sudden death disease, sweet orange cultivation depends on the use of resistant rootstocks. Rangpur lime was mainly replaced by Swingle citrumelo and Sunki mandarin rootstocks, more drought-sensitive ones. The diversification of scion selections is also desirable aiming at the increasing demand for not from concentrate orange juice (NFC) that requires high-quality fruits. In this work, we evaluated the performance of 6 selections of Valencia (IAC, Dom Joao, Late Burjasot IVIA 35-2, Rhode Red SRA 360, Temprana IVIA 25 and Campbell) and Natal IAC sweet oranges grafted onto Swingle citrumelo and Sunki mandarin. The planting occurred in 2001 under rain-fed cultivation in Bebedouro, northern Sao Paulo state, Brazil. The outline was made through randomized blocks in a 7 × 2 factorial design (selections × rootstock), with 4 replications and 2 trees in unit. Both rootstocks performed well in the region. Sunki mandarin rootstock induced greater tree size and production per plant to the scion selections, 38 and 21%, respectively, plus higher precocity of production compared to Swingle citrumelo. The later determined a greater productive efficiency, as well as a greater percentage of juice in general, albeit with lower concentrations of soluble solids and acidity. Natal IAC, Valencia IAC and Rhode Red Valencia selections presented a higher accumulated production, on average, 218.6 kg∙plant−1 (2004 – 2008), and a higher productive efficiency (kg fruit∙m−3 of canopy) due to their smaller tree size. All assessed selections produced fruits with high soluble solids content that were suitable for juice processing.

EFFECT OF FOLIAR APPLICATION SALICYLIC ACID ON CITRUS ROOTSTOCKS TOLERANCE TO SOIL SALINITY

This experiment was carried out at the private nursery located at Baquba city/ Diyala governorate during 2015 agricultural season on three years old Citrus rootstocks seedlings to study the effect foliar application of salicylic acid on seedlings tolerance to soil salinity. The experiment included 24 treatment represented three factors: soil salinity levels (1.14,4.62 and 5.30 dSm-1) , two levels of salicylic acid (0 and 250 mg.l -1) and four citrus rootstocks (Sour orange, Cleopatra mandarin, Volkamariana lemon and Troyercitrange ),and their interactions with three replications . The results showed that: increasing soil salinity reduced most studied growth parameters (number and length of branches, number of leaves and fresh weight of the vegetative and root system). Salicylic acid application caused an increment in number of leaves, fresh and dry weight of root system. Citrus rootstocks Troyercitrange was superior on other rootstocks by giving highest values branches length, whereas Cleopatra mandarin rootstock was superior in the number of leaves.

Interaction between Phytophthora nicotianae and Candidatus Liberibacter asiaticus damage to citrus fibrous roots

Huanglongbing (HLB) is associated with the phloem-limited bacterium, Candidatus Liberibacter asiaticus (Las). Phytophthora nicotianae (P.n.) causes root rot of citrus, which reduces water and nutrient uptake by citrus fibrous roots. The discovery that Las damage to fibrous roots occurs before tree canopy symptoms develop led to the prediction that Las root infection directly damages roots and may interact with soil-borne pathogens to cause further damage. Hence, comparison of root damage by Las and P.n. alone or in combination was carried out on seedlings of Cleopatra mandarin (Citrus reticulata Blanco) rootstock to evaluate the possible interaction of Las and P.n. and their relative contribution to fibrous root loss. The results demonstrated that i) roots of seedlings have a similar level of damage when inoculated with Las or P.n., and coinoculation causes comparable damage as each pathogen alone; and ii) Las infection increases and decreases P.n. infection incidence overtime without following a clear progression.

Mandarina Dancy: una nueva alternativa para la citricultura

Las principales regiones citrícolas del mundo se encuentran ubicadas entre los 20 a 40° de latitud norte y sur. En estas condiciones los frutos de mandarina obtienen las mejores calidades internas y externas. En el piedemonte llanero de Colombia (trópico bajo) se cultiva la selección regional conocida como Arrayana (Citrus reticulata Blanco). Esta variedad se caracteriza por una alta concentración de la cosecha en los meses de diciembre y enero debido a la presencia de una sola floración principal en el año (dos semanas después del inicio de lluvias); y calidad externa aceptable que le impide ser altamente competitiva con el creciente mercado de mandarinas importadas. Ambas condiciones disminuyen la rentabilidad de los citricultores de la región. Con el propósito de identificar y desarrollar genotipos de mandarina que obtengan calidades sobresalientes en condiciones del trópico bajo, se evaluó en el Centro de Investigación La Libertad de Corpoica, en Villavicencio (Meta), desde el año 2000, la variedad Dancy. A cada árbol se le llevaron registros anuales de: crecimiento, producción por planta y características físicas y químicas de los frutos. Cada árbol se tomó como unidad experimental, siendo en total seis; a la información se le realizó estadística descriptiva. La información de la variedad Dancy (Citrus reticulata Blanco var. Dancy) se comparó con la información experimental de la mandarina Arrayana; ambas injertadas en el patrón mandarina Cleopatra (Citrus reshni hort. ex Tanaka). La calidad sobresaliente de fruto de Dancy (SST: 10,8; IM: 18,1; peso fresco: 145,85 g) y producción acumulada confirma la adaptación de la variedad a las condiciones del piedemonte del Meta; mientras que la buena aceptación de los consumidores, sugiere su recomendación para ser plantada en el piedemonte llanero como complementaria a la producción de Arrayana. El clon evaluado de Dancy es susceptible a Alternaria lo que podría limitar su cultivo en régimen de lluvias bimodal y de alta HR % en el trópico medio.

<b>The influence of rootstock and time of harvest on the fruit quality during storage of in two grapefruit cultivars

The effects of the ‘Cleopatra’ mandarin and ‘Swingle’ citrumelo rootstocks and time of harvest on the quality of cold-stored (13°C and 90% R.H.) ‘Ruby Red’ and ‘Star Ruby’ grapefruit grown under the tropical conditions prevalent in Ceará state, Brazil, were evaluated. Fruit quality was assessed by mass loss and peel color, the percentage of juice, soluble solids, titratable acidity, pH, maturity index, and ascorbic acid content. The results suggested that ‘Ruby Red’ and ‘Star Ruby’ grapefruit presented similar amounts of soluble solids, pH, titratable acidity and ascorbic acid levels at harvest, and the trends over the course of storage followed similar patterns for both cultivars, regardless of rootstock. The influence of scion-rootstock combination on the studied variables was dependent on the time of harvest. The peel color of ‘Ruby Red’ grafted on ‘Swingle’ citrumelo is more vivid and redder when harvested in October than when harvested in August. ‘Ruby Red’ and ‘Star Ruby’ grapefruit harvested in October are sweeter, less acidic, juicier, and richer in ascorbic acid than those harvested in August. ‘Cleopatra’ mandarin rootstock might favor ascorbic acid levels at harvest, but the fruit may lose more weight during storage.

Assessing Five Citrus Rootstocks for NaCl Salinity Tolerance Using Mineral Concentrations, Proline and Relative Water Contents as Indicators

A B S T R A C T Changes in concentrations of Na, Cl and K, proline and Relative Water Contet (RWC) of five citrus species (Cleopatra mandarin, Carrizo citrange, Tiwanica, Bacraii and Shaker) grown in four NaCl salinity levels (0, 25, 50 and 75 mM NaCl) for the purpose of assessing their magnitude of susceptibility to salinity and estimating the salt tolerance degree were studied. The Na and Cl concentrations increased whilst K concentration in leaves decreased with increasing NaCl concentration in the rootzone. Shaker and Cleopatra mandarin accumulated optimal concentration of the ions in their tissues. Increasing NaCl concentration reduced RWC and increased proline content in plant tissues. Shaker and Cleopatra mandarin rootstocks maintained relatively higher leaf RWC and proline in comparison to other rootstocks. Cleopatra mandarin and Shaker showed to be markedly less affected by salinity up to 50 mM NaCl and could bear the highest salinity levels (75 mM) imposed in this study.

First report of the fungus Fomitiporia maxonii Murrill causing citrus wood rot in commercial orange and grapefruit groves in Cuba

Cuban citriculture has recently been affected by important pests and diseases including black citrus aphid Toxoptera citricida Kirkaldy, citrus leafminer Phyllocnistis citrella Stainton, Asiatic citrus psyllid Diaphorina citri Kuwayama, Citrus tristeza disease, and huanglongbing. This complex of ‘invasive species’ is thought to be contributing to the increasing decline of commercial citrus groves. During several surveys carried out in commercial citrus areas of several provinces in Cuba, symptoms of dieback, characterized by the presence of abundant dry branches and wood rot were detected on Criolla Valencia orange, Marsh grapefruit trees on sour orange, and Cleopatra mandarin rootstocks. Samples of branches and trunk wood were processed and a fungus was isolated from all samples. Morphological, physiological and molecular characterization demonstrated that the isolated agent is Fomitiporia maxonii Murrill. The incidence of affected trees was high in most surveyed groves, reaching 100% in old groves. Symptoms similar to the ones found in naturally infected trees were reproduced on trees inoculated with pure cultures of the fungus, and the fungus was recovered in culture from inoculated trees, thus fulfilling Koch's postulates. This is the first report of an association of F. maxonii with citrus wood rot in Cuba.

Effect of trickle irrigation on root development of the wet bulb and 'pera' orange tree yield in the state of São Paulo, Brazil

The aim of this study was to evaluate the effect of different microirrigation designs on root system distribution in wet bulb region, orange orchard yield and quality of orange fruits. The experiment was installed as random blocks with five treatments and four replicates in an orchard of 'Pêra' orange trees grafted on 'Cleopatra' mandarin rootstock. The treatments consisted of: one drip line (T1), two drip lines (T2), four drip lines (T3) per planting row, microsprinkler irrigation (T4) and without irrigation (T5). Irrigation treatments favored yield and ºBrix. The treatment with a single drip line (T1) showed the greatest quantity of roots in relation to the treatments T2 and T3.

Efeito da carga pendente na qualidade de frutos de laranjeira 'Valência'

Algumas espécies de citros apresentam produção irregular ao longo dos anos. Além da safra irregular, a alternância de produção pode interferir na qualidade dos frutos, característica cada vez mais valorizada pelo mercado citrícola. O objetivo do trabalho foi avaliar o efeito da carga pendente na qualidade dos frutos da laranjeira 'Valência'. O experimento foi conduzido com laranjeiras 'Valência' enxertadas em tangerineiras 'Cleópatra' em condição de campo. Em janeiro de 2007, metade das plantas teve todos os seus frutos retirados, enquanto a outra metade permaneceu intacta. As plantas que tiveram seus frutos retirados apresentaram, em setembro de 2007, floração mais intensa e, portanto, uma Alta Carga de frutos (AC, 752 frutos/árvore) em 2008, quando comparadas às plantas que não tiveram seus frutos retirados, que apresentaram Baixa Carga de frutos (BC, 317 frutos/árvore). Os frutos maduros, colhidos em dezembro de 2008, foram analisados quanto à massa, teor de sólidos solúveis, acidez titulável, espessura e cor da casca, teor de suco e número de sementes. Na safra seguinte, de 2009, as avaliações das características físicoquímicas dos frutos foram repetidas nas mesmas árvores, mas durante quatro momentos entre o período de frutificação e a colheita, em novembro de 2009. Na safra de 2008, houve diferença na massa individual dos frutos com valores de 172 e 158g nas plantas BC e AC, respectivamente. O teor de sólidos solúveis, acidez titulável, teor de suco nos frutos, espessura da casca e o índice tecnológico foram semelhantes entre os tratamentos, nas safras de 2008 e 2009. Entretanto, vale considerar que, como a produção de frutos nas plantas AC, na safra de 2008, foi 2,2 vezes maior se comparada às das plantas BC (AC: 2,9 caixas/planta e BC: 1,3 caixa/planta), a quantidade total de sólidos solúveis produzida por planta também foi maior. Não houve influência da carga pendente de frutos no teor de açúcares (glicose, frutose e sacarose) no suco e na cor da casca durante o desenvolvimento dos frutos. Apesar de reduzir a massa do fruto, a diferença de carga pendente observada em laranjeira 'Valência' não influenciou na qualidade dos frutos quando considerado, como destino da fruta, a indústria citrícola.

Rootstocks Affect Tree Growth, Yield, and Juice Quality of ‘Marsh’ Grapefruit

Two adjacent rootstock trials were conducted in the east coast Indian River region of Florida with ‘Marsh’ grapefruit (Citrus paradisi Macf.) scion. The objective was to find rootstocks to replace sour orange (C. aurantium L.) because of losses to citrus tristeza virus, and to replace Swingle citrumelo [C. paradisi × Poncirus trifoliata (L.) Raf.] because of its limited usefulness in certain poorly drained coastal sites. The trials were conducted in randomized complete blocks with 12 single-tree replicates spaced 4.6 × 6.9 m. The soils were of the Wabasso and Riviera series. The first trial consisted largely of trees on citrange [C. sinensis (L.) Osb. × P. trifoliata] and citrumelo rootstocks, ‘Cipo’ sweet orange (C. sinensis), and various hybrid rootstocks. The second trial involved mandarin rootstocks (C. reticulata Blanco) and sour orange and related rootstocks. Trees were grown for 7 years and yield and juice quality data were collected for the last 4 years of that period. Those rootstocks identified as the most promising, based on combinations of smaller tree size and high productivity and juice quality, were two Sunki mandarin × Swingle trifoliate orange (TF) hybrids (C-54, C-146), a Sunki mandarin × Flying Dragon TF hybrid, C-35 citrange, and a Cleopatra mandarin × Rubidoux TF hybrid (×639). The trees on these five rootstocks cropped well leading to soluble solids (SS) values of 3000 to 4000 kg/ha when they were 7-years old. The trees on C-54 and C-146 were relatively large, somewhat taller than trees on sour orange, whereas those on C-35 and the Sunki × Flying Dragon hybrid were smaller and similar to sour orange in tree height. Fruit quality among the trees on C-35 and the Sunki × Flying Dragon hybrid had relatively high SS concentration (better than sour orange), and the other three rootstocks had relatively lower solids concentration (poorer than sour orange). The trees on C-35 and the Sunki × Flying Dragon hybrid would be good candidates for higher density orchards.

Effect of foliar sprays with Copper and Zinc in the vegetative characters of citrus rootstocks

This experiment was carried out in the lath house, Department of Horticulture, College of Agriculture, University of Baghdad during growing season of 2004. Sour orange, mandarin and grapefruit seedling with 6 months old were foliar sprayed with CuSO4. H2O at a rate of 1 gm/ l. water and ZnSO4. H2O at a rate of 2 gm/ l water while the control treatment was sprayed with distilled water. After two weeks half the number of the seedlings were inoculated with Phytophthora citrophthora to investigate the influence of these chemicals in controlling the gummosis in these different rootstocks through their vegetative growth. The experimental results shows that the type of rootstock influenced the vegetative growth parameters.i.e. Soure orange seedlings significantly characterized by the highest number of root branches 41.64 branch/ seedling. Mandarin rootstocks shows the highest plant height of 28.95 cm and root length of 15.01 cm. Grapefruit rootstocks gave the highest dry weight of vegetative and root growth from the other types (2.02 gm, 1.12 gm/ plant). The treatments were significantly influenced the all rootstocks by increasing or decreasing average growth rates. Spraying plants without inoculation (T3) causes 16.14% an increases in leaf area and the average of plant height by 11.07% and the average number of root branches by 21.64% and average of root length by 13.18%. The interaction between the types of the rootstocks and the chemicals indicated that grapefruit seedling sprayed with Zn was superior in the height of plant, dry weight of vegetative and roots growth, leaf area, while the interaction between foliar sprays with Zn and inoculation and the mandarin gave the highest root length. The same treatment with sour orange seedling gave the highest number of root branches.

Citrus asymmetric somatic hybrids produced via fusion of gamma-irradiated and iodoacetamide-treated protoplasts

The objective of this study was to produce citrus somatic asymmetric hybrids by fusing gamma-irradiated protoplasts with iodoacetamide-treated protoplasts. Protoplasts were isolated from embryogenic suspension cells of grapefruit (Citrus paradisi Macfad.) cultivars Ruby Red and Flame, sweet oranges (C. sinensis Osbeck) 'Itaboraí', 'Natal', Valencia', and 'Succari', from 'Satsuma' (C. unshiu Marcow.) and 'Changsha' mandarin (C. reticulata Blanco) and 'Murcott' tangor (C. reticulata x C. sinensis). Donor protoplasts were exposed to gamma rays and receptor protoplasts were treated with 3 mmol L-1 iodoacetamide (IOA), and then they were fused for asymmetric hybridization. Asymmetric embryos were germinated, and the resulting shoots were either grafted onto sour orange, rough lemon or 'Swingle' (C. paradisi x Poncirus trifoliata) x 'Sunki' mandarin rootstock seedlings, or rooted after dipping their bases in indol-butyric acid (IBA) solution. The products were later acclimatized to greenhouse conditions. Ploidy was analyzed by flow cytometry, and hybridity was confirmed by amplified fragment length polymorphism (AFLP) analysis of plantlet DNAsamples. The best treatment was the donor-recipient fusion combination of 80 Gy-irradiated 'Ruby Red' protoplasts with 20 min IOA-treated 'Succari' protoplasts. Tetraploid and aneuploid plants were produced. Rooting recalcitrance was solved by dipping shoots' stems in 3,000 mg L-1 IBA solution for 10 min.

Seasonal and diurnal changes in photosynthetic limitation of young sweet orange trees

This study tests the hypothesis that potted sweet orange plants show a significant variation in photosynthesis over seasonal and diurnal cycles, even in well-hydrated conditions. This hypothesis was tested by measuring diurnal variations in leaf gas exchange, chlorophyll fluorescence, leaf water potential, and the responses of CO 2 assimilation to increasing air CO 2 concentrations in 1-year-old ‘Valência’ sweet orange scions grafted onto ‘Cleopatra’ mandarin rootstocks during the winter and summer seasons in a subtropical climate. In addition, diurnal leaf gas exchange was evaluated under controlled conditions, with constant environmental conditions during both winter and summer. In relation to our hypothesis, a greater rate of photosynthesis is found during the summer compared to the winter. Reduced photosynthesis during winter was induced by cool night conditions, as the diurnal fluctuation of environmental conditions was not limiting. Low air and soil temperatures caused decreases in the stomatal conductance and in the rates of the biochemical reactions underlying photosynthesis (ribulose-1,5-bisphosphate (RuBP) carboxylation and RuBP regeneration) during the winter compared to the values obtained for those markers in the summer. Citrus photosynthesis during the summer was not impaired by biochemical or photochemical reactions, as CO 2 assimilation was only limited by stomatal conductance due to high leaf-to-air vapor pressure difference ( VPD) during the afternoon. During the winter, the reduction in photosynthesis during the afternoon was caused by decreases in RuBP regeneration and stomatal conductance, which are both precipitated by low night temperature.

In Vitro Propagation of Citrus Rootstocks

Present investigation was conducted to standardize a protocol for in-vitro propagation of citrus rootstocks viz. Rough lemon, Cleopatra mandarin Pectinifera and Troyer citrange. The shoot tip explant was found better for callus induction of these rootstocks than the nodal segment. Maximum callus formation (40.0% and 23.3%) of shoot tip explants was obtained in Cleopatra mandarin, Pectinifera, and Rough lemon and Troyer citrange, respectively in treatment MS basal media + 0.5mg/l Kin, 2.0mg/l NAA, and 2.0mg/l 2, 4-D. Furthermore, the maximum number of shoots per explant was obtained through the callus in Pectinifera, Rough lemon and Cleopatra mandarin in MS basal media + BAP 1mg/l. Maximum rooting of shoots (1.11%) was noted in rootstock Rough lemon followed by Cleopatra mandarin for the ½ MS media supplemented with 10mg/l IBA. Although the callus development and bud proliferation was recorded in rootstock Troyer citrange however, shoot and root formation did not occur. The potting media consisting of soil, sand and FYM in the ratio of 1:1:1 by volume was better with maximum survival rate of hardened plants six weeks after transferring to the pots under greenhouse for Rough lemon followed by Pectinifera and Cleopatra mandarin rootstock.

Growth, yield and fruit quality of ‘Marisol’ clementine grown on four rootstocks in Egypt

To evaluate the most appropriate rootstocks for mandarin production in Egypt, vegetative growth, yield and fruit quality of ‘Marisol’ clementine (as newly introduced cultivar in Egypt) grafted on Sour orange (the common rootstock), Cleopatra mandarin, Carrizo citrange and ‘Swingle’ citrumelo were evaluated under the Egyptian conditions during 2004/2005 and 2005/2006 seasons. Trees were grown in a private farm at ‘Wady El-Mullak’ region, Ismailia Governorate (Latitude, 30°36′ N; longitude, 32°14′ E; Altitude, 10 m above sea level). ‘Marisol’ clementine trees budded on Sour orange showed higher vegetative growth parameters (canopy circumference and diameter, tree volume, scion trunk girth) than trees on Carrizo citrange, ‘Swingle’ citrumelo and Cleopatra mandarin rootstocks, except the tree height which was shorter than those on Carrizo citrange and ‘Swingle’ citrumelo (in the first season) or similar (in the second season), while the trees budded on Cleopatra mandarin were the shortest. The highest affinity was found with the Sour orange, followed by Cleopatra mandarin and Carrizo citrange, while the lowest affinity was found with ‘Swingle’ citrumelo. Trees on Sour orange produced the higher yield than those on Cleopatra mandarin, ‘Swingle’ citrumelo and Carrizo citrange rootstocks. The trees on Sour orange had the highest average yield of two seasons (26.36%, 19.51% and 17.6% over those on Cleopatra mandarin, Carrizo citrange and ‘Swingle’ citrumelo, respectively); however, those budded on Cleopatra mandarin had the lowest one. Trees on all rootstocks exhibited relatively little alternate bearing index, and the trees on Carrizo citrange significantly showed lower alternate bearing index. Fruit weight, volume, dimensions and shape, peel thickness and percentage, rag percentage and juice content were not significantly affected by rootstock. However, fruit gravity, colour, firmness and juice TSS, acidity, TSS/acid ratio and ascorbic acid contents were significantly affected by rootstock. Sour orange produced fruits with high gravity, firmness and acidity and low fruit colour, TSS and TSS/acid ratio, indicating that Sour orange retarded fruit maturity and, therefore, it is not recommended as a rootstock for this cultivar (whereas its fruit maturation is extra early), despite of its high fruit production. While, Carrizo citrange produced fruits with low gravity, firmness and acidity and best colour, high TSS and TSS/acid ratio, followed by Cleopatra mandarin and ‘Swingle’ citrumelo rootstocks. Carrizo citrange, Cleopatra mandarin and ‘Swingle’ citrumelo can be considered as suitable rootstocks for ‘Marisol’ clementine under the Egyptian conditions.