Sour Orange Rootstock Research Articles

Response of Citrus rootstocks to iron deficiency under high pH conditions

Turkey is one of the major citrus producing countries in the Mediterranean Basin. Approximately 90% of the total citrus production in Turkey is carried out in the Mediterranean Region. Soil of the Mediterranean region is calcareous and because sour orange is tolerant to high pH, the rootstocks is widely used in this region. Sour orange rootstock, which is well adapted to calcareous soils, has positive effects on yield and quality, but is extremely sensitive to Citrus Tristeza Virus disease. Because sour orange is very sensitive to tristeza, there is a need to find an alternative rootstock that is well adapted to calcareous soils and has good fruit yield and quality. For this purpose, 16 citrus rootstock and genotypes could be used as a rootstock, were tested against high-pH conditions for iron chlorosis in growth chamber. At the end of this experiment, Tuzcu 891 sour orange, Gou Tou sour orange and Antalya Cleopatra mandarin were the most tolerant; Duncan grapefruit, Tuzcu 31-31 sour orange, Sunki mandarin, Nasnaran mandarin, Cleopatra mandarin x Swingle citrumelo hybrid, Carrizo citrange, C-35 citrange and Marumi kumquat were moderate tolerant; Volkameriana, Swingle citrumelo, Pomeroy trifoliate and Sarawak bintangor were sensitive; and a local trifoliate was found to be the most sensitive to iron chlorosis in a high pH medium.

Long-term effect of Tylenchulus semipenetrans on citrus tree quality in reclaimed land of Egypt

Citrus fruit yield is considered a short-term response to the citrus nematode,Tylenchulus semipenetrans damage and therefore this study addressed parametersmeasuring overall appearance of the sampled trees. Soil and roots from 20 trees ineach of three mature: 'banzaheer' lemon, 'Baladi' mandarin, and ‘Navel’ orange andone immature: ‘Navel’ orange orchards, all grafted on sour orange rootstock, inEgypt were sampled for the citrus nematode, T. semipenetrans, in February 2011 toinvestigate their correlations with tree parameters (tree height and vigor, canopydiameter, and trunk circumference) that reflect long-term nematode damage of thesampled trees. The correlation between pairs of these four parameters were alwayspositive and generally with high significant levels. Each of the four parameters wasnot significantly correlated with fruit yield of the mature trees but each of tree heightand vigor, and canopy diameter was correlated with fruit yield of the immature Navelorange. The relationships between pairs of these biotic parameters and T.semipenetrans population density in fibrous roots and soil were not consistent.Eleven edaphic factors in mandarin and mature orange orchards were measuredand compared. Both soils were dominated by rough grainy particles of sand. Levelsof potassium, calcium, phosphorus, ammonium and nitrate as well as soil solutionpH, organic matter content and electric conductivity in the soil samples weresignificantly (P ≤ 0.01) different between the mandarin and orange orchards. Toachieve better economic revenue of citriculture, local tackling of T. semipenetransproblem in newly reclaimed areas of Egypt was discussed.

COMPARATIVE EFFECT OF ONE SYNTHETIC BIOSTIMULANTS AND MICROBIAL BIOSTIMULANT (Azospirillum lipoferum) ON YIELD AND QUALITY OF WASHINGTON NAVEL ORANGE FRUITS.

Foliar sprays with synthetic biostimulants or microbial biostimulants PGPR (plant growth promoting rhizobacteria) were used . They contain amino acids, macro and micro elements, humic acid and vitamins . Also its direct effect in release stimulants, nutrients, antibiotics, biosides and sidrofores or activation of these microorganisms in plant rhizosphere in activation and improving plant growth. This study was carried out during 2013 and 2014 seasons on 10 years old Washington navel orange (Citrus sinensis Osbeck) trees budded on sour orange (Citrus aurantium L.) rootstock, grown in a private orchard located at Motobus, Kafr El Sheikh Governorate, to study the effect of synthetic stimulants (Furdose) and microbial biostimulant (Azospirillum lipoferum )on fruit set, dropping, yield and fruit quality. Furdose as a commercial synthetic biostimulant and microbial biostimulant Azospirillum lipoferum were used as foliar application alone or in combination at two stages, before flowering(first mach) or after fruit set(first may) or before flowering and after fruit set. The obtained results revealed that, fruit set and drop percentages, yield and fruit quality were u significantly affected by Furdose and Azospirillum lipoferum treatments alone or in combination in both seasons . The data cleared that, both stimulators enhanced fruit set percentage, yield and fruit quality of Washington navel orange trees . Azospirillum lipoferum alone or combined with Furdose was more effective on improving the productivity and fruit quality .The T6 (foliar spray of A. lipoferum after fruit set), T7 ((foliar spray of A. lipoferum before flowering and after fruit set) and T10 (foliar spray of Furdose plus A. lipoferum before flowering and after fruit set) were the most effective treatments on yield and fruit quality. It increased fruit set, yield and fruit quality in terms of fruit number, fruit kg/tree, fruit firmness, soluble solids content, reducing and total sugars and vitamin C. Fruit drop was decreased without significant differences among them in both seasons. Thus spraying with Azospirillum lipoferum after fruit set T6 ( foliar spray of A. lipoferum after fruit set) ) gave 112.4 and 115.7 kg/tree compared with T7 (foliar spray with Azospirillum lipoferum before flowering and after fruit set) 108.7 and 121.4 kg/tree and T10 ((foliar spray the combination of them before flowering and after fruit set) 114.7 and 130.3 kg/tree during both seasons, respectively . The use of ( Azospirillum lipoferum ) is recommended for increasing fruit yield and quality such as firmness, SSC, V.C and total sugars which may be increase the fruit ability to handling stages and longest shelf life, and gave the highest of net return per feddan and the increase in net return over control. when used alone or with synthetic biostemulants ( Furdose) compared with the use of synthetic biostemulants ( Furdose) alone .

IMPROVING YIELD AND FRUIT QUALITY OF WASHINGTON NAVEL ORANGE USING FOLIAR APPLICATIONS OF SOME NATURAL BIOSTIMULANTS.

Field experiment was carried out during two successive seasons of 2012 and 2013 on Washington Navel sweet orange cultivar (Citrus sinemsis, L) onto sour orange rootstock (C. aurantium , L) grown in well drainage clay loam soil of a commercial orchard located in Shiwah Valley (30°51'55.78N, 31°16'23.14E), near Aga city, Dakahleia Governorate, Egypt. The investigation was designed to throw some light on the effect of two natural biostimulants, i.e., Milagrow at 10, 15 and 20 ppm (extracted from pollen grains of rape seed (Brassica napus) as a source of brassinolide phytohormone) and yeast extract at 1000, 1500 and 2000 ppm on fruit set, fruit drop, yield and fruit quality of Washington Navel orange trees. The natural biostimulants were tested as foliar sprays at full bloom stage and one month later. Data indicated that, all biostimulants treatments increased fruit set, yield and fruit quality and decreased fruit drop as compared with control treatment. Data also revealed that, foliar sprays of trees by Milagrow at 15 and 20 ppm were superior for inducing the highest increase of fruit set and yield, in addition yeast extract at 2000 ppm comparing with rest concentrations of both tested biostimulants. On the other hand, no significant differences were observed among all tested concentrations of two natural biostimulants with respect to fruit weight in two seasons. The foliar applications of Milagrow and/or yeast extract increased fruit SSC and reduced acidity contents in fruit juice as compared with control treatment. Moreover, it was noticed that trees sprayed with two tested biostimulants gave the best results for reducing fruit drop. It could be recommended that best treatment for increasing yield and improving fruit quality was spraying Washington Navel sweet orange cultivar with Milagrow at 20 ppm and yeast extract at 2000 ppm during full bloom stage and one month later especially in the same conditions to experimental area.

Mapping sequences involved in induction of decline by Citrus tristeza virus T36 on the sour orange rootstock.

Historically, decline (or tristeza) has been a devastating disease of citrus caused by Citrus tristeza virus (CTV). Decline is a man-made disease based largely on propagation of sweet orange, grapefruit, and mandarins on the sour orange rootstock. In Florida, the major problem caused by CTV has been decline, since severe stem-pitting isolates are absent. Although this disease can be controlled by using alternative rootstocks, there are soils in which all other rootstock choices are less desirable in terms of fruit quality and yield. A major goal has been to develop measures that allow growers to use the sour orange rootstock in the presence of CTV. Florida has 2 predominant strains of CTV, a decline (T36) strain and a non-decline strain (T30). A first step was to map the viral determinant that induces decline. This was done by creating hybrids with T30 sequences substituted into T36 to identify sequences correlated with loss of decline symptoms. This project was delayed considerably because greenhouse assays to definitively assay decline symptoms did not work. In order to examine decline in field trees, a permit from the US Department of Agriculture Biotechnology Regulatory Service was obtained to test the recombinant-DNA-produced virus hybrids. This permit required that we test small trees inoculated with CTV at the time of planting. Under these conditions, those constructs that retained the T36 p23 and 3ʹ non-translated sequences induced greater amounts of stunting.

First report on citrus dry rot in sour orange rootstock in Texas

A grapefruit tree on sour orange rootstock in a residential property in Mission, TX was suspected to have citrus dry root rot disease based on symptoms. The causal organism was isolated from the infected root samples and based on fungal cultural and microscopic morphology and PCR, it was confirmed to be Fusarium solani (Martius) Appel & Wollenweber emend. Snyder & Hansen. A total of 10 healthy sour orange rootstock seedlings were inoculated using conidial suspension of the fungus by the standard root-dip method. After 9 month post inoculation, the inoculated fungus was re-isolated from root and stem sections of these plants. Plants were smaller in size and displayed the classical symptoms of dry rot. The fungal colonies were confirmed to be F. solani based on fungal morphology and PCR. This is the first report of F. solani infecting sour orange rootstock plants in Texas.

A historical note on two unreported obstacles for cross-protecting mature citrus trees against severe Citrus tristeza virus isolates.

Letter to the Editor A historical note on two unreported obstacles for cross-protecting mature citrus trees against severe Citrus tristeza virus isolates. M Bar-Joseph 1* The S Tolkowsky Laboratory, ARO, The Volcani Center, Bet Dagan 50250, Israel. *Correspondence to: mbjoseph@gmail.com Citation: Bar-Joseph M. 2015. A historical note on two unreported obstacles for cross-protecting mature citrus trees against severe Citrus tristeza virus isolates. J Cit Pathol. iocv_journalcitruspathology_28534. During the years 1970 to 1986 the Israeli citrus industry had undertaken a costly and ambitious program for suppressing the outbreak of a Citrus tristeza virus (CTV) epidemic. For comprehensive reviews of CTV and the tristeza disease see Dawson et al. (2013), Moreno et al. (2008), and Bar-Joseph et al. (1989). The program, which involved millions of ELISA tests, was a coordinated effort of virus research, extension, and regulatory agencies funded by the local citrus marketing board and the Ministry of Agriculture. These major commitments of CTV control by a “search and destroy” strategy were based on statistical analyses indicating that CTV infection rates throughout citrus areas were low (Bar-Joseph et al. 1989). Because of the absence of reliable diagnostic methods to differentiate between mild and severe CTV isolates at early stages of infection, the program policy was to eliminate every tree that showed a positive ELISA reaction. An increase in the incidence of CTV detection during 1983 to 1985 and grower reluctance to cooperate with timely removal of symptomless infected trees, pointed to the need for reevaluating CTV infection rates. Results in 1986 suggested that despite the suppression efforts, which for economic reasons had been already reduced a few years earlier, there were about 50,000 undetected infected trees, spread over 5000 hectares (Bar-Joseph et al. 1989). It was also apparent from the high ratio of symptomless to declining trees that the majority of these sweet orange on sour orange rootstock trees were carriers of “mild” CTV isolates. Trees infected with such isolates remained symptomless for 5 to 10 years, even when the isolates were infecting a decline sensitive combination of sweet orange scions on sour orange rootstocks. Cost-benefit analyses indicated that locating these symptomless trees among the millions of citrus trees cultivated at that time in Israel would have involved testing and compensation costs far beyond the industry’s funding resources. Once the CTV suppression program came to a halt, testing the mild isolates from symptomless trees for their ability to protect trees in plots with severe decline causing isolates became an option. In 1988 a cross protection iocv_journalcitruspathology_28534 experiment to prevent decline was established in a mature (around 20 years old) Valencia orange grove grafted on sour orange. The experimental plot was part of the Yachin Company Morasha plantation located east of Tel Aviv. In this area an extremely severe isolate Mor-T (Ben-Zeev et al. 1988), belonging to the VT strain (Mawassi et al. 1993; Shalitin et al. 1994) was causing rapid decline of Minneola tangelo, Valencia, and Shamouti orange trees at early stages of natural infection. Trees of sensitive combinations infected by Mor-T were showing quick decline long before the virions pervaded the canopies to allow routine detection by ELISA (Ben-Zeev et al. 1988). For mild strain cross protection we used several CTV isolates belonging to the VT strain, including Ach-T, Miqveh-T, and Miqveh-127K (Mawassi et al. 1993; Shalitin et al. 1994), obtained from mature Shamouti orange trees on sour orange stocks that had been infected for several years with CTV, and did not show observable differences when compared with uninfected Shamouti orange trees. Screen house tests showed that, unlike the original VT and Mor-T isolates, these mild VT isolates did not induce seedling yellows when graft inoculated to sour orange seedlings. In addition, simultaneous placing of a Valencia bud and CTV inoculum buds on 1-year-old sour orange seedlings resulted in severe chlorosis of the sprouting Valencia shoot when the buds were infected with Mor-T, while similar Valencia buds on plants simultaneously grafted with the Ach-T and Miqveh-T inocula allowed the development of apparently normal shoots, similar to mock inoculated control plants. The cross protection experiment was conducted on a 2 ha plot, essentially still free of CTV infected trees, located west of the Morasha citrus planted area. The experimental design was simple: each of the protective isolates maintained in Citrus macrophylla, was graft-inoculated along entire rows of about 50 to 60 trees each, with at least 2 replications. Rows on the orchard edges and in the middle of the plot were left as unprotected controls. Trees were graft inoculated on about 1 cm lateral branches at a height of about 60 to 80 cm on 2 sides of each tree. The

A NEW APPROACH TO FRONT CITRUS IRON CHLOROSIS: ORGANO-MINERAL FERTILIZERS FROM GLASS-MATRIX AND ORGANIC BIOMASSES

The aim of the present paper was to investigate the agronomical responses of a fertilizer able to release nutrients on the basis of plant-demand, glass-matrix based fertilizer (GMF). Nutrient release was stimulated by mixing the glass-matrix with organic components such as digested vine vinasse (DVV) or meat-meal (MM), added with the aim to increase GMF biological affinity toward roots. Laboratory tests and short-term pots trials showed that the mixture GMF+DVV increased nutrient availability and plant growth. In the following stage these mixtures were tested for their ability to contrast in calcareous soils citrus iron chlorosis, one of major abiotic stresses affecting fruit tree crops in the Mediterranean area. Three year studies were conducted: i) in pots, on ‘Tarocco ScirA¨â€™ orange trees [Citrus sinensis (L.) Osbeck] grafted on Swingle citrumelo and ii) in field, on Tarocco grafted on sour orange rootstock [C. aurantium (L.) Osbeck], by comparing GMF and its mixtures with DVV and MM to a synthetic chelate application. The GMF+DVV mixture was able to supply adequately micronutrients, particularly iron, reducing the chlorosis symptoms, increasing the leaf SPAD index and concentration, and decreasing the Fe index.

Evaluation of Some New Navel Orange Cultivars Budded on Sour Orange and Volkamer Lemon Rootstocks

Wady El-Mollak, El-Sharqia Governorate, Egypt during two successive seasons (2012 and 2013) to evaluate flowering, fruit set, fruit drop, yield, fruit quality, mineral and total carbohydrates content of some newly introduced Navel orange cultivars (New Hall, Navelina, Navelate, Lane Late, Cara Cara, Spring, Fisher, Parent, Fukumoto and Leng). These cultivars were grafted on two commercial

Farklı anaçlar üzerine aşılı bazı virüsten ari altıntop çeşitlerinin meyve kalite özellikleri

Sanitation studies against virus and virus like diseases causing large economic losses in citrus plantations in Turkey were begun at Antalya Citrus Research Institute in 1988. As a result of the study, some virus-free grapefruit varieties (Redblush, Rio Red, Ray Ruby, Henderson, Star Ruby and Marsh Seedless) budded on Local sour orange and Troyer citrange rootstocks were planted at breeding parcel in 1995. Effects of rootstocks on fruit quality properties were investigated in these grapefruit varieties. Local sour orange and Troyer citrange affected similarly on the fruit quality of grapefruit cultivars. It could be suggested that these rootstocks could be recommended for grapefruit growing.

First Report of Armillaria Root Rot Caused by Armillaria mellea Infecting Carrizo Citrange and Sour Orange Rootstocks in Turkey.

Citrus rootstocks, Carrizo citrange (Citrus sinensis [L.] Osb. × Poncirus trifoliata [L.] Raf.) and sour orange (C. aurantium L.) grown in containers filled with 5 liters of potting mix of 40% peat and 60% volcanic tuff declined in a 0.2-ha commercial nursery in Adana, Turkey, between 2004 and 2007. Seedlings with symptoms of root rot were found with an average disease incidence of 20% among 1,000 Carrizo citrange seedlings and 10% among 15,000 sour orange seedlings. The potting mixture preparation unit was located next to an oak tree (Quercus sp.) showing symptoms of Armillaria root rot. Six- to 12-month-old seedlings of both rootstocks were stunted and the crowns were necrotic with the presence of white mycelium. Mycelial fans were observed beneath the bark of infected roots and they expanded into the crown. The root systems and nearby potting mix contained rhizomorphs. Thus, Armillaria spp. was suspected as a possible causal agent. Three diseased crowns and three rhizomorphs were surface-sterilized with 1% NaClO for 1 min and cultured on benomyl-dichloran-streptomycin containing selective medium (3) at 25°C in the dark for 1 week. Six isolates transferred to 1.5% malt extract agar at 33°C in the dark for 7 weeks consistently yielded abundant aerial hyphae and mean diameter growth range was 4 to 21 mm and the mycelium margin was regular (1). To confirm pathogen identity, total DNA was extracted using the PowerSoil DNA Isolation Kit (MO BIO Laboratories, Inc., CA) directly from 7-day-old cultures grown in potato dextrose broth (PDB). The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (5) and sequenced. The sequences were 99% identical to that of Armillaria mellea isolates from Japan (AB510880) and China (KF032535). This confirmed the identity of the causal agent as A. mellea (Vahl.) P. Kumm. Ten 3-month-old seedlings of Carrizo citrange and sour orange were transplanted into steam-sterilized potting mix and inoculated with wood pieces of oak (Quercus sp.) colonized by the fungus (two pieces for each container) (2). The oak wood pieces were sterilized prior to the colonization by the pathogen. Plants were maintained in a greenhouse (23 to 25°C) until symptoms appeared. Ten non-inoculated seedlings from each rootstock served as controls and were maintained in the same environment. After 4 months, the crowns of the seedlings developed necrotic areas and root systems contained rhizomorphs on all inoculated seedlings and fungus was re-isolated from crowns and rhizomorphs. All control plants remained disease-free and no fungus was re-isolated. A. mellea was reported to infect citrus rootstocks in Spain in 1999 (4). To our knowledge, this is the first report of Armillaria root rot caused by A. mellea infecting Carrizo citrange and sour orange rootstocks in Turkey. This indicates that citrus rootstocks could be at risk for infection and sterilization of the potting mix and good sanitation practices in nurseries are very important.

Diverse DNA extraction methods and PCR primers for detection of Huanglongbing-associated bacteria from roots of ‘Valencia’ sweet orange on sour orange rootstock

Fibrous root samples from Huanglongbing symptomatic (S) and asymptomatic (AS) ‘Valencia’ sweet orange trees (Citrus sinensis) grafted onto sour orange (C. aurantium) rootstock were analyzed using different DNA extraction procedures and primers to detect Candidatus Liberibacter asiaticus. Root sampling procedure was modified from the conventional use of soil probe to reduce fatigue, and to facilitate sample collection. DNA extraction kits including Qiagen DNeasy, Mo Bio PowerSoil and PowerPlant generated root DNA suitable for polymerase chain reaction (PCR) diagnostic assays. Quantitative PCR (qPCR) using HLBaspr primers and probe on root DNA extracts from a total of 206 samples from 60 AS trees showed unreliable results for the presence of Ca. L. asiaticus. Except for one sample, all the remaining samples gave negative qPCR result using LJ900fpr primers and probe. Further analysis of roots samples from S and AS trees indicate that HLBaspr is not suitable for Ca. L. asiaticus diagnosis in root samples. Leaf samples from all 60 AS trees showed negative qPCR result with HLBaspr. Conventional PCR (cPCR) using OI1/OI2c primers on 10 randomly selected root samples, from the 206 samples, produced non-specific amplification products which were easily distinguished from products specific to Ca. L. asiaticus seen in the positive control. The same root samples did not produce any amplification product in cPCR using A2/J5 primers. Any of the above mentioned cPCR or qPCR assays could accurately detect Ca. L. asiaticus in S leaf samples of Ca. L. asiaticus-infected trees. Root samples from 10 (5 S and 5 AS) additional trees analyzed by cPCR using A2/J5 and Las606/LSS primers and qPCR using LJ900fpr and CQULA (CQULA04F/CQULA04R, and TaqMan probe CQULAP10) clearly showed that all these primers are efficient in detecting Ca. L. asiaticus in root samples. There was no difference in frequency and consistency of Ca. L. asiaticus detection for root samples collected near the tree trunk compared to the roots collected about 1.8m from the trunk. Ca. L. americanus was not detected in either root or leaf samples.

Effect of Saline Water Irrigation on Sour Orange and Volkamer Lemon Seedling Rootstocks

Effect of Saline Water Irrigation on Sour Orange and Volkamer Lemon Seedling Rootstocks

Acquisition and transmission of selected CTV isolates by Aphis gossypii

Citrus tristeza virus (CTV) is a severe threat to the citrus industry. Disease symptoms and severity may vary depending on the CTV isolates. These are responsible for the decline of trees grafted on sour orange rootstock, or stem pitting on some citrus commercial cultivars regardless of rootstock. In the Calabria region (Italy), CTV was first reported on cultivars imported from other countries. However, recent observations suggested that natural spread of CTV was occurring and a study was needed to determine the epidemiological status and aphid transmission of CTV in Calabria. The role played by local A. gossypii in the spread of CTV was analyzed in the laboratory using various viral acquisition, inoculation periods with three different CTV isolates. Single aphid vectors acquired CTV after a minimum of 30min acquisition access period (AAP) and were able to transmit the virus after a 60min inoculation access period (IAP) to healthy plants. A minimum of four aphid vectors were needed to reach 50% transmission probability. The results suggested that the three tested strains are transmitted by A. gossypii in a semi-persistent mode. The results demonstrated that local A. gossypii population can acquire and transmit efficiently the tested virus isolates with serious implications on the virus spread.

First Report of Mature Citrus Trees Being Affected by Fusarium Wilt in Tunisia.

Citrus is an important crop in Tunisia and over 98% of trees of all varieties are grafted on sour orange rootstock. Since September 2010, unusual wilt symptoms have been observed in Takilsa, Bni-Khaled, and Manzel Bouzalfa fields that eventually caused tree death. The disease was observed on 10- to 25-year-old trees of sweet orange (Citrus sinensis) 'Washington Navel' and on 'Clementine' tangerines (C. tangerina) 'Cassar,' 'Hernandina,' and 'MA3,' all grafted on sour orange (C. aurantum) 'Bigarade Gou Tou.' The most conspicuous symptoms were wilting of sections of the canopy, chlorosis and epinasty of young leaves, and discoloration of vascular tissue. No root rot was observed. The problem was widespread with a disease incidence of 45 to 67%. Similar symptoms were described by Timmer et al. (2) on Mexican lime (C. aurantiifolia) nursery plants and some other species of citrus. Three representative isolates of Fusarium oxysporum Schlechtend.:Fr. from crown were single-spored and identified by the production of characteristic, three- to five-celled, sickle-shaped macroconidia with foot-shaped basal cells, ellipsoid microconidia borne in false heads on short monophialides, and chlamydospores in culture (1). The internal transcribed spacer (ITS) region of rDNA and the elongation factor (TEF 1-α) were amplified with primers ITS1/ITS4 and (TEF1/TEF2), respectively. GenBank accessions of ITS region are KC282838, KC282839, and KC282840, for TEF 1-α region are KF531633, KF537336, and KF537337, showed 99% homology with isolates of F. oxysporum in Fusarium-ID data. Pathogenicity tests were conducted on 7-month-old seedlings of sour orange using 10 plants for each of the three isolates. Prior to inoculation, roots were scraping with a sterile scalpel and plants were dipped in a conidial suspension of F. oxysporum (106 conidia ml-1) for 10 min. Each seedling was planted in a separate pot containing 0.7 liter of sterile soil. Non-inoculated plants with scraped roots dipped in sterile distilled water served as controls. Plants were irrigated and placed in a greenhouse at 24 ± 2°C and 12-h photoperiod. One month after inoculation, leaf chlorosis was observed and 2 months later, 90% of inoculated plants presented a severe wilt. Symptoms on infected plants were similar to those observed in the field. F. oxysporum was successfully re-isolated from the stems, thereby completing Koch's postulates. Genomic DNA was isolated from the re-isolations and PCR amplification of the ITS region was performed with the same primers. There was 100% nucleotide identity with sequences of the original isolates. To our knowledge, this is the first report of fusarium wilt of citrus trees in Tunisia. The pathogen may represent a new form species because previously, the disease was only reported from lime and lemon.

Growth and photosynthetic response of young ‘Navelina’ trees budded on to eight citrus rootstocks in response to iron deficiency

Citrus trees growing in the Mediterranean region suffer from iron (Fe) deficiency because of the presence of high levels of carbonate ions in calcareous soils. In this context we have evaluated the effects of different citrus rootstocks on photosynthetic capacity and plant development of young ‘Navelina’ orange trees under Fe deprived conditions. Leaf number, shoot length, plant dry mass, leaf chlorophyll (Chl) concentration, net photosynthetic rate (PN), stomatal conductance (gS), leaf transpiration rate (E), intercellular CO2 concentration (Ci) and photosynthetic water use efficiency (WUE) of ‘Navelina’ orange scion budded on to eight citrus rootstocks with different agronomic characteristics were investigated. Significant decreases in leaf number, shoot length and plant dry mass under high pH conditions were observed. Plants on Tuzcu 31 31 and Gou Tou sour orange rootstocks were the least affected in terms of plant growth. The highest reduction in the leaf Chl content was observed in (-)Fe plants of Navelina on local trifoliate and C-35 citrange. These rootstocks also had significantly reduced PN, gS and E rates in the (-)Fe treatment. Shoots budded on Tuzcu 31 31 and Gou Tou sour oranges were the least affected by the induced Fe deficiency.

EFFECT OF APPLYING SURFACE AND BUBBLER IRRIGATION SYSTEMS ON FRUITFUL WASHINGTON NAVEL ORANGE TREES PRODUCTION

A field experiment was conducted at a private farm at Giza in the seasons of 2011 and 2012 to study and evaluate water utilization efficiency, vegetative and roots growth parameters, fruiting measurements, fruit quality and leaf mineral content of Washington Navel orange trees under two irrigation systems. Trees under study aged 35 years budded on sour orange rootstock and grown on clayey loamy soil. Trees were surface irrigated since the farm initiation, then subjected to bubbler and surface irrigation systems in the recent study for comparison. The obtained results pointed out that, surface irrigation consumptive use was (7480 and 7310 m3/fed. in the two seasons) followed by bubbler irrigation system (4302 and 3913 m3/fed.). Water consumptive values increased as soil moisture maintained high by surface irrigation. Monthly water use was low after January and then increased to reach its maximum during June, July and August and then decreased again. On the other hand, bubbler irrigation system supported an increase in water utilization efficiency up to 59.4 %. Bubbler irrigation system increased both vegetative and root growth parameters i.e., (shoot length, leaf area, root length, number of roots and dry weight). Moreover, bubbler irrigation system resulted in a significant increase in fruiting parameters (yield kg per tree, number of fruits/tree, fruit weight g.). In addition to that most of both physical and chemical studied fruit characteristics were improved by bubbler than the surface irrigation method during the first and second seasons. However, leaf mineral content (N, P and K) was not significantly affected by both investigated irrigation methods in the two seasons of study. Bubbler irrigation system results in more effective roots (< 2 mm) in length and number compared with the surface one. This increase was reflected in improved yield and quality of orange production. In brief, it could be concluded and recommended for Washington Navel orange trees grown on clay loamy soil to change surface to bubbler irrigation system for saving more irrigation water with better fruit yield, fruit quality, system and increasing water utilization efficiency to 59.4 %.

Effects of Rootstock/Scion Combinations on the Flavor of Citrus Fruit

We examined sensory quality, total soluble solids (TSS) and acidity levels, and aroma volatiles compositions of 'Or' and 'Odem' mandarins grafted on sour orange (SO), Volkamer lemon (Volka), and US-812 rootstocks; 'Valencia' oranges grafted on SO, Volka, and ×639 rootstocks; and a new pummelo × grapefruit hybrid cv. 'Redson' grafted on SO, Volka, and macrophylla rootstocks. TSS and acidity levels of all species were lower in juice of fruits on Volka than on SO. Sensory quality evaluations revealed that 'Odem' mandarins and 'Redson' fruits grown on SO were preferred to those on Volka but the rootstocks had no notable effects on flavor perception of 'Or' mandarins and 'Valencia' oranges. Chromatographic analysis revealed that contents of aroma volatiles, especially terpenes, in homogenized segments of 'Odem' and 'Redson' but not of 'Or' and 'Valencia' were significantly lower on Volka than on SO. Overall, the effects of rootstocks on citrus fruit flavor depended on specific rootstock/scion interactions. Furthermore, the flavor of some varieties grown on Volka was inferior to that on SO because of lower TSS and acidity levels and lower aroma volatiles contents.

MUTUAL EFFECT BETWEEN THREE ORANGE CVS. AND SOUR ORANGE AND VOLKAMERIANA ROOTSTOCKSS IN NEWLY RECLAIMED LANDS

This study was carried out in Wadi EL- Technologia in Ismailia Governorate, Egypt, during 2010 and 2011 seasons. Washington Navel (N.O.), Valencia (V.O.) and Baladi orange (B.O.) trees budded on Sour orange (S.O.) and Volkamer lemon (V.L.) were grown in sandy soil under drip irrigation system from a well has salinty of (1100 ppm).This investigation aimed to study the effect of the two citrus rootstocks on vegetative growth, yield, fruit quality, leaf mineral content of the three studied scions as well as the effect of such scions on root system growth of both rootstocks. The obtained results indicated that, Volkamer lemon rootstock recorded the highest significant values of vegetative growth, yield and fruit quality except T.S.S% and ascorbic acid content . Sour orange rootstock gave the highest significant effect on values of leaf mineral content (N, P, K, Mg, Fe, Zn and Cu) however V.L. showed the highest significant value. while, Ca leaf content recorded insignificantly difference between both rootstocks. Leaf Mn, content was significantly the highest with S.O. in both seasons. Root fresh and dry weight were the highest significantly with V.L. rootstock. From the showed result, one can recorded that V.O. scion significantly increased the vigour of V.L. root fresh and dry weight. While, B.O. scion showed significantly the lowest vigoure of V.L. root fresh and dry weight. On the other hand, N.O. scion gave a midiate result between V.O. and B.O. scions on root fresh and dry weight.

STUDTYING THE RESPONSE OF TANGARIN SCIONS GROWN ON SOUR ORANG ROTSTOCK FOR BUDDING DATE, APPLICATION METHOD AND LEVELS OF STRUCTUR ACTA AGRO COMPOUND FERTILIZER

This study were conducted at lath house / Hort . & Landscape Design/ Coll. of Agriculture and Forestry during 2010 and 2011 growing seasons on Tangarin transplants which were budded on sour orange rootstock to know the effect of autumn budding date (1/10/2010 and 15/10/2010) and foliar or soil application of structure fertilizer at two levels for each method (2 and 4 ml. L-1). The application of the fertilizer was done twice a season, with 20 days intervals, the first was done when the scion length was 45cm (at 15/4/2011). Results indicated that the first date of budding was dominated over the second date of budding in the leaves Zn level, transplants leave number, transplants leaves area, main stem length and diameter and lateral branches number. For the effect of method application and levels of structure fertilizer, results showed that soil application of the fertilizer at the level of 2 ml. L-1 gave the highest means of leaves N level, leaves dry weight, leaves area, transplant leaves area and main stem length, which were dominated over most other treatments. Meanwhile the heighest means of leaves chlorophyll, leaves fresh weight and leaves Zn level were in the treatment soil application of structure at 4 ml. L-1 level. In the case of the interaction between budding date and method and level of structure fertilizer, the best one was that between first budding date and soil application of the fertilizer at the level of 2 ml. L-1, which gave the highest means of leaves N and Zn levels, leaves dry weight, leaves dry weight percentage, leaves area, leaves number, transplants leaves area and main stem length.