Trifoliate Orange Rootstock Research Articles

Transcription-related metabolic regulation in grafted lemon seedlings under magnesium deficiency stress

Magnesium is one of the essential nutrients for plant growth, and plays a pivotal role in plant development and metabolism. Soil magnesium deficiency is evident in citrus production, which ultimately leads to failure of normal plant growth and development, as well as decreased productivity. Citrus is mainly propagated by grafting, so it is necessary to fully understand the different regulatory mechanisms of rootstock and scion response to magnesium deficiency. Here, we characterized the differences in morphological alterations, physiological metabolism and differential gene expression between trifoliate orange rootstocks and lemon scions under normal and magnesium-deficient conditions, revealing the different responses of rootstocks and scions to magnesium deficiency. The transcriptomic data showed that differentially expressed genes were enriched in 14 and 4 metabolic pathways in leaves and roots, respectively, after magnesium deficiency treatment. And the magnesium transport-related genes MHX and MRS2 may respond to magnesium deficiency stress. In addition, magnesium deficiency may affect plant growth by affecting POD, SOD, and CAT enzyme activity, as well as altering the levels of hormones such as IAA, ABA, GA3, JA, and SA, and the expression of related responsive genes. In conclusion, our research suggests that the leaves of lemon grafted onto trifoliate orange were more significantly affected than the roots under magnesium-deficient conditions, further indicating that the metabolic imbalance of scion lemon leaves was more severe.

Metabolomic and transcriptomic analyses reveal the effects of grafting on blood orange quality.

Blood orange (Citrus sinensis L.) is a valuable source of nutrition because it is enriched in anthocyanins and has high organoleptic properties. Grafting is commonly used in citriculture and has crucial effects on various phenotypes of the blood orange, including its coloration, phenology, and biotic and abiotic resistance. Still, the underlying genetics and regulatory mechanisms are largely unexplored. In this study, we investigated the phenotypic, metabolomic, and transcriptomic profiles at eight developmental stages of the lido blood orange cultivar (Citrus sinensis L. Osbeck cv. Lido) grafted onto two rootstocks. The Trifoliate orange rootstock provided the best fruit quality and flesh color for Lido blood orange. Comparative metabolomics suggested significant differences in accumulation patterns of metabolites and we identified 295 differentially accumulated metabolites. The major contributors were flavonoids, phenolic acids, lignans and coumarins, and terpenoids. Moreover, transcriptome profiling resulted in the identification of 4179 differentially expressed genes (DEGs), and 54 DEGs were associated with flavonoids and anthocyanins. Weighted gene co-expression network analysis identified major genes associated to 16 anthocyanins. Furthermore, seven transcription factors (C2H2, GANT, MYB-related, AP2/ERF, NAC, bZIP, and MYB) and five genes associated with anthocyanin synthesis pathway (CHS, F3H, UFGT, and ANS) were identified as key modulators of the anthocyanin content in lido blood orange. Overall, our results revealed the impact of rootstock on the global transcriptome and metabolome in relation to fruit quality in lido blood orange. The identified key genes and metabolites can be further utilized for the quality improvement of blood orange varieties.

Relative Influence of Rootstock and Scion on Asian Citrus Psyllid Infestation and Candidatus Liberibacter asiaticus Colonization

The citrus industry in Florida faces a destructive endemic disease, known as huanglongbing (HLB), associated with Candidatus Liberibacter asiaticus (CLas), a phloem-limited bacterium, and transmitted by the Asian citrus psyllid (ACP). Rootstocks are regarded as critical to keep citrus production commercially viable and help trees cope with the disease. Although most scions are susceptible, some rootstocks are HLB-tolerant and may influence ACP infestation and CLas colonization and therefore the grafted tree tolerance. This study aimed to elucidate the relative influence of rootstock and scion on insect vector infestation and CLas colonization under natural HLB-endemic conditions. Seven commercial rootstock cultivars with different genetic backgrounds were grafted with ‘Valencia’ sweet orange (Citrus sinensis) or were self-grafted (non-‘Valencia’) and planted in an open field where ACP and CLas were abundant. ACP infestation was determined weekly during periods of leaf flushing, and leaves and roots were analyzed every 3 months to determine CLas titers. Trees with ‘Valencia’ scion were more attractive to the psyllids than non-‘Valencia’ scions. This was also associated with a higher number of bacteria and a larger abundance of foliar HLB symptoms. The influence of the rootstock on the psyllid attraction of grafted ‘Valencia’ scion was less evident, and leaf CLas titers were similar regardless of the rootstock. Among the non-‘Valencia’ scions, Carrizo had the lowest and US-942 the highest leaf CLas titers. Root CLas titers also varied among cultivars, and standard sour orange roots harbored more bacteria than some trifoliate orange hybrid rootstocks such as US-942. In some trees, CLas was detected first in the roots 4 months after planting, but root CLas titers remained low throughout the study. In contrast, leaf CLas titers increased over time and were considerably higher than root titers from 7 months until the end of the study, 15 months after planting. Overall, the results of this study demonstrate a greater relative influence of the scion than the rootstock on ACP infestation and CLas colonization during the early stages of infection. This suggests that other cultivar-specific traits, such as the ability to tolerate other stresses and to absorb water and nutrients more efficiently, along with influences on the scion phenology, may play a larger role in the rootstock influence on the grafted tree tolerance during the later stages of HLB progression.

First report of Fusarium oxysporum and Fusarium solani causing root rot on trifoliate orange rootstock in China.

Trifoliate orange (Poncirus trifoliata L) is a thorny tree of the Rue family, which is extensively used as citrus rootstock in China. In January 2021, several leaf yellowing, declining, and wilting citrus seedlings grafted on trifoliate orange rootstock with rotted main roots were observed in orchards located in Wuhan city, Hubei, China. In old orchards, the incidence of diseased roots was approximately 90%. Diseased roots from seven plants were collected and cut into small pieces (0.2 to 0.5 cm). These pieces were then surface-sterilized using 0.1% mercury bichloride for 3 min, 75% ethanol for 3 min, rinsed with sterile distilled water for several times, and then placed on potato dextrose agar (PDA) supplemented with 0.05% lactic acid (v/v), and incubated at at 25±2°C in dark. Fifty-threesingle-conidium isolates with morphological characteristics similar to Fusarium spp. were obtained (Leslie and Summerell 2006), which displayed two kinds of colony morphology. Thirty isolates showed white to orange-white abundant aerial mycelium in rings and acquired a yellow to orange pigmentation, tweenty-three isolates showed white to pink, fluffy aerial mycelium in rings and acquired an orange to red pigmentation. Isolate WG-1 and HrmY-9 from each group were used for future identification. The average colony growth rate of WG-1 and HrmY-9 on PDA was 0.95±0.06 and 0.69±0.11 mm/day, n=4, respectively. WG-1 produced numerous oval, unicellular microconidia without septa, 4.03-9.87×1.01-5.13 µm, n=80 and very few macroconidia with two to four septa, narrowed at both ends, 11.08-22.64×1.67-4.91 µm, n=30. HrmY-9 produced numerous curved macroconidia with three to four septa, 18.03-37.33×2.16-7.8 µm, n=80, microconidia were unicellular, oval, and 5.33-16.19×1.74-6.51 µm, n=50. Sequences of internal transcribed spacer (ITS), translation elongation factor 1-alpha (EF-1α), and DNA-directed RNA polymerase largest subunit (RPB1) genes were amplified with the primers ITS1/ITS4, EF1a-F/EF1a-R, and RPB1-F5/RPB1-R8, respectively (White et al. 1990, O'Donnell et al. 1998, O'Donnell et al. 2010), sequenced and deposited in GenBank. Sequences of isolate WG-1 (GenBank accession No. ON045437, ON063232 and ON089664) and HrmY-9 (GenBank accession No. ON045438, ON063233 and ON089665) were 100% identical with the corresponding sequences of Fusarium oxysporum (OM876904, JF430180, and MT568959) and F. solani (MT605584, MK617767, and MT305110), respectively. Based on above results, WG-1 and HrmY-9 was identified as F. oxysporum and F. solani, respectively. Pathogenicity test were performed on healthy one-year-old trifoliate orange seedlings by dipping their injured roots into conidial suspension (50 ml, 1×106 conidia/mL) for 1 h and the rest of conidial suspension was added to the pot after replanting to make sure the inoculum was in contact with the roots. Roots of control plants were inoculated with sterilized water. All experiments were repeated twice. All plants were cultured at 26°C under a 16-h light/dark cycle. Typical symptoms developed on most of inoculated seedlings two months post inoculation. No disease symptoms appeared on control plants. Same colonies were reisolated from the inoculated roots, confirming Koch's postulates. To our knowledge, this is the first report of F. oxysporum and F. solani causing root rot on trifoliate orange rootstock in China. The identification of F. oxysporum and F. solani as the causal agents of the observed root rot on trifoliate orange rootstock is critical to the prevention and control of this disease in the future.

A novel bud mutant of navel orange (Citrus sinensis) shows tolerance to chlorosis in acidic and magnesium-deficient soils

Interveinal chlorosis in old leaves is a common occurrence in citrus orchards in southern China. The present study investigates the ‘Langfeng’ navel orange (LF, Citrus sinensis) grafted onto a Trifoliate orange (TO, Poncirus trifoliata) rootstock, which exhibits healthy green leaves, and the ‘Newhall’ navel orange (NHE, C. sinensis) grafted onto TO, which has typical magnesium (Mg) deficiency-induced chlorosis. Chemical analysis of the rhizosphere soil revealed that the pH values were around 3.92 and that both Mg and calcium (Ca) were significantly deficient in the rhizosphere soil of both grafting combinations (LF/TO and NHE/TO). Furthermore, the chlorotic leaves of NHE/TO had significantly lower levels of Mg, Ca, and phosphorus (P), and the green leaves of NHE/TO had significantly lower levels of Mg and Ca compared to the green leaves of the LF/TO. This suggests that Mg deficiency may be the primary cause of chlorosis in NHE/TO. A greenhouse study using the same graft combinations showed that the LF/TO plants had better growth than the NHE/TO, possibly by promoting Mg uptake and/or improving Mg distribution to leaves, thereby increasing carbon dioxide (CO2) assimilation and photosynthesis, optimizing carbohydrate distribution, and increasing plant biomass. This results in a phenotype that is tolerant to Mg deficiency. In conclusion, these findings suggest that the LF navel orange could be utilized in the development of new citrus varieties with improved Mg-use efficiency.

Transcriptome Analysis of Citrus Dwarfing Viroid Induced Dwarfing Phenotype of Sweet Orange on Trifoliate Orange Rootstock

Dwarfed citrus trees for high-density plantings or mechanized production systems will be key for future sustainable citrus production. Citrus trees consist of two different species of scion and rootstock. Therefore, any observed phenotype results from gene expression in both species. Dwarfed sweet orange trees on trifoliate rootstock have been produced using citrus dwarfing viroid (CDVd). We performed RNA-seq transcriptome analysis of CDVd-infected stems and roots and compared them to non-infected controls. The identified differentially expressed genes validated with RT-qPCR corresponded to various physiological and developmental processes that could be associated with the dwarfing phenotype. For example, the transcription factors MYB13 and MADS-box, which regulate meristem functions and activate stress responses, were upregulated in the stems. Conversely, a calcium-dependent lipid-binding protein that regulates membrane transporters was downregulated in the roots. Most transcriptome reprogramming occurred in the scion rather than in the rootstock; this agrees with previous observations of CDVd affecting the growth of sweet orange stems while not affecting the trifoliate rootstock. Furthermore, the lack of alterations in the pathogen defense transcriptome supports the term “Transmissible small nuclear ribonucleic acid,” which describes CDVd as a modifying agent of tree performance with desirable agronomic traits rather than a disease-causing pathogen.

Effects of scion-rootstock interaction on citrus fruit quality related to differentially expressed small RNAs

Rootstock affects the performance of the scion on productivity and fruit quality. Scions on trifoliate orange rootstock could produce better quality of fruits than on other commonly used rootstocks. This phenomenon has been well documented, but genetic factors affecting the fruit quality through interaction of scion and rootstock remained unclear. Fruits in different developmental stages from the Daya mandarin grafted on two genetically divergent rootstocks (Trifoliate orange (Poncirus trifoliata) (Z) and Hongju (Citrus reticulata) (H)) were used for fruit quality, expression of small RNA, and degradome sequencing analysis. Total soluble solids (TSS) of fruit on Z rootstock were significantly higher than those of on H. In contrast, titratable acid (TA) of fruit were lower on Z rootstock. One hundred and eight known and 145 novel microRNAs (miRNA), as well as 555 target genes were identified by in silico analysis and degradome sequencing. One hundred and twenty-nine differentially expressed miRNAs (DEMs) were identified by comparison of miRNA expression between the Daya mandarins grafted on two rootstocks in three different developmental stages. Correlation analysis with the fruits from three navel orange cultivars on two rootstocks showed that four DEMs (Cre-miR159-3p, Cre-miR160a, Cre-miR171b and Cre-miR399-3p) were significant correlated to TSS or TA in some of scion/rootstock combinations. Expressions of Cre-miR399-3p and its target gene INVE demonstrated consistent correlations with fruit quality of four scion varieties grated on Z rootstock, indicating that Cre-miR399–3p and its target gene INVE may be one of the key factors affecting fruit quality in Poncirus trifoliata rootstock.

First Report of Citrus Bent Leaf Viroid and Citrus Dwarfing Viroid in Argentina

Citrus Bent Leaf Viroid (CBLVd) and Citrus Dwarfing Viroid (CDVd), from genus Apscaviroid, are two of the widely distributed citrus viroids among the eight reported to date. They have been found to induce reduction in canopy volume and fruit production in citrus trees on trifoliate and trifoliate orange hybrids rootstocks. Moreover, citrus trees infected only with CBLVd or in combinations with Citrus Exocortis Viroid (CEVd), Hop Stunt Viroid (HSVd) and CDVd have been associated with a poor development of the root system. Samples of citrus trees showing viroid symptoms collected from citrus orchards in Tucumán, Salta, and Jujuy provinces (NW region in Argentina) were initially indexed on citron (Citrus medica) and then analyzed by s-PAGE. These samples were found to be infected with different viroid species, among them, CEVd and HSVd have been already identified. In order to determine the presence of other viroids, we performed a RT-PCR assay using specific primers for CBLVd, CDVd, CBCVd and CVd-V. Forty two samples including 15 lemons, 15 oranges, 8 grapefruits, 2 citrumelos and 2 Cleopatra mandarins were analyzed so far. On the basis of amplification of the appropriately sized DNA, CDVd was detected in thirty eight samples and CBLVd in all grapefruit samples. CBCVd and CVd-V were not found in any samples to date. Analysis of the sequence of amplicons revealed 96% and 97% identity with CBLVd GenBank reference sequences, and 96% to 98% with CDVd GenBank reference sequences. This is the first report of CBLVd and CDVd in citrus trees in Argentina.

Effect of Grafting Dates on Success and Growth of Kumquat (Fortunella japonica Swingle) Sapling

An experiment was carried out to study the effect of grafting dates on the success and growth of kumquat sapling during 2017-18 at Banepa, Kavre to standardize suitable grafting time. The experiment was conducted in a single factor completely randomized design with five treatments and three replications. The treatments consisted of five grafting dates which viz., 25th November, 10th December, 25th December, 10th January and 25th January. Scion collected from the mother plant of kumquat was grafted onto two years old trifoliate orange rootstock by side veneer method at 15 days intervals under screen house. The data were recorded at every 30 days interval and found a significant effect of grafting dates on most of the economically important parameters such as graft success percent, the mortality of sprouted grafts, sapling height, number of leaves per sapling and leaf area. The result revealed that 100% graft success was observed on the grafts prepared in January. The highest mortality (13.68±0.58%) was reported on 25th November grafted sapling. The sapling height (39.68±3.68 cm), number of leaves per sapling (23.12±3.43) and leaf area (16.34±1.05 cm2) were found superior for 10th January grafted sapling while the number of primary and secondary branches per sapling were found non-significant for all grafting dates. Therefore, the study revealed that 10th January was the most suitable time for grafting of kumquat under Kavre, Nepal conditions.

Characteristics of boron distribution in the ‘Newhall’ navel orange plant with two root systems

Grafting is a technique that provides a substantial way to enhance nutrient utilization thereby improves plant growth and yield quality. Although it is commonly practised in horticultural crops, the impact of scion-rootstock interaction on nutrient distribution is still unclear. Here, ‘Newhall’ navel orange plants grafted on Trifoliate orange (T) as the original rootstock were inarched with trifoliate orange (N/Tt combination) or carrizo citrange (N/Tc combination) rootstock seedlings. The experimental plants were treated with isotope 10B solution for 7 weeks to investigate the effect of different inarched rootstocks on B distribution and translocation by using a two-root system. From this study, the original rootstock played a more dominant role in B distribution to scion tissues than the inarching rootstock either in N/Tt or N/Tc combination. From inarched combinations, the carrizo citrange in the N/Tc combination had a higher ability to distribute B to new leaves, new twigs and old twigs than trifoliate orange in the N/Tt combination. However, the original rootstock of N/Tt distributed more B to scion tissues than N/Tc and the B concentration in old leaves and new leaves of N/Tt plants was significantly higher than that of N/Tc plants. These results suggest that scion B status is influenced by the B distribution of two inarching rootstocks in an inarching plant, as well as the affinity between the inarching rootstock and grafted plant. In addition, by either adding 10B to the inarching rootstock or original rootstock, we could detect 10B in the other rootstock root in both N/Tt and N/Tc combinations. The results further suggest that B can translocate from rootstock to leaves and then, re-translocate from scion to rootstock through the cycling of B transportation.

Peel Oil Components of Clementine Mandarin on Different Rootstocks

The aim of this research is to identify rootstock that can synthesize the maximum level of oxygenated compounds. Peel oil was extracted using mechanical presses and eluted using n-hexane. Finally compounds were analyzed using GC-FID and GC-MS. Twenty-four, Twenty-seven and twenty-six compounds were identified in Trifoliate orange, Orlando tangelo and Murcott rootstocks, respectively Limonene (% 92.55 to 93.09) and myrcene (%1.59 to %1.70) were the main compounds. Among the three rootstocks studied, Orlando tangelo demonstrated the maximum level of oxygenated compounds. As a result of our research, we can express that the rootstocks can affect the amount of oxygenated compounds.

Next-Generation Sequencing Identification and Characterization of MicroRNAs in Dwarfed Citrus Trees Infected With Citrus Dwarfing Viroid in High-Density Plantings.

Citrus dwarfing viroid (CDVd) induces stunting on sweet orange trees [Citrus sinensis (L.) Osbeck], propagated on trifoliate orange rootstock [Citrus trifoliata (L.), syn. Poncirus trifoliata (L.) Raf.]. MicroRNAs (miRNAs) are a class of non-coding small RNAs (sRNAs) that play important roles in the regulation of tree gene expression. To identify miRNAs in dwarfed citrus trees, grown in high-density plantings, and their response to CDVd infection, sRNA next-generation sequencing was performed on CDVd-infected and non-infected controls. A total of 1,290 and 628 miRNAs were identified in stem and root tissues, respectively, and among those, 60 were conserved in each of these two tissue types. Three conserved miRNAs (csi-miR479, csi-miR171b, and csi-miR156) were significantly downregulated (adjusted p-value < 0.05) in the stems of CDVd-infected trees compared to the non-infected controls. The three stem downregulated miRNAs are known to be involved in various physiological and developmental processes some of which may be related to the characteristic dwarfed phenotype displayed by CDVd-infected C. sinensis on C. trifoliata rootstock field trees. Only one miRNA (csi-miR535) was significantly downregulated in CDVd-infected roots and it was predicted to target genes controlling a wide range of cellular functions. Reverse transcription quantitative polymerase chain reaction analysis performed on selected miRNA targets validated the negative correlation between the expression levels of these targets and their corresponding miRNAs in CDVd-infected trees. Our results indicate that CDVd-responsive plant miRNAs play a role in regulating important citrus growth and developmental processes that may participate in the cellular changes leading to the observed citrus dwarf phenotype.

Performance of ‘Valência’ sweet orange grafted on trifoliate orange hybrid rootstocks

Abstract The objective of this work was to evaluate tree size, production, and fruit quality of ‘Valência’ sweet orange (Citrus sinensis) grafted on various trifoliate orange rootstocks, in order to select genotypes with a high performance. Twenty rootstock genotypes were evaluated, including trifoliate orange hybrids with mandarin (citrandarins) and with grapefruit (citrumelos), as well as ‘Rangpur’ lime. The experiment was implemented in the northwestern region of the state of Paraná, Brazil, in a 6.0×2.5 m spacing, in a sandy soil under subtropical and rainfed conditions. The statistical model used was the randomized complete block design with four replicates and four trees per plot. Tree size and fruit yield and quality were analyzed during three consecutive harvest seasons. Data were subjected to the analysis of variance, and means were grouped by the Scott-Knott test. Principal component analysis and agglomerative hierarchical clustering were also carried out. F.80-18, F.80-5, and F.80-3 citrumelos and IPEACS-239 citrandarin are adequate rootstock options for ‘Valência’ sweet orange, with dwarf trees and a high production efficiency. These rootstocks, except F.80-18, are also adequate options to obtain oranges with good industrial properties.

Standardization of Grafting Time of Mandarin (Citrus reticulata Blanco) in Central Mid Hill of Nepal

ABSTRACT An investigation was carried out to study the performance of mandarin grafts during 2017–18 at Banepa, Kavre to standardize suitable grafting time for two mandarin varieties. The experiment was conducted in two factorial Completely Randomized Design (CRD) with 10 treatments and three replications. The treatments consisted of combinations of five grafting dates (25th November, 10th December, 25th December, 10th January and 25th January) and two mandarin varieties (Dhankuta Local and Ota Ponkan). Scion collected from mother plants of selected varieties were grafted onto a trifoliate orange rootstock by side veneer method in the screen house. The results showed that grafting dates significantly affect the graft success and subsequent growth of grafted sapling of mandarin varieties. The highest graft success (100%) was observed on the grafts prepared in January. The sapling height (47.58 ± 1.93 cm), leaf area (32.74 ± 2.98 cm2), number of primary branches per sapling (3.16 ± 0.20) and increase in diameter above union (17.78 ± 1.47%) were recorded maximum on the grafts prepared on 25th January while the number of leaves per sapling (26.81 ± 1.84) was found superior for 10th January grafted sapling. Most of the important parameters viz., graft success percent, sapling height and leaf area were found non-significant for varieties but the number of leaves per sapling (23.99 ± 1.51), number of primary branches per sapling (2.72 ± 0.21), increase in diameter above union (16.24 ± 0.88%) and at union (13.72 ± 1.54%) was found maximum for Ota Ponkan. Therefore, the study revealed that late January was the most suitable time of grafting for both varieties of mandarin under Kavre, Nepal conditions.

Bazı Turunçgil Anaçlarında Tuza Tolerans için In vitro Testleme

Turunçgiller coğrafi dağılımlarından dolayı tuzluluğa hassas bölgelerde yetiştirilen ürünler arasında önemli bir yerdedir. Testleme metotları, ıslah ve ürün geliştirme programlarında önemli bir konuma sahiptir. Yapılan bu çalışmada in vitro koşullarda Kleopatra mandarini (Citrus reshni Tan.), Turunç (Citrus aurantium L.), Kaba limon (Citrus jambhiri Lush.), Volkamer limon (Citrus volkameriana Tan &amp; Pasq.), Carrizo sitranjı (Poncirus trifoliata L. Raf. × Citrus sinensis L. Osbeck) ve Üç yapraklı (Ponciru trifoliata Raf.) gibi bazı turunçgil anaçlarının farklı NaCl konsantrasyonlarında tuza olan tepkilerini belirlemek amaçlanmıştır. Söz konusu turunçgil anaçlarına ait tohumlar 0, 45, 90 ve 135 mM NaCl içeren MS ortamında in vitro tohum çimlendirilme testine tabi tutulmuştur. Genel olarak bütün tuz konsantrasyonlarında en yüksek çimlenme Volkamer Limon ve Turunç anacından elde edilirken, en düşük çimlenme Kaba limon ve Üç yapraklı anacında gerçekleşmiştir. Sonuç olarak bu çalışmayla turunçgil anaçlarında tuza toleransı belirlenmesinde in vitro koşulların hızlı testleme de kullanılabileceği kanısına varılmıştır.

No detection of seed transmission of citrus tatter leaf virus in ‘Meyer’ lemon

Citrus tatter leaf virus (CTLV), a strain of apple stem grooving virus, is a virus of citrus that is of commercial importance for trifoliate orange (Poncirus trifoliata) and trifoliate hybrid rootstocks. Bud-union crease is a CTLV-induced incompatibly symptom observed with these rootstocks and citrus scions which results in stunted tree growth. CTLV is a regulated pathogen for most citrus budwood certification programs worldwide. Due to the requisite virus testing, commercially supplied scion budwood would therefore seldom be a point of contamination. However, citrus rootstocks are primarily propagated by seed and the potential for seed transmission of CTLV in citrus is unclear and remains a potential source of infection. A single, unconfirmed report of seed transmission of CTLV in ‘Eureka’ lemon (Citrus × limon) exists, and although this report was not of a rootstock cultivar, it does point to the risk of seed transmission in citrus and close relatives in the family Rutaceae. CTLV-positive ‘Meyer’ lemon (C. × limon) trees in an experimental plot in the Eastern Cape Province of South Africa presented an opportunity to again test seed transmission in citrus. Seed was obtained from the infected ‘Meyer’ lemon trees, and 1164 seedlings were grown in an insect-secure greenhouse and screened for CTLV in pooled batches by conventional and real-time RT-PCR. No positive samples were detected and results indicated a lack of virus seed transmission in ‘Meyer’ lemon. Findings of this study are therefore not supportive of CTLV seed transmission in citrus.

Citrus dwarfing viroid reduces canopy volume by affecting shoot apical growth of navel orange trees grown on trifoliate orange rootstock

Author(s): Lavagi-Craddock, I; Campos, R; Pagliaccia, D; Kapaun, T; Lovatt, C; Vidalakis, G | Abstract: Citrus dwarfing viroid (CDVd) infection of navel orange trees (Citrus sinensis (L.) Osb.) on ‘Rich 16-6’ trifoliate orange (Poncirus trifoliata (L.) Raf.) rootstock has been previously reported to reduce canopy volume by approximately 50%. We demonstrated that the reduction in tree size of CDVd-infected citrus resulted from a g20% reduction in the apical growth of individual shoots within the tree canopy. We also demonstrated that the reduced canopy volume of the CDVd-infected trees is a long lasting phenotype comparable to that of ‘Flying Dragon’ rootstock, which is known to reduce citrus tree size.

Boron mitigates citrus root injuries by regulating intracellular pH and reactive oxygen species to resist H+-toxicity

Boron (B)-deficiency and H+-toxicity are important limiting factors for plants growth in acid soils. High B supply may reduce H+-toxicity-induced inhibition of growth in citrus. Trifoliate orange rootstock seedlings were irrigated with nutrient solution containing either 0 μM or 10 μM H3BO3 at two pH levels (pH4 (H+-toxicity) and pH6 (normal)). The results showed that H+-toxicity without B severely hampered main root elongation. Simultaneously, oxidative damage caused by H+-toxicity led to severe damage to the apical structure of root such as root crown abscission. However, B application promoted the root length, root cell viability and reduced cell wall (CW) thickness of root tips under H+-toxicity. Additionally, B application reduced the H+-toxicity-induced reactive oxygen species (ROS) accumulation in roots as characterized by lower fluorescence intensity of H2O2 and O2- staining. Moreover, 31P-NMR (31P nuclear magnetic resonance) spectra revealed B application regulated the pH of vacuoles and cytoplasm in root tips by reducing phosphoenolpyruvate carboxykinase (PEPCase) activity while enhancing NADP malic enzyme (NADP-ME) activity during H+-toxicity. Collectively, our results demonstrate that B supply alleviates H+-toxicity and promotes root growth by reducing ROS accumulation, attenuating intracellular acidic microenvironment to ensure normal chemical reactions in root tip cells.

Effects of Bacteria and IBA on the Rooting of Bitter Orange (Citrus aurantium L.) and Trifoliate Orange (Poncirus trifoliata Raf.) Cuttings

In this study, the effects of Agrobacterium rubi A-18 and Bacillus OSU-142 bacterial strains alone and in combination with 1000, 2000, 4000 ppm IBA on rooting of bitter orange and trifoliate orange citrus rootstock in softwood, semi-hardwood and hardwood cuttings were investigated. In the case of IBA solution, Agrobacterium rubi A-18 and Bacillus OSU-142 were prepared in solution at a concentration of 1x10 9 bacteria / ml and applied to steel. Application is made in the mist propagation system, in the perlite are planted in the environment. Steels kept in the fogging environment for 3 months were removed at the end of this period and rooting rates (%), callus formation rates (%) and survival rates (%) were determined. According to the results of the research, the rooting rates of the steels taken at different periods were found to be low. The highest rooting rates of bitter orange softwood cuttings were 2000 ppm IBA + OSU-142 (6.67%), semi-hardwood cuttings OSU-142 (20.00%), and 4000 ppm IBA + OSU-142 (20.00%) in hardwood cuttings. It has been not rooting in trifoliate orange softwood cuttings, the highest rooting was in the case of semi-hardwood cuttings with 4000 ppm IBA + OSU-142 (26.67%), in hardwood cuttings 1000 ppm IBA + OSU-142, 2000 ppm IBA + OSU-142, 4000 ppm IBA + OSU-142, 1000 ppm IBA + A-18, 2000 ppm IBA + A-18 and 4000 ppm IBA + A-18 (20.00%). According to the cuttings pick-up period, the rooting rates of bitter orange are not different between the periods, in the trifoliate orange the hardwood cuttings were found to be higher. As a result, it can be said that plant growth promoting bacteria and IBA applications have no effect on rooting in the softwood, semi-hardwood and hardwood cuttings of the bitter orange and trifoliate orange citrus rootstocks, it can be said that studies on rooting in these rootstocks can be useful in different bacterial breeds

Response of Grafting Height on Growth Success of Acid Lime (Citrus aurantifolia Swingle) Saplings

A field experiment was conducted at Agriculture Research Institute Tarnab, Peshawar, to determine the best grafting height for the highest success of grafting and the maximum growth of Sapling during 1st January to 30th December 2017. Scions were collected from the mother plant ‘Kaghazi lime’ grown under screen house and grafted onto one-year-old trifoliate orange Sapling rootstocks by shoot-tip method at 4cm, 8cm, 12cm, 16cm and 20cm height from the collar region as the treatment. The grafts were planted inside the closed tunnel made from bamboo splits, jute and plastic sheet at 10×8cm spacing in 64×100cm experimental plots laid out in randomized complete block design (RCBD) with four replications containing 80 grafts per plot. Treatments were allotted on the experimental plots randomly. The success of grafting was not affected by the height of grafting however, growth of Sapling was found significantly affected by the height of grafting. Observation taken on Sapling after one year of grafting revealed that the maximum scion height (42.13cm), the highest number of leaves per Sapling (47.50), the highest growth of scion diameter (55.61%), maximum length of primary branches (31.19cm), maximum number of secondary branches per Sapling (3.24), the highest length of secondary branches (11.59cm), the highest canopy volume (15440cm3) and the highest graft spread (24.35cm) were found on the Sapling grafted at 16cm height of the trifoliate orange rootstock. Hence, from the study it is concluded that the most suitable height of grafting acid lime on trifoliate orange rootstock was 16cm.