Grapefruit Trees Research Articles

Seasonal Dynamic of NO3− and K+ in a Citrus Crop Irrigated by Different Water Qualities

This study evaluated the effect of (i) irrigation water source: transfer (TW) and reclaimed water (RW), and (ii) crop phenological stage: winter rest (WR), flowering-sprouting (FS), and fruit growth (FG), on NO3− and K+ dynamics in soil and leaf of a citrus crop. The experiment was carried out during the 2018 and 2019 growing seasons on adult ‘Star Ruby’ grapefruit trees (Citrus paradisi Macf.). The concentration of both nutrients was periodically measured in soil and leaf samples and continuously monitored in the soil soluble fraction with nutrient sensors. Moreover, soil NO3− leaching was indirectly estimated by the periodic measurement of the leaf enrichment in 15N isotope (15Nleaf). The two water sources showed a different nutrient loading. Thus, NO3− and K+, were approximately 5 and 7 times higher, respectively, in the RW. Furthermore, the average contents of NO3− and K+ in the soil samples from the RW treatment were 10.1 and 19.7%, respectively, higher than in TW, with the highest soil NO3− leaching observed in RW treatment. In line with this, the mean contents of NO3− and K+ in the leaves from the RW treatment were 106.9 and 30.4% higher than the TW ones. As for the different phenological stages, in the FG stage, the lowest concentrations of NO3− in the soil samples and the highest in the leaf tissue were observed after a high soil leaching event. In this study the nutrient sensors measurements varied according to the dynamic of NO3− and K+ in the soil samples. The use of RW promoted an accumulation of NO3− and K+ in the soil and leaves of grapefruit trees, but also enhanced soil NO3− leaching, indicating that the proper management of this water source is necessary to avoid soil contamination. The mobilization of NO3− and K+ from soil to leaf was the highest in the FG stage, to ensure fruit development and vegetative growth.

Study on the Population and Composition of Parasitic Nematodes related to Da Xanh Pomelo (Citrus maxima) in Tien Giang Province, Vietnam

Da Xanh grapefruit is a fruit tree with many nutrients and high economic value. However, nematode attack is one of the factors that limit productivity. Based on the approach of surveying gardens with symptoms of yellow leaves and root rot, collect and analyze samples. Results of surveying the composition of plant parasitic nematodes in Tien Giang province discovered 11 genera belonging to 8 families of plant parasitic nematodes present in the soil and root zone of Da Xanh grapefruit trees. Thus, 12 nematode species have been identified including: Aphelenchus avenae, C. onoensis, Helicotylenchus crenacauda, H. digonicus, P. coffeae, Rotylenchulus reniformis, Rotylenchus dalhousiensis, Tylenchorhynchus leviterminalis, Tylenchulus semipenetrans, Xiphinema insigne, X. longicaudatum. The species T. semipenetrans appeared at 80% and 76.67% in soil and root samples, which is an important species that needs to be controlled; P. coffeae and R. reniformis are dominant in roots and should be of concern as populations increase. Besides, it also shows that in garden samples with yellow leaf and root rot symptoms, the population of T. semipenetrans nematodes is very high compared to previous studies.

Assessment of Grapefruit Expressing Anti-NodT Antibody for Huanglongbing Resistance

Growers rely on broad-spectrum agrochemicals to manage one of the most economically important fruit tree diseases, huanglongbing (HLB, citrus greening disease), presumptively caused by the gram-negative bacterium ‘ Candidatus Liberibacter asiaticus’ ( CLas). Although genetic resistance would be an attractive alternative to chemical management, this option is not yet available for HLB. Here, we tested whether a single chain variable fragment (scFv) antibody targeting the predicted CLas outer membrane transporter NodT can inhibit CLas growth or HLB disease development when expressed in ‘Duncan’ grapefruit ( Citrus × paradisi). CLas NodT is similar to TolC and could be involved in Type I secretion and virulence. The scFv antibody was expressed in grapefruit trees as a C-terminal translational fusion to the Flowering Locus T protein of Poncirus trifoliata (FT-scFv) to promote expression in the phloem. Wild-type and FT-scFv-expressing transgenic lines were challenged with CLas using three inoculation approaches: psyllid-mediated inoculation, vegetative graft inoculation, and natural exposure in grove-like conditions. With the first two approaches, HLB symptom expression and CLas bacterial titers in FT-scFv grapefruit lines were not significantly different from wild-type controls. In the grove trial, one FT-scFv line exhibited a slight, but significant, reduction in canopy chlorosis compared to wild-type controls. Wild-type and FT-scFv lines were similar in all other metrics. We conclude that the expression of anti-NodT FT-scFv antibody in grapefruit did not decrease HLB susceptibility. Although our approach was unsuccessful, we hope that documenting our results will be useful for those seeking to develop HLB-resistant citrus germplasm in the future. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Involvement of Phytophthora citrophthora and Phytophthora nicotianae in severe decline and gummosis of grapefruit (Citrus x paradisi Macfad.) in southern Türkiye

AbstractSince the summer of 2020, severe decline and gummosis were observed on 20‐ to 30‐year‐old grapefruit trees cv. Star Ruby in Antalya province in the Western Mediterranean region of Türkiye. Grapefruit trees were examined in affected commercial orchards in Aksu, Manavgat, Muratpaşa and Serik counties, located near the coast of the Mediterranean Sea. Symptomatic trees exhibited leaf discoloration, defoliation and severe dieback, as well as dark, water‐soaked lesions with gum exudates, characteristic of Phytophthora infections, formed on the bark of the main stem and major limbs. No Phytophthora species could be isolated from these bark tissues, while two were obtained from soil samples taken from around symptomatic trees. Based on morphological characteristics, isolates were identified as P. citrophthora and P. nicotianae. Identifications were confirmed by sequencing of the internal transcribed spacer (ITS) and the cytochrome oxidase I (cox1) gene regions. Pathogenicity tests, carried out by inoculations of the main stems and branches of grapefruit seedlings cv. Star Ruby indicated that both species were pathogenic. All P. citrophthora and P. nicotianae isolates obtained in this work were sensitive to mefenoxam. EC50 values of P. citrophthora isolates were between 0.284 and 0.285 μg mL−1, whereas those of P. nicotianae were between 0.288 and 0.291 μg mL−1. Phytophthora citrophthora was previously known to cause disease on citrus in Türkiye, but this is the first report of P. nicotianae causing citrus gummosis in the country. Because P. nicotianae is more widespread than P. citrophthora, it should be considered a threat to citrus cultivation in this region of Türkiye.

Co-Occurrence Analysis of Citrus Root Bacterial Microbiota under Citrus Greening Disease.

Candidatus Liberibacter asiaticus (CLas) is associated with Citrus Huanglongbing (HLB), a devastating disease in the US. Previously, we conducted a two-year-long monthly HLB survey by quantitative real-time PCR using root DNA fractions prepared from 112 field grapefruit trees grafted on sour orange rootstock. Approximately 10% of the trees remained CLas-free during the entire survey period. This study conducted 16S metagenomics using the time-series root DNA fractions, monthly prepared during twenty-four consecutive months, followed by microbial co-occurrence network analysis to investigate the microbial factors contributing to the CLas-free phenotype of the aforementioned trees. Based on the HLB status and the time when the trees were first diagnosed as CLas-positive during the survey, the samples were divided into four groups, Stage H (healthy), Stage I (early), II (mid), and III (late) samples. The 16S metagenomics data using Silva 16S database v132 revealed that HLB compromised the diversity of rhizosphere microbiota. At the phylum level, Actinobacteria and Proteobacteria were the predominant bacterial phyla, comprising >93% of total bacterial phyla, irrespective of HLB status. In addition, a temporal change in the rhizosphere microbe population was observed during a two-year-long survey, from which we confirmed that some bacterial families differently responded to HLB disease status. The clustering of the bacterial co-occurrence network data revealed the presence of a subnetwork composed of Streptomycetaceae and bacterial families with plant growth-promoting activity in Stage H and III samples. These data implicated that the Streptomycetaceae subnetwork may act as a functional unit against HLB.

A host‐derived chimeric peptide protects citrus against Huanglongbing without threatening the native microbial community of the phyllosphere

AbstractIntroductionThe application of host‐derived antibacterial peptides has been highlighted as a potential efficacious and safe tool for the treatment of Huanglongbing (HLB), the most devastating disease of citrus. However, pathogenic bacteria such as HLB‐causing Candidatus liberibacter asiaticus (CLas) often develop resistance against the host antibacterial peptides. We showed that chimeras containing two different host antibacterial peptides not only retain antibacterial activity but also overcome bacterial resistance and enhance plant defence responses. Also, chimeric peptides can have an off‐target impact on the structure and function of plant‐associated microbiomes. However, there is a lack of understanding of the impact of the chimeric peptide therapy on the microbial structure in the citrus phyllosphere while reducing the CLas titre. Here, we aim to evaluate the efficacy of a chimeric peptide (UGK17) to reduce CLas titre, inducing plant defence response and impacting the microbiome associated with the citrus phyllosphere.Material and MethodLeaf samples were collected from orange and grapefruit trees in Texas and identified as old and young leaves according to their maturity. We collected three different types of leaves based on their infection and symptoms: healthy, symptomatic (infected with typical symptoms), and asymptomatic (infected without symptoms). In planta assay was performed by dipping the leaves in the 0, 5 and 25 μM of UGK17 solutions for 48 h. The quantifications of CLas titre and pathogenesis‐related (PR) gene expression were done by quantitative polymerase chain reaction (qPCR) and reverse transcription‐qPCR, respectively. Amplicon sequencing was done to evaluate the impact of UGK17 on individual bacterial community structures. In addition, we performed an ex planta assay to assess the effect of UGK17 on the growth of bacterial isolates including Liberibacter crescens instead of unculturable CLas predominant in the phyllosphere.ResultThe UGK17 treatment reduced the CLas titre in both asymptomatic and symptomatic citrus leaves, regardless of the age of the leaves. The UGK17 application augmented the PR gene expression. In ex planta assay, the growth of L. crescens along with four other strains belonging to the family Rhizobiaceae, was significantly inhibited by the UGK17 while the growth of 74 strains were unaffected. Additionally, there was no statistically significant changes in the microbial community structure with UGK17 treatment.ConclusionOur results suggest that the chimeric peptide therapy is a promising solution to combat HLB by targeting mainly Gram‐negative pathogens and enhancing the plant immune responses without impairing the indigenous microbial community in the citrus phyllosphere.

Uptake of micronutrients in severely HLB-affected grapefruit trees grown on Florida Indian River flatwood soils

Citrus greening (HLB, huanglongbing) is caused by the phloem-limited bacterium Candidatus Liberibacter asiaticus and vectored by the Asian citrus psyllid. To combat HLB-induced nutrient uptake issues, growers use higher fertilizer application rates to prolong the producing life of affected trees. However, current nutrient recommendations in Florida were created in pre-HLB times and must be adjusted. Therefore, the objective of this study was to compare granular and liquid fertilization to identify best application methods for uptake of micronutrients into both belowground and aboveground components of HLB-affected grapefruit grown on flatwood soils. A large-scale field study consisting of 6-year-old HLB-affected “Ruby Red” grapefruit trees grafted on “sour orange” rootstock was conducted in the Florida Indian River District. Eight different treatments consisting of four liquid and four granular fertilizers with 1×, 2×, and 4× the current University of Florida, Institute of Food and Agricultural Sciences recommended rates of boron, zinc, manganese, and iron were applied three times a year (granular), biweekly (liquid), or weekly (liquid), for 3 years. Analyses of nutrients in soil, root, and leaf were conducted every 6 months throughout the study. Higher rates of boron, zinc, and manganese were observed in the soil of plots treated with liquid fertilizers with 2× and 4× the micronutrient recommendations. Root and leaf micronutrient analysis revealed significant differences in boron, zinc, manganese, and iron among treatments which varied between seasons. This study demonstrated that ground-applied micronutrient overdoses and application methods impacted nutrient uptake, however, no patterns with soil concentrations and tree uptake were established.

Trunk Injection of Oxytetracycline for Huanglongbing Management in Mature Grapefruit and Sweet Orange Trees.

Huanglongbing (HLB) is a devastating bacterial disease associated with 'Candidatus Liberibacter asiaticus'. The location of the pathogen within the vasculature of the tree has left growers with limited options for the effective management of the disease. Trunk injection is a crop protection technique that applies therapeutics directly into the xylem of woody tree species and allows for their systemic uptake and transport, which may provide more effective management of vascular diseases such as HLB. In this study, mature 'Valencia' and 'Hamlin' sweet orange (Citrus sinensis) and 'Duncan' grapefruit (C. paradisi) trees were injected with oxytetracycline (OTC) in the spring and/or fall to evaluate the effects of injection timing and response to injection. In addition to seasonal evaluations of tree health and bacterial titer, preharvest fruit drop, yield, and fruit quality were measured at harvest to determine the effects of OTC injection. The benefits associated with injection included a reduction in fruit drop, an increase in fruit yield and fruit size, and improvements in juice quality. However, results varied due to the timing of injection and were not consistent across all three varieties. Residue analysis at different time points after injection suggests that trunk injection effectively delivers therapeutics to mature citrus trees. This study provides fundamental information on the short-term benefits associated with trunk injection of OTC for HLB management in citrus groves. The potential for use of trunk injection at the commercial scale and the possible risks are discussed.

Grapefruit Root and Rhizosphere Responses to Varying Planting Densities, Fertilizer Concentrations and Application Methods.

Huanglongbing (HLB) disease has caused a severe decline in citrus production globally over the past decade. There is a need for improved nutrient regimens to better manage the productivity of HLB-affected trees, as current guidelines are based on healthy trees. The aim of this study was to evaluate the effects of different fertilizer application methods and rates with different planting densities on HLB-affected citrus root and soil health. Plant material consisted of 'Ray Ruby' (Citrus × paradisi) grapefruit trees grafted on 'Kuharske' citrange (Citrus × sinensis × Citrus trifoliata). The study consisted of 4 foliar fertilizer treatments, which included 0×, 1.5×, 3× and 6× the University of Florida Institute of Food and Agriculture (UF/IFAS) recommended guidelines for B, Mn and Zn. Additionally, 2 ground-applied fertilizer treatments were used, specifically controlled-release fertilizer (CRF1): 12-3-14 + B, Fe, Mn and Zn micronutrients at 1× UF/IFAS recommendation, and (CRF2): 12-3-14 + 2× Mg + 3× B, Fe, Mn and Zn micronutrients, with micronutrients applied as sulfur-coated products. The planting densities implemented were low (300 trees ha-1), medium (440 trees ha-1) and high (975 trees ha-1). The CRF fertilizer resulted in greater soil nutrient concentrations through all of the time sampling points, with significant differences in soil Zn and Mn. Grapefruit treated with ground-applied CRF2 and 3× foliar fertilizers resulted in the greatest bacterial alpha and beta diversity in the rhizosphere. Significantly greater abundances of Rhizobiales and Vicinamibacterales were found in the grapefruit rhizosphere of trees treated with 0× UF/IFAS foliar fertilizer compared to higher doses of foliar fertilizers.

Effects of various soil structure and irrigation regimes on rio-red grapefruit yield and morpo-physiology

The research was carried out in 2011 using Rio-Red grapefruit trees in Research Station of Cukurova University, Agricultural Faculty, Citrus experiment Station, Adana Latitude, 5°2 ’ N Longitude, 6°50’ E, altitude 27 m).In the study, it was aimed to determine the effects of the amount of irrigation water applied at different levels to the trees growing in soils of different soil texture on fruit development and yield, tree trunk development, tree canopy volume development, leaf area index(LAI) and photosynthesis rate. The research area soils contain three different groups in terms of resistivity values and the trees are grown in soils electrical conductivity (ECa) with T1: 86-109, T2: 23-37 and T3: 62-72 ECavalues.In the experiment, three different irrigation levels I100, I70 and I50 water was applied. The average amount of irrigation water applied to grapefruit trees ranged from 332,48 mm (I100) to 178,92 mm (I50). Actual plant water consumption was between 810.5 mm (I100) and 694.4 mm (I50) according to the water budget method. Yields related to irrigation on trees in the plot varied between 883 (I70) and 828 (I50) kg per tree on average. It has been determined as 1050 kg on average from the fully irrigated I100. Photosynthesis values were measured as 2.64 umol/m2/s for I50, 3.48 umol/m2/s for I70 and 4.77 umol/m2/s for I100. Consequently, the effects of irrigation treatmentson fruit yield are not statistically significant, water reduction can be recommended for the region in order to save water for the farmers in this study.

The First Record of Ero aphana (Araneae: Mimetidae) in Egypt

Sawers, M.A.R., S.M.O. El-Bishlawy, M.F. Hassan and G.M.S. Sallam. 2023. The First Record of Ero aphana (Araneae: Mimetidae) in Egypt. Arab Journal of Plant Protection, 41(1): 15-17. https://doi.org/10.22268/AJPP-41.1.015017 This investigation presents a new record, Ero aphana (Walckenaer, 1802) (Araneae: Mimetidae) in the Egyptian fauna. It was found in the Experimental Station of the Faculty of Agriculture, Cairo University, Giza Governorate, Egypt on grapefruit trees (Citrus paradise) on October 1, 2018. Six Specimens; one male and five Juveniles of E. aphana were collected and identified. In addition, notes on the description, environmental conditions and collection data of this species are given. Photos of general habitus and palpal organ of the male and measurements of leg segments are illustrated. Keywords: Araneae, Mimetidae, Ero aphana, new record, Egypt

PM 7/31 (2) Citrus tristeza virus

<scp>PM</scp> 7/31 (2) Citrus tristeza virus

Estimation of stomatal conductance by infra-red thermometry in citrus trees cultivated under regulated deficit irrigation and reclaimed water

The aim of this study was to evaluate the robustness of infra-red thermometry to estimate stomatal conductance (gs) in grapefruit trees. For this purpose, the ability of several thermal indices to determine gs was tested for different: (i) irrigation strategies: full irrigation (FI) and regulated deficit irrigation (RDI), (ii) water sources: transfer water (TW) -optimal for agricultural uses- and saline reclaimed water (RW) and (iii) phenological stages: flowering-sprouting (FS) and fruit growth (FG). During two growing seasons, measurements of gs and canopy temperature (Tc) were taken in 14-year-old ´Star Ruby´ grapefruit trees (Citrus paradisi Macf.,). Air temperature (Ta) was also recorded and then the derived thermal indices: Tc-Ta, and CWSI (crop water stress index) were calculated. Subsequently, thermal-gs correlations were established at different averaged thermal data intervals, and VPD (vapour pressure deficit) and PAR (photosynthetically active radiation) conditions. The results indicated that both, water quality and deficit irrigation, affected negatively gs and Tc during FG. In addition, the highest r2 values in thermal indices-gs correlations were found when i) the thermal data was averaged 60 min before the gs measurement, ii) gs was measured over a wide range of VPD (between 0 and 3.5 kPa), and iii) PAR was 1200 µmol m−2 s−1. The ability of the thermal indices to estimate gs improved under RDI and RW conditions, when compared to the control treatment (TW-FI). Moreover, the thermal indices that more accurately estimated gs were Tc-Ta and CWSI in FS (P < 0.001), and the absolute values of Tc in FG (P < 0.001). Overall, thermal indices obtained by infra-red sensors could be a useful tool to estimate gs in grapefruit trees. However, irrigation treatment, water quality, tree phenological stage and environmental conditions (VPD and PAR) must be considered when interpreting thermal indices-gs correlations.

Root-Shoot Nutrient Dynamics of Huanglongbing-Affected Grapefruit Trees

With huanglongbing (HLB) causing a reduction in fine root mass early in disease progression, HLB-affected trees have lower nutrient uptake capability. Questions regarding the uptake efficiency of certain fertilizer application methods have been raised. Therefore, the goals of this study are to determine if nutrient management methods impact nutrient translocation and identify where in the tree nutrients are translocated. Destructive nutrient and biomass analysis were conducted on field grown HLB-affected grapefruit trees (Citrus × paradisi) grafted on 'sour orange' (Citrus × aurantium) rootstock under different fertilizer application methods. Fertilizer was applied in the form of either 100% soluble granular fertilizer, controlled release fertilizer (CRF), or liquid fertilizer. After three years, the entire tree was removed from the grove, dissected into eight different components (feeder roots, lateral roots, structural roots, trunk, primary branches, secondary branches, twigs, and leaves), weighed, and then analyzed for nutrient contents. Overall, application methods showed differences in nutrient allocation in leaf, twig, and feeder root; however, no consistent pattern was observed. Additionally, leaf, twig, and feeder roots had higher amount of nutrients compared to the other tree components. This study showed that fertilization methods do impact nutrient contents in different components of HLB-affected trees. Further research should be conducted on the impact of different fertilizer application methods and rates on HLB-affected trees.

Early Performance of Recently Released Rootstocks with Grapefruit, Navel Orange, and Mandarin Scions under Endemic Huanglongbing Conditions in Florida

Huanglongbing (HLB), which is believed to be caused by the phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas), has decimated Florida’s citrus production. Grapefruit production has declined 75%, mandarin 78%, and sweet orange 52% due to the high sensitivity of commercial scions and rootstocks to the disease. New combinations of scions and hybrid rootstocks may provide better performance than current commercial selections for Florida’s fresh citrus production, particularly in the Indian River District. The objective of this study was to evaluate and compare University of Florida rootstocks and other recently released rootstocks grafted with grapefruit, navel orange, and mandarin scions by measuring tree growth and HLB tolerance. Three independent large-scale field trials were established in September 2019 in Fort Pierce, FL, USA. Trial 1 (T1) included 36 rootstocks with ‘Ray Ruby’ grapefruit as the scion; Trials 2 and 3 (T2 and T3, respectively) included 30 rootstocks with ‘Glenn’ navel orange F-56-11 and ‘UF-950’ mandarin as the scion, respectively. Tree canopy volume, trunk diameter, CLas titer, HLB severity index, and leaf nutrient concentrations were evaluated during 2020 and 2021. Significant differences among rootstock-scion combinations were found in each trial for most of the assessed traits. In T2, UFR-15 consistently developed the largest ‘Ray Ruby’ grapefruit trees during both years. In T3, ‘Glenn’ navel orange F-56-11 trees were larger on C-22, and US-802. Similarly, US-802 and US-942 generated the largest ‘UF-950’ mandarin trees. Overall, trees had optimum levels of macro- and micronutrients except for calcium. CLas infection and HLB visual index varied among scion-rootstock combinations, especially during the first year of growth when intensive flushing was produced. Generally, trees grew vigorously with WGFT+50-7 and Willits inducing the lowest HLB symptoms in all evaluations. Production and fruit quality need to be evaluated to determine the suitability of potential scion-rootstock combinations that can confer consistent economical and biological advantages under the current HLB scenario in the Indian River District.

Population dynamics of Citrus tristeza virus (CTV) in single aphid-transmitted sub-isolates of the South African GFMS12 isolate.

Grapefruit trees in South Africa have been cross protected against severe stem pitting genotypes of Citrus tristeza virus (CTV) since the 1920s using a mild strain initially called 'Nartia' but later referred to as grapefruit mild strain 12 (GFMS12).In the current study, the GFMS12 isolate was used as the source for single aphid transmissions (SAT) using Toxoptera citricida, commonly called the brown citrus aphid (BrCA). The BrCA-transmitted CTV sub-isolates were analyzed by the heteroduplex mobility assay (HMA), serological assays, genetic marker analysis (GMA), and selected sub-isolates were biologically indexed. Reverse transcription PCR of genomic regions was conducted using universal primers followed by cloning the PCR products, HMA and sequence analysis; nine genotypes of CTV were identified in the complex of GFMS12, including both severe and mild genotypes. A singleBrCAtransmitted up to six CTV genotypes simultaneously in one sub-isolate. The HMA was found to be a rapid, reliable tool for the identification of genotypes and can be useful in the development of CTV management strategies and budwood certification programs.

Impact of Ground Applied Micronutrients on Root Growth and Fruit Yield of Severely Huanglongbing-Affected Grapefruit Trees

Citrus greening (huanglongbing, HLB) is a bacterial disease caused by Candidatus Liberibacter asiaticus (CLas) and vectored by the Asian citrus psyllid (Diaphorina citri) (ACP). No cure is yet available, and as a result, increased fertilizer applications continue to be a major management method used to prolong the productive life of affected trees. However, questions remain regarding proper fertilizer rates and in what form these nutrients should be applied to increase tree health and yield. Therefore, the goal of this study was to identify optimum micronutrient application forms and rates to increase root growth, canopy size and fruit yield as well as reduce leaf and root CLas cycle threshold (Ct) value of HLB-affected grapefruit trees (Citrus × paradisi Macfad). A large-scale field study consisting of six-year-old HLB-affected ‘Ruby Red’ grapefruit trees grafted on ‘sour orange’ (Citrus × aurantium) rootstock was conducted in the Florida Indian River District. Eight different treatments consisting of four granular and four liquid fertilizers with 1×, 2×, and 4× the current University of Florida, Institute of Food and Agricultural Sciences recommended rates of boron, zinc, manganese, and iron were applied for three times a year (granular), biweekly (liquid), or weekly (liquid), for three years. Root density, length and diameter, root, and leaf CLas Ct value, canopy volume, visual HLB symptoms, and fruit yield were measured throughout the study. Regardless of treatment, tree health declined over time, and no significant impact on severely HLB-affected grapefruit tree health was detected within the three-year time frame of the study. This was the first study to solely compare the impact of ground applied micronutrient application rates and methods on HLB-affected grapefruit tree health in Florida’s Indian River District. More time would be needed to determine the potential benefits of increased micronutrient performance of HLB-affected grapefruit trees.

IMPROVING THE ECONOMIC EFFICIENCY OF GRAPEFRUIT FARMS IN PHUC NINH COMMUNE - YEN SON DISTRICT - TUYEN QUANG PROVINCE

The study surveyed 90 grapefruit farms in Phuc Ninh commune, Yen Son district, Tuyen Quang province and adopted a number of economic research methods to evaluate and analyze factors affecting the economic efficiency of grapefruit production. The results of the study show that grapefruit is a fruit tree with high economic value, a key crop, contributing to income growth, poverty reduction for people in Phuc Ninh commune. In recent years, the area, productivity, and output of grapefruits of farms in Phuc Ninh commune have been constantly increasing. However, the selling price is not stable, the market for products is difficult, leading to the economic efficiency of grapefruit production of farmers is not high and unsustainable. The research results also show that a number of factors positively influence the economic efficiency of grapefruit production of farms, such as production scale, investment capital, VietGap model, age of grapefruit trees, and product-selling time. On that basis, the study proposed a number of solutions to improve the economic efficiency of grapefruit production of farms in Phuc Ninh commune.

Biochemical Origin of Raman-Based Diagnostics of Huanglongbing in Grapefruit Trees.

Biotic and abiotic stresses cause substantial changes in plant biochemistry. These changes are typically revealed by high-performance liquid chromatography (HPLC) and mass spectroscopy-coupled HPLC (HPLC-MS). This information can be used to determine underlying molecular mechanisms of biotic and abiotic stresses in plants. A growing body of evidence suggests that changes in plant biochemistry can be probed by Raman spectroscopy, an emerging analytical technique that is based on inelastic light scattering. Non-invasive and non-destructive detection and identification of these changes allow for the use of Raman spectroscopy for confirmatory diagnostics of plant biotic and abiotic stresses. In this study, we couple HPLC and HPLC-MS findings on biochemical changes caused by Candidatus Liberibacter spp. (Ca. L. asiaticus) in citrus trees to the spectroscopic signatures of plant leaves derived by Raman spectroscopy. Our results show that Ca. L. asiaticus cause an increase in hydroxycinnamates, the precursors of lignins, and flavones, as well as a decrease in the concentration of lutein that are detected by Raman spectroscopy. These findings suggest that Ca. L. asiaticus induce a strong plant defense response that aims to exterminate bacteria present in the plant phloem. This work also suggests that Raman spectroscopy can be used to resolve stress-induced changes in plant biochemistry on the molecular level.

Effect of irrigation practices upon yield and fruit quality of four grapefruit (Citrus paradisiMac.) cultivars

AbstractTwo strategies of irrigation were applied during the phase of fruit growth in 30-year-old grapefruit trees (Citrus paradisi Mac.) of four varieties (cv. Marsh SRA 8, cv. Shambar SRA 22, cv. Frost Marsh, cv. Ruby). For the first strategy (T1), the trees were irrigated every week at 100% crop evapotranspiration (ETc), while for the second strategy (T2) at 60% ETc. At harvest time, tree yield was estimated along with fruit quality and water productivity. T1 strategy significantly increased the tree yield, the fruit weight and the juice content. Although an increase in water productivity (crop yield/total water use) was achieved during the water stress experiment for three out of the four varieties. The main effect of the T2 strategy was a significant increase of qualitative (commercial and nutritional) attributes like total soluble solids (TSS), citric acid, ascorbic acid (Vitamin C) and phenolic content. In addition, strategy T2 increased the maturation index and the fruits had sweeter flavor for two varieties. These results lead to the conclusion that in mature grapefruit trees, optimal irrigation practice provided better fruit yield, while water stress practices favor the accumulation of specific nutritional elements and improve specific fruit quality parameters, especially for cv. Ruby.