Citrus Industry Research Articles

Citrus Industry Agglomeration and Citrus Green Total Factor Productivity in China: An Empirical Analysis Utilizing a Dynamic Spatial Durbin Model

In the context of increasingly severe resource and environmental constraints, examining the impact of citrus industry agglomeration on the green total factor productivity (GTFP) of citrus is of great importance for the sustainable development of the citrus industry and is crucial for promoting the green, high-quality growth of China’s agricultural sector. In this study, the global Malmquist–Luenberger productivity index (GMLPI) model was used to measure the GTFP of mandarins and tangerines based on inter-provincial panel data from China’s major citrus-producing regions between 2007 and 2022. The dynamic spatial Durbin model was employed to empirically analyze the effects of citrus industry agglomeration on the GTFP of mandarins and tangerines, including the disaggregation of its spatial spillover effects. The results indicate that, in terms of temporal dynamics, the GTFP, technical progress index (GTC), and technical efficiency index (GEC) of mandarins and tangerines significantly fluctuated, especially during the period from 2007 to 2015. Regional disparities in GTFP and the GTC are more pronounced for mandarins than for tangerines, while the GEC shows greater regional disparities for tangerines than for mandarins. The intensification of citrus industry agglomeration has had a significant positive impact on the GTFP of mandarins and tangerines, both locally and in neighboring regions. The spatial correlation of the green total factor productivity of mandarins and tangerines fluctuated; mandarins showed significant spatial aggregation in some years, while tangerines showed significant spatial dispersion in several years. The local Moran scatterplot further reveals the significant negative spatial autocorrelation of mandarin and tangerine green total factor productivity from 2007 to 2022. The direct, indirect, and total effects of citrus industry agglomeration on the GTFP of mandarins and tangerines are significant and positive in both the short- and long-term, with short-term benefits exceeding long-term effects. Consequently, enhancing regional cooperation and exchange while advancing citrus industry agglomeration is essential for sustained productivity growth.

Construction of an Infectious Clone of Citrus Chlorotic Dwarf-Associated Virus and Confirmation of Its Pathogenicity.

Citrus chlorotic dwarf disease (CCDD) seriously affects the citrus industry. Citrus chlorotic dwarf-associated virus (CCDaV) is speculated to be the causal agent of CCDD. However, this speculation has not been confirmed by fulfilling Koch's postulates. In this study, an infectious clone comprising a 1.6-fold tandem CCDaV genome in the binary vector pBinPLUS was constructed and agro-inoculated into 'Eureka' lemon (Citrus limon) seedlings through vacuum infiltration. At 60 days postinoculation, 25% of the 'Eureka' lemon seedlings developed symptoms of crinkling and curling that were the same as those associated with the wild-type virus. Western blotting and graft transmission assays confirmed that the infectious clone systemically infected 'Eureka' lemon seedlings. In addition, CCDaV can establish infection on three more Citrus species and one hybrid, although at different infection rates. These findings support that CCDaV is the primary causal agent of CCDD. The infectious CCDaV clone will allow further studies on the functions of viral proteins and molecular interactions of CCDaV with its hosts.

Virus-Induced Gene Silencing Simultaneously Exploits ‘Attract and Kill’ Traits in Plants and Insects to Manage Huanglongbing

Abstract The vector-borne disease Huanglongbing (HLB) causes severe economic losses to citrus production worldwide with no available cure. Herein, we applied virus-induced gene silencing technology to engineer citrus that preferentially attracted and specifically killed Diaphorina citri, the vector associated with HLB. We engineered the infectious citrus tristeza virus (CTV-T36) clone to carry three truncated genes. The triple construct (CTV-tAwd-tWnt-tPDS) produces small interfering RNAs (siRNAs) against phytoene desaturase, PDS, to yield a phenotype with visual, olfactory, and gustatory cues that preferentially attracted D. citri. In addition, siRNAs targeted two genes related to flight in D. citri, abnormal wing disc (DcAwd) and wingless (DcWnt), that caused wing malformations and decreased survival in psyllids that fed on plants inoculated with the engineered virus. During two successive generations, D. citri reared on CTV-tAwd-tWnt-tPDS-inoculated plants exhibited higher mortality across life stages as well as reduced fecundity and fertility as compared with those reared on non-infected plants or CTV-wt-inoculated plants. Furthermore, CTV-tAwd-tWnt-tPDS-inoculated plants shortened the lifespan of D. citri by more than 20 days. Morphological abnormalities were noted in those adults that did successfully emerge on plants inoculated with CTV-tAwd-tWnt-tPDS, including cocked wings with a bowl-shaped depression and/or a convex shape. Phloem sap from CTV-tAwd-tWnt-tPDS-inoculated plants decreased the survival of D. citri adults, confirming that siRNAs were present in the sap of these plants. Collectively, we provide proof of concept for a novel variant of the attract-and-kill method where the cultivated crop is potentially transformed into a hyper-attractive population and transmission sink for a phytopathogen vector.

Transcriptomic profiling of 'Candidatus Liberibacter asiaticus' in different citrus tissues reveals novel insights into Huanglongbing pathogenesis.

'Candidatus Liberibacter asiaticus' (Las) is a gram-negative bacterial pathogen associated with citrus huanglongbing (HLB) or greening disease. Las is transmitted by the Asian citrus psyllid (ACP) where it colonizes the phloem tissue, resulting in substantial economic losses to citrus industry worldwide. Despite extensive efforts, effective management strategies against HLB remain elusive, necessitating a deeper understanding of the pathogen's biology. Las undergoes cell-to-cell movement through phloem flow and colonizes different tissues in which Las may have varying interactions with the host. Here, we investigate the transcriptomic landscape of Las in citrus seed coat vasculatures, enabling a complete gene expression profiling of Las genome and revealing unique transcriptomic patterns compared to previous studies using midrib tissues. Comparative transcriptomics between seed coat, midrib and ACP identified specific responses and metabolic states of Las in different host tissue. Two Las virulence factors that exhibit higher expression in seed coat can suppress callose deposition. Therefore, they may contribute to unclogging sieve plate pores during Las colonization in seed coat vasculature. Furthermore, analysis of regulatory elements uncovers a potential role of LuxR-type transcription factors in regulating Liberibacter effector gene expression during plant colonization. Together, this work provides novel insights into the pathogenesis of the devastating citrus HLB.

Use Efficiency, Reduction Potential, and Effects of Fertilizers on Carbon Emissions in China’s Major Citrus Regions

Enhancing the efficiency of fertilizer utilization and advancing fertilizer reduction efforts constitutes a pivotal initiative for augmenting the quality and productivity of the citrus industry; this constitutes an indispensable prerequisite for attaining green and sustainable development. Utilizing panel data from seven prominent mandarin-producing regions and seven prominent tangerine-producing regions in China spanning from 2002 to 2022, this study employed the stochastic frontier analysis (SFA) method to develop a translog production function model for precisely measuring the fertilizer use efficiency for mandarins and tangerines. Employing the calculated optimal fertilizer use rates, we further ascertained the fertilizer reduction potential for mandarin and tangerine; then, we estimated the associated carbon emission reduction potential within these key citrus regions. The research revealed the following findings: the overall level of citrus fertilizer use efficiency in China is comparatively low, with the mean values for mandarin and tangerine fertilizer use efficiency being merely 0.4403 and 0.3887, respectively, indicating substantial room for improvement by approximately 60%; substantial potential exists for decreasing fertilizer use in China’s citrus industry, with average reduction potentials of 66.27% for mandarins and 64.83% for tangerines, signifying a notable redundancy in fertilizer application within major citrus-producing areas. The magnitude of carbon emission reduction potential through the diminution of citrus fertilizer use is tremendous. When optimal fertilizer rates are applied, the average carbon emission reductions resulting from fertilizer reduction in mandarins and tangerines amount to 815.8681 kg/hm2 and 602.3551 kg/hm2, respectively. The average carbon reduction potential for mandarins and tangerines reach levels of 55.9673% and 61.1299%, respectively, both surpassing the threshold of 55%. Significant differences exist in the technical efficiency of fertilizer input, reduction potential, and carbon emission mitigation potential among major citrus-producing regions. Citrus orchards in Guangdong exhibit higher potential for fertilizer reduction but demonstrate a relatively low level of technical efficiency. In contrast, Hunan Province shows an opposite trend, necessitating the development of region-specific strategies. Therefore, to minimize citrus fertilizer use and augment the technical efficiency of citrus fertilizer, it is imperative to comprehensively integrate and promote the “three new” technologies aimed at reducing fertilizer use and enhancing its efficiency within the citrus industry; implement a regional coordinated development strategy for citrus fertilizer reduction; and intensify policy guidance, publicity, and training efforts related to citrus fertilizer reduction, efficiency enhancement, and carbon emissions reduction.

Recent progress in the understanding of Citrus Huanglongbing: from the perspective of pathogen and citrus host.

Citrus Huanglongbing (HLB) is a devastating disease spread by citrus psyllid, causing severe losses to the global citrus industry. The transmission of HLB is mainly influenced by both the pathogen and the citrus psyllid. The unculturable nature of the HLB bacteria (Candidatus Liberibacter asiaticus, CLas) and the susceptibility of all commercial citrus varieties made it extremely difficult to study the mechanisms of resistance and susceptibility. In recent years, new progress has been made in understanding the virulence factors of CLas as well as the defense strategies of citrus host against the attack of CLas. This paper reviews the recent advances in the pathogenic mechanisms of CLas, the screening of agents targeting the CLas, including antimicrobial peptides, metabolites and chemicals, the citrus host defense response to CLas, and strategies to enhance citrus defense. Future challenges that need to be addressed are also discussed.

Carboxymethyl cellulose-induced Cryptococcus laurentii improves disease resistance and regulates phenylpropane and reactive oxygen metabolism in grapefruit

Green mould disease poses a significant threat to the citrus industry. Cryptococcus laurentii can stimulate the fruit defence system, whereas the use of antagonistic yeast alone demonstrates limited efficacy. This study investigated the molecular mechanisms of C. laurentii cultured with carboxymethyl cellulose (CMCC. laurentii), and evaluated the effects of CMCC. laurentii on phenylpropane and reactive oxygen metabolism in grapefruit fruit. Transcriptome analysis revealed that the upregulation of gene expression associated with yeast growth and antagonistic ability occurred in CMCC. laurentii after 72 h cultivation. Meanwhile, CMCC. laurentii reduced lesion diameter and disease incidence in fruit. This treatment promoted phenylpropane metabolism by activating PAL, C4H, 4CL, POD, and PPO and increasing the secondary metabolites. CMCC. laurentii also activated the AsA-GSH cycle, enhanced the activities of SOD and CAT, and reduced the accumulation of H2O2 and O2•-. The results suggested that CMCC. laurentii maintained high postharvest fruit quality in grapefruit fruit by elevating the phenylpropane and reactive oxygen metabolism.

Drought-mediated oxidative stress and its scavenging differ between citrus hybrids with medium and late fruit maturation

Drought stress is a major environmental factor limiting citrus productivity. Still, differences in drought sensitivity between citrus hybrids of different maturation periods have so far not been reported. Here, we selected a medium-maturing (Fertile orange: FO (Citrus reticulata cv. Fertile orange) and a late-maturing citrus hybrid (Newhall Navel orange: NO (Citrus sinensis Osbeck cv. Newhall) and determined the physiological and biochemical traits of leaves, roots, wood and bark. Our results showed that drought significantly decreased net photosynthetic rate (Pn), stomatal conductance (Gs) and transpiration rate (Tr) of citrus leaves. Oxidative stress upon drought was indicated by enhanced foliar malondialdehyde (MDA) and hydrogen peroxide contents, as well as a stimulation of the anti-oxidative system. This stimulation included the contents of dehydroascorbic acid (DHA), glutathione (GSH) and oxidized glutathione (GSSG) in leaves, roots, wood and bark, as well as activities of antioxidative enzymes of glutathione reductase (GR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD) and peroxidase (POD). The late maturing NO hybrid not only showed better general physiological performance as indicated by increased Pn in leaves, but also higher biochemical ROS scavenging and osmotic capacity as indicated by increased ascorbic acids (ASA), DHA, and proline contents, as well as activities of enzymes of SOD, POD, ASA/DHA and GSH/GSSG ratios in the investigated tissues compared to the FO hybrid under drought and control conditions. Analysis of molecular mechanisms of signaling, regulatory and functional genes expression are suggested for future studies to elucidate the complex interplay of molecular, biochemical and physiological responses of citrus hybrids to drought.

Confirmation of Candidatus Liberibacter asiaticus in Asian Citrus Psyllids and Detection of Asian Citrus Psyllids in Commercial Citrus in Georgia (U.S.A.).

The Asian citrus psyllid (ACP) is the vector of Candidatus Liberibacter asiaticus (CLas), the causal agent of citrus greening or Huanglongbing (HLB), one of the most devastating citrus diseases worldwide. The citrus industry in Georgia (U.S.A.) is in the process of a rapid expansion, and based on experiences with HLB in Florida, there is great concern about the potential impacts of HLB on this emerging industry. Prior to 2023, ACP had been identified in residential citrus trees in isolated Georgia counties but little to no testing of psyllids for CLas had occurred. However, in 2023, one individual psyllid collected from Chatham County was confirmed positive for CLas by PCR and sequencing. Furthermore, during 2023, ACP adults and nymphs were identified for the first time in a Georgia commercial citrus grove. The finding of ACP in a commercial planting represents a significant risk for CLas dissemination, and thereby has the potential to stall the rapid expansion of Georgia's citrus industry. In the coming years, surveillance and testing of ACP from commercial groves will be essential for the early detection and management of HLB and its vector to reduce HLB spread within Georgia's commercial groves.

Comparative transcriptomic analyses of diploid and tetraploid citrus reveal how ploidy level influences salt stress tolerance.

Citrus is an important fruit crop for human health. The sensitivity of citrus trees to a wide range of abiotic stresses is a major challenge for their overall growth and productivity. Among these abiotic stresses, salinity results in a significant loss of global citrus yield. In order to find straightforward and sustainable solutions for the future and to ensure citrus productivity, it is of paramount importance to decipher the mechanisms responsible for salinity stress tolerance. Thisstudy aimed to investigate how ploidy levels influence salt stress tolerance in citrus by comparing the transcriptomic responses of diploid and tetraploid genotypes. In a previous article we investigated the physiological and biochemical response of four genotypes with different ploidy levels: diploid trifoliate orange (Poncirus trifoliata [L.] Raf.) (PO2x) and Cleopatra mandarin (Citrus reshni Hort. Ex Tan.) (CL2x) and their respective tetraploids (PO4x, CL4x). In this study, we useda multifactorial gene selection and gene clustering approach to finely dissect the influence of ploidy level on the salt stress response of each genotype. Following transcriptome sequencing, differentially expressed genes (DEGs) were identified in response to salt stress in leaves and roots of the different citrus genotypes. Gene expression profiles and functional characterization of genes involved in the response to salt stress, as a function of ploidy level and the interaction between stress response and ploidy level, have enabled us to highlight the mechanisms involved in the varieties tested. Saltstress induced overexpression of carbohydrate biosynthesis and cell wall remodelling- related genes specifically in CL4x Ploidy level enhanced oxidative stress response in PO and ion management capacity in both genotypes. Results further highlighted that under stress conditions, only the CL4x genotype up- regulated genes involved in sugar biosynthesis, transport management, cell wall remodelling, hormone signalling, enzyme regulation and antioxidant metabolism. These findings provide crucial insights that could inform breeding strategies for developing salt-tolerant citrus varieties.

Loop-Mediated Isothermal Amplification Assay for the Detection of Citrus Canker Causing Bacterial Variant, Xanthomonas citri pv. citri Aw Strain.

Citrus canker, a highly transmissible bacterial disease, has three major types, with Asiatic canker (Canker A), caused by Xanthomonas citri pv. citri (Xcc A), being the most widespread and severe, affecting most citrus varieties. Xcc A has two mild variants, Xcc A* and Aw with a limited host range, reported in Southwest Asia and Florida, respectively. Since 2015, the canker caused by Xcc Aw has been being reported in the Rio Grande Valley of South Texas where the Texas commercial citrus industry is located. In 2016, a more severe Canker A was reported in the upper Texas gulf coast region, north of the Rio Grande Valley, posing a potential threat to the Texas citrus industry. Given that existing diagnostic methods cannot reliably distinguish Xcc Aw from Xcc A, we developed a loop-mediated isothermal amplification (LAMP) assay specific to Xcc Aw (LAMP-Aw) for rapid, field-based identification of this bacterial variant. The detection limit of LAMP-Aw was ~4.52 Log10 copies of the target molecule. This study also evaluated the field applicability of the LAMP-Aw assay by coupling the LAMP-Aw assay with a lateral flow immunoassay system.

Full-length transcriptome characterization and analysis of Carrizo Citrange and molecular insights into pathogen defense.

Citrus huanglongbing (HLB) is a major challenge that impacts the flourishing of the citrus industry. Therefore, analyzing the genomic information of HLB-resistant or tolerant citrus resources is crucial for breeding HLB-resistant citrus varieties. The Carrizo citrange, a hybrid of Citrus sinensis and Poncirus trifoliata, plays a pivotal role in citrus cultivation. However, its genetic explorations are difficult due to the absence of a reference genome or full-length transcriptome. In order to enhance our understanding of the genetic information of citrange, we conducted a full-length transcriptomic sequencing of multiple tissues from the Carrizo citrange using the PacBio Sequel II platform. Moreover, we performed gene ontology (GO) annotation, gene functional annotation, simple sequence repeats (SSR) types analysis, as well as identification of lncRNAs, alternative splicing events, and analysis of pathogen defense-related genes. Results showed that a total of 43,452 isoforms were generated, with 43,307 of them being annotated. GO annotation indicated the involvement of these isoforms in various biological processes, cellular components, and molecular functions. The coding sequence length of the isoforms ranged from 1,000 to 4,000 base pairs (bp). Moreover, we have discovered 54 varieties of transcription factors and regulators, along with 16 classifications of genes associated with resistance. Among all types of SSRs, trimer type SSRs were the most abundant. 130 lncRNAs were predicted to be highly reliable in the isoforms of the Carrizo citrange, with alternative splicing events identified, and the most frequent being retained intron. The analysis of gene family expansion and contraction revealed a significant increase in pathogen defense-related genes within the Carrizo citrange. The results of this study will be of great value for future investigations into gene function in citrange and for expanding the genetic pool for breeding citrus varieties resistant or tolerant to HLB.

Effects of Cover Crops on Weed Suppression in the Inter-Row Spaces of Citrus Orchards

Abstract A multi-year study was carried out at two citrus groves with mature trees in Southwest Florida in the United States to evaluate the effects of cover cropping on the citrus inter-row as a sustainable weed management strategy in the Florida citrus production system. Two cover crop (CC) mixes (legume + nonlegume species and only non-legume species) were compared with a no-CC grower standard management (GSM) that utilized the herbicide paraquat for weed suppression in the citrus tree inter-row spaces. We gathered data on the biomass and density of both cover crops and weeds, during the spring and summer/fall CC planting seasons throughout the study years. Both mixes of CCs effectively reduced weed density in the citrus inter-row by 58 to 99% (P<0.05), depending on the growing season and study locations, compared to GSM. Additionally, there were no significant differences observed between the different CC mixes. Similarly, both CC mixes reduced the weed biomass by 95 to 99% (P<0.05) in the citrus inter-row compared to the GSM. However, weed suppression by CCs varied between growing seasons, mainly due to differences in germination and establishment of the CCs in each season.

Transcriptome reanalysis and gene expression of 13 detoxification genes for avermectin and pyridaben resistance in Panonychus citri

Citrus red mites (P. citri) are key pests affecting citrus production worldwide due to pesticide resistance. The resistance mechanisms of ten pesticides are known, but a comprehensive study using transcriptome data is missing. This study employed deeptools, cuffdiff, rmats, bcftools and other software to examine gene expression variation, alternative splicing (AS), and mutations in mite resistance. The research highlighted that pesticides can regulate gene transcription, and red mites with resistance increase cytochrome P450, glutathione S-transferases, carboxylesterase, and acetylcholinesterase expression. Pyridaben also induces new AS events. Fluazinam-induced mites show mRNA splicing peaking earlier than transcription, both peaking at one day and returning to baseline after two days. AS profiles are similar in different mite populations with overlapping pesticide resistances. Lastly, specific mitochondrial SNPs in mites might mediate resistance against select pesticides.

Estimation of the soluble solid content of citrus based on the fractional-order derivative and optimal band combination algorithm.

The soluble solid content (SSC) is a primary characteristic index for evaluating the internal quality of citrus fruits. The development of rapid and nondestructive SSC detection techniques can help address the current issues of postharvest quality grading in China's citrus industry. In this study, a total of 261 experimental samples, including 70 Murcott, 91 Clementine, and 100 Navel orange, were divided into prediction and validation sets in a 7:3 ratio. After obtaining the reflection spectra and SSCs, SNV-FOD (Standard Normal Variate-Fractional-Order Derivative) was used to process the spectra, and the optimal band combination algorithm was introduced to select SSC-sensitive bands. Then, the obtained optimal dual-band combination was input into eight regression models for comparison, and the best performing models stacked ensemble models was selected. Finally, the H-ELR (HyperOpt-optimized ensemble learning regression) model, optimized using a Bayesian function, was applied for the effective estimation of SSC for three common citrus varieties in Guangxi, Murcott, Clementine, and Navel oranges. The results show that (1) the SNV-FOD preprocessing method proposed in this study improved the correlation coefficient with the SSC from 0.546 to 0.836 compared to that of the original spectrum, (2) the optimal dual-band combination (969 and 1069nm) constructed by integrating the differential index and 1.2-order derivative yielded the most accurate results (RPD=2.13), and (3) the H-ELR model, based on HyperOpt optimization, achieved good estimated performance (RPD=2.46). PRACTICAL APPLICATION: This research contributes to the development of practical SSC prediction instruments with excellent universality and ease of application.

First report of citrus yellow vein clearing virus (CYVCV) on citrus in Italy.

In March 2024, symptoms of vein clearing (Fig. S1) were observed on leaves of six lemon (Citrus limon (L.) Burm. f.) trees grown in a private garden in Palma Campania (Campania region, Italy). Symptoms strongly resembled those of yellow vein clearing disease, caused by Potexvirus citriflavivenae (citrus yellow vein clearing virus, CYVCV), genus Potexvirus, sub-genus Mandarivirus (Loconsole et al., 2012; Cui et al., 2018). CYVCV was reported in Pakistan, India, China, Iran, Turkey, Korea and USA (Abrahamian et al., 2024; Catara et al., 1993; EPPO, 2024; Sun and Yokomi, 2024; Jin et al., 2024). Since 2022, considering the potential impact of this emerging virus, CYVCV has been included in the EPPO alert list and it has not been reported in any European Union (EU) Member State where the virus is not regulated. To ascertain possible infection with CYVCV, leaf samples were collected and tested by reverse transcription polymerase chain reaction (RT-PCR). Total nucleic acids (TNAs) from leaves of the symptomatic lemon and non-symptomatic lemon and sweet orange (Citrus sinensis (L.) Osbeck) trees grown in the same garden, were extracted using the silica-capture extraction method (Foissac et al. 2001). TNAs were tested by RT-PCR using CYVCV specific primers (Table S1) designed by Chen et al., (2014) targeting the coat protein gene. All symptomatic trees and an asymptomatic sweet orange from the same garden tested positive generating an amplicon of the expected size (612 bp). Direct Sanger sequencing of amplicons obtained from two symptomatic lemons and one non-symptomatic sweet orange (An PP842725-PP842727) followed by BLAST search showed 97.9-98.08% sequence identity (query coverage 100%) with CYVCV isolates previously reported from a mandarin (An OQ418501) and a lemon (An OQ418493) in California. In contrast, no amplicons were detected in samples from non-symptomatic lemon trees. Virus identity was confirmed by RT-PCR with different primers (Table S1) targeting the RNA-dependent RNA polymerase gene of CYVCV. Amplicons of the expected size (832 bp) were obtained only from samples previously tested positive to the virus and their sequences determined by Sanger sequence (An PQ284953-PQ284955) showed 97.98-98.11% identity (query coverage 100%) with CYVCV sequence previously reported from a mandarin (An OR251443) in New Delhi. Since CYVCV is transmitted by insects (Önelge et al., 2011a, 2011b, Zhang et al., 2018, 2019), TNAs (Foissac et al., 2001) from Aphis aurantii infesting symptomatic lemons, and of A. spiraecola and Dialeurodes citri infesting symptomatic lemon and non-symptomatic sweet orange trees were assayed by RT-PCR with primer pairs designed by Chen et al., (2014). Three samples of 15 specimens from three different trees were tested for each insect. In contrast to D. citri, which tested negative, an amplicon of 612 bp was detected from A. aurantii and A. spiraecola and Direct sequencing of amplicons (An PP842721-PP842724) confirmed the nature of the virus and showed that insect-derived viral sequences shared nucleotide identity of 99.3-100% with those from the infected trees. Altogether, these data support that CYVCV is present in Southern Italy. Likely, it has been introduced illegally through infected citrus propagation material. Given the large A. aurantii and A. spiraecola populations in the areas where CYVCV has been detected, a fast spread of the virus to other areas of Campania region can be expected. Even if the impact of CYVCV on citrus production in Italy remains to be assessed, prompt and extensive surveys may be helpful to establish the actual distribution of the virus. This would allow for a better evaluation of appropriate measures to be adopted to achieve sustainable citrus production. At the best of our knowledge, this is the first report of CYVCV in Italy and in the EU territory.

Citrus bliss: potassium, sodium, and calcium silicates secrets for post-harvest diseases of fruit defense

Biotic stress significantly challenges the global citrus industry. Major post-harvest issues include diseases caused by Penicillium digitatum, Penicillium italicum, Geotrichum citri-aurantii, Alternaria alternata, and Phytophthora citrophthora. The negative impact of chemical fungicides on the environment and health necessitates eco-friendly alternatives. This study examines the effectiveness of sodium, potassium, and calcium silicates against common citrus diseases. In vitro tests evaluated mycelial growth inhibition using silicate concentrations from 0 to 10,000 ppm after 7 days at 25°C. Sodium silicate showed the highest efficacy, completely inhibiting P. digitatum and P. italicum at 2000 ppm. Potassium and calcium silicates achieved 100% inhibition against Penicillium spp. at a concentration of 1%. In vivo tests on Sidi Aissa clementines assessed the preventive and curative effects of 1, 2, and 6% silicate salt solutions. Sodium silicate prevented 41% of brown rot, 72% of sour rot, and 100% of green mold at 6%. Calcium silicate at 6% significantly reduced blue mold and black rot by 32% and 74%, respectively. Sodium silicate was most effective in curative treatments, suggesting its potential as a pre- or post-harvest spray to control P. digitatum, P. italicum, and G. citri-aurantii.

Efficacy of antibiotics and bactericides against Xanthomonas axonopodis pv. citri causing bacterial canker disease of acid lime (Citrus aurantifolia)

Diseases are the major constraints for citrus production which impede the fruit yield and quality. Citrus suffers from a number of diseases caused by fungi, bacteria, viruses and viriods. Among these diseases, canker caused by Xanthomonas axonopodis pv. citri, foot rot or gummosis caused by Phytophthora spp., twig blight caused by Diplodia natalensis and Fusarium spp. Three antibiotics and three bactericides viz., Streptocycline, Kasugamycin 5% + Copper oxychloride 45% WP, Kasugamycin, Bacterimycin, Copper oxychloride 50% WP, Copper hydroxide 53.8% W/W were evaluated for their effectiveness in controlling the growth of Xanthomonas axonopodis pv. citri at the Department of Plant Pathology, College of Agriculture, Ummendganj-Kota, (Agricultural University, Kota) Rajasthan. Inhibition was highest in case of copper oxychloride 50% WP (34.20 mm) followed by bronopol 27% (28.90 mm) and streptocycline 90% W/W (12.48 mm) at 500 ppm concentration and no inhibition zone was found in kasugamycin. All the antibiotics/bactericides inhibited bacterial growth at higher concentrations.

Classifying adaxial and abaxial sides of diseased citrus leaves with selected hyperspectral bands and YOLOv8

Huanglongbing (HLB; citrus greening) and citrus canker are invasive diseases afflicting Florida citrus groves, causing financial losses through yield loss, smaller fruit, blemishes, premature fruit drop and/or eventual tree death. Often, symptoms of these diseases resemble those of other disease or disorders. Early detection of HLB and canker via in-grove leaf inspection can permit more effective mitigation tactics and management of groves. Autonomous, vision-based disease scouting in a grove offers a financial benefit to the Florida citrus industry. This study investigates the potential of hyperspectral reflectance imagery (HSI) for detecting and classifying these conditions in the presence of other, less consequential leaf defects. Leaves with visible symptoms of HLB, canker, zinc deficiency, scab, melanose, greasy spot, and a control set were collected and both sides were imaged with a line-scan hyperspectral camera. Spectral bands from this imagery were selected using two methods: an unsupervised method based on principal component analysis (PCA), a supervised method based on linear discriminant analysis (LDA), which were compared with randomly selected bands as a control. The YOLOv8 network architecture was trained to classify each side of these leaves with each band combination. LDA-selected bands from the front of the leaves yielded an overall classification accuracy of 87.09 %, with higher recall of melanose and precision of control than any other model tested. Leaves with HLB and zinc deficiency were classified most accurately, with both band selection methods yielding F1 scores of at least 0.955 and 0.934, respectively. These findings favor the use of supervised band selection for HSI-based in-grove disease detection.

Overexpressing CsSABP2 enhances tolerance to Huanglongbing and citrus canker in C. sinensis.

Huanglongbing (HLB) and citrus canker, arising from Candidatus Liberibacter asiaticus (CaLas) and Xanthomonas citri pv. Citri (Xcc), respectively, have been imposing tremendous losses to the global citrus industry. Systemic acquired resistance (SAR) has been shown to be crucial for priming defense against pathogen in citrus. Salicylic acid (SA) binding protein 2 (SABP2), which is responsible for converting methyl salicylate (MeSA) to SA, is essential for full SAR establishment. Here, we characterized the functions of four citrus SABP2 genes (CsSABP2-1, CsSABP2-1V18A , CsSABP2-2 and CsSABP2-3) against HLB and citrus canker. In vitro enzymatic assay revealed that all four proteins had MeSA esterase activities, and CsSABP2-1 and CsSABP2-1V18A has the strongest activity. Their activities were inhibited by SA except for CsSABP2-1V18A. Four genes controlled by a strong promoter 35S were induced into Wanjincheng orange (Citrus sinensis Osbeck) to generate transgenic plants overexpressing CsSABP2. Overexpressing CsSABP2 increased SA and MeSA content and CsSABP2-1V18A had the strongest action on SA. Resistance evaluation demonstrated that only CsSABP2-1V18A had significantly enhanced tolerance to HLB, although all four CsSABP2s had increased tolerance to citrus canker. The data suggested the amino acid Val-18 in the active site of CsSABP2 plays a key role in protein function. Our study emphasized that balancing the levels of SA and MeSA is crucial for regulating SAR and conferring broad-spectrum resistance to HLB and citrus canker. This finding offers valuable insights for enhancing resistance through SAR engineering.