Assessment of optical properties and Monte-Carlo based simulation of light propagation in citrus infected by Penicillium italicum.

This original work investigated the optical properties and Monte-Carlo (MC) based simulation of light propagation in the flavedo of Nanfeng tangerine (NF) and Gannan navel orange (GN) infected by Penicillium italicum. The increase of absorption coefficient (µa) at around 482 nm and the decrease at around 675 nm were both observed in infected NF and GN during storage, indicating the accumulation of carotenoids and loss of chlorophyll. Particularly, the µa in NF varied more intensively than GN, but the limited differences of reduced scattering coefficient (µs') were detected while postharvest infection. Besides, MC simulation of light propagation indicated that the photon packets weight and penetration depth at 482 nm in NF were reduced more than in GN flavedo, while there were almost no changes at the relatively low absorption wavelength of 926 nm. The simulated absorption energy at 482 nm in NF and GN presented more changes than those at 675 nm during infection, thus could provide better detection of citrus diseases. Furthermore, PLS-DA models can discriminate healthy and infected citrus, with the accuracy of 95.24 % for NF and 98.67 % for GN, respectively. Consequently, these results can provide theoretical fundamentals to improve modelling prediction robustness and accuracy.

Xanthomonas citri subsp. citri type III effector PthA4 directs the dynamical expression of a putative citrus carbohydrate-binding protein gene for canker formation.

Xanthomonas citri subsp. citri (Xcc), the causal agent of citrus canker, elicits canker symptoms in citrus plants because of the transcriptional activator-like (TAL) effector PthA4, which activates the expression of the citrus susceptibility gene CsLOB1. This study reports the regulation of the putative carbohydrate-binding protein gene Cs9g12620 by PthA4-mediated induction of CsLOB1 during Xcc infection. We found that the transcription of Cs9g12620 was induced by infection with Xcc in a PthA4-dependent manner. Even though it specifically bound to a putative TAL effector-binding element in the Cs9g12620 promoter, PthA4 exerted a suppressive effect on the promoter activity. In contrast, CsLOB1 bound to the Cs9g12620 promoter to activate its expression. The silencing of CsLOB1 significantly reduced the level of expression of Cs9g12620, which demonstrated that Cs9g12620 was directly regulated by CsLOB1. Intriguingly, PhtA4 interacted with CsLOB1 and exerted feedback control that suppressed the induction of expression of Cs9g12620 by CsLOB1. Transient overexpression and gene silencing revealed that Cs9g12620 was required for the optimal development of canker symptoms. These results support the hypothesis that the expression of Cs9g12620 is dynamically directed by PthA4 for canker formation through the PthA4-mediated induction of CsLOB1.

Identification of Biomarkers Associated with Phyllosticta citricarpa Tolerance.

Citrus black spot (CBS) is a fungal disease caused by Phyllosticta citricarpa Kiely, (McAlpine Van der Aa), with most cultivars being susceptible to infection. Currently, disease control is based on the application of protective fungicides, which is restricted due to resistance, health and environmental concerns. Although using natural products for disease management is gaining momentum, more advances are required. This study obtained the metabolic profiles of the essential oil and cuticular waxes of two citrus cultivars with a varying susceptibility to CBS infection using gas chromatography-mass spectrometry. A multivariate data analysis identified possible biomarker compounds that contributed to the difference in susceptibility between the two cultivars. Several identified biomarkers were tested in vitro for their antifungal properties against P. citricarpa. Two biomarkers, propanoic acid and linalool, were able to completely inhibit pathogen growth at 750 mg/L and 2000 mg/L, respectively.

Progressive alterations in mineral contents in citrus genotypes toward Alternaria citri causing brown spot of citrus.

Brown spot of citrus caused by Alternaria citri is one of the emerging threats to the successful production of citrus crops. The present study, conducted with a substantial sample size of 50 leaf samples for statistical reliability, aimed to determine the change in mineral content in citrus leaves after brown spot disease attack. Leaf samples from a diverse range of susceptible citrus varieties (Valentia late, Washington navel, and Kinnow) and resistant varieties (Citron, Eruka lemon, and Mayer lemon) were analyzed. Significant variations (p ≤ 0.05) in mineral contents were observed across reaction groups (inoculated and un-inoculated), types (resistant and susceptible), and varieties of citrus in response to infection of Alternaria citri. The analysis of variance showed significant changes in mineral levels of citrus leaves, including nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), zinc (Zn), sodium (Na), iron (Fe), and copper (Cu). The results indicate that the concentration of N and P differed by 6.63% and 1.44%, respectively, in resistant plants, while susceptible plants showed a difference of 6.07% and 1.19%. Moreover, resistant plants showed a higher concentrations of K, Ca, Mg, Zn, Na, Fe, and Cu at 8.40, 2.1, 1.83, 2.21, 1.58, 2.89, and 0.36 ppm respectively, compared to susceptible plants which showed concentrations of 5.99, 1.93, 1.47, 1.09, 1.24, 1.81, and 0.31 ppm respectively. Amounts of mineral contents were reduced in both resistant as well as susceptible plants of citrus after inoculation. Amount of N (8.56), P (1.87) % while K (10.74), Ca (2.71), Mg (2.62), Zn (2.20), Na (2.08), Fe (3.57) and Cu (0.20) ppm were recorded in un-inoculated group of citrus plants that reduced to 3.15 and 0.76% and 3.66, 1.40, 0.63,0.42, 0.74, 1.13 and 0.13 ppm in inoculated group respectively. It was accomplished that susceptible varieties contained lower ionic contents than resistant varieties. The higher concentrations of ionic contents in resistant citrus varieties build up the biochemical and physiological processes of the citrus plant, which help to restrict spread of pathogens. Further research could explore the interplay between mineral nutrition and disease resistance in citrus, potentially leading to the development of new disease-resistant varieties.

A Detection Algorithm for Citrus Huanglongbing Disease Based on an Improved YOLOv8n.

Given the severe impact of Citrus Huanglongbing on orchard production, accurate detection of the disease is crucial in orchard management. In the natural environments, due to factors such as varying light intensities, mutual occlusion of citrus leaves, the extremely small size of Huanglongbing leaves, and the high similarity between Huanglongbing and other citrus diseases, there remains an issue of low detection accuracy when using existing mainstream object detection models for the detection of citrus Huanglongbing. To address this issue, we propose YOLO-EAF (You Only Look Once-Efficient Asymptotic Fusion), an improved model based on YOLOv8n. Firstly, the Efficient Multi-Scale Attention Module with cross-spatial learning (EMA) is integrated into the backbone feature extraction network to enhance the feature extraction and integration capabilities of the model. Secondly, the adaptive spatial feature fusion (ASFF) module is used to enhance the feature fusion ability of different levels of the model so as to improve the generalization ability of the model. Finally, the focal and efficient intersection over union (Focal-EIOU) is utilized as the loss function, which accelerates the convergence process of the model and improves the regression precision and robustness of the model. In order to verify the performance of the YOLO-EAF method, we tested it on the self-built citrus Huanglongbing image dataset. The experimental results showed that YOLO-EAF achieved an 8.4% higher precision than YOLOv8n on the self-built dataset, reaching 82.7%. The F1-score increased by 3.33% to 77.83%, and the mAP (0.5) increased by 3.3% to 84.7%. Through experimental comparisons, the YOLO-EAF model proposed in this paper offers a new technical route for the monitoring and management of Huanglongbing in smart orange orchards.

The effects of core microorganism community on flavor compounds and active substances during the aging process of Citri Reticulatae Pericarpium.

Citri Reticulatae Pericarpium (CRP) is a traditional herbal and food spice, the flavor and active compounds content of Xinhui CRP improves with aging. To investigate the pattern of microbial community succession during the aging of Xinhui CRP and its correlation with changes in flavor compounds, the high-throughput sequencing, HPLC, and GC-IMS were used to analyze the microbial community, flavonoids, and flavor compounds of five different aging years in this study. The results revealed different dominant microbial communities in Xinhui CRP at different aging time, and unclassified Bacteria were the predominant bacterial genus during 10-15 years of aging. As the aging time increases, the abundance of microbial community decreases and gradually stabilizes. At the fungal genus level, Xeromyces (>99 %) were the dominant genus during the 10-15 years aging time and had a significant correlation with polymethoxyflavones (PMFs), and the concentrations of PMFs increased with the progression of aging years. The GC-IMS results revealed distinctive flavor profiles in Xinhui CRP across different aging years, floral and fruity aromas, such as heptanal, 3-methyl-3-butenol, and 1-butanol, among others, with increasing aging years. A comprehensive correlation analysis further elucidates the close relationship between the core microorganism community and flavor formation in Xinhui CRP (p < 0.05). Notably, Pseudomonas and Escherichia Shigella exhibited significant correlations with beta-pinene and alpha-pinene, whereas Aureobasidium and Sarcopodium were associated with nerol and α-phellandrene (p < 0.05). This study provides new ideas for accelerating the good quality and flavor of Xinhui CRP during the aging process from the perspective of key microorganisms.

Soil Microbial Communities in Lemon Orchards Affected by Citrus Mal Secco Disease.

Mal secco is a vascular disease of citrus caused by the mitosporic fungus Plenodomus tracheiphilus. Soil containing infected plant material constitutes an inoculum source for root infections. In this study, the soil bacterial and fungal communities of five lemon orchards located in Syracuse Province (Sicily, Italy) affected by mal secco were analyzed. Soil samples were collected under lemon tree canopies and subjected to total genomic DNA extraction. The fungal DNA was detected through qPCR in all orchards, with variable concentrations. Bacterial and fungal communities were profiled using 16S and ITS amplicon-based high-throughput sequencing, respectively. According to our results, the relative abundances of the most represented bacterial phyla (e.g., Proteobacteria, Actinobacteriota, Acidobacteriota) changed across the orchards, while in the fungal community, the phylum Ascomycota was dominant, with Basidiomycota and Mortierellomycota abundances fluctuating. On the whole, ß diversity analysis showed significant variation in the composition of the soil microbial communities across the orchards. This result was confirmed by the analysis of the core community (taxa present at ≥ 75% of total samples), where putative beneficial bacteria resulted in significantly enriched fungus-infected soil samples, suggesting complex microbial interactions. Our findings shed light on the composition and diversity of the soil microbiome in lemon orchards with the occurrence of mal secco infections.

Biocontrol efficacy of Pseudomonas mediterranea PVCT 3C against Plenodomus tracheiphilus: In vitro and in planta mechanisms at early disease stages.

In this study, we investigated the biocontrol activity of the P. mediterranea strain PVCT 3C against Mal secco, a severe disease of citrus caused by the vascular fungus Plenodomus tracheiphilus. In vitro, bacterial diffusible compounds, volatile organic compounds and culture filtrates produced by PVCT 3C reduced the mycelial growth and conidial germination of P. tracheiphilus, also affecting the mycelial pigmentation. The application of bacterial suspensions by leaf-spraying before the inoculation with the pathogen on plants of the highly susceptible species sour orange and lemon led to an overall reduction in incidence and disease index, above all during the early disease stage. PVCT 3C genome was subjected to whole-genome shotgun sequencing to study the molecular mechanisms of action of this strain. In silico annotation of biosynthetic gene clusters for secondary metabolites revealed the presence of numerous clusters encoding antimicrobial compounds (e.g. cyclic lipopeptides, hydrogen cyanide, siderophores) and candidate novel products. During the asymptomatic disease phase (seven days post-inoculation), bacterial treatments interfered with the expression of different fungal genes, as assessed with an NGS and de novo assembly RNA-seq approach. These results suggest that P. mediterranea PVCT 3C or its secondary metabolites may offer a potential effective and sustainable alternative to contain P. tracheiphilus infections via integrated management.

Role of chitinase expression in the virulence of Lecanicillium lecanii against citrus black aphid (Toxoptera aurantii).

Chitinase plays a vital role in the virulence of entomopathogenic fungi (EPF) when it infects host insects. We used gene recombination technology to express chitinase of three strains of Lecanicillium lecanii: Vl6063, V3450, and Vp28. The ORF of ChitVl6063, ChitV3450 and ChitVp28 were inserted into the fungal expression vector pBARGPE-1, which contained strong promoter and terminator, respectively, to construct a chitinase overpressing plasmid, then transformed the wild-type strain with blastospore transformation method. The virulence of the three recombinant strains against Toxoptera aurantii was improved by overproduction of ChitVl6063, ChitV3450, and ChitVp28, as demonstrated by significantly lower 3.43 %, 1.72 %, and 1.23 % fatal doses, respectively, according to an insect bioassay. Similarly, lethal times of recombinants (ChitVl6063, ChitV3450 and ChitVp28) were also decreased up to 29.51 %, 30.46 % and 33.90 %, respectively, compared to the wild-type strains. Improving the expression of chitinase is considered as an effective method for the enhancement of the EPF value. The efficacy could be enhanced using recombinant technology, which provides a prospecting view for future insecticidal applications.

Metagenomic Analysis of Rhizospheric Bacterial Community of Citrus Trees Expressing Phloem-Directed Antimicrobials.

Huanglongbing, also known as citrus greening, is currently the most devastating citrus disease with limited success in prevention and mitigation. A promising strategy for Huanglongbing control is the use of antimicrobials fused to a carrier protein (phloem protein of 16 kDa or PP16) that targets vascular tissues. This study investigated the effects of genetically modified citrus trees expressing Citrus sinensis PP16 (CsPP16) fused to human lysozyme and ß-defensin-2 on the soil microbiome diversity using 16S amplicon analysis. The results indicated that there were no significant alterations in alpha diversity, beta diversity, phylogenetic diversity, differential abundance, or functional prediction between the antimicrobial phloem-overexpressing plants and the control group, suggesting minimal impact on microbial community structure. However, microbiota diversity analysis revealed distinct bacterial assemblages between the rhizosphere soil and root environments. This study helps to understand the ecological implications of crops expressing phloem-targeted antimicrobials for vascular disease management, with minimal impact on soil microbiota.

Morpho-physiological and biochemical characterization of Kinnow (Citrus reticulata) in response to canker pathogens (Xanthomonas axonopodis pv. citri).

Fruits play an important role in human life on our planet, since they supply a variety of essential services. One of the paramount crops in Pakistan is Citrus reticulata (Kinnow), which plays a vital role in the country's economy. The citrus crops are confronted with various challenges such as fungi, bacteria, nematodes, and viruses, all of which have adverse effects on the quality and yield of the fruits. Citrus canker, in particular, stands as the most fatal disease, affecting numerous citrus species worldwide, inflicting devastating consequences. The objective of this study was to evaluate the impact of citrus canker on the morphology, physiology of leaves, and the quality of citrus fruits. The research was conducted in four major citrus-producing tehsils of the Sargodha district. The study found significant differences in morphological and physiological traits between healthy fruits and those infected with citrus canker. Healthy fruits exhibited higher values in fruit weight (FW) of 149.02 g, peel thickness (PT) of 3.76 g, rag weight (RW) of 35.95 g, leaf area (LA) of 22.49 cm2, and juice weight compared to the citrus canker-infected fruits. The significant variations in fruit weight, juice weight, chlorophyll content, vitamin C content were present between healthy and diseased fruits and leaves. A biochemical study revealed that healthy fruits had greater levels of total soluble solids (TSS), TSS-acid ratio, vitamin C, and reducing power (RP), but citrus canker-infected fruits had a higher acidity percentage. The significant decreases in important morphological and physicochemical characteristics, emphasizing the necessity for immediate disease control techniques to safeguard the citrus sector and maintain food security.

Selenium-Mediated Shaping of Citrus Rhizobiome for Promotion in Root Growth and Soil Phosphorus Activation.

Selenium (Se) has been widely reported to affect plant growth, nutrient cycling, and the rhizobiome. However, how Se shapes the rhizobiome and interacts with plants remains largely elusive. Pot and hydroponic experiments were employed to elucidate the regulatory mechanism of Se in the citrus rhizobiome. Compared to the control, soil Se application significantly increased the root biomass (34.7%) and markedly reduced rhizosphere HCl-P, H2O-P, NaHCO3-IP, and residual-P of citrus, which were related to the variation of citrus rhizobiome. Se primarily enriched Proteobacteria and Actinobacteria as well as the phosphorus (P) functional genes phod and pqqc. Further study revealed that Se altered the metabolite profile of root exudate, particularly enhancing the abundance of l-cyclopentylglycine, cycloleucine, l-proline, l-pipecolic acid, and inositol, which played a key role in reshaping the citrus rhizobiome. These metabolites could serve as both nutrient sources and signaling molecules, thus supporting the growth or chemotaxis of the functional microbes. These bacterial taxa have the potential to solubilize P or stimulate plant growth. These findings provide a novel mechanistic understanding of the intriguing interactions between Se, root exudate, and rhizosphere microbiomes, and demonstrate the potential for utilizing Se to regulate rhizobiome function and enhance soil P utilization in citrus cultivation.

Distribution and dynamic changes of Huanglongbing pathogen in its insect vector Diaphorina citri.

The Asian citrus psyllid (ACP) Diaphorina citri Kuwayama is the leading vector of Candidatus Liberibacter asiaticus (CLas), the causative agent of citrus Huanglongbing (HLB) disease. The distribution and dynamics of CLas within ACP are critical to understanding how the transmission, spread and infection of CLas occurs within its host vector in nature. In this study, the distribution and titer changes of CLas in various tissues of ACP 5th instar nymphs and adults were examined by fluorescence in situ hybridization (FISH) and real-time quantitative PCR (qPCR) techniques. Results demonstrated that 100% of ACP 5th instar nymphs and adults were infected with CLas following feeding on infected plants, and that CLas had widespread distribution in most of the tissues of ACP. The titers of CLas within the midgut, salivary glands and hemolymph tissues were the highest in both 5th instar nymphs and adults. When compared with adults, the titers of CLas in these three tissues of 5th instar nymphs were significantly higher, while in the mycetome, ovary and testes they were significantly lower than those of adults. FISH visualization further confirmed these findings. Dynamic analysis of CLas demonstrated that it was present across all the developmental ages of ACP adults. There was a discernible upward trend in the presence of CLas with advancing age in most tissues of ACP adults, including the midgut, hemolymph, salivary glands, foot, head, cuticula and muscle. Our findings have significant implications for the comprehensive understanding of the transmission, dissemination and infestation of CLas, which is of much importance for developing novel strategies to halt the spread of CLas, and therefore contribute to the efficient prevention and control of HLB.

Unraveling the antifungal composition of bitter orange decoction against the melon pathogen Fusarium jinanense.

Bitter orange (Citrus aurantium) is an important source of essential oils with high antimicrobial activities, however the composition and antifungal potential of the decoction peels is little explored. This study assessed the peel decoction's chemical profile at the secondary metabolism level and its antifungal activity against the melon phytopathogen Fusarium jinanense. The decoction's antifungal potential was investigated using a bioassay-guided fractionation approach based on Solid-Phase Extraction (SPE) and LC-HRMS/MS analysis. Coumarins and flavones were the most abundant classes of compounds in the high-value fractions responsible for up to 61% of the mycelial inhibition of F. jinanense. Overall, this study has presented for the first time the chemical composition, the antifungal potential of the decoction of C. aurantium peels and the compounds associated with these results. This strategy can guide the exploration of under-explored food sources and add value to compounds or fractions enriched with bioactive compounds.

A limited concentration range of diaphorin, a polyketide produced by a bacterial symbiont of the Asian citrus psyllid, promotes the in vitro gene expression with bacterial ribosomes.

Diaphorin is a polyketide produced by "Candidatus Profftella armatura" (Gammaproteobacteria: Burkholderiales), an obligate symbiont of a devastating agricultural pest, the Asian citrus psyllid Diaphorina citri (Hemiptera: Psyllidae). Physiological concentrations of diaphorin, which D. citri contains at levels as high as 2-20 mM, are inhibitory to various eukaryotes and Bacillus subtilis (Firmicutes: Bacilli) but promote the growth and metabolic activity of Escherichia coli (Gammaproteobacteria: Enterobacterales). Our previous study demonstrated that 5-mM diaphorin, which exhibits significant inhibitory and promoting effects on cultured B. subtilis and E. coli, respectively, inhibits in vitro gene expression utilizing purified B. subtilis and E. coli ribosomes. This suggested that the adverse effects of diaphorin on B. subtilis are partly due to its influence on gene expression. However, the result appeared inconsistent with the positive impact on E. coli. Moreover, the diaphorin concentration in bacterial cells, where genes are expressed in vivo, may be lower than in culture media. Therefore, the present study analyzed the effects of 50 and 500 µM of diaphorin on bacterial gene expression using the same analytical method. The result revealed that this concentration range of diaphorin, in contrast to 5-mM diaphorin, promotes the in vitro translation with the B. subtilis and E. coli ribosomes, suggesting that the positive effects of diaphorin on E. coli are due to its direct effects on translation. This study demonstrated for the first time that a pederin-type compound promotes gene expression, establishing a basis for utilizing its potential in pest management and industrial applications.IMPORTANCEThis study revealed that a limited concentration range of diaphorin, a secondary metabolite produced by a bacterial symbiont of an agricultural pest, promotes cell-free gene expression utilizing substrates and proteins purified from bacteria. The unique property of diaphorin, which is inhibitory to various eukaryotes and Bacillus subtilis but promotes the growth and metabolic activity of Escherichia coli, may affect the microbial flora of the pest insect, potentially influencing the transmission of devastating plant pathogens. Moreover, the activity may be exploited to improve the efficacy of industrial production by E. coli, which is often used to produce various important materials, including pharmaceuticals, enzymes, amino acids, and biofuels. This study elucidated a part of the mechanism by which the unique activity of diaphorin is expressed, constructing a foundation for applying the distinct property to pest management and industrial use.

Berberine hydrochloride delays citrus sour rot mainly by disrupting carbohydrate and energy metabolism of Geotrichum citri-aurantii spores.

Citrus sour rot is a common postharvest citrus disease caused by Geotrichum citri-aurantiiti, which has led to enormous economic losses, particularly during rainy seasons. In this study, we aimed to clarify the impact of berberine hydrochloride (BH), the hydrochloride form of an isoquinoline alkaloid, on the control efficiency of citrus sour rot and its antifungal mode against G. citri-aurantii. Results demonstrated that BH markedly impede the propagation of G. citri-aurantii by delaying the spores development from dormant stage into swollen and germinating stages, with the MIC and MFC value of 0.08 and 0.16 g L-1, respectively. When the artificially inoculated citrus fruit in control group were totally rotted, the disease incidence of BH-treated groups decreased by 35.00%-73.30%, which effectively delayed the disease progression and almost did not negatively affect fruit quality. SEM observation, CFW and PI staining images revealed that BH caused significant damage to both the cell membrane and cell wall of G. citri-aurantii spores, whereas only the cell membrane of the mycelium was affected. The impact of cell wall was related to the block of chitin and ß-1,3-glucan synthesis. Transcriptome results and further verification proved that 0.5 × MIC BH treatment affected the glycolysis pathway and TCA cycle mainly by inhibiting the production of acetyl-CoA and pyruvate. Subsequently, the activities of key enzymes declined, resulting in a further decrease in ATP levels, ultimately inhibiting the germination of spores. In conlusion, BH delays citrus sour rot mainly by disrupting carbohydrate and energy metabolism of G. citri-aurantii spores.

CRISPR/Cas12a-Responsive Smart DNA Hydrogel for Sensitive Electrochemiluminescence Detection of the Huanglongbing Outer Membrane Protein Gene.

Citrus Huanglongbing (HLB) is known as the cancer of citrus, where Candidatus Liberibacter asiaticus (CLas) is the most prevalent strain causing HLB. In this study, we report a novel electrochemiluminescence (ECL) biosensor for the highly sensitive detection of the CLas outer membrane protein (Omp) gene by coupling rolling circle amplification (RCA) with a CRISPR/Cas12a-responsive smart DNA hydrogel. In the presence of the target, a large number of amplicons are generated through RCA. The amplicons activate the trans-cleavage activity of CRISPR/Cas12a through hybridizing with crRNA, triggering the response of smart DNA hydrogel to release the encapsulated AuAg nanoclusters (AuAg NCs) on the electrode and therefore leading to a decreased ECL signal. The ECL intensity change (I0 - I) is positively correlated with the concentration of the target in the range 50 fM to 5 nM, with a limit of detection of 40 fM. The performance of the sensor has also been evaluated with 10 samples of live citrus leaves (five HLB negative and five HLB positive), and the result is in excellent agreement with the gold standard qPCR result. The sensing strategy has expanded the ECL versatility for detecting varying levels of dsDNA or ssDNA in plants with high sensitivity.

Application of edible nanocomposites from chitosan/fenugreek seed mucilage/selenium nanoparticles for protecting lemon from green mold.

Green (Penicillium digitatum) mold can severely endanger the citrus fruits production and quality. Targeting the protection of lemon fruits from green mold infestations with nanobiotechnology approach, the fenugreek seed mucilage (FM) was extracted and exploited for biosynthesis of selenium (SeNPs) nanoparticles; their nanocomposites (NCs) with chitosan (CT) was constructed and employed as antifungal materials and edible coating (ECs) to protect lemon fruits against green mold. The nanoparticles formation and conjugations were verified by infrared (FTIR) analysis and electron microscopy. The FM-synthesized SeNPs had particles average of 8.35 nm, were the NCs of them with CT had size mean of 49.33 nm and charged with +22.8 mV. The CT/FM/SeNPs composite exhibited superior antifungal actions toward P. digitatum isolates, up to 32.2 mm inhibition diameter and 12.5 mg/mL inhibitory concentration, which exceeded the actions of imazilil. The microscopic screening of exposed P. digitatum to NCs clarified their mycelial destructive action within 30 h. The coating of infected lemons with fabricated NCs led to complete elimination of green mold development after 10 days of coating, without any infestation remarks. The innovative fabrication of NCs from CT/FM/SeNPs is strongly suggested to protect citrus crops from green mold and preserve fruits quality.

Discovery of Antibacterial Compounds against Xanthomonas citri subsp. citri from a Marine Fungus Aspergillus terreus SCSIO 41202 and the Mode of Action.

Citrus canker, caused by Xanthomonas citri subsp. citri (Xcc), is a severe citrus disease. Currently, copper-containing pesticides are widely used to manage this disease, posing high risks to the environment and human health. This study reports the discovery of naturally occurring anti-Xcc compounds from a deep-sea fungus, Aspergillus terreus SCSIO 41202, and the possible mode of action. The ethyl acetate extract of A. terreus was subjected to bioassay-guided isolation, resulting in the discovery of eight anti-Xcc compounds (1-8) with minimum inhibitory concentrations (MICs) ranging from 0.078 to 0.625 mg/mL. The chemical structures of these eight metabolites were determined by integrative analysis of various spectroscopic data. Among these compounds, Asperporonin A (1) and Asperporonin B (2) were identified as novel compounds with a very unusual structural skeleton. The electronic circular dichroism was used to determine the absolute configurations of 1 and 2 through quantum chemical calculation. A bioconversion pathway involving pinacol rearrangement was proposed to produce the unusual compounds (1-2). Compound 6 exhibited an excellent anti-Xcc effect with a MIC value of 0.078 mg/mL, which was significantly more potent than the positive control CuSO4 (MIC = 0.3125 mg/mL). Compound 6 inhibited cell growth by disrupting biofilm formation, destroying the cell membrane, and inducing the accumulation of reactive oxygen species. In vivo tests indicated that compound 6 is highly effective in controlling citrus canker disease. These results indicate that compounds 1-8, especially 6, have the potential as lead compounds for the development of new, environmentally friendly, and efficient anti-Xcc pesticides.

Enterobacteriaceae as a Key Indicator of Huanglongbing Infection in Diaphorina citri.

Extensive microbial interactions occur within insect hosts. However, the interactions between the Huanglongbing (HLB) pathogen and endosymbiotic bacteria within the Asian citrus psyllid (ACP, Diaphorina citri Kuwayama) in wild populations remain elusive. Thus, this study aimed to detect the infection rates of HLB in the ACP across five localities in China, with a widespread prevalence in Ruijin (RJ, 58%), Huidong (HD, 28%), and Lingui (LG, 15%) populations. Next, microbial communities of RJ and LG populations collected from citrus were analyzed via 16S rRNA amplicon sequencing. The results revealed a markedly higher microbial diversity in the RJ population compared to the LG population. Moreover, the PCoA analysis identified significant differences in microbial communities between the two populations. Considering that the inter-population differences of Bray-Curtis dissimilarity in the RJ population exceeded those between populations, separate analyses were performed. Our findings indicated an increased abundance of Enterobacteriaceae in individuals infected with HLB in both populations. Random forest analysis also identified Enterobacteriaceae as a crucial indicator of HLB infection. Furthermore, the phylogenetic analysis suggested a potential regulatory role of ASV4017 in Enterobacteriaceae for ACP, suggesting its possible attractant activity. This research contributes to expanding the understanding of microbial communities associated with HLB infection, holding significant implications for HLB prevention and treatment.