Citrus Disease Research Articles

Genetic diversity and population structure of the Asian citrus psyllid in China.

The Asian citrus psyllid (ACP) is the main vector of Citrus Huanglongbing, the most damaging citrus disease, causing significant financial losses in the citrus industry. Global warming has expanded the habitat of this pest, allowing it to continue its northward migration to China. Population genetic information of ACP is fundamentally essential for species management. This study investigated the genetic diversity and population structure of Chinese ACP using the mitochondrial cytochrome oxidase subunit I gene by dataset comprised 721 sequences from 27 geographic sites in China. Low haplotype diversity (0.323 ± 0.022) and low nucleotide diversity (0.00071 ± 0.00007) were observed in the entire population, which may indicate recent founder events. Twenty-three haplotypes were identified and clustered into 2 haplogroups: haplogroup I and haplogroup II. Haplogroup II included only 2 unique haplotypes, which occurred exclusively in the Southwest China ACP population. Genetic differentiation analyses were also indicative of Southwest China population was significantly differentiated from the remaining populations. Demographic history analysis showed that ACP population in China has experienced demographic expansion. Our results provided a better understanding of the genetic distribution patterns and structures of ACP populations in China.

Citrus Disease Classification Model Based on Improved ConvNeXt

Citrus Disease Classification Model Based on Improved ConvNeXt

High species diversity in Diaporthe associated with citrus diseases in China.

Species in Diaporthe have broad host ranges and cosmopolitan geographic distributions, occurring as endophytes, saprobes and plant pathogens. Previous studies have indicated that many Diaporthe species are associated with Citrus. To further determine the diversity of Diaporthe species associated with citrus diseases in China, we conducted extensive surveys in major citrus-producing areas from 2017-2020. Diseased tissues were collected from leaves, fruits, twigs, branches and trunks showing a range of symptoms including melanose, dieback, gummosis, wood decay and canker. Based on phylogenetic comparisons of DNA sequences of the internal transcribed spacer regions (ITS), calmodulin (cal), histone H3 (his3), translation elongation factor 1-alpha (tef1) and beta-tubulin (tub2), 393 isolates from 10 provinces were identified as belonging to 36 species of Diaporthe, including 32 known species, namely D. apiculata, D. biconispora, D. biguttulata, D. caryae, D. citri, D. citriasiana, D. compacta, D. discoidispora, D. endophytica, D. eres, D. fusicola, D. fulvicolor, D. guangxiensis, D. hongkongensis, D. hubeiensis, D. limonicola, D. litchii, D. novem, D. passifloricola, D. penetriteum, D. pescicola, D. pometiae, D. sackstonii, D. sennicola, D. sojae, D. spinosa, D. subclavata, D. tectonae, D. tibetensis, D. unshiuensis, D. velutina and D. xishuangbanica, and four new species, namely D. gammata, D. jishouensis, D. ruiliensis and D. sexualispora. Among the 32 known species, 14 are reported for the first time on Citrus, and two are newly reported from China. Among the 36 species, D. citri was the dominant species as exemplified by its high frequency of isolation and virulence. Pathogenicity tests indicated that most Diaporthe species obtained in this study were weakly aggressive or non-pathogenic to the tested citrus varieties. Only D. citri produced the longest lesion lengths on citrus shoots and induced melanose on citrus leaves. These results further demonstrated that a rich diversity of Diaporthe species occupy Citrus, but only a few species are harmful and D. citri is the main pathogen for Citrus in China. The present study provides a basis from which targeted monitoring, prevention and control measures can be developed. Citation: Xiao XE, Liu YD, Zheng F, et al. 2023. High species diversity in Diaporthe associated with citrus diseases in China. Persoonia 51: 229-256. doi: 10.3767/persoonia.2023.51.06.

Citrus transcription factor CsERF098 cooperates with CsWRKY70 to participate in response of fruit to green mold

As plant-specific transcription factors (TFs), AP2/ERF can participate in regulating disease resistance in plants. Currently, researches on regulation of disease resistance of AP2/ERF TFs were mainly focused on model plants, and the regulatory mechanisms in non-model plants such as citrus fruit, an important economical fruit which is seriously infected by Penicillium digitatum, are still unclear. In this study, transcriptional activator CsERF098 overexpression enhanced the resistance of citrus fruit against green mold. Transcriptome sequencing revealed that CsERF098 was involved in four disease resistance pathways, including salicylic acid (SA) signaling pathway, lignin and waxy biosynthesis pathway, chitinase and jasmonic acid signaling pathway. CsERF098 could bind to promoter of SA pathway CsSAMT and CsSABP2, activate the transcriptional activities of CsSAMT, CsSABP2, CsTLP1b and CsTLP. Furthermore, the interaction of CsERF098 and CsWRKY70 was confirmed, which enhanced the trans-activation of CsERF098 on CsSAMT and CsSABP2. These results indicated that CsERF098 could mediate salicylic acid signaling pathway and enhance the synergistic regulation of CsSAMT and CsSABP2 through interaction with CsWRKY70, thereby in controlling the resistance of citrus fruit to Penicillium digitatum. The present study provides new thoughts on the role and mechanism of AP2/ERF transcription factor involved in regulating citrus disease resistance.

Comparative Analysis of Inhibitor Binding to Peroxiredoxins from Candidatus Liberibacter asiaticus and Its Host Citrus sinensis.

The peroxiredoxins (Prxs), potential drug targets, constitute an important class of antioxidant enzymes present in both pathogen and their host. The comparative binding potential of inhibitors to Prxs from pathogen and host could be an important step in drug development against pathogens. Huanglongbing (HLB) is a most devastating disease of citrus caused by Candidatus Liberibacter asiaticus (CLa). In this study, the binding of conoidin-A (conoidin) and celastrol inhibitor molecules to peroxiredoxin of bacterioferritin comigratory protein family from CLa (CLaBCP) and its host plant peroxiredoxin from Citrus sinensis (CsPrx) was assessed. The CLaBCP has a lower specific activity than CsPrx and is efficiently inhibited by conoidin and celastrol molecules. The biophysical studies showed conformational changes and significant thermal stability of CLaBCP in the presence of inhibitor molecules as compared to CsPrx. The surface plasmon resonance (SPR) studies revealed that the conoidin and celastrol inhibitor molecules have a strong binding affinity (KD) with CLaBCP at 33.0µM, and 18.5µM as compared to CsPrx at 52.0µM and 61.6µM, respectively. The docked complexes of inhibitor molecules showed more structural stability of CLaBCP as compared to CsPrx during the run of molecular dynamics-based simulations for 100ns. The present study suggests that the conoidin and celastrol molecules can be exploited as potential inhibitor molecules against the CLa to manage the HLB disease.

Phyto-extracts Mediated Biological Control of Citrus Canker

Citrus is second most important fruit crop and has significance economic importance in Pakistan. In Pakistan 2.17 million tonnes citrus was produced on area of 1.94 million acre. Citrus is mostly cultivated in Punjab and affected by different types of plant pathogens. Citrus canker is the most harmful disease among the major diseases of citrus which is caused by Xanthomonas axonopodis pv. citri. The copper based fungicides are mostly employed to manage the citrus canker in the field but excessive use of chemicals have negatively impacted the environment and warrant the need to find out organic solutions therefore the current study was aimed at identifying suitable plants extracts for the control of citrus canker bacterium. Isolation of the bacterium X.axonopodis was done through streaking on agar plate technique. Morphological and bio-chemical tests such as gram staining, KoH test, catalase test and starch hydrolysis test were performed to examine the bacteria X.axonopodispv. citri. Plant extracts were evaluated, in vitro, against the X.axonopodis pv. citri through paper disc method which showed the inhibition zone against the disease. The 100 percent extract of garlic, ginger, aloevera, moringa were used used along with the streptomycin as a positive control. The inhibition zone was 11.67mm and 10.83mm due to garlic and moringa extracts respectively while it was 16.67mm in case of positive control. The ginger and aloevera extracts proved ineffective against the citrus canker bacterium.The efficacy of garlic and moringa extracts were also checked against the X. axonopodis pv. citri under glasshouse conditions. The inoculum was sprayed on Kinnow plants, with three replicates, for each extract and data was recorded 15, 20, 25, 30 and 35 days post inoculation (dpi).The recorded disease severity percentage, after 35dpi, on garlic and moringa treated plants were 9.67% and 14.27% respectively while the 27% disease severity was recorded on control (plants sprayed with autoclaved distilled water). The garlic extract proved to be most effective followed by moringa extract which could be used as a potential organic solution to control citrus canker.

Etiology and management of citrus Melanose disease in Pakistan: A review

Diaporthe species are important pathogens of many hosts, including economically important crops. They cause severe melanose disease, stem-end rot of fruits, and gummosis of perennial plants worldwide. Among the Diaporthe species, Diaporthe citri is responsible for causing melanose disease. Melanose disease harms fruit, leaves, twigs, branches, and in certain cases, the main stem of trees of any age. The melanose infection can affect practically all citrus cultivars. Citrus melanose disease is a persistent and incurable disease leading to a massive loss of output in the citrus industry. Due to the lack of resistant cultivars, the failure of chemical treatments, and the dangers to environmental health, large-scale research is being conducted to develop a long-term remedy. Recently, biological control agents (BCAs) have been used as an alternative to fungicides to manage citrus melanose disease. In this review, we highlighted some significant aspects of melanose disease (Diaporthe citri) in citrus, such as its history, morphology, disease cycle, pathogenicity symptoms, and impact on the economy of the citrus industry. The current literature assists the researchers in averting melanose disease in citrus, developing genetically resistant cultivars, and ecofriendly management against Diaporthe citri. Keywords: Diaporthe citri, Melanose, Symptoms, Transmission, Disease cycle, Control management

Implementation and assessment of the classical biological control program against the huanglongbing vector, Trioza erytreae, in the Canary islands

The African citrus psyllid Trioza erytreae (Del Guercio) (Hemiptera: Triozidae) is one of the most threatening pests for Mediterranean citriculture. It vectors the phloem-limited bacteria Candidatus liberibacter spp, the causal agent of huanglongbing (HLB), the most devastating citrus disease worldwide. Although HLB has yet to be recorded in Europe, T. erytreae has established in the Macaronesia Islands of Madeira (Portugal) and the Canary Islands (Spain), and in mainland Europe. In 2017, a classical biological control program was implemented, and Tamarixia dryi (Waterston) (Hymenoptera: Eulophidae) was released in an experimental citrus orchard in the Canarian Island of Tenerife in the spring of 2018. This study aimed to analyze i) the distribution and spatio-temporal dispersion of T. dryi, ii) the seasonal trend of T. erytreae and parasitism rates of T. dryi in the field and iii) the effect of T. dryi on T. erytreae population densities in the Canary Islands three consecutive years after the release of the parasitoid. Our results showed that T. dryi successfully established in the island of Tenerife and dispersed in four out of five surrounding islands where T. erytreae was present. Two years after the release of T. dryi, the proportion of sites infested by the psyllid decreased from more than 80% to less than 5% in the three main islands: Tenerife, La Palma, and Gran Canaria. Furthermore, the population density of T. erytreae was extremely low in the sites where it was present two and three years after the release of T. dryi. Parasitism rates remained higher than 40% throughout the sampling periods. Overall, our three-year study shows that the parasitoid T. dryi reduced and controlled the Candidatus liberibacter spp vector, the causal agent of HLB, T. erytreae in the Canary Islands.

Poor shoot and leaf growth in Huanglongbing-affected sweet orange is associated with increased investment in defenses.

Citrus disease Huanglongbing (HLB) causes sparse (thinner) canopies due to reduced leaf and shoot biomass. Herein, we present results demonstrating the possible mechanisms behind compromised leaf growth of HLB-affected 'Valencia' sweet orange trees by comparing morphological, transcriptome, and phytohormone profiles at different leaf development phases (1. buds at the start of the experiment; 2. buds on day 5; . 3. leaf emergence; 4. leaf expansion; and 5. leaf maturation) to healthy trees. Over a period of 3 months (in greenhouse conditions), HLB-affected trees had ≈40% reduction in growth traits such as tree height, number of shoots per tree, shoot length, internode length, and leaf size compared to healthy trees. In addition, buds from HLB-affected trees lagged by ≈1 week in sprouting as well as leaf growth. Throughout the leaf development, high accumulation of defense hormones, salicylic acid (SA) and abscisic acid (ABA), and low levels of growth-promoting hormone (auxin) were found in HLB-affected trees compared to healthy trees. Concomitantly, HLB-affected trees had upregulated differentially expressed genes (DEGs) encoding SA, ABA, and ethylene-related proteins in comparison to healthy trees. The total number of cells per leaf was lower in HLB-affected trees compared to healthy trees, which suggests that reduced cell division may coincide with low levels of growth-promoting hormones leading to small leaf size. Both bud dieback and leaf drop were higher in HLB-affected trees than in healthy trees, with concomitant upregulated DEGs encoding senescence-related proteins in HLB-affected trees that possibly resulted in accelerated aging and cell death. Taken together, it can be concluded that HLB-affected trees had a higher tradeoff of resources on defense over growth, leading to sparse canopies and a high tree mortality rate with HLB progression.

Effect of tree height and spraying methods on Diaphorina citri kuwayama endosymbionts in the context of Huanglongbing disease management in citrus orchards.

Huanglongbing (HLB) (caused by Candidatus Liberibacter asiaticus) is the most damaging disease of citrus around the world. This study investigated the effects of citrus tree height on Diaphorina citri Kuwayama mortality, endosymbiont responses, and HLB distribution. The results reveal that the age of citrus trees plays a significant role in psyllid mortality. Interestingly, the cumulative mean mortality (%) of psyllids over the seven-day observation period was higher (31.50±0.03) when four-year-old (501A1, 502A2, 501A3) citrus trees were sprayed with a US-SMART mechanical sprayer. In contrast, the psyllids mortality was 0.09±0.23 for the 13-year-old citrus trees (104A2, 104A3, 104C1) sprayed with a US-SMART mechanical sprayer and 9.10±0.05 for 13-year-old (502A2, 502B2, 502D1) citrus trees sprayed with a fixed US-SMART mechanical sprayer. Our findings also revealed that psyllids from both four- and 13-year-old citrus trees carried Candidatus Carsonella ruddii species and Wolbachia, the primary and secondary endosymbionts, respectively. Surprisingly, infection rates of these endosymbionts remained consistent across different age groups, as confirmed by quantitative polymerase chain reaction analysis. Furthermore, our study highlights the significance of tree height as a proxy for tree age in influencing HLB occurrence. Specifically, four-year-old citrus trees subjected to the US-SMART mechanical sprayer for citrus psyllid control demonstrated effective disease management compared to 13-year-old (104A2, 104A3, 104C1) citrus trees sprayed with US-SMART mechanicalsprayers. Additionally, the investigation explored the impact of tree height on HLB distribution. In four-year-old trees, no significant correlation between HLB disease and tree height was observed, potentially due to effective spray coverage with US-SMART mechanical sprayer. However, in 13-year-old (104A2, 104A3, 104C1) citrus tree sprayed with US-SMART mechanical sprayer, a positive correlation between tree height and HLB disease was evident. This research provides valuable insights into the complex interaction between citrus tree age, psyllid endosymbionts responses, and HLB distribution. These results emphasize effective HLB management strategies, especially in orchards with diverse tree age populations, ultimately contributing to the long-term sustainability of citrus cultivation. © 2023 Society of Chemical Industry.

Denoising Diffusion Probabilistic Models and Transfer Learning for citrus disease diagnosis.

Plant Disease diagnosis based on deep learning mechanisms has been extensively studied and applied. However, the complex and dynamic agricultural growth environment results in significant variations in the distribution of state samples, and the lack of sufficient real disease databases weakens the information carried by the samples, posing challenges for accurately training models. This paper aims to test the feasibility and effectiveness of Denoising Diffusion Probabilistic Models (DDPM), Swin Transformer model, and Transfer Learning in diagnosing citrus diseases with a small sample. Two training methods are proposed: The Method 1 employs the DDPM to generate synthetic images for data augmentation. The Swin Transformer model is then used for pre-training on the synthetic dataset produced by DDPM, followed by fine-tuning on the original citrus leaf images for disease classification through transfer learning. The Method 2 utilizes the pre-trained Swin Transformer model on the ImageNet dataset and fine-tunes it on the augmented dataset composed of the original and DDPM synthetic images. The test results indicate that Method 1 achieved a validation accuracy of 96.3%, while Method 2 achieved a validation accuracy of 99.8%. Both methods effectively addressed the issue of model overfitting when dealing with a small dataset. Additionally, when compared with VGG16, EfficientNet, ShuffleNet, MobileNetV2, and DenseNet121 in citrus disease classification, the experimental results demonstrate the superiority of the proposed methods over existing approaches to a certain extent.

Transcriptional insights of citrus defense response against Diaporthe citri

Citrus melanose, caused by Diaporthe citri, is one of the most important and widespread fungal diseases of citrus. Previous studies demonstrated that the citrus host was able to trigger the defense response to restrict the spread of D. citri. However, the molecular mechanism underlying this defense response has yet to be elucidated. Here, we used RNA-Seq to explore the gene expression pattern at the early (3 days post infection, dpi) and late (14 dpi) infection stages of citrus leaves in response to D. citri infection, and outlined the differences in transcriptional regulation associated with defense responses. The functional enrichment analysis indicated that the plant cell wall biogenesis was significantly induced at the early infection stage, while the callose deposition response was more active at the late infection stage. CYP83B1 genes of the cytochrome P450 family were extensively induced in the callus deposition-mediated defense response. Remarkably, the gene encoding pectin methylesterase showed the highest upregulation and was only found to be differentially expressed at the late infection stage. Genes involved in the synthesis and regulation of phytoalexin coumarin were effectively activated. F6’H1 and S8H, encoding key enzymes in the biosynthesis of coumarins and their derivatives, were more strongly expressed at the late infection stage than at the early infection stage. Collectively, our study profiled the response pattern of citrus leaves against D. citri infection and provided the transcriptional evidence to support the defense mechanism.

Risk-based regionalization approach for area-wide management of HLB vectors in the Mediterranean Basin.

Huanglongbing (HLB) is one of the most devastating citrus diseases worldwide. It is associated with the non-culture bacteria Candidatus Liberibacter spp., which can be transmitted by grafting and/or the psyllid vectors Diaphorina citri (ACP) and Trioza erytreae (AfCP). Although HLB has not been reported in the Mediterranean Basin to date, both vectors are present, and thus represent a serious threat to the citrus industry in this region. Resistant citrus cultivars or effective therapeutic treatments are not currently available for HLB. Nevertheless, area-wide pest management via coordinated management efforts over large areas has been implemented in Brazil, China and the USA for HLB control. This study proposes an open access flexible methodology to address area-wide management of both HLB vectors in the Mediterranean Basin. Based on a risk-based approach which considers climatic information and other variables that may influence vector introduction and spread, such as conventional, organic, abandoned and residential citrus areas as well as transportation corridors, an area-wide management division in pest management areas (PMAs) is proposed. The size and location of these PMAs were estimated by means of a hierarchical clustering algorithm with spatial constraints whose performance was assessed under different configuration scenarios. This proposal may assist policymakers and the citrus industry of the citrus-growing areas of the Mediterranean Basin in risk management planning in the case of the spread of HLB vectors or a possible introduction of the disease. Additionally, it may be a valuable resource to inform opinion dynamic models, enabling the identification of pivotal factors for the success of control measures.

Naming entity recognition of citrus pests and diseases based on the BERT-BiLSTM-CRF model

Naming entity recognition of citrus pests and diseases based on the BERT-BiLSTM-CRF model

Effect of Individual Protective Covers on Young ‘Valencia’ Orange (Citrus sinensis) Tree Physiology

Huanglongbing (HLB), an important citrus disease, causes many physiological and anatomical changes such as phloem dysfunction, imbalance in carbohydrate partitioning, decrease in leaf chlorophyll, and nutritional imbalances in the affected trees, ultimately resulting in tree decline. In Florida, HLB is associated with phloem-limited bacteria Candidatus Liberibacter asiaticus (CLas), and it is vectored by the Asian citrus psyllid (Diaphorina citri). No cure for HLB has been found, and most of the HLB management efforts have been focused on vector control or exclusion, improved nutrient management, and the use of HLB-tolerant rootstocks. Individual protective covers (IPCs) are a type of psyllid exclusion tool that is increasingly used by growers for HLB management of newly planted citrus trees. However, no studies have evaluated their influence on citrus tree physiology. This study investigated the effect of IPCs and different rates of insecticides on CLas infection and different physiological attributes, including soluble (glucose, fructose, and sucrose) and nonsoluble (starch) carbohydrates, leaf chlorophyll, and leaf macronutrients and micronutrients over 2.5 years of field growth. The treatments (tree cover and insecticides rate) were applied in newly planted ‘Valencia’ sweet orange (Citrus sinensis) trees grafted on ‘Cleopatra’ (C. reticulata) rootstock. The IPCs prevented CLas transmission and accumulation of foliar starch, sucrose, and glucose commonly associated with HLB. IPC-covered trees had more leaf chlorophyll-a and chlorophyll-b than noncovered trees and more leaf nitrogen (N) and zinc (Zn). Our findings suggest that IPCs effectively prevent CLas infection and maintain the physiological health of young citrus trees under heavy HLB pressure. Therefore, IPCs are recommended as an important component of integrated pest management for this devastating disease.

Detection of citrus diseases in complex backgrounds based on image–text multimodal fusion and knowledge assistance

Diseases pose a significant threat to the citrus industry, and the accurate detection of these diseases represent key factors for their early diagnosis and precise control. Existing diagnostic methods primarily rely on image models trained on vast datasets and limited their applicability due to singular backgrounds. To devise a more accurate, robust, and versatile model for citrus disease classification, this study focused on data diversity, knowledge assistance, and modal fusion. Leaves from healthy plants and plants infected with 10 prevalent diseases (citrus greening, citrus canker, anthracnose, scab, greasy spot, melanose, sooty mold, nitrogen deficiency, magnesium deficiency, and iron deficiency) were used as materials. Initially, three datasets with white, natural, and mixed backgrounds were constructed to analyze their effects on the training accuracy, test generalization ability, and classification balance. This diversification of data significantly improved the model’s adaptability to natural settings. Subsequently, by leveraging agricultural domain knowledge, a structured citrus disease features glossary was developed to enhance the efficiency of data preparation and the credibility of identification results. To address the underutilization of multimodal data in existing models, this study explored semantic embedding methods for disease images and structured descriptive texts. Convolutional networks with different depths (VGG16, ResNet50, MobileNetV2, and ShuffleNetV2) were used to extract the visual features of leaves. Concurrently, TextCNN and fastText were used to extract textual features and semantic relationships. By integrating the complementary nature of the image and text information, a joint learning model for citrus disease features was achieved. ShuffleNetV2 + TextCNN, the optimal multimodal model, achieved a classification accuracy of 98.33% on the mixed dataset, which represented improvements of 9.78% and 21.11% over the single-image and single-text models, respectively. This model also exhibited faster convergence, superior classification balance, and enhanced generalization capability, compared with the other methods. The image-text multimodal feature fusion network proposed in this study, which integrates text and image features with domain knowledge, can identify and classify citrus diseases in scenarios with limited samples and multiple background noise. The proposed model provides a more reliable decision-making basis for the precise application of biological and chemical control strategies for citrus production.

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.

Iron Competition as an Important Mechanism of Pulcherrimin-Producing Metschnikowia sp. Strains for Controlling Postharvest Fungal Decays on Citrus Fruit.

This study identified and tested fruit-isolated Metschnikowia yeasts against three major postharvest citrus pathogens, namely, Penicillium digitatum, Penicillium italicum, and Geotrichum citri-aurantii, and further evaluated the impact of FeCl3 on the biocontrol efficiency of pulcherrimin-producing M. pulcherrima strains. Based on the characterization of the pigmented halo surrounding the colonies and the analysis of the D1/D2 domain of 26S rDNA, a total of 46 Metschnikowia sp. were screened and identified. All 46 Metschnikowia strains significantly inhibited the hyphal growth of Penicillium digitatum, Penicillium italicum, and Geotrichum citri-aurantii, and effectively controlled the development of green mold, blue mold and sour rot of citrus fruit. The introduction of exogenous FeCl3 at certain concentrations did not significantly impact the pulcherriminic acid (PA) production of pigmented M. pulcherrima strains, but notably diminished the size of pigmented zones and the biocontrol efficacy against the three pathogens. Iron deficiency sensitivity experiments revealed that P. digitatum and P. italicum exhibited higher sensitivity compared to G. citri-aurantii, indicating that iron dependence varied among the three pathogens. These results suggested that M. pulcherrima strains, capable of producing high yields of PA, possessed great potential for use as biocontrol agents against postharvest citrus diseases. The biocontrol efficacy of these yeasts is mainly attributed to their ability to competitively deplete iron ions in a shared environment, with the magnitude of their pigmented halo directly correlating to their antagonistic capability. It is worth noting that the level of sensitivity of pathogens to iron deficiency might also affect the biocontrol effect of pulcherrimin-producing M. pulcherrima.

Multi-Locus Sequence Analysis Reveals the Genetic Diversity and Population Differentiation of Candidatus Liberibacter Asiaticus in China

Huanglongbing (HLB) is a devastating citrus disease caused by Candidatus Liberibacter asiaticus (CLas). Since its initial outbreak in Guangdong Province, China, it has spread to 10 provinces and caused significant economic losses. Hence, assessing CLas genetic diversity and demographic history is crucial for HLB epidemic prevention and control. In this study, we collected 500 leaf samples of CLas-infected plants from 10 provinces. We performed multi-loci sequence analysis on four gene fragments (omp, DnaA, GroEL, and SDE1) to explore the genetic differentiation and diversity of CLas in China. Our results indicated low nucleotide diversity (0.00005 ± 0.00001) in CLas, with the absence of significant systematic geographic structure in its distribution. Molecular variance analysis revealed predominant (81.7%) genetic variations within the population, with a minor variation (18.3%) occurring between populations as well as Yunnan provinces. In the Fujian population, significant gene exchange occurred with the other nine populations. Significant negative values in Tajima’s D and Fu’s FS neutrality tests indicated historical population expansions. The nucleotide mismatch distribution curve exhibits a single peak pattern, further supporting the expansion events. Our findings hold potential for advancing epidemiological research and providing suggestions for effective strategies to mitigate the spread of CLas and control HLB.

Possible economic losses on the oranges production chain of Peru due to introduction of Huanglongbing (HLB): Simulation of prospective scenarios to 2045

Huanglongbing (HLB) is a citrus disease known for causing significant production losses, and its potential introduction into Peru looms on the horizon. The aim of this study was to assess the potential economic losses within the Central Jungle's orange production chain, specifically in the Region Junín. This assessment involved simulating the spread of HLB under prospective scenarios spanning from 2026 to 2045, aiming to estimate the cost-benefit of preventing these losses through the implementation of a national phytosanitary program (PNF). The methodology employed in this study comprised administering questionnaires to local growers and estimating economic losses across three scenarios. The first scenario assumed a baseline production trend without HLB presence, while the second scenario considered an epidemiological situation with HLB but without the implementation of a PNF. The third scenario factored in HLB with varying degrees of adoption among PNF-affiliated growers. The findings highlight several risk factors contributing to the potential spread of HLB in Junín. The epidemiological model reveals that HLB can swiftly render young trees unproductive. Cumulatively, economic losses from 2026 to 2045 could reach a staggering US$ 371,146 thousand if no intervention takes place. However, this figure could be significantly reduced to US$ 44,890 thousand if 100% of growers embrace the PNF. Such public policy measures would not only prevent production losses but also generate substantial social benefits. These scenarios underscore the stark negative impacts HLB could inflict on the local orange production chain. The implementation of the PNF proves to be a critical intervention, preventing production losses, preserving jobs, and safeguarding related economic activities. Without timely public intervention, the economic losses at stake could render the agribusiness sector unsustainable.