Search Results (14)

Phytoplasmas are obligate intracellular parasitic bacteria that infect over 1000 plant species globally, causing devastating diseases characterized by yellowing, witches’ broom, phyllody, and significant yield losses in economically important crops. The unculturable nature of these pathogens has historically hindered their study; however, advances in molecular biology and genomics have substantially accelerated progress over the past two decades. This review provides a comprehensive overview of current knowledge on phytoplasma diseases and control technologies. In terms of taxonomy, phytoplasmas are currently classified into 37 16Sr groups with over 150 subgroups based on 16S rRNA gene analysis, and approximately 50 ‘Candidatus Phytoplasma’ species have been formally named. Genomic studies have revealed that phytoplasmas possess highly reduced genomes (530–1350 kb) lacking many essential metabolic pathways, reflecting their obligate parasitic lifestyle. Regarding pathogenesis, secreted effector proteins such as SAP (Secreted Aster Yellows Witches’ Broom Protein), TENGU (tengu-su inducer), and SWP (Secreted Wheat Blue Dwarf Protein) manipulate plant hormone signaling and developmental processes, leading to characteristic disease symptoms. Detection technologies have evolved from traditional microscopy to molecular methods, including nested PCR, real-time quantitative PCR, loop-mediated isothermal amplification (LAMP), and CRISPR/Cas-based systems (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein), with AI-based image recognition and remote sensing emerging as promising tools for large-scale field monitoring. Integrated management strategies encompassing agricultural practices, insect vector control, biological control agents, induced resistance, and breeding for resistance are discussed. Finally, future research directions, including functional genomics, microbiome-based approaches, and precision agriculture technologies, are highlighted. This review aims to provide researchers and practitioners with a systematic reference for understanding phytoplasma biology and developing effective disease management strategies. Full article

This retrospective review traces personal encounters along the complex path of plant yellowing diseases—graft-transmissible disorders historically attributed to elusive viruses, but later linked to phloem-invading, wall-less bacteria known as Mollicutes. These include two plant-infecting genera: the cultivable Spiroplasma and the non-cultivable ‘Candidatus Phytoplasma’. A third group—the walled, psyllid-transmitted Candidatus Liberibacter—was later implicated in closely similar syndromes. This shift in understanding marked a major turning point in plant pathology, offering new insights into yellowing diseases characterized by stunting, decline, and poor or deformed growth. The review focuses on key syndromes: citrus little leaf disease (LLD), or citrus stubborn disease (CSD), caused by Spiroplasma citri; and several Mollicute -related disorders, including safflower phyllody, Bermuda grass yellowing, and papaya dieback (PDD) (Nivun Haamir), the latter linked to ‘Candidatus Phytoplasma australiense’. Despite differing causes and vectors, citrus LLD-CSD and PPD share an erratic, unpredictable pattern of natural outbreaks—sometimes a decade apart—hindering grower engagement and sustained control efforts. While scientific understanding has deepened, practical management remains limited. The recent global spread of Huanglongbing (HLB), caused by Candidatus Liberibacter species, underscores the urgent need for improved strategies to manage this resilient group of phloem-limited bacterial pathogens. Full article

In Graneros, O’Higgins Region, Chile, the mallow psyllid (Russelliana solanicola Tuthill, 1959) from Malva nicaeensis L. was identified as a potential vector of ‘Candidatus Phytoplasma pruni’. Over an 8-month period, 2089 specimens of a species of Psylloidea, including immatures and adults, were captured. We only selected the adults used for transmission trials in Catharanthus roseus (L.) G. Don (periwinkle) plants. By nested PCR, using primer pairs for phytoplasma detection in 16S rRNA and IdpA genes, 7 out of 113 (6.2%) periwinkle plants used in transmission trials were found to be infected by phytoplasmas. Insects that fed on these plants also tested positive for the same phytoplasmas. Periwinkle plants never showed virescence and phyllody, as commonly occurs with phytoplasma 16SrIII-J infection due to the effector SAP54. In this case, using primer pairs for the SAP54 gene, an amplification product was never obtained. Virtual restriction fragment length polymorphism (RFLP) analysis of F2nR2 fragments indicated that the phytoplasma, found in both periwinkle plants and insects used in transmission trials, belongs to the 16SrIII-J ribosomal subgroup. The COI gene of the psyllids samples was amplified and sequenced, showing a similarity ranging from 84.84% to 85.02% with R. solanicola from Solanum tuberosum L. The mitochondrial genome of the psyllid was also sequenced, revealing a 14,835 bp circular DNA molecule with 37 genes. The mallow psyllid transmitted the phytoplasma 16SrIII-J to periwinkle plants. The molecular identification of the insect does not match the morphological one, indicating that the mallow psyllid may constitute a cryptic species within the polyphagous R. solanicola species. This is the first report of a psyllid as a vector of the phytoplasma 16SrIII-J. Full article

Monitoring sesame plant health and detecting disease early are essential to reducing disease spread and facilitate effective management practices. In this research, we developed an image classification model to detect bacterial blight-infected, phyllody-infected, and healthy sesame crops. Since images were necessary to carry out this study, we collected 2300 images at the Gondar and Humera Agriculture Research Centers and directly from the field in Metema. Since the collected images were limited, to increase the number of images in the dataset, we used image augmentation with different variations. In the image preprocessing step, we used a median filter for noise filtering, and contrast stretching techniques were used for image contrast and brightness enhancement. SegNet semantic segmentation, which is deep convolution neural network-based architecture, was used to segment the leaf part of the image from the background. In the feature extraction and classification steps, a deep convolutional neural network was used. Finally, we evaluated the proposed model and compared it with two recent deep convolution neural network models, namely, Xception and InceptionV3. The proposed model for the classification of sesame diseases achieved better accuracy, with 96.67% testing accuracy, 97.78% validation accuracy, and 98% training accuracy. Full article

Cucumber plants (Cucumis sativus) displaying symptoms of phyllody, sterility, and flower virescence were observed in fields located in the Dianbai district of Guangdong province, China. Total DNA was extracted from the symptomatic plants; this was followed by molecular detection using a set of universal phytoplasma primer pairs, R16mF2/mR1, P1/P7, and SecYF1(II)/SecYR1(II). This resulted in the PCR amplification of products corresponding to expected sizes of 1.4 kb, 1.8 kb and 1.7 kb, respectively. The 16S rDNA sequence obtained exhibited 100% similarity with the eggplant phyllody phytoplasma, the ‘Cleome rutidosperma’ witches’ broom phytoplasma, and the ‘Desmodium ovalifolium’ witches’ broom phytoplasma strain DeOWB, all of which belong to the 16SrII group. Phylogenetic analysis, based on the 16S rDNA gene and SecY gene sequences, confirmed the close affiliation of the detected phytoplasma isolate, tentatively designated as cucumber phyllody phytoplasma (CuPh) China isolate, with the 16SrII-A subgroup. Additionally, virtual restriction fragment length polymorphism (RFLP) analysis of the 16S rDNA sequence revealed a pattern that was identical to that of the 16SrII-A subgroup. This is the first report of cucumber phyllody phytoplasma in China. Full article

Phytoplasmas are intracellular pathogenic bacteria that infect a wide range of plant species, including agriculturally important crops and ornamental trees. However, our understanding of the relationship between symptom severity, disease progression, and phytoplasma concentration remains limited due to the inability to inoculate phytoplasmas mechanically into new plant hosts. The present study investigated phytoplasma titer dynamics and symptom development in periwinkle and tomato, both infected with the same potato purple top (PPT) phytoplasma strain using a small seedling grafting approach. Virescence, phyllody, and witches’-broom (WB) symptoms sequentially developed in periwinkle, while in tomato plants, big bud (BB, a form of phyllody), cauliflower-like inflorescence (CLI), and WB appeared in order. Results from quantitative polymerase chain reaction (qPCR) targeting the PPT phytoplasma’s 16S rRNA gene revealed that in both host species, phytoplasma titers differed significantly at different infection stages. Notably, the highest phytoplasma concentration in periwinkles was observed in samples displaying phyllody symptoms, whereas in tomatoes, the titer peaked at the BB stage. Western blot analysis, utilizing an antibody specific to PPT phytoplasma, confirmed substantial phytoplasma presence in samples displaying phyllody and BB symptoms, consistent with the qPCR results. These findings challenge the conventional understanding that phytoplasma infection dynamics result in a higher titer at later stages, such as WB (excessive vegetative growth), rather than in the early stage, such as phyllody (abnormal reproductive growth). Furthermore, the PPT phytoplasma titer was markedly higher in periwinkles than in tomato plants, indicating differing susceptibilities between the hosts. This study reveals distinct host responses to PPT phytoplasma infection, providing valuable insights into phytoplasma titer dynamics and symptom development, with implications for the future management of agricultural disease. Full article

Phytoplasmas are associated with important bacterial diseases, causing severe symptoms in agricultural and ornamental crops. ‘Candidatus Phytoplasma rubi’, associated with the Rubus stunt in raspberries (Rubus idaeus) and blackberries (Rubus subgenus Rubus), causes shortened internodes, elongated sepals, proliferation, phyllody, and virescence. The recently published genome of ‘Ca. P. rubi’ RS enabled a comprehensive genomic comparison to the complete genomes of 16SrV phytoplasmas, comprising strains of the flavescence dorée-associated phytoplasma CH and two ‘Candidatus Phytoplasma ziziphi’ strains. Besides the typical transporters and metabolic features of phytoplasmas, the phosphorolysis of sucrose and the utilization of the carboxylic acid L-lactate became apparent for the 16SrV-group. With respect to the effector repertoire and the encoded immunodominant membrane proteins involved in host colonization, the group revealed conserved features that comprise the variable membrane proteins A and B. However, SAP11- and SAP54 orthologs were limited to ‘Ca. P. rubi’ RS and ‘Ca. P. ziziphi’. Genome-sequence-based phylogenetic analysis supports the close relationship of these genomes relative to alder yellows phytoplasmas. The analyses supported the impact of the mobilome on phytoplasma evolution but also highlighted that there is the possibility of identifying phytoplasmas with a larger metabolic repertoire in the future. Full article

Cassava witches’ broom disease (CWBD) is one of the main diseases of cassava in Southeast Asia (SEA). Affected cassava plants show reduced internodal length and proliferation of leaves (phyllody) in the middle and top part of the plant, which results in reduced root yields of 50% or more. It is thought to be caused by phytoplasma; however, despite its widespread distribution in SEA still little is known about CWBD pathology. The overarching goal of this study was to review and corroborate published information on CWBD biology and epidemiology considering recent field observations. We report the following: (1) CWBD symptoms are conserved and persistent in SEA and are distinct from what has been reported as witches’ broom in Argentina and Brazil. (2) In comparison with cassava mosaic disease, another major disease of cassava in SEA, symptoms of CWBD develop later. (3) Phytoplasma detected in CWBD-affected plants belong to different ribosomal groups and there is no association study available indicating phytoplasma as the causing agent of CWBD. These findings are essential clues for designing surveillance and management strategies and for future studies to better understand the biology, tissue localization and spatial spread of CWBD in SEA and other potential risk areas. Full article

Two unrelated plant species, green pea and parthenium weed, harboring typical phytoplasma symptoms, were discovered in Yunlin, Taiwan. Green pea (Pisum sativum.) and parthenium weed (Parthenium hysterophorus L.) are both herbaceous annual plants belonging to the Fabaceae and Asteraceae families, respectively. Displayed symptoms were witches’ broom, phyllody and virescence, which are typical indications of phytoplasma infection. Pleomorphic phytoplasma-like bodies were observed under the transmission electron microscope in the sieve elements of symptomatic green pea and parthenium weed. The iPhyClassifier-based virtual RFLP study demonstrated that the phytoplasma associated with the diseased plants belongs to the 16SrII-V subgroup. The disease symptoms of both plants can be explained by the identification of PHYL1 and SAP11 effectors, identical to those of peanut witches’ broom phytoplasma. The phytoplasma strains identified in this study present a very close phylogenetic relationship with other 16SrII-V subgroup phytoplasma strains discovered in Taiwan. These results not only convey the local status of the 16SrII-V subgroup phytoplasma strains but also encourage attention to be given to preventing the spread of this threat before it becomes pervasive. Full article

Phytoplasma-associated diseases such as phyllody and little leaf are critical threats to sesame cultivation worldwide. The mechanism of the dramatic conversion of flowers to leafy structures leading to yield losses and the drastic reduction in leaf size due to Phytoplasma infection remains yet to be identified. Cytosine methylation profiles of healthy and infected sesame plants studied using Whole Genome Bisulfite Sequencing (WGBS) and Quantitative analysis of DNA methylation with the real-time PCR (qAMP) technique revealed altered DNA methylation patterns upon infection. Phyllody was associated with global cytosine hypomethylation, though predominantly in the CHH (where H = A, T or C) context. Interestingly, comparable cytosine methylation levels were observed between healthy and little leaf-affected plant samples in CG, CHG and CHH contexts. Among the different genomic fractions, the highest number of differentially methylated Cytosines was found in the intergenic regions, followed by promoter, exonic and intronic regions in decreasing order. Further, most of the differentially methylated genes were hypomethylated and were mainly associated with development and defense-related processes. Loci for STOREKEEPER protein-like, a DNA-binding protein and PP2-B15, an F-Box protein, responsible for plugging sieve plates to maintain turgor pressure within the sieve tubes were found to be hypomethylated by WGBS, which was confirmed by methylation-dependent restriction digestion and qPCR. Likewise, serine/threonine-protein phosphatase-7 homolog, a positive regulator of cryptochrome signaling involved in hypocotyl and cotyledon growth and probable O-methyltransferase 3 locus were determined to be hypermethylated. Phytoplasma infection-associated global differential methylation as well as the defense and development-related loci reported here for the first time significantly elucidate the mechanism of phytoplasma-associated disease development. Full article

Phytoplasmas are obligate cell-wall-less plant pathogenic bacteria that infect many economically important crops, causing considerable yield losses worldwide. Very little information is known about phytoplasma–host plant interaction mechanisms and their influence on sesame yield and oil quality. Therefore, our aim was to explore the ultrastructural and agro-physio-biochemical responses of sesame plants and their effects on sesame productivity and oil quality in response to phytoplasma infection. Sesame leaf samples exhibiting phyllody symptoms were collected from three experimental fields during the 2021 growing season. Phytoplasma was successfully detected by nested- polymerase chain reaction (PCR) assays using the universal primer pairs P1/P7 and R16F2n/R16R2, and the product of approximately 1200 bp was amplified. The amplified product of 16S rRNA was sequenced and compared with other available phytoplasma’s 16S rRNA in the GenBank database. Phylogenetic analysis revealed that our Egyptian isolate under accession number MW945416 is closely related to the 16SrII group and showed close (99.7%) identity with MH011394 and L33765.1, which were isolated from Egypt and the USA, respectively. The microscopic examination of phytoplasma-infected plants revealed an observable deterioration in tissue and cell ultrastructure. The primary and secondary metabolites considerably increased in infected plants compared with healthy ones. Moreover, phytoplasma-infected plants showed drastically reduced water content, chlorophyll content, growth, and yield components, resulting in 37.9% and 42.5% reductions in seed and oil yield, respectively. The peroxide value of the infected plant’s oil was 43.2% higher than that of healthy ones, suggesting a short shelf-life. Our findings will provide a better understanding of the phyllody disease pathosystem, helping us to develop effective strategies for overcoming such diseases. Full article

Phytoplasma-infected Chinese cherry (Cerasus pseudocerasus L.) exhibits symptoms of phyllody and stiff fruit. To reveal the molecular mechanism of stiff fruit, the current study integrated transcriptome with metabolome. Results showed that the differentially expressed genes and the differentially accumulated metabolites were related to a high proportion of two aspects: pathogen resistance and signaling or regulatory functions, and the molecular mechanism of stiff fruit that were majorly induced by plant biotic stress response via phytohormones signal transduction, especially signal pathways of salicylic acid, auxin, and abscisic acid. Notably, there was a large overlap between phytoplasma stress response and drought stress response genes. Phytohormone content displayed significant difference that abscisic acid and salicylic acid content of phytoplasma-infected fruit were higher than that of healthy fruit, whereas zeatin, jasmonic acid, and IAA showed the opposite results. In addition, the expression of key candidate genes, including IAA4, IAA9, IAA14, IAA31, ARF5, ARF9, GH3.1, GH3.17, SAUR20, SAUR32, SAUR40, PR1a, PRB1, TGA10, SnRK2.3, and AHK2, was responsible for cherry stiff fruit. In conclusion, the current study contributed a foundation for understanding the molecular mechanism of cherry phyllody disease on stiff fruit, a better understanding of fruit development, and found the potential candidate genes involved in cherry stiff fruit, which could be used for further research in associated fields. Full article

In the 2019–2020 growing season, two corn fields located in İmamoğlu town (Adana Province, Turkey) were surveyed following the appearance of phytoplasma-like symptoms on maize plants. A total of 40 samples were collected and tested in first-round and nested PCR using universal primer pairs P1/P7 and R16F2n/R16R2, respectively. All maize-diseased plants reacted positively, whilst no PCR amplifications were obtained from asymptomatic plants. Blast sequence analysis of R16F2n/R16R2-primed amplicons from different maize isolates showed 99.2% to 100% of identity with the 16S rRNA gene of Ligustrum witches’ broom phytoplasma (LiWBP). To gain additional molecular information on the 16S ribosomal RNA and 23S rRNA intergenic spacer region of LiWBP, not identified previously, the P1/P7-primed amplicons were also sequenced and analyzed. The results show that maize isolates from Turkey share 99.6% to 100% of identity among them, whereas the highest identity found (91%) was with members of groups 16SrII and 16SrXXV (peanut and tea witches’ broom groups, respectively). This distant relationship between LiWBP and members of 16SrII and XXV was also confirmed by RFLP and phylogenetic analyses. This is the first finding of LiWBP on maize in nature, where it was found responsible for phyllody disease of corn plants in Turkey. The additional molecular information acquired in this study on the 16S–23S rRNA intergenic spacer region of LiWBP further corroborates its distant relationship to any other phytoplasma groups. Full article

New genotypes of winter oilseed rape bred under the Czech breeding program were subjected to performance tests within the framework of inter-institutional pre-tests. At four monitored localities in the Czech Republic, field trials were carried out on 50 genotypes in the years 2015 to 2017. In these trials, evaluations were made on infestation by the fungal pathogens Leptosphaeria maculans, Leptosphaeria biglobosa, and Sclerotinia sclerotiorum, as well as the level of infestation caused by phytoplasmas. The evaluation of new oilseed rape genotypes confirmed a medium to high level of resistance to phoma stem canker and Sclerotinia stem rot compared to the resistant reference varieties. The most severe infestations caused by Leptosphaeria spp. were observed in Chlumec nad Cidlinou in 2015 (mean severity score 22.38%) and in Opava in 2016 (mean severity score 20.72%). The same trend was observed for infestations caused by S. sclerotiorum, where the most damage to trial plots were observed at the same localities, in 2015 in Chlumec nad Cidlinou (mean severity score 36.85%) and in 2016 in Opava (mean severity score 18.84%). PCR determination of Leptosphaeria spp. showed that 98% of sampled leaves in autumn season showing symptoms were infected by L. maculans, while the remaining 2% were identified as bearing L. biglobosa. Molecular detection of infected parts of oilseed rape plants with symptoms of phyllody confirmed in all cases the presence of phytoplasma isolates from the 16SrI Aster Yellows group. Full article