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Phytoplasmas are small, wall-less bacteria that infect plants and multiply within insects. This Special Issue compiles ten articles that explore the molecular characterization and host-pathogen interactions of phytoplasmas. The articles cover topics such as the genetic diversity and epidemiology of grapevine-associated phytoplasmas, the impact of phytoplasma infection on grapevine physiology, multilocus genotyping of phytoplasmas associated with grapevine bois noir, the presence of phytoplasmas in citrus crops, the epigenetic effects of phytoplasma infection in sesame plants, the transmission pathways of sandalwood spike disease, advances in phytoplasma detection methods, and updates in phytoplasma taxonomy. These findings contribute to our understanding of phytoplasma biology and host interactions, emphasizing the need for ongoing research in this field. [Extracted from the article]

Simple Summary: Phytoplasmas are minute bacteria that infect many plant species, causing economic losses and impacting agriculture. Early diagnosis is crucial to effective disease management. A symptom database, iPhyDSDB, was developed by retrieving nearly 35,000 phytoplasma DNA sequences from the NCBI nucleotide database and identifying 945 plant species associated with phytoplasma diseases. The database includes curated links to symptom images and detailed disease information. Implemented on a web-based interface using MySQL and PHP, iPhyDSDB features advanced search functionality. This tool helps farmers, growers, researchers, and educators efficiently query based on plant host and symptom type, aiding in the identification and management of phytoplasma-related diseases. Phytoplasmas are small, intracellular bacteria that infect a vast range of plant species, causing significant economic losses and impacting agriculture and farmers' livelihoods. Early and rapid diagnosis of phytoplasma infections is crucial for preventing the spread of these diseases, particularly through early symptom recognition in the field by farmers and growers. A symptom database for phytoplasma infections can assist in recognizing the symptoms and enhance early detection and management. In this study, nearly 35,000 phytoplasma sequence entries were retrieved from the NCBI nucleotide database using the keyword "phytoplasma" and information on phytoplasma disease-associated plant hosts and symptoms was gathered. A total of 945 plant species were identified to be associated with phytoplasma infections. Subsequently, links to symptomatic images of these known susceptible plant species were manually curated, and the Phytoplasma Disease Symptom Database (iPhyDSDB) was established and implemented on a web-based interface using the MySQL Server and PHP programming language. One of the key features of iPhyDSDB is the curated collection of links to symptomatic images representing various phytoplasma-infected plant species, allowing users to easily access the original source of the collected images and detailed disease information. Furthermore, images and descriptive definitions of typical symptoms induced by phytoplasmas were included in iPhyDSDB. The newly developed database and web interface, equipped with advanced search functionality, will help farmers, growers, researchers, and educators to efficiently query the database based on specific categories such as plant host and symptom type. This resource will aid the users in comparing, identifying, and diagnosing phytoplasma-related diseases, enhancing the understanding and management of these infections. [ABSTRACT FROM AUTHOR]

The corn stunt disease is a major threat to maize production in Brazil. In addition to the more common insect vector Dalbulus maidis (Hemiptera: Cicadellidae), the African species Leptodelphax maculigera (Hemiptera: Delphacidae) was recently found in the Brazilian states of Goiás, Paraná and Santa Catarina, raising concern regarding its potential ability to transmit stunt pathogens. We confirmed the presence of L. maculigera in the state of Rio Grande do Sul by conducting a population survey with yellow sticky traps and light traps in three different sites, although it corresponded to only 2.3% of the D. maidis population captured during the same period. Molecular analysis via RT-qPCR multiplex confirmed the simultaneous infection of L. maculigera by two corn stunt pathogens—Maize rayado fino virus (MRFV) and Maize bushy stunt phytoplasma (MBSP)—in 76.9% of the samples, while the remaining 23.1% showed single infection by MRFV. The confirmation of infectivity by two stunt pathogens in L. maculigera will aid in the outlining of management strategies for this insect vector. [ABSTRACT FROM AUTHOR]

Phytoplasmas can induce complex and substantial phenotypic changes in their hosts in ways that favour their colonisation, but the mechanisms underlying these changes remain largely unknown. Jujube witches' broom (JWB) disease is a typical phytoplasma disease causing great economic loss in Chinese jujube (Ziziphus jujuba Mill.). Here, we reported an effector, PHYL1JWB from Candidatus Phytoplasma ziziphi, which implicated in inducing abnormal floral organogenesis. Utilising a combination of in vivo and in vitro methods, we investigated the influence of PHYL1JWB on the proteins associated with floral development. Our findings reveal that PHYL1JWB facilitates the proteasome‐mediated degradation of essential flower morphogenetic regulators, including AP1, SEP1, SEP2, SEP3, SEP4, CAL, and AGL6, through a distinctive pathway that is dependent on the activity of the 26S proteasome, thus obviating the requirement for lysine ubiquitination of the substrates. Further, the Y2H analysis showed that the leucine at position 75th in second α helix of PHYL1JWB is fundamental for the interactions of PHYL1JWB with AP1 and SEP1‐4 in jujube and Arabidopsis. Our research carry profound implications for elucidating the contribution of PHYL1JWB to the aberrant floral development in diseased jujube, and help to establish a robust theoretical underpinning for the prophylaxis and therapy of JWB disease. Summary Statement: How Candidatus Phytoplasma ziziphi induces abnormal floral development in their hosts is largely unknown. Here we reported a novel effector, PHYL1JWB, mediates the degradation of flower morphogenetic regulators by relying on the 26S proteasome and acting independently of lysine ubiquitination. [ABSTRACT FROM AUTHOR]

Background: Little leaf disease caused by phytoplasma infection is a significant threat to eggplant (also known as brinjal) cultivation in India. This study focused on the molecular characterisation of the phytoplasma strains and insect vectors responsible for its transmission and screening of brinjal germplasm for resistance to little leaf disease. Results: Surveys conducted across districts in the Tamil Nadu state of India during 2021–2022 showed a higher incidence of phytoplasma during the Zaid (March to June), followed by Kharif (June to November) and Rabi (November to March) seasons with mean incidence ranging from 22 to 27%. As the name indicates, phytoplasma infection results in little leaf (reduction in leaf size), excessive growth of axillary shoots, virescence, phyllody, stunted growth, leaf chlorosis and witches' broom symptoms. PCR amplification with phytoplasma-specific primers confirmed the presence of this pathogen in all symptomatic brinjal plants and in Hishimonus phycitis (leafhopper), providing valuable insights into the role of leafhoppers in disease transmission. BLAST search and phylogenetic analysis revealed the phytoplasma strain as "Candidatus Phytoplasma trifolii". Insect population and disease dynamics are highly influenced by environmental factors such as temperature, relative humidity and rainfall. Further, the evaluation of 22 eggplant accessions revealed immune to highly susceptible responses where over 50% of the entries were highly susceptible. Finally, additive main effect and multiplicative interaction (AMMI) and won-where biplot analyses identified G18 as a best-performing accession for little leaf resistance due to its consistent responses across multiple environments. Conclusions: This research contributes essential information on little leaf incidence, symptoms, transmission and resistance profiles of different brinjal genotypes, which together ensure effective and sustainable management of this important disease of eggplants. [ABSTRACT FROM AUTHOR]

Background: Protein posttranslational modifications (PTMs) are fast and early responses to environmental changes, including pathogen infection. Jujube witches' broom (JWB) is a phytoplasma disease causing great economic loss in jujube production. After phytoplasma infection, the transcriptional, translational, and metabolic levels in jujube were activated, enabling it to survive during phytoplasma invasion. However, no study has yet reported on PTMs in jujube. Lysine crotonylation (Kcr) and lysine succinylation (Ksu) have been popular studies in recent years and their function in plant phytoplasma-stress responses remains unclear. Results: Here, 1656 crotonylated and 282 succinylated jujube proteins were first identified under phytoplasma-stress, of which 198 were simultaneously crotonylated and succinylated. Comparative analysis revealed that 656 proteins, 137 crotonylated and 43 succinylated proteins in jujube were regulated by phytoplasma infection, suggesting that Kcr was more universal than Ksu. Kcr differentially expressed proteins (DEPs) were related to ribosomes, photosynthetic and carbon metabolism, while Ksu DEPs were mainly involved in carbon metabolism, the TCA cycle and secondary metabolite biosynthesis. The crosstalk network among proteome, crotonylome and succinylome showed that DEPs related to ribosomal, peroxidases and glutathione redox were enriched. Among them, ZjPOD51 and ZjPHGPX2 significantly increased at the protein and Kcr level under phytoplasma-stress. Notably, 7 Kcr sites were identified in ZjPHGPX2, a unique antioxidant enzyme. After inhibitor nicotinamide (NAM) treatment, GPX enzyme activity in jujube seedlings was reduced. Further, site-directed mutagenesis of key Kcr modification sites K130 and/or K135 in ZjPHGPX2 significantly reduced its activity. Conclusions: This study firstly provided large-scale datasets of Kcr and Ksu in phytoplasma-infected jujube and revealed that Kcr modification in ZjPHGPX2 positively regulates its activity. [ABSTRACT FROM AUTHOR]

Among grapevine yellows, Bois noir (BN), associated with 'Candidatus Phytoplasma solani', represents the biggest threat in the main wine-growing areas worldwide, causing significant losses in berry quality and yields. BN epidemiology involves multiple plant hosts and several insect vectors, making considerably complex the development of effective management strategies. Since application of insecticides on the grapevine canopy is not effective to manage vectors, BN management includes an integrated approach based on treatments to the canopy to make the plant more resistant to the pathogen and/or inhibit the vector feeding, and actions on reservoir plants to reduce possibilities that the vector reaches the grapevine and transmit the phytoplasma. Innovative sustainable strategies developed in the last twenty years to improve the BN management are reviewed and discussed. [ABSTRACT FROM AUTHOR]

Trachyspermum ammi is a traditional medicinal plant and is widely used for curing various diseases in humans. During a 2022 survey, yellowing symptoms associated with phytoplasma disease were observed in Bhopal. The disease was detected by direct and nested PCR using phytoplasma-specific primers in symptomatic plant leaf samples. The suspected ~ 1.2 kb amplified amplicons were sequenced and submitted in GenBank under accession number OQ216747. The phytoplasma isolate showed the highest 99.42% sequence identity and phylogenetic relationships with the 16 S ribosomal RNA gene of an isolate of aster yellows phytoplasma ('Candidatus Phytoplasma asteris'; 16SrI group). This is the first report of 'Ca. P. asteris' (16SrI) associated with the yellows disease of T. ammi. [ABSTRACT FROM AUTHOR]

Phytoplasma disease is one of the most serious infectious diseases that affects the growth and development of mulberry. Long non-coding RNAs (lncRNAs) play an important role in plants' defense systems; however, the contribution of lncRNAs in the response to phytoplasma infection in mulberry is still largely unknown. Herein, strand-specific RNA sequencing was performed to profile the mRNAs and lncRNAs involved in the response to phytoplasma infection in mulberry, and a total of 4169 genes were found to be differentially expressed (DE) between healthy and phytoplasma-infected leaves. Moreover, 1794 lncRNAs were identified, of which 742 lncRNAs were DE between healthy and infected leaves. Target prediction showed that there were 68 and 44 DE lncRNAs which may function as cis and trans-regulators, targeting 54 and 44 DE genes, respectively. These DE target genes are associated with biological processes such as metabolism, signaling, development, transcriptional regulation, etc. In addition, it was found that the expression of the antisense lncRNA (MuLRR-RLK-AS) of the leucine-rich repeat receptor-like protein kinase gene (MuLRR-RLK) was decreased in the phytoplasma-infected leaves. Interestingly, it was found that overexpression of MuLRR-RLK-AS can inhibit the expression of MuLRR-RLK. Moreover, it was found that the expression levels of PTI-related and MAPK genes in the transgenic MuLRR-RLK Arabidopsis plants were significantly higher than those in the wild-type plants when inoculated with pathogens, and the transgenic plants were conferred with strong disease resistance. Our results demonstrate that MuLRR-RLK-AS, as a trans-regulatory factor, can inhibit the expression of the MuLRR-RLK gene and is a negative regulatory factor for mulberry resistance. The information provided is particularly useful for understanding the functions and mechanisms of lncRNAs in the response to phytoplasma infection in mulberry. [ABSTRACT FROM AUTHOR]

In recent years, phytoplasma diseases have increased and become serious in Egypt. Samples of carrot plants exhibiting resemble symptoms of phytoplasma diseases were collected from seven different cultivated areas in El Qalyubia governorate during the growing seasons 2021 and 2022; to detect phytoplasma infection used Light microscopy, Dienes' stain, transmission electron microscopy (TEM), and Nested-PCR. Dodder (Cuscuta campestris), leafhopper (Hebata decipiens), and seed transmission were used to study the transability of phytoplasma. The obtained results showed pleomorphic bodies in infected phloem tissues treated with Dienes' stain as irregular patches of intensely dark blue stained cells. However, a light microscope observed significant abnormal changes in infected tissues compared with healthy ones. Transmission electron microscopy (TEM) that observed phytoplasma units in the phloem tissue and deterioration in the ultrastructure of infected plants including malformed cells, thickness, and abnormal shape of the cell wall. But, due to inconsistent distribution within the plant, low titer, and fluctuation often hamper accurate phytoplasma detection. Therefore, a PCR was used to detect phytoplasma infection using the universal primer pairs P1/P7 and R16F2n/R16R2 that produce fragments at 1200 bp. For transmission of phytoplasma in carrot, dodder, and leafhoppers gave positive results and mechanical transmission gave negative results. Our results will provide a better understanding of the effects of phytoplasma infection in carrots, helping us to develop effective strategies for overcoming such diseases. [ABSTRACT FROM AUTHOR]

Climate change has facilitated the introduction, establishment, and movement of invasive species in northern regions, enabling the colonization of previously unsuitable areas. While the responses of insects to these changes have been increasingly studied, our understanding of how such alterations impact trophic interactions still requires further research to make reliable predictions about the spread of diseases in a warming world. Phytoplasmas, a group of obligate parasitic unculturable Mollicutes, primarily rely on leafhoppers (Hemiptera: Cicadellidae) for transmission, spread, and survival. Phytoplasmas are associated with over 600 diseases affecting more than 1,000 plant species, including berries, grapevines, and other small fruits. In North America, diseases such as grapevine yellows, blueberry stunt, and strawberry green petal diseases have been linked to phytoplasma strains transmitted by known leafhopper species. However, the number of phytoplasma diseases has significantly increased in North America over the past decade, suggesting the presence of unidentified vectors or an abundance of leafhopper vectors. This short review provides an overview of the current knowledge on leafhoppers as vectors of phytoplasmas to berries, focusing on the last decade's research in Canada. This paper also explores the potential implications of climate change on this pathosystem, including the anticipated range expansion of leafhopper species, changes in phytoplasma acquisition and transmission, and the risk of new leafhopper-transmitted plant-pathogen introductions through the arrival of new leafhopper species. [ABSTRACT FROM AUTHOR]

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Worldwide phytoplasma diseases pose great threat to the sustainability of the palm family members viz., coconut, arecanut, date palm, oil palm and ornamental palms causing setbacks in economic and livelihood security. So far, at least eight Candidatus Phytoplasma species belonging to different 16Sr groups have been reported to be associated with coconut. This includes Ca. P. asteris (lethal wilt disease in India; 16Sr IB), Ca. P. oryzae (Coconut root (wilt) disease in India, Weligama leaf wilt disease in Sri Lanka; 16Sr XIB), Ca. P. cynodontis (Coconut yellow decline in Malaysia; 16Sr XIV), Ca. P. malaysianum (Malayan yellow dwarf phytoplasma in Malaysia; 16Sr XXXIIB), Ca. P. palmicola (Cape St. Paul wilt in Ghana, Awka wilt in Nigeria; 16Sr XXIIB), Ca. P. cocostanzaniae (lethal yellowing in East Africa; 16Sr IVC), Ca. P. noviguineense (Coconut bogia syndrome in Papua new Guinea) and Ca. P. palmae (Coconut lethal yellowing in Americas and Caribbean region; 16Sr IVA,B,E). Though there are several reports on insects transmitting coconut phytoplasmal diseases, except for LY in Florida and RWD in India, the vectors remain elusive. Susceptibility of date palms to phytoplasmal diseases viz., lethal yellowing, Alwijam, White Tip Dieback (WTD) and Slow Decline (SD) or El Arkish' are emerging concerns in Arabian countries and North Africa. Oil palm is a potential host of diverse groups (16SrI, 16SrXI, 16Sr XIV and 16SrXXXII) of phytoplasma in many parts of the world. Yellow leaf disease caused by 16SrI, 16SrXI and16SrXIV group phytoplasmas is one of the major diseases limiting the productivity of arecanut in south India. Many ornamental palm species harbour a wide array of phytoplasma groups that could serve as an intermediary mode of transmission to cultivated palms. Large scale movement of ornamental palms through international trade warrants the need for strengthening the international quarantine networks and bio-security measures to contain the spread of these phytopathogenic mollicutes. Despite rapid progress accomplished in taxonomy using molecular approaches many palm phytoplasma isolates are yet to be characterized for the assignment of specific taxonomic status. Due to its confinement to phloem, non-uniform distribution and sub-minimal titres in palms, molecular detection is many atimes intriguing. Palm-phytoplasmal interaction and transmission mechanism by auchenorrhynchan fauna are poorly understood. As a victim of climate change, phytoplasma diseases in synergy with survival superiority of insect vectors are extremely challenging to comprehend and evolve effective suppression mechanism. Management approaches involving surveillance, eradication and containment of the disease in newly emerging areas along with resistance breeding to ensure sustainable income to the farmers are discussed in this chapter. [ABSTRACT FROM AUTHOR]

Phytoplasma, plant pathogenic Mollicutes that have a trans-kingdom life cycle, are insect transmitted and have been found to be associated with yield affecting traits in a large number of taxa. Many peculiar symptoms observed in the host taxa are often results of dramatic alterations in the normal development program that are generally controlled at the meristematic regions located in the shoot apices. Phytoplasma being vasculature limited are thus able to bring about genetic reprogramming in the regions of host plant that are far removed from their natural niche namely sieve elements of the phloem. Several proteins secreted by phytoplasma in the host plants have been identified and termed as effector molecules namely SAP54, SAP11, TENGU, SAP21 etc. that enable the colonisation, survival, spread of phytoplasma and also bring about dramatic alterations in the host plant. Nevertheless, the mechanisms underlying these peculiar phenomena are far from understood and remain a challenging area for the phytoplasma biologists. A thorough understanding of the processes involved is needed to provide platforms for developing control measures for phytoplasma associated diseases that will also enhance basic understanding on the plant developmental programs affected. [ABSTRACT FROM AUTHOR]

Pathosystem associated with phytoplasmas in forest plants is an emerging threat to forest productivity and biodiversity. Diseases caused by or associated with phytoplasmas occur in hundreds of commercial and native plants, causing minor to extensive damage. Phytoplasmas are wall-less, phloem-limited, insecttransmitted, plant pathogenic bacteria that are transmitted by phloem-sap feeding insects of the order Hemiptera under the families such as Cicadellidae, Delphacidae, Cixiidae, Derbidae, Psyllidae and rarely by Pentatomidae and Tingidae. Disease transmission occurs very quickly, often plants become infected before adopting any management strategies. The single most effective management practice of managing the vector in agricultural/horticultural crop is to cover plants with insect exclusion netting but this is not feasible and practical in the case of forest trees. Because of these limitations, researchers are shifting to manipulation genetics in host plants to affect vector populations and transmission of pathogen but big lacunae exists in our knowledge on the vectors of phytoplasma diseases in Indian forestry. We review the literature addressing the phytoplasma diseases in forest species, the lacunae existing in the insect vectors and the need for determining the vectors for possible management of phytoplasma diseases in forest trees. [ABSTRACT FROM AUTHOR]

Among grapevine yellows, Bois noir (BN), associated with ‘Candidatus Phytoplasma solani’, represents the biggest threat in the main wine-growing areas worldwide, causing significant losses in berry quality and yields. BN epidemiology involves multiple plant hosts and several insect vectors, making considerably complex the development of effective management strategies. Since application of insecticides on the grapevine canopy is not effective to manage vectors, BN management includes an integrated approach based on treatments to the canopy to make the plant more resistant to the pathogen and/or inhibit the vector feeding, and actions on reservoir plants to reduce possibilities that the vector reaches the grapevine and transmit the phytoplasma. Innovative sustainable strategies developed in the last twenty years to improve the BN management are reviewed and discussed.

The November 2024 issue of the Journal of Plant Pathology features Editors' Choice papers that highlight global research on plant diseases and their pathogens. The articles cover topics such as the spread of Flavescence dorée disease of grapes in Europe, the presence of Ralstonia in Eucalyptus trees in Southeast Asia, environmental conditions favoring Wheat Stem Rust in East Africa, susceptibility of pea germplasm to Uromyces viciae-fabae in India, and the evolution of fungicide-resistant Phytophthora strains in Mexico. Each paper provides valuable insights for managing plant diseases and offers practical implications for disease control strategies. The research presented in these papers sheds light on the complex interactions between pathogens and plants, emphasizing the importance of integrated disease management approaches. [Extracted from the article]

Phytoplasmas are intracellular plant pathogens that heavily rely on host cell nutrients for survival and propagation due to their limited ability to synthesize essential substrates. The endoplasmic reticulum (ER), which plays a vital role in various cellular processes, including lipid and protein biosynthesis, is an attractive target for numerous intracellular pathogens to exploit. This study investigated the impact of potato purple top (PPT) phytoplasma infection on the ER in tomato plants. Abnormal accumulation of ER-resident proteins, disrupted ER network structures, and formation of protein aggregates in the phloem were observed using confocal microscopy and transmission electron microscopy, indicating a phytoplasma-infection-induced disturbance in ER homeostasis. The colocalization of phytoplasmas with the accumulated ER-resident proteins suggests an association between ER stress, unfolded protein response (UPR) induction, and phytoplasma infection and colonization, with the ER stress response likely contributing to the host plant's defense mechanisms. Quantitative real-time PCR revealed a negative correlation between ER stress/UPR activation and PPT phytoplasma titer, implying the involvement of UPR in curbing phytoplasma proliferation. Inducing ER stress and activating the UPR pathway effectively decreased phytoplasma titer, while suppressing the ER-resident protein, binding immunoglobulin protein (BiP) increased phytoplasma titer. These results highlight the ER as an intracellular battleground where phytoplasmas exploit host components for survival and multiplication, while host plants deploy defense mechanisms to counteract the invasion. Understanding the intricate interactions between phytoplasmas and plant hosts at the subcellular level, particularly within the ER, provides valuable insights for developing new strategies to control phytoplasma diseases. [ABSTRACT FROM AUTHOR]

This study determined the diversity of Cicadellidae species infesting various field crops (i.e., wheat, barley, chickpeas, lentils, corn, vegetables, sunflower, peanuts, onion, sesame, tobacco, watermelon, melon, tomato, pepper, eggplant, alfalfa, cucumber, bean, potato) grown in southeastern Anatolia region, Turkey. The second major aim of the study was to determine whether the species could serve as potential vectors for viruses and phytoplasma diseases. Field surveys were conducted through 2015 and 2016 in Adıyaman, Diyarbakır, Mardin and Şanlıurfa provinces situated in southeastern Anatolia region of the country. The survey timing was adjusted according to the phenological stages of the crops grown in the region. Samples were collected either by D-Vac or sweep net based on the phenological stage of the surveyed crop. A total of 100 net sweeps were swept at 5 different places in the field (20 nets at each sampling place) or D-Vac was run for 2 minutes at five different random places within the field. A total of 33 species belonging to 7 Cicadellidae sub-families were recorded. The most frequently observed species in the region were Asymmetrasca decedens, Empoasca decipiens, Zyginidia sohrab, Z. pullula, Circulifer haematoceps, Psammotettix striatus, P. alienus and P. provincialis. A total of 26, 16, 12 and 11 species were recorded from Diyarbakır, Şanlıurfa, Mardin and Adıyaman provinces, respectively. The study suggests that P. alienus, P. provincialis, P. striatus and C. haematoceps were frequently recorded from the surveyed region and could be considered as potential vectors of viruses and pyhtoplasma in maize, wheat and other crops. Therefore, further studies should be focused on disease spread through reported species in the current study. [ABSTRACT FROM AUTHOR]

The almond, a commercially important tree nut crop worldwide, is native to the Mediterranean region. Stone fruit trees are affected by at least 14 'Candidatus Phytoplasma' species globally, among which 'Candidatus Phytoplasma asteris' is one of the most widespread phytoplasma infecting Prunus dulcis, causing aster yellows disease. Recently, almond plantations of Nauni region were consistently affected by phytoplasma, as evidenced by visible symptoms, fluorescent microscopic studies and molecular characterization. During several surveys from May to September 2020- 2022, almond aster yellows phytoplasma disease showing symptoms such as chlorosis, inward rolling, reddening, scorching and decline with an incidence as high as 40%. Leaf samples were collected from symptomatic almond trees and the presence of phytoplasma was confirmed through fluorescent microscopic studies by employing DAPI (4, 6-diamino-2-phenylindole) that showed distinctive light blue flourescent phytoplasma bodies in phloem sieve tube elements. The presence of phytoplasma in symptomatic almond trees was further confirmed using nested PCR with specific primer pairs followed by amplification of 16S rDNA and 16S-23S rDNA intergenic spacer (IS) fragments. Sequencing and BLAST analysis of expected amplicon of the 16S rDNA gene confirmed that the almond phytoplasma in Himachal Pradesh was identical to the aster yellows group phytoplasma. Phylogenetic analysis of 16S rDNA almond phytoplasma also grouped 'Prunus dulcis' aster yellows phytoplasma within 16SrI-B subgroup showed 94% nucleotide identity with 'Prunus dulcis' phytoplasma PAEs3 and 'Prunus dulcis' phytoplasma PAE28 from Iran. This research presents the first host report of 'Candidatus Phytoplasma asteris' infecting almonds in India, expanding the knowledge of the diversity and distribution of phytoplasma strains affecting almond trees globally. [ABSTRACT FROM AUTHOR]

Jujube witches' broom disease (JWB), caused by Candidatus Phytoplasma ziziphi, is the most destructive phytoplasma disease threatening the jujube industry. Tetracycline derivatives treatments have been validated to be capable of recovering jujube trees from phytoplasma infection. In this study, we reported that oxytetracycline hydrochloride (OTC-HCl) trunk injection treatment could recover more than 86% of mild JWB-diseased trees. In order to explore the underlying molecular mechanism, comparative transcriptomic analysis of healthy control (C group), JWB-diseased (D group) and OTC-HCl treated JWB-diseased (T group) jujube leaves was performed. In total, 755 differentially expressed genes (DEGs), including 488 in 'C vs. D', 345 in 'D vs. T' and 94 in 'C vs. T', were identified. Gene enrichment analysis revealed that these DEGs were mainly involved in DNA and RNA metabolisms, signaling, photosynthesis, plant hormone metabolism and transduction, primary and secondary metabolisms, their transportations, etc. Notably, most of the DEGs identified in 'C vs. D' displayed adverse change patterns in 'D vs. T', suggesting that the expression of these genes was restored after OTC-HCl treatment. Our study revealed the influences of JWB phytoplasma infection and OTC-HCl treatment on gene expression profiling in jujube and would be helpful for understanding the chemotherapy effects of OTC-HCl on JWB-diseased jujube. [ABSTRACT FROM AUTHOR]

Santalum album is susceptible to sandal spike, an infectious disease caused by phytoplasma. The disease spreads through phloem feeding insect vectors. As high economic losses are reported due to this disease, the present study was aimed at assessing the status of spike disease in commercially grown sandalwood plantations in Sri Lanka. Specific objectives of the study were to evaluate the distribution, prevalence and severity of the disease in the studied plantations. A survey covering five districts was conducted in 13 commercially grown sandalwood plantations. Total number of plants, total number of affected plants, total number of major branches of the canopy of the affected plants, total number of affected major branches of the selected plants, total number of completely damaged plants, total number of severely damaged plants, total number of moderately damaged plants and total number of lightly damaged plants were counted for each plantation. Survey data were tabulated and analyzed using descriptive methods. The highest prevalence of the spike disease (30.11%) was recorded in Beragala estate and the lowest prevalence (0.36%) was recorded in Mahao 1 estate. In Godigamuwa estate, percentage of completely damaged plants (9.93%) was equal to that of severely damaged plants. In Beragala estate, the majority (39.12%) of the plants were shown to have low damages. Diyaluma and Belihuloya estates were shown to have 39.72% and 75.00% medium damaged plants respectively. In the case of Matale, only low damaged plants were found. Completely damaged plants were not found in Tangalle, Belihuloya, Matale and Mahao estates. The aim of this study is to increase understanding of nature and severity of sandal spike disease among Sri Lankan fields in order to encourage cultivation with resistant on spike disease to discover best management practices. The increased cultivation of sandalwood plantations has significant importance, and it is essential to strengthen the economic ties to overcome current economic crisis. [ABSTRACT FROM AUTHOR]

Simple Summary: Phytoplasma diseases are a major threat to economically important crops and are usually only managed after the disease has occurred. In this study, the presence of two phytoplasmas in the aster yellows group were detected in insect samples collected from different agricultural settings in South Germany during a biodiversity survey. We used these findings to apply a proactive document-assess-monitor-act (DAMA) protocol to assess the potential for phytoplasma disease outbreaks in croplands in Bavaria, Germany. Notably, we carried out a phylogenetic triage and assessment to generate a risk heat map to select a minimum of seven leafhopper species that may serve as insect vectors of aster yellow phytoplasmas. To detect the presence of aster yellow phytoplasma in susceptible crops (e.g., wheat and barley) in Bavaria, we suggest specific monitoring activities and screening of these insect species as a proactive measure. This is the first time the DAMA protocol is applied in the field of phytopathology. Phytoplasma diseases pose a substantial threat to diverse crops of agricultural importance. Management measures are usually implemented only after the disease has already occurred. Early detection of such phytopathogens, prior to disease outbreak, has rarely been attempted, but would be highly beneficial for phytosanitary risk assessment, disease prevention and mitigation. In this study, we present the implementation of a recently proposed proactive disease management protocol (DAMA: Document, Assess, Monitor, Act) for a group of vector-borne phytopathogens. We used insect samples collected during a recent biomonitoring program in southern Germany to screen for the presence of phytoplasmas. Insects were collected with malaise traps in different agricultural settings. DNA was extracted from these mass trap samples and subjected to PCR-based phytoplasma detection and mitochondrial cytochrome c oxidase subunit I (COI) metabarcoding. Phytoplasma DNA was detected in two out of the 152 insect samples analyzed. Phytoplasma identification was performed using iPhyClassifier based on 16S rRNA gene sequence and the detected phytoplasmas were assigned to 'Candidatus Phytoplasma asteris'-related strains. Insect species in the sample were identified by DNA metabarcoding. By using established databases, checklists, and archives, we documented historical associations and records of phytoplasmas and its hosts in the study region. For the assessment in the DAMA protocol, phylogenetic triage was performed in order to determine the risk for tri-trophic interactions (plant–insect–phytoplasma) and associated disease outbreaks in the study region. A phylogenetic heat map constitutes the basis for risk assessment and was used here to identify a minimum number of seven leafhopper species suggested to be monitored by stakeholders in this region. A proactive stance in monitoring changing patterns of association between hosts and pathogens can be a cornerstone in capabilities to prevent future phytoplasma disease outbreaks. To the best of our knowledge, this is the first time that the DAMA protocol has been applied in the field of phytopathology and vector-borne plant diseases. [ABSTRACT FROM AUTHOR]

In a 2022 survey conducted in Jahrom, Fars province, Iran, the dog rose yellows (DRY) disease was observed in Rosa canina L. plants. The disease manifested as severe yellowing, leaf curling, reduced flowering, abnormal flowers and stunted growth (Fig. 1). DNA from 15 symptomatic and four asymptomatic plants were analyzed for phytoplasma presence. Nested PCR with P1/P7 and R16F2n/R16R2 primers (Lee et al., 1998) yielded 1.25 kbp fragments exclusively from symptomatic plants. The sequences from these samples were identical and one was submitted to GenBank (Accession No. OQ332406). BLAST analysis revealed that the Jahrom DRY phytoplasma sequence matched with two Iranian 16SrI-B strains: Bajgah Tragopogon dubius phyllody (KR262955) and Zarghan onion yellows (MG519854). Phylogenetic analysis placed DRY phytoplasma within the 16SrI group, closet to the 16SrI-B subgroup (Fig. 2). In Iran, 16SrI-B phytoplasma subgroup has a wide host range and at least 11 plant species are reported as hosts of this subgroup (Esmaeilzadeh-Hosseini et al., 2023). Fifteen infected plants relative to 250 plants assessed, showed a noticeable distribution of the DRY disease. This report marks the first association of a 16SrI-B phytoplasma with DRY disease in Iran. Circulifer haematoceps leafhopper has been previously reported as vector of rapeseed phyllody phytoplasma, a 16SrI-B subgroup strain (Salehi et al., 2011) in Iran. However, the ability of C. haematoceps to transmit this 16SrI-B subgroup phytoplasma to dog rose is yet to be tested. [ABSTRACT FROM AUTHOR]

The reaction of pepper breeding lines under organic production conditions to Verticillium wilt, viruses and phytoplasma was observed at Maritsa Vegetable Crop Research Institute, Plovdiv, Bulgaria during two successive years. The diseases severity was recorded, when symptoms of Verticillium dahliae, viruses and Phytoplasma diseases were deeply expressed. The Verticillium dahliae attack index for early production breeding lines varied widely from 15.04% for line O58/14 to 43.83% for O26/16. For kapia type materials, the attack rate of Verticillium wilt ranged from 39.27% (O17/15) to 46.68% (O79/16). The highest index of attack by the disease was established for the powder breeding line (OP69/16) - 49.85%. The viruses which were monitored belong to groups of tobamoviruses, cucumoviruses and tospoviruses and were only 5.00% in breeding lines for early production. The Phytoplasma development was from 10.51% (O12/15) to 32.92% (O38/14). It was established that among studied diseases Verticillium wilt (42.41%) was more dangerous for studied pepper breeding lines in organic conditions followed by Phytoplasma disease (20.67%) and viruses (0.59%). [ABSTRACT FROM AUTHOR]

Background: Flavescence dorée (FD) is a grapevine disease caused by phytoplasma and it is one of the most destructive pathologies in Europe. Nowadays, the only strategies used to control the epidemics are insecticides against vector, but more sustainable techniques are required. Completely resistant Vitis vinifera varieties have not been uncovered yet, but differences in susceptibility among cultivars and spontaneous recovery from FD symptoms have been observed. The grapevine cultivar 'Tocai friulano' shows very low susceptibility to FD but its defence strategy to counteract the phytoplasma spread has not been deciphered yet. In this work, the mechanisms occurring within 'Tocai friulano' FD-infected plants were examined in depth to identify the phytoplasma distribution and the defence pathways involved. Results: In 'Tocai friulano' symptoms of FD-infection remained confined near the area where they appeared during all the vegetative season. Analyses of secondary phloem showed a total absence of FD phytoplasma (FDp) in the trunk and its disappearance in 2-year-old arms from July to November, which was different from 'Pinot gris', a highly susceptible variety. Diverse modulations of defence genes and accumulation of metabolites were revealed in 1-year-old canes of 'Tocai friulano' FD-infected plants, depending on the sanitary status. Symptomatic portions showed high activation of both jasmonate- and salicylate-mediated responses, together with a great accumulation of resveratrol. Whereas activation of jasmonate-mediated response and high content of ε-viniferin were identified in asymptomatic 1-year-old cane portions close to the symptomatic ones. Conclusion: Successful defence mechanisms activated near the symptomatic areas allowed the compartmentation of FD symptoms and phytoplasmas within the infected 'Tocai friulano' plants. These results could suggest specific agronomical practices to be adopted during FD management of this variety, and drive research of resistance genes against FD. [ABSTRACT FROM AUTHOR]

In this study, infections that may emerge from viruses and phytoplasmas were investigated in carrot cultivation fields in the Ankara and Konya provinces, which are located in the Central Anatolia Region of Turkey and have the largest agricultural areas of the country. A total of 272 symptomatic and asymptomatic carrot plants, together with their root and leaf parts, were collected from 61 fields by performing periodic field studies during the plant vegetation periods between 2018–2019. Samples were tested against carrot virus Y (CarVY), carrot red leaf virus (CtRLV), carrot red leaf virus-associated RNA (CtRLVaRNA), carrot mottle virus (CMoV), carrot torradovirus 1 (CaTV), carrot yellow leaf virus (CYLV), carrot thin leaf virus (CTLV) and cucumber mosaic virus (CMV) agents by Reverse Transcriptase-PCR (RT-PCR). To determine phytoplasmas, samples were tested using universal primers by nested PCR. Molecular tests conducted to investigate the aforementioned viruses produced negative results, but phytoplasma infections were widely found. 16SrVI-A "Candidatus Phytoplasma trifolii" and 16SrI-B "Aster yellows" subgroups were detected by in vitro/in silico RFLP and sequencing analyses. Disease incidence caused by both phytoplasma groups was 39.34%. This study determined for the first time that 16SrVI and 16SrI groups cause severe infections in the carrot fields of Turkey. [ABSTRACT FROM AUTHOR]

Given the potential for urban green spaces to provide fresh and healthy environments for humans, exploring the issues that threaten plants in these places is crucial. Phytoplasma‐related symptoms were encountered on some plants in urban green spaces in the province of Kerman, southeastern Iran, between 2017 and 2019. Affected periwinkles and petunias exhibited phytoplasma disease symptoms, including virescence, phyllody, and witches'‐broom. However, ball or disc‐like shoot proliferation symptoms were noticed on the trunks and branches of pine trees. PCR was performed with phytoplasma‐detecting universal primers, targetting and amplifying the 16S rRNA gene, and determining whether phytoplasmas are implicated in the symptomatic plants. The infection of the symptomatic plants was confirmed using nested‐PCR amplification of expected DNA sizes for phytoplasmas. No product, however, was amplified from sampled symptomless plants. The sequencing of nested‐PCR products was performed to obtain sequences encasing the standard F2nR2 fragments. The resulted sequences were submitted to iPhyClassifier, the universal phytoplasma classification platform, for the taxonomic assignment of the found phytoplasmas compared with previously identified 'Candidatus Phytoplasma' species, groups, and subgroups. The results revealed that phytoplasma strains related to the species 'Ca. P. trifolii' (16SrVI‐A subgroup) infect periwinkles and pines. However, strains from the species 'Ca. P. aurantifolia' (16SrII‐D subgroup) and 'Ca. P. phoenicium' (16SrIX‐C subgroup) were found in petunias and periwinkles, respectively. To the best of our knowledge, phytoplasmas from the 16SrVI‐A and 16SrII‐D subgroups are the first reported to infect these plants in Kerman province, while a related strain from the subgroup 16SrIX‐C is the first recorded to infect periwinkles in Iran and the second in the world. [ABSTRACT FROM AUTHOR]

This article reports the first case of a phytoplasma disease in Celosia argentea, a tropical flower commonly known as plumed cockscomb or silver cockscomb, in Taiwan. The diseased plants exhibited symptoms such as abnormal branching, shortened internodes, and misshaped leaves. The disease was caused by a strain related to 'Ca. P. aurantifolia' and belonged to the 16SrII-A subgroup. This finding expands our understanding of phytoplasma diseases and their impact on plant species in Taiwan and globally. [Extracted from the article]

A study conducted in southern Switzerland has identified the first instance of a 'Candidatus Phytoplasma fragariae'-related strain infecting Corylus avellana, commonly known as hazel. Phytoplasmas are associated with serious diseases in various plants, and infected woody species can be difficult to detect due to their asymptomatic nature. The study found two hazel trees positive for phytoplasmas, with genetic analysis confirming their relation to 'Ca. P. fragariae'. Further research is needed to determine the potential threat of this strain to forest trees and hazelnut orchards, as well as to identify potential insect vectors. [Extracted from the article]

In a walnut orchard in Turkey's Mersin province in the summer of 2021, phytoplasma related symptoms such as abnormal formations in flowers (phyllody), proliferation of shoots, reddish leaves or general yellowing and stunting were observed on Crepis foetida plants. Total nucleic acid from collected plant samples was extracted using CTAB method. The R16F1/R0 and R16F2n/R2 universal primer pairs were used and all symptomatic Crepis plants yielded positive results by nested PCR (nPCR). There were no PCR products found in walnut or asymptomatic Crepis samples. Four PCR products were sequenced, and one was submitted to GenBank (Accession Number: OM681509). The results were confirmed by using BLASTn search, virtual RFLP and phylogenetic analysis. To the best of our knowledge, this is the first report of a phytoplasma belongs to pigeon pea witches' broom group (16SrIX) associated with Crepis phyllody disease of C. foetida. [ABSTRACT FROM AUTHOR]

Almond witches'-broom (AlmWB) is a serious phytoplasma disease of stone fruits; thus far reported from Iran and Lebanon. In the present study the host range of two Iranian AlmWB phytoplasma strains, known as PEAB and AlKI, were examined through graft-inoculation assay. Two-year-old stone fruit seedlings of almond (three cultivars), peach, plum, Myrobalan plum, apricot and sweet cherry were separately graft-inoculated by scions obtained from symptomatic almond seedlings infected by PEAB or AlKI phytoplasma strains. The presence of phytoplasma in the inoculated seedlings, and the type and development of symptoms were evaluated and recorded monthly over one year. Results showed that both phytoplasma strains could be transmitted to almond ('Pooya', 'Mamaei' and 'Talkhe' cultivars), peach and plum seedlings. The disease symptoms were more obvious in almond cultivars. AlmWB phytoplasma strains could not be detected in the inoculated sweet cherry and the Myrobalan plum seedlings. On the other hand, infection of apricot seedlings could only be detected in seedlings inoculated with the PEAB strain. The homologous of the AYWB SAP11 effector protein, known to play a crucial role in phytoplasma infection and symptom expression, was sequence-analyzed in both PEAB and AlKI strains. The SAP11 nucleotide sequence of AlKI strain was identical to that of the SA213 AlmWB phytoplasma strain from Lebanon. Analysis showed high SAP11 sequence diversity between AlmWB phytoplasmas and phytoplasma strains of other 16Sr groups. Despite poor sequence conservation, the structural features and the motifs of SAP11 protein were conserved between AlmWB and distantly related phytoplasma strains; speculating a similar function for this gene in diverse phytoplasmas. [ABSTRACT FROM AUTHOR]

Phytoplasmas are associated with many plant diseases. In palms, lethal bronzing disease, Texas Phoenix palm decline, and coconut lethal yellowing decline are some of them. In Sri Lanka, coconut leaf wilt decline has been reported in the Weligama area of the Southern province, and the disease is called Weligama coconut leaf wilt disease (WCLWD). Unlike other phytoplasma diseases of palms, WCLWD shows slow disease progress. Pathogen detection entirely relies on nested polymerase chain reaction (PCR). However, inconsistencies in pathogen detection have been experienced, i.e., symptomatic plants often produce negative results. The objectives of this study were to reconsider the choice of primers and to determine the best sampling tissue types for consistent detection of the pathogen. Among the six universal primer combinations tested, P1/Tint nested with fU5/rU3 produced consistent results. BLASTn searches of the sequences showed 99–100% similarity to sugarcane white leaf disease (SWL) or grassy shoot (SGS) disease-causing phytoplasma. The optimized nested PCR protocol was successful, with the minimum success rating of 88% and 100% specificity. Midribs of milky white bud leaf samples were the best tissue type for rapid detection. Systemic movement of the pathogen and a tentative latent period were also reported. The findings are helpful in the early detection of the disease. [ABSTRACT FROM AUTHOR]

Little leaf and yellowing symptoms associated with phytoplasma disease were observed in Pyracantha angustifolia in Turkey. Amplification (through nested PCR) and virtual restriction fragment length polymorphism (V-RFLP) confirmed the presence of phytoplasma in the symptomatic plants the phylogeny based on the R16F2n/R2 sequences of the P. angustifolia phytoplasma was established and the sequence analysis showed that the isolate had 98.7% similarity to 'Candidatus Phytoplasma australasia', a member of the 16SrII-D subgroup. This is the first world report of a phytoplasma in P. angustifolia and its first identification in the Republic of Türkiye. [ABSTRACT FROM AUTHOR]

SUMMARY: 'Candidatus Phytoplasma tritici' ('Ca. P. tritici') is an insect‐borne obligate pathogen that infects wheat (Triticum aestivum) causing wheat blue dwarf disease, and leads to yield losses. SWP12 is a potential effector secreted by 'Ca. P. tritici' that manipulates host processes to create an environment conducive to phytoplasma colonization, but the detailed mechanism of action remains to be investigated. In this study, the expression of SWP12 weakened the basal immunity of Nicotiana benthamiana and promoted leaf colonization by Phytophthora parasitica, Sclerotinia sclerotiorum, and tobacco mild green mosaic virus. Moreover, the expression of SWP12 in wheat plants promoted phytoplasma colonization. Triticum aestivum WRKY74 and N. benthamiana WRKY17 were identified as host targets of SWP12. The expression of TaWRKY74 triggered reactive oxygen species bursts, upregulated defense‐related genes, and decreased TaCRR6 transcription, leading to reductions in NADH dehydrogenase complex (NDH) activity. Expression of TaWRKY74 in wheat increased plant resistance to 'Ca. P. tritici', and silencing of TaWRKY74 enhanced plant susceptibility, which indicates that TaWRKY74 is a positive regulator of wheat resistance to 'Ca. P. tritici'. We showed that SWP12 weakens plant resistance and promotes 'Ca. P. tritici' colonization by destabilizing TaWRKY74. Significance Statement: Phytoplasma is an important group of plant pathogens, and infection of wheat (Triticum aestivum) can lead to yield reduction. Understanding the pathogenic mechanism of wheat blue dwarf phytoplasma effectors will help to improve the prevention and control strategies of wheat phytoplasma diseases. [ABSTRACT FROM AUTHOR]

Lethal bronzing (LB) is a fatal palm disease caused by the phytoplasma 'Candidatus Phytoplasma aculeata'. This disease causes significant economic losses in palm industries and landscapes. The American palm cixiid, Haplaxius crudus, recently was identified as the vector of the phytoplasma. However, knowledge about LB phytoplasma transmission is limited due to the lack of a method to generate phytoplasma-infected insects in the laboratory. In this study, the acquisition and transmission of the LB phytoplasma by H. crudus were investigated. Successful acquisitions of the phytoplasma by H. crudus were observed at 2 days acquisition access period on LB-infected palm spear leaves. Analyses revealed increased phytoplasma infection rates of H. crudus with longer acquisition access periods and latent periods. A significantly higher phytoplasma infection rate was shown after various acquisition access periods and latent periods than the infection rate of the field-collected H. crudus population. Transmission of the phytoplasma from LB-infected spear leaves to sucrose media by H. crudus also was observed using digital PCR assays. These results further support the vector status of H. crudus and offer valuable information to understand LB phytoplasma transmission. Additionally, these results generate a critical baseline for future LB phytoplasma--vector research by providing a way to generate vectors with high phytoplasma infection rates in the laboratory setting. [ABSTRACT FROM AUTHOR]

In this study, Russian olive trees exhibiting witches'-broom symptoms were collected from urban green areas in Tabriz, in the northwest of Iran. PCR analysis confirmed that phytoplasma caused the disease and, according to the resulting Sanger sequencing electropherogram, a mixed infection with two or more phytoplasma species within the Russian olive trees was revealed. Next-generation sequencing analyses, using the Illumina method, were performed on total DNA from the infected Russian olive plants to recognize the microbial genomic content and assemble the whole genome of the causative pathogen(s). The use of MetaphlAn2 and Kraken2 to analyze species composition revealed the very diverse and unique compositions of different Prokaryotic and Eukaryotic species within the infected plants. Several bacteria and fungi were discovered inside the samples, among which Mycoplasmatota was significantly dominating. Interestingly, the results also revealed a high level of endosymbiotic bacteria and Archaea (Methanobacteria) genome contents within the samples. Bowtie2, metaSPAdes, and CD-HIT pipelines were used to perform the initial genome assembly, and the whole genome of the notable phytoplasma species was assembled and submitted to Genbank. [ABSTRACT FROM AUTHOR]

Tobacco (Nicotiana tabacum) is among the agricultural products with the highest added value in Turkey. Although frequently associated with its negative effects on human health, it also provides important contributions to the Turkish economy with the employment it creates in rural areas and continues to be a strategic product. Many postgraduate theses and studies related to the sociological and economic importance of the production of this plant, which is of great importance for our country, have been carried out. However, there are very limited studies on plant diseases in tobacco production areas in Turkey. Phytoplasma is one of the important plant pathogens that cause yield loss in tobacco. Since available data on phytoplasma diseases on tobacco was very scarce worldwide, field surveys to collect samples showing phytoplasma infection-like symptoms such as yellowish color changes, leaf blisters, proliferation, dwarfism, and other physical abnormalities were carried out in Çanakkale and Balıkesir provinces of Turkey from June to August 2021. The presence of phytoplasmas in six samples was confirmed by 16S ribosomal DNA amplification by nested-PCR using universal phytoplasma primer sets, which also suggested the pathogen associated with the symptoms on tobacco. According to phylogenetic study and virtual-RFLP analysis using AluI and MseI endonuclease enzymes, the six Turkish tobacco phytoplasma strains all belong to group 16SrXII and have more than 99% nucleotide sequence identity with some members of 'Candidatus Phytoplasma solani' of the taxonomic subgroup 'stolbur' (16SrXII-A). Genetic distances analysis indicated that group 16SrI was more closely related to 16SrXII than 16SrVI, in agreement with the groups clustering in the phylogenetic tree. Neutrality tests found that 16SrI and 16SrXII groups are experiencing expanding or bottleneck selections, probably due to new mutations in the 16S rRNA gene fragment. Meanwhile, 16SrVI populations are shown to be undergoing balancing selections, indicating that its isolates have evolved for a long time. [ABSTRACT FROM AUTHOR]

During 2021 surveys, greengage witches'-broom (GWB) and decline (GD) diseases were respectively observed in Fars and Yazd provinces of Iran. Presence of phytoplasma in the symptomatic plants was confirmed by PCR amplifications of 16S rRNA gene. Sequence analyses showed affiliation of the GWB and GD phytoplasmas to'Candidatus Phytoplasma phoenicium' (16SrIX-B) and'Ca. P. aurantifolia' (16SrII-C) related strains, respectively. This is the first report of phytoplasma diseases of greengage in Iran and probably in the world. [ABSTRACT FROM AUTHOR]

Simple Summary: Phytoplasmas are vector-borne and graft-transmissible bacteria that cause various plant diseases, leading to severe economic losses. Since phytoplasmas cannot be cultured in cell-free media, their identification and taxonomy rely on molecular techniques and gene sequences. In this article, we summarize the recent advances in phytoplasma taxonomy from three different aspects, including (i) nomenclature (naming Candidatus Phytoplasma species); (ii) classification (group and subgroup assignment based on 16S rRNA gene sequences); and (iii) identification (fine differentiation of phytoplasma strains). In addition, some important issues, especially those related to recognizing new 'Candidatus Phytoplasma' species, are discussed. This information will be helpful for rapid diagnosis of phytoplasma diseases and accurate taxonomic identification of both emerging and known phytoplasma strains. Phytoplasmas are pleomorphic, wall-less intracellular bacteria that can cause devastating diseases in a wide variety of plant species. Rapid diagnosis and precise identification of phytoplasmas responsible for emerging plant diseases are crucial to preventing further spread of the diseases and reducing economic losses. Phytoplasma taxonomy (identification, nomenclature, and classification) has lagged in comparison to culturable bacteria, largely due to lack of axenic phytoplasma culture and consequent inaccessibility of phenotypic characteristics. However, the rapid expansion of molecular techniques and the advent of high throughput genome sequencing have tremendously enhanced the nucleotide sequence-based phytoplasma taxonomy. In this article, the key events and milestones that shaped the current phytoplasma taxonomy are highlighted. In addition, the distinctions and relatedness of two parallel systems of 'Candidatus phytoplasma' species/nomenclature system and group/subgroup classification system are clarified. Both systems are indispensable as they serve different purposes. Furthermore, some hot button issues in phytoplasma nomenclature are also discussed, especially those pertinent to the implementation of newly revised guidelines for 'Candidatus Phytoplasma' species description. To conclude, the challenges and future perspectives of phytoplasma taxonomy are briefly outlined. [ABSTRACT FROM AUTHOR]

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Santalum album commonly known as Indian sandalwood, is extensively exploited due to its demand in the international market for essential oil. In the Indian subcontinent, the species is approaching commercial extinction due to overexploitation and sandal spike disease caused by phytoplasma. Molecular detection using PCR and RFLP is reported for disease diagnosis. In the present study, a single-step, stringent PCR-based assay was developed to detect the sandal spike phytoplasma. The titre estimation revealed that the marker maintained detection sensitivity up to 0.8 ng of template DNA. Subsequent to validation of the marker in a larger number of symptomatic individuals, this diagnostic assay can be routinely used to detect the pathogen. It will facilitate early detection and enable plantation managers to take adequate measures to control the spread of the disease. [ABSTRACT FROM AUTHOR]

Symptoms of phytoplasma diseases, including witches' brooms, shoot proliferation, little leaf, yellowing and decline were observed in eleven species of bamboos in eight states of India. Symptomatic bamboo samples were indexed for phytoplasma presence using universal phytoplasma‐specific 16S rRNA gene primer pairs. Sequence comparison analysis and virtual RFLP analysis of 16S rRNA sequences indicated that the symptomatic bamboo samples of Dendrocalamus asper, Dendrocalamus strictus and Pseudoxytenanthera stocksii from Tripura, Uttar Pradesh, Uttarakhand and New Delhi and Bambusa bambos, Bambusa nutans, Bambusa pallida,Bambusa tulda,Dendrocalamus hamiltonia and D. strictus from Karnataka were infected with 'Candidatus Phytoplasma australasia'‐related strains (16SrII‐C or 16SrII‐D); Bambusa vulgaris,D. asper and P. stocksii from Karnataka were positive for 'Ca. P. asteris' strains (16SrI‐B), and one phytoplasma in B. nutans from Sikkim was identified as 'Ca. P. cynodontis' strain (16SrXIV‐A). Weeds and leafhoppers from the vicinity of bamboo plantations were also tested, and 16SrII group of phytoplasmas was identified in eight symptomatic weed species (Ageratum conyzoides,Cannabis sativa,Cleome viscosa,Datura stramonium, Parthenium hysterophorus,Ocimum canum, Phyllanthus niruri and Tephrosia purpurea) from five different states and one leafhopper species (Mukaria spledida) from three states. These results suggest that wide genetic diversity of phytoplasma exists in various bamboo species in different states of India. The report of 16SrI‐B, 16SrII‐D and 16SrXIV‐A subgroups of phytoplasmas infecting eight bamboo species except D. strictus are the first records in the world. [ABSTRACT FROM AUTHOR]

Aims: This study was conducted to determine the phytoplasma diseases of pepper plants in Hatay province between 2016 and 2019. Methods and Results: Samples of pepper (Capsicum annuum), sesame (Sesamum indicum), basil (Ocimum basilicum), tomato (Solanum lycopersicum) and bindweed (Convolvulus arvensis) which had typical phytoplasma symptoms and insect (Cicadellidae spp.) samples were collected from the pepper fields. Empoasca sp., Cicadulina bipunctata, Psammotettix sp., Balchutha hebe, Euscelidius sp., Anaceratagallia laevis and Exitianus capicola were found as potential insect vectors of the phytoplasmas as descending order of population densities. T-budding grafting technique was successful for phytoplasma transmission from infected sesame and basil plants to healthy periwinkle (Catharanthus roseus) plants in controlled conditions. Phytoplasmas were detected in pepper, tomato, basil, sesame and bindweed and from some insect samples. Total nucleic acid isolation was accomplished by the CTAB method. Direct and Nested PCR were used employing R16F1/R16R0 and R16F2n/R16R2 primer pairs respectively. Conclusions: DNA of positive samples were sequenced, and uploaded to Genbank, and were identified as Ca. Phytoplasma trifolii on pepper (MT993358), sesame (MT994434), tomato (MT992754), basil (MT994432), Empoasca sp. (MT994430), Exitianus capicola (MT994433), Euscelidius sp. (MT994431); and as Ca. Phytoplasma solani on binweed (MT993422) and tomato (MT992796). Significance and Impact of the Study: According to our knowledge, this study is the first to identify and upload to Genbank of Ca. Phytoplasma trifolii on basil and Empoasca sp., Exitianus capicola and Euscelidius sp. as insect vectors of the diseases in Turkey. [ABSTRACT FROM AUTHOR]

Jujube witches' broom disease (JWB), one of the most serious phytoplasma diseases, usually results in the destruction of Chinese jujube (Ziziphus jujuba Mill.). Although most jujube cultivars are sensitive to JWB, we found a few genotypes that are highly resistant to JWB. However, the molecular mechanism of phytoplasma resistance has seldom been studied. Here, we used Chinese jujube "T13," which has strong resistance to JWB, and a typical susceptible cultivar, "Pozao" ("PZ"), as materials to perform comparative transcriptome, hormone, and regulation analyses. After phytoplasma infection, the differential expression genes (DEGs) were detected at all three growth phases (S1, S2, and S3) in "PZ," but DEGs were detected only at the first growth phase in "T13." Meanwhile, no phytoplasma was detected, and the symptoms especially witches' broom caused by JWB were not observed at the last two growth phases (S2 and S3) in "T13." Protein–protein interaction analysis also showed that the key genes were mainly involved in hormone and reactive oxygen species (ROS) signaling. In addition, during the recovered growth phase in "T13" from S1 to S2, the level of hydrogen peroxide (H2O2) was significantly increased and then decreased from S2 to S3. Moreover, jasmonic acid (JA) was significantly accumulated in "PZ" diseased plants, especially at the S2 phase and at the S2 phase in "T13," while the content of salicylic acid (SA) decreased significantly at the S2 phase of "T13" compared to that in "PZ." The changes in H2O2 and JA or SA were consistent with the changes in their key synthesis genes in the transcriptome data. Finally, exogenous application of an SA inhibitor [1-aminobenzotriazole (ABT)] rescued witches' broom symptoms, while the contents of both JA and MeJA increased after ABT treatment compared to the control, demonstrating that exogenous application of an SA inhibitor rescued the symptoms of jujube after phytoplasma infection by decreasing the contents of SA and increasing the contents of JA and MeJA. Collectively, our study provides a new perspective on the transcriptional changes of Chinese jujube in response to JWB and novel insights that the crosstalk of JA and SA signaling communicated together to contribute to "T13" JWB resistance. [ABSTRACT FROM AUTHOR]