1,721,025 research outputs found
Outlook on relevant phytoplasma diseases in Europe
No full textPhytoplasma-associated diseases are among the most important in grapevine and fruit trees production in
Europe. Severe losses were described especially for grapevine and apple causing sometimes the total
production loss. A short description of symptomatology and epidemiological features in those species are
described
Phytoplasma and phytoplasma diseases: a review of recent research
Full text linkNumerous yellows-type diseases of plants have been associated with wall-less prokaryote pathogens – phytoplasma over the last 40 years. These pathogens cannot be grown in axenic culture so that advances in their study are mainly achieved by molecular techniques. Severe disease epidemics associated with a phytoplasma presence have been described worldwide. These include coconut lethal yellowing in Africa and the Caribbean, grapevine yellows in major viticultural areas and various diseases affecting stone and pome fruit plants. Phytoplasma-infected plants exhibit symptoms suggesting a profound disturbance in the normal balance of growth regulators and also yellows symptoms, but very often the symptomatology is not diagnostic. Detection and characterization of phytoplasmas infecting different plant species are now possible with molecular methods, based on the study of 16S rDNA polymorphisms. Molecular diversity of phytoplasmas is also demonstrated by studying genes coding the ribosomal proteins S3, tuf, SecY, amp, imp and other genes. Four phytoplasma genomes have been fully sequenced, including those of two ‘Candidatus Phytoplasma asteris’ strains, and those of strains of ‘Ca. P. mali’ and ‘Ca. P. australiense’. Three of these genomes contain large amounts of repeated DNA sequence, and the fourth carries multiple copies of almost 100 genes. Considering that phytoplasmas have unusually small genomes, these repeats might be related to their transkingdom habitat and to their pathogenic activity. An outlook of recent findings in the field is also reported
Multigene differentiation of 'Candidatus Phytoplasma solani' strains from different geographic origins and diverse host species.
No full textThe knowledge of genetic variability in phytoplasmas is a fundamental resource for the study of their epidemiology and a valuable support to improve the monitoring and the management of their associated diseases. Multigene analyses have been used widely to characterize phytoplasmas strains providing relevant information about their epidemiology. ‘Candidatus Phytoplasma solani’ is associated with “bois noir” (BN) in grapevines and yellowing in many other cultivated and wild plant species such as tomato, pepper, bindweed, causing serious damages in many parts of the world. The epidemiology of the diseases associated with this phytoplasma is very complex considering its wide host range distribution, the interactions with both host plant and insect vectors, and the diffusion of the bacterium through infected plant propagation material. The genetic variability of 'Ca. P. solani' strains, in different host species and in several geographic areas was widely studied by genotyping selected non-ribosomal genes. The polymerase chain reaction coupled with restriction fragment length polymorphism analyses and sequencing was applied to samples collected during more than 20 years in Italy, Portugal, Hungary and Serbia in a multigene analysis on vmp1, stamp and tuf genes. A total of 116 'Ca. P. solani' strains was examined and allowed the differentiation of 26 genetic variants confirming the differential variability of the studied genes. In particular, the vmp1 and stamp genes showed the presence of 14 and 5 RFLP profiles, respectively, while the tuf gene grouped all tested strains into two profiles. In the vmp1 gene sequences it was registered the largest variability; the V3-RsaI RFLP profile was the most present in the Italian grapevine samples tested. A large part of the samples tested were collected in Italy and Serbia; in the comparison between the two geographic areas only one genetic variant was found in common, confirming the local distribution of the strains. Considering the time frame of the sample collection and the geographical distribution of the variants identified, it appears that populations of this phytoplasma are generally less variable on local scale leading in some case to the emergence of epidemic strains. In particular, the grapevine samples collected during 2020 in Tuscany revealed the predominance of tuf type-a strain and showed the same variant in all the samples, indicating the possible emergence of an epidemic BN strain in that region. In addition, the identification of two stamp variants (St5 and St10) that have shown specific epidemiological characteristics linked to different virulence in the field indicates the need to continue to study and to monitor the disease with specific molecular analyses considering that the strains with different virulence can lead to epidemic infections with significant economic damages. The presence of mixed infections with different phytoplasmas indicate another important element to consider for the ‘Ca. P. solani’-associated diseases epidemiology. These results confirm that except for tuf gene there is no specificity of ‘Ca. P. solani’ variants linked to different host species and different epidemiological cycles. Their differentiation can be explained by geographic distribution of host and insect vectors, year of infection and epidemic outbreaks registered during the time. Strains diversity combined with epidemiological data are useful also to identify sources of inoculum, new host species and to monitor the spreading of the phytoplasma both locally and on a larger environmental scale for focused management purposes
Phytoplasmas associated with grapevine yellows : an overview
No full textPhytoplasmas are obligate intracellular bacterial parasites restricted to the phloem sieve elements of the infected plants and are transmitted by phloem-sucking insects belonging to the families Cicadellidae, Cixidae, Psyllidae, Delphacidae and Derbidae. They are associated with diseases of several hundred plant species, including some economically important crops. Grapevine yellows (GY) is a worldwide disease complex caused by genetically different phytoplasmas. GY-affected Vitis vinifera shows leaf enrollment accompanied by yellowing or reddening, rubbering of the canes and desiccated clusters. Epidemiology of the different GY diseases, undistinguishable based on symptoms observation, strictly depends on the involved phytoplasma because of the insect-vector specificity and their behavior. GY diseases are attributed to infections by at least seven distinct phytoplasmas. In Europe, the GY diseases Flavescence dorée (FD) and Palatinate grapevine yellows (PGY, present only in Germany), are associated with phytoplasmas classified in the ribosomal group 16SrV, while Bois noir (BN) is attributed to phytoplasmas classified in stolbur group (ribosomal subgroup 16SrXII-A). In Australia, Australian grapevine yellows is attributed to ‘Ca. Phytoplasma australiense’ (ribosomal subgroup 16SrXII-B), and to ‘Ca. Phytoplasma australasia’ (ribosomal group 16SrII). Grapevine yellows in Virginia is associated with ‘Ca. Pytoplasma asteris’-related strains (ribosomal group 16SrI) and X-disease group (ribosomal group 16SrIII) phytoplasmas. In order to distinguish each GY from the others, an important research topic focuses on developing molecular tools for specific identification of GY-associated phytoplasmas. In Europe, the employment of such methods for the certain exclusion of FD and BN phytoplasmas from grapevine certified propagating material is becoming urgent. PCR-based techniques allowed development of useful tools for the identification of phytoplasmas associated with GY diseases. Standard protocols include nested PCR amplification of phytoplasma 16S rDNA using universal or group specific primers and RFLP analyses in order to determine the taxonomic (ribosomal group/subgroup) affiliation. Further molecular characterization, performed by sequence analyses on genes less conserved than 16S rDNA, found additional markers useful for developing suitable analytical tests for faster and specific detection of FD and BN phytoplasmas. Up to now, innovative molecular approaches developed to this aim are: (i) Real Time PCR and reverse transcription – Real Time PCR for the detection of phytoplasmas causing FD and BN; (ii) nanobiotransducer for detecting FD phytoplasmas; (iii) multiplex nested PCR for simultaneous identification of FD and BN phytoplasmas; (iv) Ligase Detection Reaction (LDR) DNA microarray to detect and distinguish FD and BN phytoplasmas.
Furthermore, multiple gene sequence analyses (Multi Locus Sequence Typing, MLST) on ribosomal (rplV-rpsC) and extra ribosomal (secY, map, uvrB, degV, hlyC, vmp, and tuf) genes highlighted an unexpected genetic heterogeneity among both FD and BN phytoplasma populations, identifying different FD- and BN-phytoplasma strains that can be associated with specific ecological niches (plant hosts, insect vectors, geographic origin). MLST analyses improved the chance to associated phytoplasma-specific molecular markers with biological features, opening new perspectives for the studies of FD and BN epidemiology
Chaturvedi Y., G.P. Rao, A.K. Tiwari, B. Duduk, A. Bertaccini. 2010. Phytoplasma on Ornamentals: Detection, Diversity and Management. Acta Phytpathologica et Entomologica Hungarica 45(1): 31-69.
No full textDuring recent years, increasing attention has been devoted to the development of field floriculture, particularly for benefit of small arming businesses that produce seedlings of perennial ornamental plants for the domestic market and for export to neighboring countries. Like other segments of agricultural economies, this industry is threatened by plant diseases, including those associated to phytoplasma nfection. Phytoplasmas cause diseases in several commercial cut flower and ornamental plant causing serious economic losses all around the
world. Therefore, phytoplasma diseases are the major constraints in profitable ornamental plants production and lowers its quantum and quality gaining international importance because of unspecific symptoms, various losses and diverse epidemiology throughout the world. Epidemics of these diseases have compelled withdrawal of many floriculture plant varieties from cultivation such as gladiolus, lily, chrysanthemum and rose. Symptoms of general yellowing and stunting of plants, proliferation of shoots, phyllody, virescence, reduced size of flowers and reddening of leaves were observed in diverse ornamental plants in botanical gardens and various floriculture farms. Knowledge of the diversity of phytoplasmas has been expanded by recent studies as well as the availability of molecular tools for pathogen identification. The diversity of the potential reservoir of disease has been increased with the discovery of new phytoplasmas hosts. Ornamental plant phytoplasmas showed wide geographical distribution. The ‘Ca. P. asteris’ belonging to 16SrI group is the major group associated with ornamentals worldwide, so far more than 42 ornamental plant species were reported as phytoplasma infected. Basing on
the sequences retrieved from GenBank identified phytoplasmas mainly belong to 16SrI, 16SrII, 16SrIII, 16SrV, 16SrVI, 16SrVII, 16SrIX, 16SrX, 16SrXII, 16SrXIII and 16SrXV groups. In this review, detailed information on occurrence, symptomatology, molecular characterization, transmission, taxonomy, genetic diversity and management approaches on phytoplasma infecting ornamental plants has been discussed
Phytoplasmas associated with apricot chlorotic leafroll disease
No full textApricot trees are affected by apricot chlorotic leafroll disease in all major cultivation areas in Europe: the disease is killing the plants few years and it widely associated with European stone fruit yellows (ESFY) ‘Candidatus Phytoplasma prunorum’ belonging to 16SrX-B. Samples from apricot trees showing typical chlorotic leafroll symptoms were collected in June/July 2010 in Serbia and Italy: 10 symptomatic and two asymptomatic plants were tested in total. In both Countries the disease was present in scattered distribution in 7 and 8 year old orchards. Phytoplasma detection was achieved by polymerase chain reaction and restriction fragment length polymorphism analyses using nested-PCR assays. Primers employed were P1/P7 followed by F1/B6 or R16F2n/R2. RFLP analyses on F1/B6 amplicons indicated the presence of 16SrXII in one of the samples from Serbia and of 16SrX-B in one of the samples from Italy. RFLP analyses with Tru1I, RsaI, HinfI, HhaI, and HpaII on R16F2n/R2 amplicons showed the presence of 16SrX-B phytoplasmas in 4 samples, two from the Italian orchard and two from the Serbian one. In the remaining three Serbian apricot samples a mixed infection of 16SrX-B and 16SrXII and a mixed infection of 16SrX-B, 16SrXII and 16SrI phytoplasmas were identified; one of the samples was negative. In two of the remaining samples from the Italian orchard a 16SrX-B and 16SrXII mixed infection was detected, while in the last sample 16SrX-B and 16SrIX-C phytoplasmas were identified. The use of nested PCR with PA2 primers on P1/P7 allow to detect 16rXII phytoplasma in the last sample from Serbia. In all the experiments carried out the two asymptomatic plants were negative.
This is the first report of presence in symptomatic apricot of phytoplasmas different from ESFY, in particular the 16SrIX-C phytoplasma is reported for the fist time in this species. Work to verify the epidemic relevance of these phytoplasmas in the apricot chlorotic leafroll disease is in progress
Phytoplasmas and Phytoplasma Diseases: A Severe Threat to Agriculture
Full text linkSeveral economically relevant phytoplasma-associated diseases are described together with an update of phytoplasma taxonomy and major biological and molecular features of phytoplasmas. Outlook about persepectives and future work to contain spread of these diseases are also reported
- …
