Pest categorisation of the non-EU phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L

Following a request from the European Commission, the EFSA Panel on Plant Health performed a pest categorisation of nine phytoplasmas of Cydonia Mill., Fragaria L., Malus Mill., Prunus L., Pyrus L., Ribes L., Rubus L. and Vitis L. (hereafter “host plants”) known to occur only outside the EU or having a limited presence in the EU. This opinion covers the (i) reference strains of ‘Candidatus Phytoplasma australiense’, ‘Ca. P. fraxini’, ‘Ca. P. hispanicum’, ‘Ca. P. trifolii’, ‘Ca. P. ziziphi’, (ii) related strains infecting the host plants of ‘Ca. P. aurantifolia’, ‘Ca. P. pruni’, and ‘Ca. P. pyri’, and (iii) an unclassified phytoplasma causing Buckland valley grapevine yellows. Phytoplasmas can be detected by available methods and are efficiently transmitted by vegetative propagation, with plants for planting acting as a major entry pathway and a long‐distance spread mechanism. Phytoplasmas are also transmitted in a persistent and propagative manner by some insect families of the Fulgoromorpha, Cicadomorpha and Sternorrhyncha (order Hemiptera). No transovarial, pollen or seed transmission has been reported. The natural host range of the categorised phytoplasmas varies from one to more than 90 plant species, thus increasing the possible entry pathways. The host plants are widely cultivated in the EU. All the categorised phytoplasmas can enter and spread through the trade of host plants for planting, and by vectors. Establishment of these phytoplasmas is not expected to be limited by EU environmental conditions. The introduction of these phytoplasmas in the EU would have an economic impact. There are measures to reduce the risk of entry, establishment, spread and impact. Uncertainties result from limited information on distribution, biology and epidemiology. All the phytoplasmas categorised here meet the criteria evaluated by EFSA to qualify as potential Union quarantine pests, and they do not qualify as potential regulated non‐quarantine pests, because they are non‐EU phytoplasmas

Commodity risk assessment of Malus sylvestris plants from United Kingdom

The European Commission requested the EFSA Panel on Plant Health to prepare and deliver risk assessments for commodities listed in Commission Implementing Regulation (EU) 2018/2019 as 'High risk plants, plant products and other objects'. This Scientific Opinion covers plant health risks posed by rooted plants and bundles of bare root plants or rooted cell grown young plants of Malus sylvestris imported from the UK, taking into account the available scientific information, including the technical information provided by the UK. All pests associated with the commodities were evaluated against specific criteria for their relevance for this opinion. Two quarantine pests (tobacco ringspot virus and tomato ringspot virus), one protected zone quarantine pest (Erwinia amylovora) and four non-regulated pests (Colletotrichum aenigma, Meloidogyne mali, Eulecanium excrescens and Takahashia japonica) that fulfilled all relevant criteria were selected for further evaluation. For Erwinia amylovora, special requirements are specified in Commission Implementing Regulation (EU) 2019/2072. Based on the information provided in the dossier, these specific requirements for E. amylovora are met. For the remaining six pests, the risk mitigation measures proposed in the technical Dossier from the UK were evaluated, taking into account the possible limiting factors. For these pests, expert judgement is given on the likelihood of pest freedom, taking into consideration the risk mitigation measures acting on the pest, including uncertainties associated with the assessment. The degree of pest freedom varies among the pests evaluated, with scales (Eulecanium excrescens and Takahashia japonica) being the pests most frequently expected on the imported bundles of bare root plants or rooted cell grown young plants. The expert knowledge elicitation indicated with 95% certainty that between 9,976 and 10,000 bundles (one bundle consisting of 5-15 plants for bare root plants or 25-50 plants for cell grown young plants) per 10,000 would be free from the above-mentioned scales

The Major Antigenic Membrane Protein of “Candidatus Phytoplasma asteris” Selectively Interacts with ATP Synthase and Actin of Leafhopper Vectors

Phytoplasmas, uncultivable phloem-limited phytopathogenic wall-less bacteria, represent a major threat to agriculture worldwide. They are transmitted in a persistent, propagative manner by phloem-sucking Hemipteran insects. Phytoplasma membrane proteins are in direct contact with hosts and are presumably involved in determining vector specificity. Such a role has been proposed for phytoplasma transmembrane proteins encoded by circular extrachromosomal elements, at least one of which is a plasmid. Little is known about the interactions between major phytoplasma antigenic membrane protein (Amp) and insect vector proteins. The aims of our work were to identify vector proteins interacting with Amp and to investigate their role in transmission specificity. In controlled transmission experiments, four Hemipteran species were identified as vectors of “Candidatus Phytoplasma asteris”, the chrysanthemum yellows phytoplasmas (CYP) strain, and three others as non-vectors. Interactions between a labelled (recombinant) CYP Amp and insect proteins were analysed by far Western blots and affinity chromatography. Amp interacted specifically with a few proteins from vector species only. Among Amp-binding vector proteins, actin and both the α and β subunits of ATP synthase were identified by mass spectrometry and Western blots. Immunofluorescence confocal microscopy and Western blots of plasma membrane and mitochondrial fractions confirmed the localisation of ATP synthase, generally known as a mitochondrial protein, in plasma membranes of midgut and salivary gland cells in the vector Euscelidius variegatus. The vector-specific interaction between phytoplasma Amp and insect ATP synthase is demonstrated for the first time, and this work also supports the hypothesis that host actin is involved in the internalization and intracellular motility of phytoplasmas within their vectors. Phytoplasma Amp is hypothesized to play a crucial role in insect transmission specificity

Coconut lethal yellowing diseases: a phytoplasma threat to palms of global economic and social significance

The recent discovery of Bogia coconut syndrome in Papua New Guinea (PNG) is the first report of a lethal yellowing disease (LYD) in Oceania. Numerous outbreaks of LYDs of coconut have been recorded in the Caribbean and Africa since the late Nineteenth century and have caused the death of millions of palms across several continents during the Twentieth century. Despite the severity of economic losses, it was only in the 1970s that the causes of LYDs were identified as phytoplasmas, a group of insect-transmitted bacteria associated with diseases in many other economically important crop species. Since the development of polymerase chain reaction (PCR) technology, knowledge of LYDs epidemiology, ecology and vectors has grown rapidly. There is no economically viable treatment for LYDs and vector-based management is hampered by the fact that vectors have been positively identified in very few cases despite many attempted transmission trials. Some varieties and hybrids of coconut palm are known to be less susceptible to LYD but none are completely resistant. Optimal and current management of LYD is through strict quarantine, prompt detection and destruction of symptomatic palms, and replanting with less susceptible varieties or crop species. Advances in technology such as loop mediated isothermal amplification (LAMP) for detection and tracking of phytoplasma DNA in plants and insects, remote sensing for identifying symptomatic palms, and the advent of clustered regularly interspaced short palindromic repeats (CRISPR)-based tools for gene editing and plant breeding are likely to allow rapid progress in taxonomy as well as understanding and managing LYD phytoplasma pathosystems