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Xylella fastidiosa Wells et al. 1987 Dutch name: n/a English name: Leaf scorch diseases on oleander, olive, almond, coffee, pecan, pear, grapevine, amenity tree species, etc.; citrus variegated chlorosis; grapevine Pierce’s disease; plum leaf scald; peach phony disease; dwarf lucerne. Status Xylella fastidiosa (hereafter abbreviated as: “Xf ”)has a quarantine status within the EU, Category IAI. This means that: - It is a harmful organism that can occur in multiple plant species or plant products - Absent in the EU (as far as is known) and poses risks to the entire community, hence it is controlled for in imports. Systematics It concerns a Gram-negative, non-spore forming, rod-shaped bacterium. Host plants Economically (and/or socially) important host plants are: Citrus latifolia (tahiti lime), Citrus reticulata (tangerine), Citrus reticulata x paradisi (tangelo), Citrus sinensis (navel orange); Vitis rupestris (sand grape), Vitis vinifera (grapevine) ; Prunus angustifolia (mountain cherry tree), Prunus dulcis (almond), Prunus persica (peach), Prunus salicina (Japanese plum) ; Pyrus sp. (pear); Ulmus sp. (elm) Nerium oleander (oleander); Coffea sp. (coffee); Medicago sativa (lucerne), Morus alba (white mulberry), Acer saccharum, Carya ilinoinensis, Liquidambar styraciflua, Platanus occidentalis. Additionally, there are numerous wild and/or economically less valuable host plants, such as: Brachiaria sp. (signal grass), Cynodon sp., Cyperus sp., Digitaria sp., Echinochloa frumentacea (Japanese millet), Fragaria vesca (wild strawberry), Lolium sp. (tufted grass), Paspalum dilatatum, Passiflora foetida, Quercus rubra, Rubus sp., Trifolium sp. (clovers), Vinca minor, and others. There are also host plants that show no symptoms. Sometimes they may show very slight stunted growth. Geographical distribution Xf has been reported to occur in: Asia: [China (Taiwan), Turkey]; Africa: [Morocco (not confirmed)]; North America: [Canada (Ontario), Mexico, USA (27 states)]; Central America: [Costa Rica]; South America: [Argentina, Brazil (9 states), Paraguay, Venezuela]. Europe: found at a single location in Italy in 2013, measures were taken. Biology Within the Xf genus, there are various strains that associate with just one host plant or that have a preference for a certain host plant. For example, it emerged that Brazilian Xf strains from citrus and © 2014 Wageningen. Het auteursrecht van deze publicatie berust bij de Nederlandse Voedsel en Warenautoriteit Niets uit deze uitgave mag zonder voorafgaande toestemming van genoemde dienst op enigerlei wijze worden vermeerderd, openbaar gemaakt of voor commerciële doeleinden worden gebruikt. Versie 3 Ingangsdatum: 12-2-2014 Pagina 1 van 4 coffee were pathogenic on grapevine. However, no natural infection on grapevine has been found in Brazil. To date, Xf strains from grape are not known to be pathogenic for peach and Xf strains from peach not for grape. Studies into the association of strains with host plants are few and incomplete. According to current insights, 4 groups can be distinguished that can possibly be defined taxonomically to a sub-species level. However, there is no full consensus on this matter yet. Xf principally spreads across large distances by means of infected plant material and (vegetative) propagation materials. Across shorter distances (on site), Xf mainly spreads naturally by various vector insects. The familiar vector insects generally cannot travel far on their own, but borne by the wind they can transmit Xf infections over large distances. Virtually all species of sucking insects that feed on sap of the Xylem (order of Hemiptera, families: Cicadellidae and Cercopidae) are potential vectors for Xf. Among them, the “Glassy-winged sharpshooter” (Homalodisca coagulata, a leafhopper) is capable of transmitting the bacterium. Uptake by insects is very fast and effective, within 2 hours. The bacterium sticks to the mouth parts and can be transmitted to a next plant directly upon subsequent feeding. Xf propagates within the insect but does not circulate in the hemolymph. No latency period is required for the transmission of the bacterium. A study conducted in the USA showed that 75 out of 100 plants examined can function as (intermediate) host plant for Xfbearing vector insects. The establishment of the bacterium in natural vegetation (potential reservoir for Xf) therefore constitutes a major risk. Following infection of a plant, Xf colonises the Xylem (wood) tissue of roots, stems and leaves. During severe and lengthy winters, infections may disappear as a result of the bacterium dying in the dormant plant tissue. In moderate areas with regular frost periods, the bacterium can survive in plant material that was infected early in the season. No indications have been found of disease transmission through contact between grape branches in moderate areas with regular frost; probably because the infection sets in too late. Symptoms / damage Citrus, “Variegated chlorosis”. Young affected trees develop stunted and distorted growth. Twigs and branches can wilt and the crown thins out. Leaf symptoms: interveinal chlorosis occurs, which strongly resembles a zinc deficiency. As the leaf ages, small, slightly raised, brown and necrotic spots emerge on the underside of the leaves, directly beneath the chlorotic spots. Grapevine, “Pierce’s disease”. Sudden partial brown dying off of the leaves, followed by yellow or red discolouration of adjacent leaf tissue. The desiccation then spreads across the leaf surface. The leaf then drops off, while the live stalk remains intact. Brown and green spots emerge on the stalk as a result of irregular ageing. Peach, “Phony disease”. Sick young shoots show stunted and retarded growth with greener and denser leaf growth. Side branches grow horizontally or downward, giving the tree a compact and round appearance. “Leaf scorch” diseases. Brown discolouration of the leaf edges and leaf ends. In an early stage of the infection, the leaf can show a slight yellowing. An assessment of symptoms does not yield definitive information about plants’ health situation during transportation or trade. Inconspicuous or young infections can go unnoticed. Zinc deficiency can cause chlorosis symptoms in grapevine and citrus that resemble Xf, but the patterns are distinguishable by a trained observer. © 2014 Wageningen. Het auteursrecht van deze publicatie berust bij de Nederlandse Voedsel en Warenautoriteit Niets uit deze uitgave mag zonder voorafgaande toestemming van genoemde dienst op enigerlei wijze worden vermeerderd, openbaar gemaakt of voor commerciële doeleinden worden gebruikt. Versie 3 Ingangsdatum: 12-2-2014 Pagina 2 van 4 In viticulture, a plant pathogenic fungus can cause symptoms that resemble grapevine’s “Pierce’s disease”. This “Esca” disease occurs in France early on in the season (June/July), after a number of hot days, while the symptoms of “Pierce’s disease” emerge after grapes have begun to turn colour. Indications for the presence of vector insects are a whitish powder on the plant surfaces. This is the result of watery excrement. Due to the large quantities of Xylem sap consumed daily by the insects (hundreds of times their own body volume), they also eject large quantities of moist excrement. This dries up to form whitish powder. Observation / sampling period Container or pot plants kept under warm conditions can, in principle, show symptoms at any time of the year, but particularly after a few weeks of rapid growth. In general, one should take into account that a period of plant growth and a warm period for the development of Xf should have preceded the moment of symptom assessment. Particularly for grapevines, the best observation time is late in the season, after the grapes have begun to turn colour. Illustrations Citrus leaf with interveinal chlorosis and slightly raised brown necrotic spots on the underside. Dropped leaves (grapevine) Partial dying (leaf scorch) Phony disease of peach © 2014 Wageningen. Het auteursrecht van deze publicatie berust bij de Nederlandse Voedsel en Warenautoriteit Niets uit deze uitgave mag zonder voorafgaande toestemming van genoemde dienst op enigerlei wijze worden vermeerderd, openbaar gemaakt of voor commerciële doeleinden worden gebruikt. Versie 3 Ingangsdatum: 12-2-2014 Pagina 3 van 4 Upper left: Coffea Arabica with yellowing and leaf scorch Right: Olive with leaf scorch Below, all three: leaf scorch in oleander Olive trees with “quick decline” and leaf scorch © 2014 Wageningen. Het auteursrecht van deze publicatie berust bij de Nederlandse Voedsel en Warenautoriteit Niets uit deze uitgave mag zonder voorafgaande toestemming van genoemde dienst op enigerlei wijze worden vermeerderd, openbaar gemaakt of voor commerciële doeleinden worden gebruikt. Versie 3 Ingangsdatum: 12-2-2014 Pagina 4 van 4