Description
ORIGIN AND SPREAD. Erwinia amylovora originated in North America where it appears to have caused an endemic disease in wild plants of Malus sylvestris, Crataegus spp., Sorbus spp. and Amelanchier spp. From these early outbreaks, the disease gradually spread to other countries. In Europe, the first cases of fire blight date back to 1957 in England, probably following the introduction of infected material, from where it rapidly spread to continental Europe. In Italy, the first reports date back to 1990 in Apulia. Trentino is now considered an area of establishment of the pathogen.
HOST PLANTS It specifically affects plants belonging to the Rosaceae family. To date there are more than 150 host species belonging to 37 different genera. Particularly susceptible to the disease are species of great economic value from an orchard point of view such as apple(Malus domestica) and pear(Pyrus communis). Also susceptible to fire blight are medlar(Mespilus spp.), quince(Cydonia spp.) and many genera of ornamental and wild plants(Crataegus spp., Cotoneaster spp., Pyracantha spp., Sorbus spp., Chaenomeles spp.).
BIOLOGY. Bacteria found on infected plants, upon vegetative recovery, escape in the form of a milky exudate, especially from the cancers they have caused, and form the potential inoculum for new infections.
Once the bacterium has colonised the plant, it develops within the plant tissues and begins to colonise intracellular spaces and/or xylem cavities. In these spaces, it releases a toxic protein that disrupts the functionality of the cell membrane of the host plant organisms in order to gain nourishment. This action results in the sudden withering of the affected part of the plant or, in the most severe cases, the entire plant with subsequent death.
The bacterium reproduces very quickly and the colonies that form tend to draw water into the tissues. These swell until mucous droplets of bacterial exudate escape outside through small fractures. Erwinia amylovora overwinters within the infected plant tissues or in the remnants of infected vegetation left in the soil.
PATHWAYS OF DISSEMINATION. The dissemination of Erwinia from plant to plant and even over great distances is entrusted to wind, rain, insects and birds. Man can also contribute to the spread through various cultivation operations, particularly pruning, and through the marketing of infected propagation material.
The flowering period is considered the most critical in terms of both the plant's receptivity to infection and the spread of the inoculum. Moreover, bees, which are so important for pollination, can contribute to infection by transporting such bacteria, which penetrate very easily through the nectaries, to the flowers. In fact, this pathogen has a passive type of penetration into the tissues of host plants, so all continuity solutions, such as wounds, lenticels, stomata and nectaries of flowers, are possible points of entry.
Since the 1990s, the Lombardy Region's Phytosanitary Service has been engaged in monitoring this organism by controlling nurseries, orchards and the regional territory in general through a network of fixed points with known hosts of E. amylovora.
PHYTOSANITARY CONTROL. The pest is no longer to be quarantined since 2019 but is still among the ORNQs (Organisms Regulated Not to be Quarantined) whose presence is not tolerated in nurseries. When outbreaks were found in Trentino territory, temporary control prescriptions were issued punctually (by area), including
- the obligation for all holders of fruit plants, vegetable gardens, hedges, trees and land on which host plants symptomatic of fire blight are found to immediately uproot any seriously compromised plant
- prompt on-site burning of infected plant residues. If it is not possible to incinerate on site, the residues can be transported to another suitable location using containment bags that isolate the material to be destroyed;
- appropriate chemical or physical disinfection of all tools and machinery, as well as clothing, used to implement the plant protection measure;
- ban in outbreak areas on planting new professional Pomoideae orchards for one year;
- ban on the movement of beehives from infected areas to other areas of the provincial territory during risk periods (from 1 April to 15 June and in any case throughout the flowering period of susceptible plants)
- ban on the use of nuclei or hives of "disposable" bees throughout the provincial territory.
- ban on the marketing and planting of host plants in the demarcated areas.
REPORTING. The presence (even suspected) of symptomatic plants must be reported immediately to the Provincial Plant Protection Service (tel. 0461-495660; e-mail serv.agricoltura@provincia.tn.it; pec serv.agricoltura@pec.provincia.tn.it)
REFERENCE REGULATIONS. Regulation (EU) 2016/ 2031; Implementing Regulation (EU) 2019/2072; Legislative Decree no. 19/2021; Decree of 13 August 2020 of the Ministry of Agriculture, Food and Forestry Policies.