Spread of European fruit tree phytoplasma diseases

The genetically closely related ‘Candidatus Phytoplasma mali’, ‘Candidatus Phytoplasma prunorum’ and ‘Candidatus Phytoplasma pyri’ are associated with economically important diseases such as apple proliferation, European stone fruit yellows and pear decline in European fruit tree areas and are spread by psyllid vectors of the superfamily Psylloidea (Hemiptera, Sternorrhyncha). Although the relationship between these phytoplasmas, their hosts and the vectoring psyllids is almost highly specific, there are some interconnections and biological factors which influence disease epidemiology and vector ecology and which should be taken into consideration for risk assessment and vector control. For a reliable risk assessment of a putative vector is important to know its population dynamics, its transmission efficiency, its host plant preferences and its epidemiological cycle. Although psyllid vectors usually show a high host plant specificity, being either monophagous or oligophagous on closely related plant species, shelter plants may serve as sources of inoculum and hence interfere with the disease spread. Therefore, the knowledge of the epidemiological cycle of both, the phytoplasma and its main vector is crucial for the development of efficient control measures.