Candidatus Phytoplasma mali
Significance: Apple proliferation disease, caused by 'Candidatus Phytoplasma mali', is considered one of the most economically important phytoplasma diseases of plants in Europe. It is of particular concern in the Mid to Southern regions of Europe where the main leafhopper insect vector for the pathogen is most abundant.
The phytoplasma is reported to affect almost all apple (Malus domestica) varieties. Significant reductions in fruit size, weight, and quality of the apples are reported. Overall tree vigor can be reduced by the phytoplasma and in some cases lead to premature tree death. The phytoplasma has also been reported from hazelnut (Corylus sp.), and pear (Pyrus communis) trees.
Recent studies in Slovenia demonstrated that the Apple proliferation phytoplasma can also naturally infect cherry (Prunus avium), apricot (P. armeniaca), and plum (P. domestica) trees. In Southwestern Slovenia, researchers found the AP phytoplasma in the roots of one asymptomatic and three symptomatic cherry trees. Symptoms included floral and phleom necrosis, wilting, or general plant decline. The AP phytoplasma was also found in two apricot trees expressing stem necrosis and leaf wilting and one plum tree expressing late blooming. Further work is required to verify if these symptoms were actually associated with the AP phytoplasma.
'Candidatus Phytoplasma mali' is not known occur in North America and propagative material of Malus is regulated by NAPPO countries to prevent its introduction. Regulatory and certification agencies should note that this recent research indicates that fruit tree species in the genus Prunus could also act as a potential pathway for spreading 'Candidatus Phytoplasma mali'.
N. Mehle, J. Brzin, J. Boben, M. Hren, J. Frank, N. Petrovic, K. Gruden, T. Dreo, I. Zezlina, G Seljak and M. Ravnikar. 2006. First report of 'Candidatus Phytoplasma mali' in stone fruits (Prunus spp.). British Society of Plant Pathology, New Disease Reports (Accepted for publication 24/11/06). Available at: http://www.bspp.org.uk/ndr/jan2007/2006-90.asp
NAPPO PAS. 2006. Fieberiella florii, a North American Leafhopper Confirmed as a Vector for Apple Proliferation Phytoplasma. North American Plant Protection Organization. Phytosanitary Alert System. Available at: http://www.pestalert.org/viewNewsAlert.cfm?naid=10