Candidatus Phytoplasma mali
Significance: Researchers in Poland have discovered that the phytoplasma responsible for Apple proliferation disease (i.e., 16SrX-A subgroup phytoplasmas, now known as 'Candidatus Phytoplasma mali'), can also be found in nature in Dahlia cultorum plants. Infected plants, which were also found to be co-infected with aster yellow phytoplasma, displayed bushy growth accompanied by shoot proliferation, narrowed leaf and flower bud deficiency.
In addition, these researchers have also shown that leaf scorch or leaf burn observed on oriental lily hybrids of the cultivar Siberia in several greenhouses in Poland were also infected with a phytoplasma belonging to 16SrX-A subgroup ('Ca. Phytoplasma mali'). 16SrX-A subgroup phytoplasmas have been reported frequently from woody plants. In Poland, they have been found in ornamental crops including rose (Kaminska & Sliwa, 2004); however, this is the first record on the occurrence of 'Ca. Phytoplasma mali' in lily plants.
Issues of Concern: Apple proliferation phytoplasma, now classified as 'Candidatus Phytoplasma mali', causes a serious disease of apples (Malus) in many parts of Europe. The phytoplasma, which is insect-vectored, is not known to occur in the NAPPO region and imported propagative material of Malus is regulated to prevent its entry. This latest research from Poland expands on the known host range for the phytoplasm and suggests that hosts other than Malus could potentially act as a pathway for the introduction of the pathogen.
M. Kaminska and H. Sliwa. 2007. (i) Mixed infection of dahlia plants in Poland with apple proliferation and aster yellows phytoplasmas. British Society of Plant Pathology (BSPP) New disease Reports 08/03/07 (http://www.bspp.org.uk/ndr/july2007/2007-29.asp), and (ii) First report of 'Candidatus Phytoplasma mali' in oriental lilies and its association with leaf scorch in Poland. BSPP New disease Reports 21/06/07 (http://www.bspp.org.uk/ndr/july2007/2007-52.asp).
See also previous NAPPO-PAS pest alert on 'Candidatus Phytoplasma mali': http://www.pestalert.org/viewNewsAlert.cfm?naid=34