First report of Candidatus phytoplasma mali in Greece and correlation with small apple fruit disorder occurring in the orchards of the pelion mountain

Abstract

The apple producing area of the Pelion Mountain suffers the last six years from the extensive phenomenon of small fruiting. Small fruit may appear in few or even all trees of the orchards as well as on few or several branches of each tree. Recovery phenomena and reappearance of the symptoms were observed. Malus xdomestica 'Starking Delicious', widely cultivated at Pelion Mountain, showed high susceptibility. Preliminary studies on the aetiology of this phenomenon were focused to physiological abnormalities in small fruits and to pathogen detection. In small fruits, a high concentration of Mn is observed. The basic colour is not modified, but anthocyanids in the phloem are reduced. Soluble solids and dry mass is decreased, but no difference in pH and acidity is measured. Small apples also show inability in reaching maturation, as they are harder and remain on the tree for many weeks after harvest. Injections with oxytetracycline in a small number of trees were carried out; in the next year a remission of the symptoms in 60% of cases was observed. In September 2005, PCR diagnostic tests for Candidatus Phytoplasma mali in symptomatic trees were performed revealing high presence of the pathogen in the region; out of the 131 trees tested, 43 were positive. The high detection rate of Candidatus Phytoplasma mali in symptomatic trees reveals the high correlation of the presence of the pathogen with small fruit disorder.