Apple sessile leaf: a new disease associated with a 'Candidatus Phytoplasma asteris' subgroup 16SrI-B phytoplasma in Lithuania

A new disease of apple (Malus domestica) has been found in the Kaisiadorys region of Lithuania. With symptoms of leaf yellowing, shoot proliferation and a previously undescribed symptom "sessile leaf", where "golden" leaves are directly attached to the trunk (Fig. 1). These symptoms differ from those of apple proliferation (AP), with enlarged stipulae, witches' broom and bronze-reddish discoloration of leaves (Baric & Dalla-Via, 2004). DNA extracted from leaves, with and without symptoms, was used as template in PCR with phytoplasma rDNA universal primers P1/P7, as previously described by Valiunas (2003). Phytoplasma infection was confirmed by amplification of 1.8 kbp rDNA fragments from all trees with (3/3), but from no trees without symptoms (0/6). RFLP and nucleotide sequence (GenBank accession no. AY734454) analysis of a 1.2 kbp DNA fragment, amplified by nested PCR using primers 16SF2n/16SR2, revealed that the phytoplasma, termed apple sessile leaf (ApSL) phytoplasma, is a member of the 16SrI-B ('Candidatus Phytoplasma asteris') subgroup.

The results of this study clearly distinguish ApSL from AP phytoplasma, 'Ca. Phytoplasma mali', a member of group 16SrX. Five subgroups of phytoplasma group 16SrI have now been identified in Lithuania: subgroup 16SrI-A in vegetables, ornamentals, and oats; subgroup 16SrI-B in ornamentals and woody plants including apple; subgroup16SrI-C in clover and Poa pratensis; and subgroups16SrI-M and 16Sr-L in ornamentals , cereals and woody plants. (Valiunas, 2003; Jomantiene et al., 2002; Staniulis et al., 2000). This first report of 'Ca. Phytoplasma asteris' infecting apple in Lithuania has considerable significance for fruit production, since apple is widely cultivated throughout Europe.