APPLE PROLIFERATION DISEASE IN CROATIAN ORCHARDS: A MOLECULAR CHARACTERIZATION OF ‘CANDIDATUS PHYTOPLASMA MALI’

I. Križanac, J. Plavec, Ž. Budinšćak, D. Ivić, D. Škorić, M. Šeruga Musić

Abstract


Apple proliferation (AP) causes major economic losses to the European apple industry. The causal agent associated with AP is ‘Candidatus Phytoplasma mali’ which belongs to the same phylogenetic cluster as two other fruit tree phytoplasmas: ‘Ca. P. pyri’ and ‘Ca. P. prunorum’. ‘Ca. P. pyri’ and ‘Ca. P. solani’ have sporadically been associated with symptomatic apples in Croatia in previous surveys. There was no molecular evidence of ‘Ca. P. mali’ presence until the start of this study, when it was confirmed for the first time. In this four-year survey (2011-2014), the detection and characterization of ‘Ca. P. mali’ from apples and psyllid vectors was carried out. Detection was based on PCR-RFLP analysis of the 16S rRNA gene. Real-time PCR was also used for amplifying ‘Ca. P. mali’ 16S rDNA and Malus domestica chloroplast tRNA leucine gene. Phylogenetic analysis of 16S rDNA and aceF gene sequences confirmed the identification of selected phytoplasma strains. Considerable aceF variability among the strains was detected, and a new, yet unrecorded aceF genotype was found. ‘Ca. P. mali’ has consistently been identified with high incidence in apple samples from Croatian continental region orchards, whereas it occurred sporadically in the coastal areas. This is the first molecular detection and characterization of ‘Ca. P. mali’ strains from both apple (Malus domestica Burkh.) and psyllid vector Cacopsylla picta (Förster) in Croatia.

Keywords


16S rDNA; aceF; variability; phylogeny; psyllids

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DOI: http://dx.doi.org/10.4454/jpp.v99i1.3799

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EDIZIONI ETS, Pisa, Italy