Molecular Study of a New Disease of Peach in Iran Associated with a Phytoplasma

Abstract

In recent years, a disease has been reported to affect peach trees in Kurdistan province of Iran causing serious losses to the production. Main symptoms of disease include leaf stunting and yellowing, which lead to failure in fruit production at harvest. For diagnosis of disease and identification of the causal agent, symptomatic leaf samples were collected in Kurdistan orchards during summer 2010 and were carried to the laboratory. Total DNA was extracted from plant samples according to the standard procedures and indexed by grafting and nested PCR using phytoplasma generic primers, P1/P7 and R16F2n/R2. PCR products were characterized by RFLP technique and direct sequencing. The 16S rDNA sequences were compared with those of other phytoplasmas in GenBank. Phytoplasma rDNA was amplified from 20 out 35 samples. The 16S rDNA sequences of the phytoplasma were identified in Peach samples which showed 98% similarity to that of "Candidatus Phytoplasma phoenicium" which is considered to be the causal agent of Almond witches' broom. Phylogenetic analysis of 16S rDNA sequences placed peach strains in Almond witches broom isolate as a member of pigeon pea witches broom (PPWB) group. Further studies on the epidemiology of "Ca. Phytoplasma phoenicium" and its vector(s) in Iran are recommended in order to identify new natural hosts and develop successful disease management programs.

Peach witches’-broom, an emerging disease associated with ‘Candidatus Phytoplasma phoenicium’ and ‘Candidatus Phytoplasma aurantifolia’ in Iran

“…P. aurantifolia' (subgroup 16SrII-C), the etiological agent of alfalfa and carrot witches '-broom (Esmailzadeh Hosseini et al, 2015;Salehi et al, 2016a), cucurbits phyllody (Salehi et al, 2015b) and apricot chlorotic leaf roll (Rasoulpour et al, 2019) in Abarkooh area, and several other plant diseases in other parts of Iran (Salehi et al, 2016b). This evidence reinforces the recent reports of the association of severe and mild peach witches'-broom (PWIB)-like diseases respectively with phytoplasmas of taxonomic groups 16SrIX (Ghayeb Zamharir, 2014) and II (Zirak et al, 2010) in Iran. In Borugerd, Sanandaj and Zarghan areas, the disease incidence was higher than in the other surveyed areas where PWIB was associated with 'Ca.…”

“…Concerning 'Ca. P. phoenicium', its previous association with PWIB-like disease was only provisional, due to the short size of the 16S rDNA nucleotide sequence analyzed, and limited to the Iranian provinces of Kurdistan, North Khorasan and Razavi Khorasan (Ghayeb Zamharir, 2014;Tarighi et al, 2018). Here, nucleotide sequence identity, presence of speciesspecific signature sequences, and phylogenetic analysis of 16S rDNA allowed the certain assignation of PWIB phytoplasma strains, identified in affected peach trees from seven Iranian provinces, to the species 'Ca.…”

“…P. omanense' in Iran (Zirak et al, 2010;Esmailzadeh Hosseini et al, 2017). Moreover, in the Iranian provinces of Kurdistan, North Khorosan and Razavi Khorosan stunting and leaf yellowing have been observed on peach trees infected by phytoplasmas provisionally identified as belonging to16SrIX group (Ghayeb Zamharir, 2014;Tarighi et al, 2018). During field surveys carried out from 2013 to 2017 in the eight main peach producing provinces of Iran, a phytoplasma-like peach witches'-broom disease (PWIB) was observed.…”