Molecular Variability and Host Distribution of 'Candidatus Phytoplasma solani' Strains from Different Geographic Origins.

Assunta Bertaccini,Bojan Duduk,Jelena Stepanović,Nicoletta Contaldo,Francesco Pacini

doi:10.3390/microorganisms9122530

Assunta Bertaccini, Bojan Duduk + Show 3 more

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https://doi.org/10.3390/microorganisms9122530

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Abstract

The knowledge of phytoplasma genetic variability is a tool to study their epidemiology and to implement an effective monitoring and management of their associated diseases. ‘Candidatus Phytoplasma solani’ is associated with “bois noir” disease in grapevines, and yellowing and decline symptoms in many plant species, causing serious damages during the epidemic outbreaks. The epidemiology of the diseases associated with this phytoplasma is complex and related to numerous factors, such as interactions of the host plant and insect vectors and spreading through infected plant propagation material. The genetic variability of ‘Ca. P. solani’ strains in different host species and in different geographic areas during the last two decades was studied by RFLP analyses coupled with sequencing on vmp1, stamp, and tuf genes. A total of 119 strains were examined, 25 molecular variants were identified, and the variability of the studied genes was linked to both geographic distribution and year of infection. The crucial question in ‘Ca. P. solani’ epidemiology is to trace back the epidemic cycle of the infections. This study presents some relevant features about differential strain distribution useful for disease monitoring and forecasting, illustrating and comparing the phytoplasma molecular variants identified in various regions, host species, and time periods.

Highlights

Reptalus panzeri and R. quinquecostatus have been reported as vectors of Bois noir” (BN) in Serbian and French vineyards, respectively [11,12], while Anaceratagallia ribauti was reported as vector of “stolbur” to broad bean plants [13]
Restriction Fragment Length Polymorphism (RFLP) and sequencing analysis on the tuf gene showed the prevalence of the tuf type b1 profile [19,20] identified in samples from Serbia, Italy, Spain, Portugal, Montenegro, and Bulgaria, while tuf type b2 was only found in two grapevine samples from Hungary
The genetic variability of the ‘Ca. P. solani’ strains and the broad range of different plant host species infected are the key points in the study of population genetic and ecology of this phytoplasma

Summary

Introduction

“Bois noir” (BN), the most widespread grapevine yellows disease, represents a worldwide threat to viticulture It is associated with the presence of ‘Candidatus Phytoplasma solani’ [1], an obligate cell-wall-lacking bacterium that belongs to the class Mollicutes and is transmitted by polyphagous phloem-feeding insects [2,3]. It is enclosed in the 16SrXII-A ribosomal subgroup and associated with the “stolbur” disease in vegetable crop species, mostly belonging to the Solanaceae (tomato, potato, and pepper) and Apiaceae (carrot, celery, and parsley) families [4,5]. Recent transmission trials conducted with insects collected in a Northern Italy vineyard showed that at least eight insect species (Aphrodes makarovi, Dicranotropis hamata, Dictyophara europaea, Euscelis incisus, Euscelidius variegatus, Laodelphax striatellus, Philaenus spumarius, and Psammotettix alienus/confinis) are vectoring

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