Multilocus Genotyping of ‘Candidatus Phytoplasma solani’ Associated with Rubbery Taproot Disease of Sugar Beet in the Pannonian Plain

Abstract

Rubbery taproot disease of sugar beet (RTD), associated with ‘Candidatus Phytoplasma solani’, appeared in 2020 on an epidemic scale in northern Serbia and southern Slovakia, situated at opposite edges of the Pannonian Plain. In the affected locations where the disease was assessed, symptomatic sugar beets were analysed for phytoplasma infection. Additionally, multilocus sequence analyses of ‘Ca. P. solani’ strains on epidemiologically informative marker genes (tuf, stamp and vmp1) were performed. Symptomatic sugar beets from other countries of the Pannonian Plain (Croatia, Hungary and Austria), one sample from Germany, and red beets from Serbia were included in the analyses. ‘Ca. P. solani’ was detected in sugar beet in all assessed countries, as well as in red beet. Molecular analyses revealed the high genetic variability of ‘Ca. P. solani’ with the presence of all four tuf-types (a, b1, b2 and d), 14 stamp genotypes (seven new) and five vmp1 profiles (one new). The most common multilocus genotype in Serbia, Slovakia, Croatia, and Hungary was dSTOLg (tuf-d/STOL/V2-TA). It was dominant on sites with epidemic RTD outbreaks in the Pannonian Plain and in several sugar beet fields with non-epidemic RTD occurrence suggesting the prevalence of a particular epidemiological pathway during the epidemic’s phases.

Epidemiological Role of Dictyophara europaea (Hemiptera: Dictyopharidae) in the Transmission of ‘Candidatus Phytoplasma solani’

“…Beside tuf-b1, at the location of Rogljevo, ruderal hillside in a traditional vine growing district of east Serbia, the tuf-d type was detected in 25% of infected C. foetida and 28% of infected D. carota (Table 2). This type was recently identified in sugar beet, parsley, and parsnip from northern Serbia [38].…”

Application of TaqMan Real-Time PCR for Detecting ‘Candidatus Arsenophonus Phytopathogenicus’ Infection in Sugar Beet

“…Several viruses caused by Beet yellows virus (BYV), beet mild yellowing virus (BMYV), beet chlorosis virus (BChV) and beet mosaic virus (BtMV) cause virus yellows (VY) disease in sugar beet, resulting in high economic losses [13]. Other bacterioses of sugar beet have been recently analysed, including the Rubbery Taproot Disease caused by 'Candidatus Phytoplasma solani' in the Pannonian Plain or a related strain from Germany [9]. The latter was discovered during a routine screening of sugar beet whilst applying a widely used phytoplasma 16S-rDNA TaqMan assay with a detection limit originally described at 10 6 [14].…”

“…Phytoplasma infection of sugar beet by 'Ca. P. solani' has also been reported for Germany [9], but the epidemiology remains unclear.…”

“…Besides the visual inspection of sugar beets, several molecular assays have been developed for detecting 'Ca. A. phytopathogenicus', including the application of the primer pair Fra4/Fra5, targeting the 16S rRNA gene [9], originally designed for the closely-related 'Candidatus Phlomobacter fragariae' that causes the marginal chlorosis of strawberries [10]. The usage of the primer pair led to the discovery of 'Ca.…”

Biology and Rearing of an Emerging Sugar Beet Pest: The Planthopper Pentastiridius leporinus

“…Phytoplasmas are bacterial pathogens (family Acholeplasmataceae ) that lack a cell wall and colonize the phloem sieve tubes of plants, resulting in various economically important crop diseases [ 10 ]. In Serbia, stolbur phytoplasma is also associated with a different disease of sugar beet, known as rubbery tap root disease [ 11 ].…”