Genetic Diversity of Tomato Black Ring Virus Satellite RNAs and Their Impact on Virus Replication.

Viral satellite RNAs (satRNAs) are small subviral particles that are associated with the genomic RNA of a helper virus (HV). Their replication, encapsidation, and movement depend on the HV. In this paper, we performed a global analysis of the satRNAs associated with different isolates of tomato black ring virus (TBRV). We checked the presence of satRNAs in 42 samples infected with TBRV, performed recombination and genetic diversity analyses, and examined the selective pressure affecting the satRNAs population. We identified 18 satRNAs in total that differed in length and the presence of point mutations. Moreover, we observed a strong effect of selection operating upon the satRNA population. We also constructed infectious cDNA clones of satRNA and examined the viral load of different TBRV isolates in the presence and absence of satRNAs, as well as the accumulation of satRNA molecules on infected plants. Our data provide evidence that the presence of satRNAs significantly affects viral load; however, the magnitude of this effect differs among viral isolates and plant hosts. We also showed a positive correlation between the number of viral genomic RNAs (gRNAs) and satRNAs for two analysed TBRV isolates.

Occurrence, Genetic Variability of Tomato Yellow Ring Orthotospovirus Population and the Development of Reverse Transcription Loop-Mediated Isothermal Amplification Assay for Its Rapid Detection.

Tomato-infecting viruses have been considered as a serious threat to tomato crops in Poland. Therefore, during 2014-2021, 234 tomato samples delivered directly by greenhouse tomato growers to Plant Disease Clinic of IPP-NRI were tested. Eight virus species: pepino mosaic virus (PepMV), tomato yellow ring orthotospovirus (TYRV), tomato spotted wilt orthotospovirus (TSWV), potato virus Y (PVY), cucumber mosaic virus (CMV), tomato black ring virus (TBRV) and tomato mosaic virus (ToMV) were detected in single or mixed infection in 89 samples. The presence of TYRV was established for the first time in Poland in 2014. Since then, its presence has been observed in single and mixed infection with TSWV and CMV. Here, we analysed the genetic variability of TYRV population based on complete nucleocapsid (N) protein gene sequence of 55 TYRV isolates. Maximum-likelihood reconstruction revealed the presence of three distinct, well-supported phylogroups. Moreover, the effect of host species on virus diversity was confirmed. Therefore, RT-LAMP assay was developed for the rapid and efficient detection of TYRV isolates that can be implemented in field and greenhouse conditions.