Characterization of Two Novel Single-Stranded RNA Viruses from Agroathelia rolfsii, the Causal Agent of Peanut Stem Rot.

Peanut stem rot is a soil-borne disease caused by Agroathelia rolfsii. It occurs widely and seriously affects the peanut yield in most peanut-producing areas. The mycoviruses that induce the hypovirulence of some plant pathogenic fungi are potential resources for the biological control of fungal diseases in plants. Thus far, few mycoviruses have been found in A. rolfsii. In this study, two mitoviruses, namely, Agroathelia rolfsii mitovirus 1 (ArMV1) and Agroathelia rolfsii mitovirus 2 (ArMV2), were identified from the weakly virulent A. rolfsii strain GP3-1, and they were also found in other A. rolfsii isolates. High amounts of ArMV1 and ArMV2in the mycelium could reduce the virulence of A. rolfsii strains. This is the first report on the existence of mitoviruses in A. rolfsii. The results of this study may provide insights into the classification and evolution of mitoviruses in A. rolfsii and enable the exploration of the use of mycoviruses as biocontrol agents for the control of peanut stem rot.

Virus Surveys in Olive Orchards in Greece Identify Olive Virus T, a Novel Member of the Genus Tepovirus.

Field surveys were conducted in Greek olive orchards from 2017 to 2020 to collect information on the sanitary status of the trees. Using a high-throughput sequencing approach, viral sequences were identified in total RNA extracts from several trees and assembled to reconstruct the complete genomes of two isolates of a new viral species of the genus Tepovirus (Betaflexiviridae), for which the name olive virus T (OlVT) is proposed. A reverse transcription-polymerase chain reaction assay was developed which detected OlVT in samples collected in olive growing regions in Central and Northern Greece, showing a virus prevalence of 4.4% in the olive trees screened. Sequences of amplified fragments from the movement-coat protein region of OlVT isolates varied from 75.64% to 99.35%. Three olive varieties (Koroneiki, Arbequina and Frantoio) were infected with OlVT via grafting to confirm a graft-transmissible agent, but virus infections remained latent. In addition, cucumber mosaic virus, olive leaf yellowing-associated virus and cherry leaf roll virus were identified.

Studies on the Occurrence of Viruses in Planting Material of Grapevines in Southwestern Germany.

Viral diseases in viticulture lead to annual losses in the quantity and quality of grape production. Since no direct control measures are available in practice, preventive measures are taken to keep the vines healthy. These include, for example, the testing of propagation material for viruses such as Arabis mosaic virus (ArMV), Grapevine fanleaf virus (GFLV) or Grapevine leafroll-associated virus 1 (GLRaV-1) and 3 (GLRaV-3). As long-term investigations have shown, GLRaV-1 (2.1%) occurs most frequently in southwestern German wine-growing regions, whereas GLRaV-3 (<0.1%) is almost never found. However, tests conducted over 12 years indicate that there is no general decline in virus-infected planting material. Thus, it can be assumed that a spread of the viruses via corresponding vectors still takes place unhindered. Beyond the examinations regulated within the German Wine Growing Ordinance, one-time tests were carried out on Grapevine Pinot gris virus (GPGV). This analysis showed that GPGV was found in 17.2% of the samples.

Mapping of the exchangeable and dispensable domains of the RNA 2-encoded 2A(HP) protein of arabis mosaic nepovirus.

The N-terminal domains of the RNA 2-encoded 2A(HP) proteins of the arabis mosaic (ArMV) and grapevine fanleaf (GFLV) nepoviruses were shown to be highly variable and a hotspot for intra- and inter-species recombination events. Chimeric ArMV-NW clones in which the N-terminal domain of 2A(HP) or the entire 2A(HP) of GFLV isolates replaced the corresponding domains of ArMV retained their infectivity, showing that the 2A(HP) proteins of ArMV-NW and GFLV are exchangeable. ArMN-NW clones with deletions of the N-terminal, core, or C-terminal domains of the ArMV-NW 2A(HP) were infectious in Chenopodium quinoa although viral RNA (especially RNA 2) accumulated at reduced levels. In contrast, deletion of the entire 2A(HP) protein or of the C-terminal two thirds of the protein abolished infectivity of the ArMV-NW clones. These results suggest that multiple functional domains are distributed throughout the 2A(HP) protein and are essential for the accumulation of viral RNA 2.