In several regions of Russia, broad distribution of RNA-containing bee viruses was found at apiaries of honey bee Apis mellifera using RT-PCR. Detected RNA-containing bee viruses are transferred simultaneously with invasion of mite Varroa destructor and lead to mass bee mortality that results in economic losses in bee breeding. In samples of Varroa destructor, bee viruses DWV and ABPV were found. High degree of RNA-containing virus (BQCV, DWV SBV, ABPV, CBPV and KBV) infection was revealed: in the average, at least 50% for bee families with mite infection. In the bee families studied in this work, mixed infection with 2-6 viruses simultaneously was detected. Amplified fragments of viruses BQCV, DWV and SBV obtained using RT-PCR were sequenced and registered in Genbank.
The fungal genus Heterobasidion includes some of the most devastating conifer pathogens in the boreal forest region. In this study, we showed that the alphapartitivirus Heterobasidion partitivirus 13 from Heterobasidion annosum (HetPV13-an1) is the main causal agent of severe phenotypic debilitation in the host fungus. Based on RNA sequencing using isogenic virus-infected and cured fungal strains, HetPV13-an1 affected the transcription of 683 genes, of which 60% were downregulated and 40% upregulated. Alterations observed in carbohydrate and amino acid metabolism suggest that the virus causes a state of starvation, which is compensated for by alternative synthesis routes. We used dual cultures to transmit HetPV13-an1 into new strains of H. annosum and Heterobasidion parviporum The three strains of H. parviporum that acquired the virus showed noticeable growth reduction on rich culturing medium, while only two of six H. annosum isolates tested showed significant debilitation. Based on reverse transcription-quantitative PCR (RT-qPCR) analysis, the response toward HetPV13-an1 infection was somewhat different in H. annosum and H. parviporum We assessed the effects of HetPV13-an1 on the wood colonization efficacy of H. parviporum in a field experiment where 46 Norway spruce trees were inoculated with isogenic strains with or without the virus. The virus-infected H. parviporum strain showed considerably less growth within living trees than the isolate without HetPV13-an1, indicating that the virus also causes growth debilitation in natural substrates.IMPORTANCE A biocontrol method restricting the spread of Heterobasidion species would be highly beneficial to forestry, as these fungi are difficult to eradicate from diseased forest stands and cause approximate annual losses of €800 million in Europe. We used virus curing and reintroduction experiments and RNA sequencing to show that the alphapartitivirus HetPV13-an1 affects many basic cellular functions of the white rot wood decay fungus Heterobasidion annosum, which results in aberrant hyphal morphology and a low growth rate. Dual fungal cultures were used to introduce HetPV13-an1 into a new host species, Heterobasidion parviporum, and field experiments confirmed the capability of the virus to reduce the growth of H. parviporum in living spruce wood. Taken together, our results suggest that HetPV13-an1 shows potential for the development of a future biocontrol agent against Heterobasidion fungi.
The present study shows that differences in pathogenicity exist among fish nodavirus strains. In challenge trials, a Japanese strain (SJ93Nag) was highly virulent to larvae of the striped jack Pseudocaranx dentex but replication was not detected in larvae of Atlantic halibut Hippoglossus hippoglossus at 6 degrees C. Conversely, a Norwegian nodavirus strain (AH95NorA) that was highly virulent to the Atlantic halibut larvae did not replicate in striped jack larvae at 20 degrees C. Occurrence of the disease viral encephalopathy and retinopathy (VER) and cumulative mortality were significantly different in the 2 species when challenged with the 2 nodavirus strains. The presence of nodavirus in nervous tissue was monitored by immunohistochemical methods. Our results support the view that the genetic diversity among nodavirus strains reflects the existence of different viral phenotypes which may be adapted to infect different host species and/or for replicating at different temperatures. Fish nodaviruses represent surveyable pathogens well suited for studying the relation between viral genotypic and phenotypic properties such as host specificity, temperature optima, neuroinvasiveness and neurovirulence.