Effect of temperature on GaRV6 accumulation and its fungal host, the conifer pathogen Gremmeniella abietina

Gremmeniella abietina RNA virus 6 (GaRV6) was studied within the European race of G. abietina. We examined 97 isolates originating from Canada, Czech Republic, Finland, Italy, Montenegro, Serbia, Spain, Switzerland, Turkey and the United States. According to direct specific quantitative reverse transcription PCR (qRT-PCR) screening based on the RNA-dependent RNA polymerase (RdRp) sequence, the virus was mostly present in Spain, but it was also found at a very low concentration in three isolates from Canada, Italy and Finland. To gain insight into the three-way interaction among temperature, GaRV6 and G. abietina, we performed an in vitro experiment with eight Spanish isolates (four infected and four uninfected) with four repetitions each. We assessed the virus expression (accumulation) based on the quantity of RdRp-encoding RNA by qRT-PCR and the G. abietina growth rate at 5, 15 and 20°C. The presence of the virus had a significant negative effect on the G. abietina growth rate, which was also significantly influenced by the temperature. However, the temperature appeared not to clearly determine the virus accumulation, and the virus accumulation did not have any influence on the growth rate of the infected G. abietina isolates. Taken together, these results suggest that the role of this virus as a relevant factor with respect to the more thermophilic nature of the Spanish population of G. abietina may be ruled out.