Effect of putative mitoviruses on growth of Gremmeniella abietina isolates in vitro and on its pathogenicity on Pinus halepensis seedlings

Abstract

Los mitovirus son virus fúngicos que han sido aislados de algunos patógenos forestales que pueden reducir la virulencia del hongo. Se ha llevado a cabo un estudio para evaluar el efecto de la temperatura, el pH y el potencial osmótico en el crecimiento micelial de aislados de G. abietina en laboratorio y para observar el efecto de la presencia de mitovirus en la patogenicidad de G. abietina en plántulas de Pinus halepensis. Los resultados del experimento in vitro mostraron que los aislados infectados con mitovirus presentaron mayor crecimiento micelial que los que no infectados en la temperatura de crecimiento óptimo de 15 ºC. No se observaron efectos en los tratamientos de modificación del pH. Se observaron variaciones en el comportamiento de los aislados infectados por mitovirus en comparación con los no infectados cuando se modificaron los potenciales osmóticos. En el experimento efectuado en el invernadero las necrosis encontradas en plántulas con aislados infectados por mitovirus fueron mayores que las que presentaron las plántulas inoculadas con aislados sin mitovirus.

Mitoviruses have been found in several forest pathogens (e.g. Cryphonectria parasitica, Gremmeniella abietina), and because they have been shown to reduce the virulence of host fungi there is a growing interest in studying their use as a biocontrol. This study was carried out to test the effect of temperature (5 ºC, 15 ºC, 25 ºC and 35 ºC), pH (4, 5, 7 and 9) and osmotic potential (-0.6, -1.2, -1.8 and -2.4 MPa) on the mycelial growth of seven G. abietina isolates under controlled laboratory conditions and to observe the effect of the presence of mitoviruses in the pathogenity of G. abietina isolates inoculated to Pinus halepensis seedlings. Four of the isolates hosted mitoviruses and three of them did not. During the in vitro experiment, mycelial growth was recorded every week for a period of 8 weeks. In the greenhouse experiment, once the seedlings started to show symptoms, disease severity was recorded during 5 weeks. At the end of the experiment, plants were carried to laboratory and necrosis length was measured in all of them. Results from in vitro experiment showed that the mitovirus-infected isolates presented larger mycelial growth than the mitovirus-free ones when at the fungi’s optimal growing temperature of 15 ºC. However, no differences in growth behavior were observed between mitovirus infected and non-infected isolates when placed under different pH modifications. When growing at certain osmotic potentials (-0.6 and -1.8 MPa) a reduction in growth of the mitovirus-infected isolates was observed. In the greenhouse experiment, larger necrosis lengths were observed in the plants inoculated with mitovirus infected isolates. The results of this experiment provide further insight into the effects of mitovirus on Gremmeniella abietina isolates.