Mycoviruses in Biological Control: From Basic Research to Field Implementation

Abstract

Mycoviruses from plant pathogens can induce hypovirulence (reduced virulence) in their host fungi and have gained considerable attention as potential biocontrol tools. An increasing number of mycoviruses that induce fungal hypovirulence, from a wide variety of taxonomic groups, are currently being reported. Successful application of these viruses in disease management is greatly dependent on their ability to spread in the natural populations of the pathogen. Mycoviruses generally lack extracellular routes of transmission. Hyphal anastomosis is the main route of horizontal mycovirus transmission to other isolates, and conidia of vertical transmission to the progeny. Transmission efficiencies are influenced by both the fungal host and the infecting virus. Interestingly, artificial transfection methods have shown that potential biocontrol mycoviruses often have the ability to infect a variety of fungi. This expands their possible use to the control of pathogens others than those where they were identified. Mycovirus research is also focused on gaining insights into their complex molecular biology and the molecular bases of fungus−virus interactions. This knowledge could be exploited to manipulate the mycovirus and/or the host and generate combinations with enhanced properties in biological control. Finally, when exploring the use of mycoviruses in field conditions, the pathogen life style and the characteristics of the disease and crops affected will deeply impact the specific challenges to overcome, and the development of biocontrol formulations and delivery methods.

Morphological, Pathogenic and Toxigenic Variability in the Rice Sheath Rot Pathogen Sarocladium Oryzae

“…Since we only observe sectorisation and hypovirulence in the isolates of two groups (Groups 1 and 2), vegetative incompatibility with Group 3 could possibly explain the high virulence and stability of the Group 3 isolates [31,32]. The difference in toxin production between the in vitro conditions and the rice sheath could also indicate that the isolates of Groups 1 and 2 are indeed infected with a mycovirus [39]. Brusini and Robin (2013) [40] observed that the transmission rate of mycoviruses is higher in the host plant of the pathogenic fungus, leading to more symptoms of the viral infection in planta than in vitro.…”

“…The spread of these mycoviruses occurs mainly through hyphal anastomosis. This process of horizontal gene transmission occurs between vegetative compatible isolates [24,36,39]. Since we only observe sectorisation and hypovirulence in the isolates of two groups (Groups 1 and 2), vegetative incompatibility with Group 3 could possibly explain the high virulence and stability of the Group 3 isolates [31,32].…”

The PoV mycovirus affects extracellular enzyme expression and fruiting body yield in the oyster mushroom, Pleurotus ostreatus

“…Even when the virus is successfully cured from a virus-infected fungal cell, impairments caused by the treatment make the cured fungal cell inappropriate for investigations of fungal-mycoviral interactions. In the method for securing an artificial virus-infected strain, infectious cDNA clones of a fungal virus for artificial infection were transformed into the virus-cured fungal strain upon integration of the infectious clones into the fungal genome based on Koch's postulates 15 . However, this method is also challenging because of the difficulty in the case of multi-segmented mycovirus 15 and the alteration of gene expression with non-homologous chromosomal integration, such as ectopic recombination 16 .…”

“…In the method for securing an artificial virus-infected strain, infectious cDNA clones of a fungal virus for artificial infection were transformed into the virus-cured fungal strain upon integration of the infectious clones into the fungal genome based on Koch's postulates 15 . However, this method is also challenging because of the difficulty in the case of multi-segmented mycovirus 15 and the alteration of gene expression with non-homologous chromosomal integration, such as ectopic recombination 16 . Therefore, in our previous investigation of PoV in P. ostreatus, virus-curing was performed by the mycelial fragmentation method followed by single colony isolation 17 .…”

“…Therefore, in our previous investigation of PoV in P. ostreatus, virus-curing was performed by the mycelial fragmentation method followed by single colony isolation 17 . A virus-cured strain (free version) of a naturally infected isolate can be obtained by a technique based on selecting progeny or fungal hyphae without the virus 15 . Virus-cured isogenic lines, which have identical genetic backgrounds, can then be established to explore direct mycovirus-fungal host interctions.…”