Abstract
Rhizoctonia solani represents an important plant pathogenic Basidiomycota species complex and the host of many different mycoviruses, as indicated by frequent detection of dsRNA elements in natural populations of the fungus. To date, eight different mycoviruses have been characterized in Rhizoctonia and some of them have been reported to modulate its virulence. DsRNA extracts of the avirulent R. solani isolate DC17 (AG2-2-IV) displayed a diverse pattern, indicating multiple infections with mycoviruses. Deep sequencing analysis of the dsRNA extract, converted to cDNA, revealed that this isolate harbors at least 17 different mycovirus species. Based on the alignment of the conserved RNA-dependent RNA-polymerase (RdRp) domain, this viral community included putative members of the families Narnaviridae, Endornaviridae, Partitiviridae and Megabirnaviridae as well as of the order Tymovirales. Furthermore, viruses, which could not be assigned to any existing family or order, but showed similarities to so far unassigned species like Sclerotinia sclerotiorum RNA virus L, Rhizoctonia solani dsRNA virus 1, Aspergillus foetidus slow virus 2 or Rhizoctonia fumigata virus 1, were identified. This is the first report of a fungal isolate infected by 17 different viral species and a valuable study case to explore the diversity of mycoviruses infecting R. solani.
Highlights
Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk] represents an important species complex of known plant pathogens, which infect a wide variety of plant species including many economically important crops [1]
The dsRNA extract of the R. solani isolate DC17 showed a diverse pattern of dsRNA fragments after gel electrophoresis indicating the presence of multiple mycoviruses
The identified RNA-dependent RNApolymerase (RdRp) belong to four different protein families (Pfam) corresponding to either the alphavirus-like superfamily, the picornavirus-like super family or the Narnaviridae
Summary
Rhizoctonia solani Kühn [teleomorph: Thanatephorus cucumeris (Frank) Donk] represents an important species complex of known plant pathogens, which infect a wide variety of plant species including many economically important crops [1]. Due to its soil-borne nature, facultative saprophytism and the wide host-range, this pathogen is difficult to control by conventional agronomic measures like fungicides, crop rotation or plant resistance [2]. To understand the epidemiology of diseases caused by Rhizoctonia, especially regarding the disease suppression observed in association with monoculture of host plants, the interaction of the fungus with its environment and, in particular, the microflora has been studied by many researchers [4]. It is well established that Rhizoctonia is significantly affected by suppressive organisms, but the nature of this biocontrol is still a matter of debate [4]. The finding that hypovirulent isolates of Rhizoctonia can be successfully used for biocontrol purposes, raised interest in the possible involvement of mycoviruses [5, 6]
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