Abstract
The cosmopolitan fungus Rhizoctonia solani has a wide host range and is the causal agent of numerous crop diseases, leading to significant economic losses. To date, no cultivars showing complete resistance to R. solani have been identified and it is imperative to develop a strategy to control the spread of the disease. Fungal viruses, or mycoviruses, are widespread in all major groups of fungi and next-generation sequencing (NGS) is currently the most efficient approach for their identification. An increasing number of novel mycoviruses are being reported, including double-stranded (ds) RNA, circular single-stranded (ss) DNA, negative sense (−)ssRNA, and positive sense (+)ssRNA viruses. The majority of mycovirus infections are cryptic with no obvious symptoms on the hosts; however, some mycoviruses may alter fungal host pathogenicity resulting in hypervirulence or hypovirulence and are therefore potential biological control agents that could be used to combat fungal diseases. R. solani harbors a range of dsRNA and ssRNA viruses, either belonging to established families, such as Endornaviridae, Tymoviridae, Partitiviridae, and Narnaviridae, or unclassified, and some of them have been associated with hypervirulence or hypovirulence. Here we discuss in depth the molecular features of known viruses infecting R. solani and their potential as biological control agents.
Highlights
The genus Rhizoctonia was initially described by French mycologist Augustin Pyramus de Candolle in 1815 [1] and belongs to the order Cantharellales, phylum Basidiomycota
Mycovirus infections are often cryptic but investigations focus on potential hypovirulence, a phenomenon that may be exploited in the context of sustainable biological control of fungal diseases
A range of RNA viruses infecting R. solani was described including members of the families Barnaviridae, Benyviridae, Botourmiaviridae, Bromoviridae, Deltaflexiviridae, Endornaviridae, Hypoviridae, Megabirnaviridae, Narnaviridae, Partitiviridae, Togaviridae, and Tymoviridae, together with unclassified mycoviruses related to the orders Serpentovirales and Bunyavirales
Summary
The genus Rhizoctonia was initially described by French mycologist Augustin Pyramus de Candolle in 1815 [1] and belongs to the order Cantharellales, phylum Basidiomycota. The fungus proliferates on the root and produces specialised T-shaped structures named “infection pads” These infection pads produce enzymes capable of digesting the plant cell wall so that the fungus penetrates and colonizes the intercellular and intracellular spaces of the root tissue. As it develops, the fungus diverts the cellular reserves of the plant for its own growth. Attempts to control R. solani by agronomic approaches, such as breeding strategies, crop rotation or chemical fungicides, proved ineffective due to the wide host range, soil-borne nature and the saprotrophitic nature of the fungus. Cryphonectria parasitica usedblight to control chestnut blight in Europe [12]
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