The Enigma of Double-stranded RNA (dsRNA) Associated with Mushroom Virus X (MVX)

New variants of pathogenic fungal viruses are emerging and they are enigmatic in revealing their molecular identity and of their origin. Double-stranded RNAs, some in non-encapsidated forms are increasingly becoming causal agents for sporadic diseases and are consistently associated with a complex profile of dsRNAs, presumably of (multiple) viral origin present in the host while the same are conspicuously absent in healthy (looking) counterparts. The emergence of an unusual Agaricus bisporus mushroom ‘patch disease ’ first reported in 1996, later termed as ‘mushroom virus X ’ (MVX), exhibited a wide range of symptoms (e.g. barren patches beside healthy looking mushrooms, arrested pins, premature opening, brown, off-colour and distortions in shape). A variable compendium of novel 26 (dsRNA) elements, ranging in sizes between 20.2 kb to 0.64 kb, several of them (~17/26) in non-encapsidated form have been shown to occur in the diseased mushroom fruiting bodies and are thought to comprise multiple viruses. Ten years on, this devastating disease is now more widespread and prevalent in a number of European countries (e.g