Exploring hypovirulence-associated DNA mycovirus to be a natural fungicide

Mycoviruses are widespread in various groups of fungi. Some mycoviruses may confer hypovirulence to their hosts, and could have potential to be used as biological control agents. Cryphonectria hypovirus 1 which was successfully used to control chestnut blight in Europe countries was a classic example. However, the potential of biological control with mycoviruses is extremely restricted by some limiting factors. Mycoviruses are usually vertically transmitted via conidia or via sexual spores occasionally, and horizontally transmitted via hyphal anastomosis which is controlled by non-self-recognition system; Most mycoviruses are absent of intercellular phase and without any transmission vector. Furthermore, hypovirulence-associated strains are very weak in nature since they could not infect plants. Recently, more and more mycoviruses were isolated in various crop pathogenic fungi, and researches suggested that the transmission properties among mycoviruses may not be the same, and some mycoviruses could transmit among vegetative incompatible individuals. Sclerotinia sclerotiorum is a notorious fungal crop pathogen with wide host range, it attacks rapeseed (Brassicae napus) and causes huge losses (more than 2.0 billion Yuan RMB) at the middle and lower reaches of the Yangtze River where more 85 % of rapeseed of China is planted. We isolated a DNA virus (named Sclerotinia sclerotiorum hypovirulence-associated DNA virus 1, SsHADV-1) from a hypovirulent strain DT-8. Our research showed that SsHADV-1 has strong infectivity that its purified particles could infect intact hyphae of S. sclerotiorum directly, virus could enter into vegetative incompatible strain through strain DT-8 when the two strains were dual cultured. We further found that SsHADV-1 could mutualistically interact with mycophagous insect (Lycoriella ingénue), and use it as transmission vector. Spraying hyphal fragments of Strain DT-8 on aerial parts of rapeseed plants could control stem rot of rapeseed efficiently. Our findings suggested that SsHADV-1 could be used to control Sclerotinia diseases with glorious potential.