Genetic individuals can be distinguished based on vegetative incompatibility in some fungi and are referred to as “genet”. They compete for resources with each other, and competition may result in disease suppression or decline, leaving a few fit genets. Double-stranded (ds) RNA of hypovirus origin, which infects healthy isolates through cytoplasmic contact and attenuates virulence, could promote decline where the population of pathogen is composed of a very few predominant genets. Previous studies on chestnut blight demonstrated that the spread of dsRNA was negatively correlated with the diversity in vegetative incompatibility in the population of the pathogen, Cryphonectria parasitica. I considered that finding applies to some diseases which remain difficult to control chemically, culturally, and, of course, biologically. Helocobasidium mompa and Rosellinia necatrix, the root rot pathogens of perennial crops, may be biocontrolled by dsRNA due to their simple population structure, their mode of epidemiology, and the high value of their individual host plants. Collaborative studies by concerned scientists are necessary to identify such viruses and to develop effective inoculation methods of indigenous genets with hypoviruses.