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Extending Chestnut Blight Hypovirus Host Range Within Diaporthales by Biolistic Delivery of Viral cDNA

¹Department of Apple Research, National Institute of Fruit Tree Science, National Agricultural Research Organization (NARO), Independent Administrative Institution, 92 Nabeyashiki, Shimokuriyagawa, Morioka, Iwate 020-0123, Japan; ²Asian Center for Bioresources and Environmental Sciences, 3-1-1, University of Tokyo, 1-1-1 Yayoi, Bunkyou-ku, Tokyo 113-8657, Japan; ³Research Institute for Bioresources, Okayama University, 2-20-1 Chu-ou, Kurashiki, Okayama 710-0046, Japan; ⁴Center for Agricultural Biotechnology, University of Maryland Biotechnology Institute, (5115 Plant Sciences Building), College Park, Maryland 20742-4450, U.S.A.

Biolistic bombardment was used to successfully transform three phytopathogenic fungal species with an infectious cDNA clone of the prototypic hypovirus, CHV1-EP713, a genetic element responsible for the virulence attenuation (hypovirulence) of the chestnut blight fungus, Cryphonectria parasitica. The fungal species included two strains each of C. parasitica and Valsa ceratosperma, as well as one strain of Phomopsis G-type (teleomorph Diaporthe Nitschke); all are members of the order Diaporthales but classified into three different genera. A subset of transformants for each of the fungal species contained CHV1-EP713 dsRNA derived from chromosomally integrated viral cDNA. As has been reported for CHV1-EP713 infection of the natural host C. parasitica, biolistic introduction of CHV1-EP713 into the new fungal hosts V. ceratosperma and Phomopsis G-type resulted in altered colony morphology and, more importantly, reduced virulence. These results suggest a potential for hypoviruses as biological control agents in plant-infecting fungal pathogens other than the chestnut blight fungus and closely related species. In addition, the particle delivery technique offers a convenient means of transmitting hypoviruses to potential host fungi that provides new avenues for fundamental mycovirus research and may have practical applications for conferring hypovirulence directly on infected plants in the field.