Studies On The Diversity Of Mycoviruses In Phomopsis Vexans And Their Preliminary Biological Characteristics

Phomopsis blight of eggplant is a major disease limiting eggplant production.First report of Phomopsis blight of eggplant on Solanum melongena caused by Phomopsis vexans in Nanjing in 1932.The disease has been reported in most parts of the world.Mycoviruses are widely distributed in fungi.Some mycoviruses cause variable effects on the phenotype of their fungal hosts,such as debilitation or changes in virulence.Therefore,they are considered potential biological control agents for fungal crop diseases.Discovery of mycoviruses will provide new materials and strategies for biological control of plant fungal diseases of study of virus taxonomic evolution and virus-host interactions.The aim of this work was to identify mycoviral infections in Phomopsis vexans,isolated from eggplant groen in China,and to estimate their potential effects on the pathogenicity of the host fungus,and molecular characterization of novel mycoviruses.The main results are as follows:(1)162 samples of infested leaves and fruits were collected from Hunan,Hubei,Jiangxi,Sichuan,Zhejiang,Fujian,Guangdong and Anhui Provinces in 2017 to 2019.87 strains were obtained from the 162 isolates,belong Phomopsis vexans.The survey of mycoviruses in Phomopsis vexans from eggplant produced in China showed hight incidence of virus infection in this fungal species,mainly for mixed infections,no discover virus-free strain.Genome organization of virus varies from 1-15 kb.(2)cDNA libraries were constructed using random hexanucleotide primers and reverse transcriptase.The gaps were filled by RT-PCR amplification using sequence-specific primers,and the terminal sequences were obtained by ligase-mediated terminal amplification.Five novel mycoviruses infecting the plant-pathogenic fungus Phomopsis vexans,including“Phomopsis vexans fusarivirus 1”(PvFV1),“Phomopsis vexans ourmia-like virus 1”(PvOLV1),“Phomopsis vexans endornavirus 2”(PvEV2),“Phomopsis vexans partitivirus 1”(PvPV1)and “Phomopsis vexans victorivirus L1”(PvVVL1).Thus,PvVVL1 has a unique genome structure and is the first reported isolate with a bi-segmented genome among mycoviruses from the victorivirus genus.PvPV1 has the first report of a Deltapartitivirus infect the fungus host.(3)By comparing the ability of pycnidia formation,pathogenicity and stress-inducing mediums phenotypic growth,it was found that mycoviruses effected the pathogenicity of host fungi on S.melongena fruits,and when PvVVL1 and PvPV1 were present alone in the host,the host pathogenicity,number of pycnidia formation and individual size were reduced,while fungal viruses disrupted the mycelial surface tension and reduced the host stress capacity under abiotic stress Stress capacity of the host under abiotic stress was reduced.This study enhances the perception of viral diversity in Phomopsis vexans and the mechanism of pycnidia formation,also provide theoretical basis for biological control of diseases.