Background Trichoderma spp. are used extensively in agriculture as biological control agents to prevent soil-borne plant diseases. In recent years, mycoviruses from fungi have attracted increasing attention due to their effects on their hosts, but Trichoderma mycoviruses have not been the subject of extensive study. We sought to discover novel mycoviruses from Trichoderma spp. and to determine the effects of the biocontrol function of Trichoderma spp. Methods Mycoviruses were screened by dsRNA extraction and metagenomic analysis. RT-PCR, 5′ RACE, and 3′ RACE were used to obtain the genome sequence. MEGA software was used to classify the new mycovirus. The effects of the identified mycovirus on the biological properties of the host strain 525 were evaluated using cucumber plants and Fusarium oxysporum f. sp. cucumerinum. Results A novel mycovirus, Trichoderma harzianum mycovirus 1 (ThMV1) (accession number MH155602), was discovered in Trichoderma harzianum strain 525, a soil-borne fungus collected from Inner Mongolia, China. The mycovirus exhibited a double-stranded RNA (dsRNA) genome with a complete genome sequence of 3160 base pairs and two open reading frames (ORFs) on the negative strand. Phylogenetic analysis indicated that it belongs to an unclassified family of dsRNA mycoviruses. The removal of ThMV1 from the host 525 strain reduced host biomass production and improved the biocontrol capability of the host for Fusarium oxysporum f. sp. cucumerinum. At same time, the presence of ThMV1 improved the growth of cucumber. Conclusion ThMV1 is a new unclassified mycovirus found in T. harzianum. It not only affects the phenotype of the host strain but also reduces its biocontrol function, which sheds light on the interaction between the mycovirus and Trichoderma spp.

A new mycovirus was identified in Trichoderma harzianum strain 137 isolated in Xinjiang province, China. The whole genome sequence of the mycovirus was determined by metagenomic sequencing, RT-PCR, and RACE cloning. The mycovirus contained two genomic segments. The first segment was 2088 bp long and contained a single ORF (ORF1) encoding the RNA-dependent RNA polymerase (RdRP) (72.26 kDa). The second segment was 1634 bp long and also contained a single ORF (ORF2) encoding a hypothetical protein of 37.472 kDa. We named this novel mycovirus “Trichoderma harzianum bipartite mycovirus 1” (ThBMV1). Phylogenetic analysis showed that ThBMV1 clusters with other unclassified dsRNA mycoviruses.Electronic supplementary materialThe online version of this article (10.1007/s00705-019-04145-9) contains supplementary material, which is available to authorized users.

Trichoderma spp. are widely used as bio-fungicides in agriculture. Induction of plant defense and mycoparasitism (killing of one fungus by another) are considered to be the most important mechanisms of Trichoderma-mediated biological control. In the present study, Mycoparasitism for the three tested pathogens. Moreover, one hundred eighty five (185) isolates were also showed inhibitory but their antagonistic potential <50% of the mycelial growth while 50 isolates showed <40% mycelial growth of F. oxysporum, 61 isolates showed <50% mycelial growth for R. solani and 3 isolates showed <50% mycelial growth for B. cinerea. These potential isolates of Trichoderma may be further exploited as a biocontrol agent against F. oxysporum, R. solani and B. cinerea as well as other soilborne phytopathogenic fungi.