A novel double-stranded RNA mycovirus isolated from Trichoderma harzianum.

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.

Complete nucleotide sequence of a novel mycovirus from Trichoderma harzianum in China.

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.

Population genetics and phylogeography of alfalfa mosaic virus in China and a comparison with other regional epidemics based on the cp gene.

Alfalfa mosaic virus (AMV) is the most pervasive epidemic virus affecting alfalfa production. However, detailed investigations on the molecular population genetics and evolutionary dynamics of AMV are scarce. This study aimed to report on a large-scale long-term survey of genetic variability in AMV populations from China and perform a comparative analysis of AMV population genetics in the three most thoroughly studied countries to date: China, Iran, and Spain. The study was based on the analysis of the coat protein gene (cp) using two analytical approaches: an analysis of molecular variance (AMOVA) and a Bayesian Markov Chain Monte Carlo approach that investigates the association between geographical origin and phylogeny. Both analytical approaches found significant genetic differentiation within localities, but not among localities nor among provinces. This observation might result from inappropriate agronomical practices involving extensive exchange of plant materials followed by rapid viral diversification within localities. In the Chinese population, both methods found that genetic diversification in AMV was strongly associated with different bioclimatic zones. Rates of molecular evolution were similar in the three countries. The estimated epidemic exponential population size and growth rate suggest that the epidemics grew faster and with higher incidence in Iran, followed by Spain and China. Estimates of the time to the most recent common ancestors suggest that AMV was first seen in Spain by the beginning of the twentieth century and later on in eastern and central Eurasia. After ruling out the existence of recombination breakpoints within the cp gene, a codon-based selection analysis per population was performed and identified many codons under significant negative selection and a few under significant positive selection; the latter varied among countries, suggesting regional differences in selective pressures.