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ABSTRACT In fungi, viral infections frequently remain cryptic causing little or no phenotypic changes. It can indicate either a long history of coevolution or a strong immune system of the host. Some fungi are outstandingly ubiquitous and can be recovered from a great diversity of habitats. However, the role of viral infection in the emergence of environmental opportunistic species is not known. The genus of filamentous and mycoparasitic fungi Trichoderma (Hypocreales, Ascomycota) consists of more than 400 species, which mainly occur on dead wood, other fungi, or as endo- and epiphytes. However, some species are environmental opportunists because they are cosmopolitan, can establish in a diversity of habitats, and can also become pests on mushroom farms and infect immunocompromised humans. In this study, we investigated the library of 163 Trichoderma strains isolated from grassland soils in Inner Mongolia, China, and found only four strains with signs of the mycoviral nucleic acids, including a strain of T. barbatum infected with a novel strain of the Polymycoviridae and named and characterized here as Trichoderma barbatum polymycovirus 1 (TbPMV1). Phylogenetic analysis suggested that TbPMV1 was evolutionarily distinct from the Polymycoviridae isolated either from Eurotialean fungi or from the order Magnaportales. Although the Polymycoviridae viruses were also known from Hypocrealean Beauveria bassiana, the phylogeny of TbPMV1 did not reflect the phylogeny of the host. Our analysis lays the groundwork for further in-depth characterization of TbPMV1 and the role of mycoviruses in the emergence of environmental opportunism in Trichoderma. IMPORTANCE Although viruses infect all organisms, our knowledge of some groups of eukaryotes remains limited. For instance, the diversity of viruses infecting fungi—mycoviruses—is largely unknown. However, the knowledge of viruses associated with industrially relevant and plant-beneficial fungi, such as Trichoderma spp. (Hypocreales, Ascomycota), may shed light on the stability of their phenotypes and the expression of beneficial traits. In this study, we screened the library of soilborne Trichoderma strains because these isolates may be developed into bioeffectors for plant protection and sustainable agriculture. Notably, the diversity of endophytic viruses in soil Trichoderma was outstandingly low. Only 2% of 163 strains contained traces of dsRNA viruses, including the new Trichoderma barbatum polymycovirus 1 (TbPMV1) characterized in this study. TbPMV1 is the first mycovirus found in Trichoderma. Our results indicate that the limited data prevent the in-depth study of the evolutionary relationship between soilborne fungi and is worth further investigation.

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.

A new partititvirus isolated from a Trichoderma harzianum strain (T673), collected in China, was characterized and annotated as Trichoderma harzianum partitivirus 2 (ThPV2). The genome of ThPV2 consists of a 1693 bp dsRNA1 encoding a putative RNA-dependent RNA polymerase (RdRp) and a 1458 bp dsRNA2 encoding a hypothetical protein. In comparative studies employing the ThPV2-infected strain (T673) and a strain cured by ribavirin treatment (virus-free strain T673-F), we investigated biological effects of ThPV2 infection. While the growth rate of the virus-infected fungus differed little from that of the cured variant, higher mycelial density, conidiospore, and chlamydospore production were observed in the virus-infected strain T673. Furthermore, both the ThPV2-infected and the cured strain showed growth- and development-promoting activities in cucumber plants. In vitro confrontation tests showed that strains T673 and T673-F inhibited several important fungal pathogens and an oomycete pathogen in a comparable manner. Interestingly, in experiments with cucumber seeds inoculated with Fusarium oxysporum f. sp. cucumerinum, the ThPV2-infected strain T673 showed moderately but statistically significantly improved biocontrol activity when compared with strain T673-F. Our data broaden the spectrum of known mycoviruses and provide relevant information for the development of mycoviruses for agronomic applications.

This paper aims to evaluate the crowd evacuation performance in a metro fire by using the limit state equation to describe the egress process. The limit state equation is established by the available time margin in fire evacuation, which comprises the evacuee's response time, behaviour time and movement time to an exit. Here, the available time margin in a fire evacuation is determined by the duration of time the smoke takes to exceed the evacuee's respiration level, the time that the smoke is detected by fire alarm and the time that the evacuee needs to respond and move to an exit during evacuation. Further, Monte Carlo simulation approach has been employed to integrate the fatality rates and the probabilities of occurrence of different scenarios in a typical metro in Xiaobailou station of station-Tianjin Line 1. Through this case study, it is shown that the evacuee's response time, behaviour time and movement time to exits can be integrated in a stochastic process model. [ABSTRACT FROM AUTHOR]