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. 2024 Feb 25;16(3):355.
doi: 10.3390/v16030355.

Identification of Mycoviruses in the Pathogens of Fragrant Pear Valsa Canker from Xinjiang in China

Chenguang Zhang  1 , Xiaoya Zheng  1 , Zhanjiang Tie  1 , Hui Xi  1 , Mai Shi  1 , Yanjun Ma  1 , Wenbin Chen  1 , Yingjie Mi  1 , Rui Yang  2 , Sifeng Zhao  1 , Xuekun Zhang  1
Affiliations

Identification of Mycoviruses in the Pathogens of Fragrant Pear Valsa Canker from Xinjiang in China

Chenguang Zhang et al. Viruses. .

Abstract

As a common disease, canker seriously affects the yield and quality of fragrant pear due to the lack of effective control measures. Some fungi have been reported to harbor rich reservoirs of viral resources, and some mycoviruses can be used as biocontrol agents against plant diseases. In this study, 199 isolates were obtained from diseased branches of fragrant pear in the main production areas of Xinjiang. Among them, 134 belonged to Valsa spp., identified using morphological and molecular biological techniques, in which V. mali was the dominant species. The mycoviruses in Valsa spp. were further identified using metatranscriptomic sequencing and RT-PCR. The results revealed that a total of seven mycoviruses were identified, belonging to Botourmiaviridae, Endornaviridae, Fusariviridae, Hypoviridae, Mitoviridae, and Narnaviridae, among which Phomopsis longicolla hypovirus (PlHV) was dominant in all the sample collection regions. The Cryphonectria hypovirus 3-XJ1 (CHV3-XJ1), Botourmiaviridae sp.-XJ1 (BVsp-XJ1), and Fusariviridae sp.-XJ1 (Fvsp-XJ1) were new mycoviruses discovered within the Valsa spp. More importantly, compared with those in the virus-free Valsa spp. strain, the growth rate and virulence of the VN-5 strain co-infected with PlHV and CHV3-XJ1 were reduced by 59% and 75%, respectively, and the growth rate and virulence of the VN-34 strain infected with PlHV were reduced by 42% and 55%, respectively. On the other hand, the horizontal transmission efficiency of PlHV decreased when PlHV was co-infected with CHV3-XJ1, indicating that PlHV and CHV3-XJ1 were antagonistic. In summary, the mycoviruses in Valsa spp. were identified in Xinjiang for the first time, and three of them were newly discovered mycoviruses, with two strains yielding good results. These results will offer potential biocontrol resources for managing pear canker disease and provide a theoretical basis for the control of fruit tree Valsa canker disease.

Keywords: Valsa spp.; biocontrol; fragrant pear canker disease; metatranscriptomics; mycovirus.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
Information on the collection of canker disease samples and identification of pathogens: (A) the sample collection site; (B) the regional distribution of the isolated strains; (C) the number of Valsa spp. identified in different regions; (D) the morphological characteristics of V. mali strains. (a) Colony characteristics of V. mali on PDA media (bars = 2 cm); (b) the conidiospore of V. mali (bars = 20 μm); (c) the longitudinal section of conidiophore (bars = 100 μm); (d) the cross-section of conidiophore (bars = 100 μm); (E) the morphology of V. malico strains. (e) The colony characteristics of V. malico on PDA medium (bars = 2 cm); (f) the conidiospore of V. malico (bars = 20 μm); (g) the longitudinal section of conidiophore (bars = 100 μm); (h) the cross-section of conidiophore (bars = 200 μm); (F) the morphology of L. niveum strains. (i) the colony characteristics of L. niveum on PDA medium (bars = 2 cm; (j) the conidiospore of L. niveum (bars = 20 μm); (k) the longitudinal section of conidiophore (bars = 100 μm); (l) the cross-section of conidiophore (bars = 200 μm).
Figure 2
Figure 2
Detection of the seven mycoviruses and their effect on the growth of Valsa spp. (A) Colony morphology of Valsa spp. strains grown on PDA plates for 5 d (bars = 2 cm); (B) the detection of mycovirus contigs in different Valsa spp. strains. The internal reference gene β-Tubulin from Valsa spp. was used as the positive control, and ddH2O was used as the negative control. (C) Frequency of mycoviruses identified in different regions; (D) the growth rates of Valsa spp. strains harboring mycoviruses. The data are presented as means ± SD (n = 4). The different letters indicate a significant difference at p < 0.01 (determined via one-way ANOVA).
Figure 3
Figure 3
The phylogenetic tree of the mycoviruses in Valsa spp. based on RdRp amino acid sequences. A maximum-likelihood tree was constructed using MEGA 11.0 with 1000 bootstrap replicates. Bootstrap values (%) obtained with 1000 replicates are indicated on the branches, and the branch lengths correspond to genetic distance. The scale bar on the lower left corresponds to genetic distance. The resulting phylogenetic tree was exported using iTOL and Adobe Illustrator 2021 software. The viruses identified in this study are shown in red.
Figure 4
Figure 4
Pathogenicity assay of VN-5 and VN-34 on the living branches and detached branches. (A) The lesions of the VN-5, VN-34, and VN-FV strains on the stems of 2-year-old fragrant pear seedlings at 15 d, The arrow indicates the magnified view of the afflicted site. (bars = 10 cm and 2 cm in the pot and stem, respectively); (B) the lesions of the VN-5, VN-34, and VN-FV strains on the detached fragrant pear branches at 15 d (bars = 2 cm); (C) the lengths of lesions caused by VN-5, VN-34, and VN-FV strains on living trunk and detached branches of fragrant pear were assessed at 15 d. CK was inoculated with noncolonized PDA plugs. The data are presented as means ± SD (n = 4). The different letters indicate a significant difference at p < 0.01 (determined via one-way ANOVA).
Figure 5
Figure 5
Horizontal transmission of PlHV and CHV3-XJ1 and their effect on the pathogenicity of the host: (A) colony morphology of the VN-10-V strain that acquired PlHV from VN-34 (bars = 2 cm); (B) colony morphology of the VS-9 strain that acquired PlHV and CHV3-XJ1 from VN-5 (bars = 2 cm); (C) the lesions of the VN-34, VN-10, and VN-10-V strains on the detached fragrant pear branches at 15 d (bars = 2 cm); (D) the lesions of the VN-5, VS-9, and VS-9-V strains on the detached fragrant pear branches at 15 d (bars = 2 cm); (E) the lesion diameters of the VN-34, VN-10, and VN-10-V strains on the detached fragrant pear branches at 15 d.; (F) the lesion diameters of the VN-5, VS-9, and VS-9-V strains on the detached fragrant pear branches at 15 d. CK was inoculated with noncolonized PDA plugs. The data are presented as means ± SD (n = 4). The different letters indicate a significant difference at p < 0.01 (determined via one-way ANOVA).
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