Search

The coat protein (CP) of plant viruses generally has multiple functions involving infection, replication, movement and pathogenicity. Functions of the CP of prunus necrotic ringspot virus (PNRSV), the causal agent of several threatening diseases of Prunus fruit trees, are poorly studied. Previously, we identified a novel virus in apple, apple necrotic mosaic virus (ApNMV), which is phylogenetically related to PNRSV and probably associated with apple mosaic disease in China. Full-length cDNA clones of PNRSV and ApNMV were constructed, and both are infectious in cucumber ( Cucumis sativus L.), an experimental host. PNRSV exhibited higher systemic infection efficiency with more severe symptoms than ApNMV. Reassortment analysis of genomic RNA segments 1-3 found that RNA3 of PNRSV could enhance the long-distance movement of an ApNMV chimaera in cucumber, indicating the association of RNA3 of PNRSV with viral long-distance movement. Deletion mutagenesis of the PNRSV CP showed that the basic motif from amino acids 38 to 47 was crucial for the CP to maintain the systemic movement of PNRSV. Moreover, we found that arginine residues 41, 43 and 47 codetermine viral long-distance movement. The findings demonstrate that the CP of PNRSV is required for long-distance movement in cucumber, which expands the functions of ilarvirus CPs in systemic infection. For the first time, we identified involvement of Ilarvirus CP protein during long-distance movement.

Plum pox, or Sharka disease, caused by infection with plum pox virus (PPV), results in enormous economic losses to the stone fruit industry. However, the frequency and distribution of PPV remain unclear in China, the world's largest stone fruit producer. Systemic visual surveys were performed on stone fruit trees in China from 2008 to 2018, and the results suggest that plum pox disease is widely distributed on common apricots ( Prunus armeniaca ) and Japanese apricots ( Prunus mume ), with an average symptoms incidence rate >30% in the latter. In samples collected from Beijing, Nanjing, Shanghai, Wuhan, Wuxi, and Yuncheng, PPV was detected in 77% (85 of 110) of collected samples by immunochromatographic (IC) strip tests and reverse transcription PCR, and 96% (67 of 70) of samples showing Sharka symptoms were PPV positive. Transmission electron microscopy revealed filamentous particles of ∼640 × 12.5 nm ( n = 19) in size and pinwheel inclusions in symptomatic plants but not in the asymptomatic and PPV-negative plants. Full-length genomes were determined for four isolates (three from Japanese apricot and one from common apricot), and phylogenetic analyses indicated that all four isolates belong to a clade PPV-D, despite slight differences in genome size. These findings not only highlight the widespread occurrence and distribution of PPV in China but also provide detailed information about the genomic characteristics and evolutionary position of PPV isolates in China.

We analyzed virus and viroid communities in five individual trees of two nectarine cultivars with different disease phenotypes using next-generation sequencing technology. Different viral communities were found in different cultivars and individual trees. A total of eight viruses and one viroid in five families were identified in a single tree. To our knowledge, this is the first report showing that the most-frequently identified viral and viroid species co-infect a single individual peach tree, and is also the first report of peach virus D infecting Prunus in China. Combining analyses of genetic variation and sRNA data for co-infecting viruses/viroid in individual trees revealed for the first time that viral synergisms involving a few virus genera in the Betaflexiviridae, Closteroviridae, and Luteoviridae families play a role in determining disease symptoms. Evolutionary analysis of one of the most dominant peach pathogens, peach latent mosaic viroid (PLMVd), shows that the PLMVd sequences recovered from symptomatic and asymptomatic nectarine leaves did not all cluster together, and intra-isolate divergent sequence variants co-infected individual trees. Our study provides insight into the role that mixed viral/viroid communities infecting nectarine play in host symptom development, and will be important in further studies of epidemiological features of host-pathogen interactions.

Background: Co-infections of Apple chlorotic leaf spot virus (ACLSV) and Cherry green ring mottle virus (CGRMV) in peach is common in China and have resulted in significant yield reductions. A reliable, sensitive and quantitive method is needed to detect and distinguish between ACLSV and CGRMV in peach., Findings: We developed a sensitive and specific SYBR Green-I based RT-qPCR for the quantification of ACLSV and CGRMV in different peach tissues, and a duplex RT-qPCR system to detect ACLSV and CGRMV simultaneously. The RT-qPCR method was optimized using standard samples transcribed by the T7 Large Scale RNA Production System in vitro. The peach genes, RNA Polymerase subunit II (RPII) and Ubiquitin 10 (UBQ10), which were used as the internal controls for the quantification assay also showed good expression stability in this system. Single RT-qPCR assays showed that CGRMV in peach accumulates to a higher level than ACLSV. The detection limits of the duplex RT-qPCR assay were 10² and 10⁴ copies for ACLSV and CGRMV, respectively. The sensitivity of the duplex RT-qPCR was as high as RT-qPCR and higher than RT-PCR., Conclusions: The SYBR Green-I RT-qPCR assay provided a sensitive, specific and reliable method for the detection and quantification of ACLSV and CGRMV in different peach tissues. The duplex RT-qPCR system provided a sensitive and specific method to detect and differentiate between ACLSV and CGRMV in a single sample. This RT-qPCR assay could be a useful tool for the routine diagnosis of these two viruses and for disease epidemiology studies in peach orchards.

Two complete nucleotide sequences of cherry green ring mottle virus (CGRMV) isolated from peach in Hebei (Hs10) and Fujian (F9) Provinces, China, were determined. Five open reading frames (ORFs) were found in the genomes of both isolates. The F9 and Hs10 isolates shared 82.2 % and 83.4-94.4 % nucleotide sequence identity, respectively, with two CGRMV isolates from cherry. Analysis of the nucleotide and amino acid sequences from the five ORFs of both isolates showed that Hs10 shares the greatest sequence identity with P1A (GenBank AJ291761) from cherry. Phylogenetic analysis indicated that CGRMV isolates from peach and cherry are closely related to members of the genus Foveavirus.

The complete nucleotide sequences of two isolates of apple chlorotic leaf spot virus (Z1 and Z3) collected from peach in Henan Province, China, were determined. The genomes of both Z1 and Z3 were found to contain three open reading frames (ORFs). Sequence analysis showed that genomic sequences of Z1 and Z3 isolates shared 67.4%-82.9% and 67.2%-82.6% identity, respectively, with the other eight isolates of ACLSV that have been reported previously. Based on the putative amino acid sequences of the products of the three ORFs, Z1 and Z3 isolates showed the greatest identity to isolate PBM1 (GenBank accession number AJ243438) from plum and the least identity with isolate Ta Tao5 (GenBank Accession Number: EU223295) from peach. Considering the low level of sequence identity between Z1/Z3 isolate and Ta Tao5 isolate, two types of ACLSV may exist in peach.

Peach (Prunus persica L.) is one of the most important and oldest stone fruits grown in China. Even though P. persica is one of the most commonly grown stone fruits in China, little is known about the biodiversity of microfungi associated with peach branch diseases. In the present study, samples were collected from a wide range of peach growing areas in China, and fungal pathogens associated with peach branch diseases were isolated. In total, 85 isolates were obtained and further classified into nine genera and 10 species. Most of the isolates belonged to Botryosphaeriaceae (46), including Botryosphaeria, Diplodia, Neofusicoccum, Phaeobotryon, and Lasiodiplodia species; Ascochyta, Didymella, and Nothophoma species representing Didymellaceae were also identified. Herein, we introduce Ascochyta prunus and Lasiodiplodia pruni as novel species. In addition, we report the first records of Nothophoma pruni, Neofusicoccum occulatum, and Phaeobotryon rhois on peach worldwide, and Didymella glomerata, Nothophoma quercina, and Phaeoacremonium scolyti are the first records from China. This research is the first comprehensive investigation to explore the microfungi associated with peach branch disease in China. Future studies are necessary to understand the pathogenicity and disease epidemiology of these identified species. [ABSTRACT FROM AUTHOR]

Several members of the genus Ilarvirus infect fruit trees and are distributed worldwide. Prunus necrotic ringspot virus (PNRSV) is one of the most prevalent viruses, causing significant losses. Cucumissativus can be infected by several ilarviruses, leading to obvious symptoms, including PNRSV, which suggests that cucumbers could be good hosts for the study of the pathogenesis of ilarviruses. Real-time quantitative PCR is an optimal choice for studying gene expression because of its simplicity and its fast and high sensitivity, while its accuracy is highly dependent on the stability of the reference genes. In this study, we assessed the stability of eleven reference genes with geNorm, NormFinder, ΔCt method, BestKeeper, and the ranking software, RefFinder. The results indicated that the combined use of EF1α and F-BOX was the most accurate normalization method. In addition, the host genes AGO1, AGO4, and RDR6 were selected to test the reliability of the reference genes. This study provides useful information for gene expression analysis during PNRSV infection and will facilitate gene expression studies associated with ilarvirus infection. [ABSTRACT FROM AUTHOR]

In the present study, we utilized high throughput and Sanger sequencing to determine the complete nucleotide sequence of a putative new ilarvirus species infecting sweet cherry, tentatively named prunus virus I (PrVI). The genome of PrVI is comprised of three RNA segments of 3474 nt (RNA1), 2911 nt (RNA2), and 2231 nt (RNA3) and features conserved motifs representative of the genus Ilarvirus. BlastN analysis revealed 68.1–71.9% nt identity of PrVI with strawberry necrotic shock virus (SNSV). In subsequent phylogenetic analysis, PrVI was grouped together with SNSV and blackberry chlorotic ringspot virus (BCRV), both members of subgroup 1 of ilarviruses. In addition, mini-scale surveys in stone fruit orchards revealed the presence of PrVI in a limited number of sweet cherries and in one peach tree. Overall, our data suggest that PrVI is a novel species of the genus Ilarvirus and it consists the fifth member of the genus that is currently known to infect Prunus spp. [ABSTRACT FROM AUTHOR]