Search Results (4)

Apples (Malus domestica), one of Iran’s oldest cultivated fruit crops, hold considerable economic importance. In this study, 170 apple leaf samples representing various commercial cultivars were collected across the country. RT-PCR screening targeted five common apple-infecting viruses and two viroids: apple chlorotic leaf spot virus (ACLSV), apple stem pitting virus (ASPV), apple stem grooving virus (ASGV), apple green crinkle-associated virus (AGCaV), apple mosaic virus (ApMV), apple scar skin viroid (ASSVd), and hop stunt viroid (HSVd). To identify additional or novel agents, 40 RT-PCR-negative samples were pooled into two composite groups and analyzed using next-generation sequencing (NGS). NGS was also performed on individual samples with mixed infections to retrieve full genomes. RT-PCR confirmed the presence of ACLSV, ASPV, ASGV, AGCaV, ApMV, and HSVd. NGS further revealed three additional pathogens: citrus concave gum-associated virus (CCGaV), apple hammerhead viroid (AHVd), and apricot vein clearing-associated virus (AVCaV), which were subsequently detected across the collection by RT-PCR. AGCaV was most prevalent (47.6%), followed by ACLSV (45.8%), HSVd (27.6%), AVCaV (20.5%), ASGV (17%), AHVd (15.2%), ASPV (14.1%), CCGaV (4.7%), and ApMV (3.5%). Mixed infections occurred in 67% of samples. Phylogenetic analysis based on CP genes (ACLSV, ASGV, AGCaV) and full genomes (AVCaV, AHVd) clustered Iranian isolates together, suggesting a common origin. This is the first report in Iran of AGCaV, CCGaV, ApMV, and AVCaV in apple, and notably, the first global report of AVCaV in a non-Prunus host. The findings provide the first comprehensive assessment of the sanitary status of apple trees in Iran. Full article

Trialeurodes vaporariorum, commonly known as the greenhouse whitefly, severely infests important crops and serves as a vector for apple scar skin viroid (ASSVd). This vector-mediated transmission may cause the spread of infection to other herbaceous crops. For effective management of ASSVd, it is important to explore the whitefly’s proteins, which interact with ASSVd RNA and are thereby involved in its transmission. In this study, it was found that a small heat shock protein (sHsp) from T. vaporariorum, which is expressed under stress, binds to ASSVd RNA. The sHsp gene is 606 bp in length and encodes for 202 amino acids, with a molecular weight of 22.98 kDa and an isoelectric point of 8.95. Intermolecular interaction was confirmed through in silico analysis, using electrophoretic mobility shift assays (EMSAs) and northwestern assays. The sHsp22.98 protein was found to exist in both monomeric and dimeric forms, and both forms showed strong binding to ASSVd RNA. To investigate the role of sHsp22.98 during ASSVd infection, transient silencing of sHsp22.98 was conducted, using a tobacco rattle virus (TRV)-based virus-induced gene silencing system. The sHsp22.98-silenced whiteflies showed an approximate 50% decrease in ASSVd transmission. These results suggest that sHsp22.98 from T. vaporariorum is associated with viroid RNA and plays a significant role in transmission. Full article

Viroids are the smallest known infectious agents that are thought to only infect plants. Here, we reveal that several species of plant pathogenic fungi that were isolated from apple trees infected with apple scar skin viroid (ASSVd) carried ASSVd naturally. This finding indicates the spread of viroids to fungi under natural conditions and further suggests the possible existence of mycoviroids in nature. A total of 117 fungal isolates were isolated from ASSVd-infected apple trees, with the majority (85.5%) being an ascomycete Alternaria alternata and the remaining isolates being other plant-pathogenic or -endophytic fungi. Out of the examined samples, viroids were detected in 81 isolates (69.2%) including A. alternata as well as other fungal species. The phenotypic comparison of ASSVd-free specimens developed by single-spore isolation and ASSVd-infected fungal isogenic lines showed that ASSVd affected the growth and pathogenicity of certain fungal species. ASSVd confers hypovirulence on ascomycete Epicoccum nigrum. The mycobiome analysis of apple tree-associated fungi showed that ASSVd infection did not generally affect the diversity and structure of fungal communities but specifically increased the abundance of Alternaria species. Taken together, these data reveal the occurrence of the natural spread of viroids to plants; additionally, as an integral component of the ecosystem, viroids may affect the abundance of certain fungal species in plants. Moreover, this study provides further evidence that viroid infection could induce symptoms in certain filamentous fungi. Full article

Composed of a naked circular non-protein-coding genomic RNA, counting only a few hundred nucleotides, viroids—the smallest infectious agents known so far—are able to replicate and move systemically in herbaceous and woody host plants, which concomitantly may develop specific diseases or remain symptomless. Several viroids have been reported to naturally infect pome and stone fruit trees, showing symptoms on leaves, fruits and/or bark. However, Koch’s postulates required for establishing on firm grounds the viroid etiology of these diseases, have not been met in all instances. Here, pome and stone fruit tree diseases, conclusively proven to be caused by viroids, are reviewed, and the need to pay closer attention to fulfilling Koch’s postulates is emphasized. Full article