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1.
In Cryphonectria parasitica, the causal agent of chestnut blight, hypovirulence is commonly associated with the presence of cytoplasmically transmissible, double-stranded RNA (dsRNA). Recently, hypovirulent isolates of C. parasitica that do not have detectable levels of dsRNA have been obtained from healing cankers on chestnut trees. In these isolates, most of the respiratory activity is cyanide-resistant and salicylhydroxamate-sensitive, indicating that the mitochondrial alternative oxidase was induced. In contrast, the respiration of virulent isolates from the same trees and most of the dsRNA-containing hypovirulent isolates from a variety of geographical locations was cyanide sensitive. In all of these isolates, the alternative oxidase could be induced by growing them in the presence of chloramphenicol, an inhibitor of mitochondrial protein synthesis. The attenuated virulence and altered respiratory phenotypes could be transferred from the dsRNA-free hypovirulent isolates to virulent strains through hyphal anastomosis. Some of the dsRNA-free hypovirulent isolates grew more slowly than virulent strains. These results indicate that, in Cryphonectria, cytoplasmically transmitted hypovirulence may have more than one cause, and that mitochondrial mutations sometimes may be involved in the generation of this phenotype.  相似文献   

2.
ABSTRACT In France, chestnut blight, caused by Cryphonectria parasitica, has been controlled since 1974 in orchards, but never in coppice forests, by releasing hypovirulent strains infected with CHV1 hypovirus. We tested the hypothesis that this biological control (BC) has lead to a decrease in blight severity, spread of hypovirulence, and change in C. parasitica populations. The low severity of chestnut blight was confirmed in the six regions studied (subdivided into zones). The remission of cankers was associated with the presence of white isolates presumed to be hypovirulent. These two parameters were also correlated, at the zonal level, to the frequency of sites where BC was used. However, the estimates of the natural background level of hypovirulence, independent of BC, ranged from 4% in forests in Dordogne to 60% in orchards in Lozère. Differences in the rate of hypovirulent isolates among regions were consistent with the diversity of vegetative compatibility (VC) types in populations of C. parasitica. The highest VC-type diversity and mean allelic diversity for known vegetative incompatibility (vic) genes were observed in Dordogne. We showed that the current diversity of VC types in populations of C. parasitica was lower than in 1981. We found 30 VC types among 1,113 isolates of C. parasitica. Ten VC types were incompatible with known EU testers, suggesting that one additional vic gene or allele at one of the six vic loci known should be present in Europe.  相似文献   

3.
Chestnut blight caused by the introduced fungus Cryphonectria parasitica has been responsible for the decline of Castanea sativa in Turkey since the 1960s. In this study, 72 C. parasitica isolates were recovered from the Marmara and Black Sea regions of Turkey showing white or cream-coloured culture morphology and were subjected to various tests to determine if they were infected by Cryphonectria hypovirus 1 (CHV-1). The vast majority of the isolates (69 out of 72) were vc type EU-1. Both mating types were found among a subsample of the isolates. The hypovirus was detected in 55 isolates by dsRNA extraction and/or virus specific RT-PCR on total RNA extracts. All but one isolates showed no or only weak phenol oxidase activity on agar medium containing tannic acid, typical of CHV-1 infected isolates. Through sequencing of a specific region of the hypovirus genome, we found that 24 hypovirus isolates belonged to the CHV-1 subtype I and six to the CHV-1 subtype F2. The distribution of the two CHV-1 subtypes in Turkey showed a clear geographic pattern. CHV-1 subtype I was only detected in the Marmara and western Black Sea region, whereas subtype F2 was restricted to the eastern part of the Black Sea region. The effectiveness of 23 hypovirulent isolates was tested against a virulent isolate on 2–3 years old chestnut sprouts. Ten hypovirulent isolates, all infected by CHV-1 subtype I, prevented canker development by more than 80 % suggesting that they might be suitable for biological control of chestnut blight in Turkey.  相似文献   

4.
M. HALAMBEK 《EPPO Bulletin》1986,16(3):533-535
The present state of chestnut blight caused by the fungus Cryphonectria parasitica in Yugoslavia is presented. Canker disease is present all over the country wherever chestnut stands occur. Field observations have shown the presence of abnormal disease symptoms at some localities. Isolates of C. parasitica from these sites varied widely in cultural characteristics and pathogenic properties, some showing the characteristics of hypovirulent strains.  相似文献   

5.
Chestnut blight has commonly been regarded as a phloem disease due to conspicuous stem cankers that result from infection by the fungal pathogen Cryphonectria (Endothia) parasitica. Stomatal conductance (gs), transpiration rate (E) and leaf water potential were measured throughout the day on leaves distal to naturally-occurring virulent (sunken bark with abundant stromata) or hypovirulent (swollen bark lacking stromata) cankers and cankers induced by inoculation with virulent or hypovirulent strains of C. parasitica. Relative to control stems, hydraulic conductivity (Kh), gs and E were reduced significantly (α = 0·05) for both natural virulent cankers, and cankers that were induced by a virulent strain. These effects were less pronounced for both natural and induced hypovirulent cankers. Isolation experiments revealed that the percentage of xylem tissue chips yielding C. parasitica was greater for virulent than for hypovirulent cankers. The data provide evidence that the localized presence of C. parasitica in cankers of American chestnut results in stomatal closure, possibly as a direct result of xylem dysfunction.  相似文献   

6.
The hypovirulence-associated mitovirus, Ophiostoma mitovirus 3a (OMV3a), has been shown to be widespread in eastern Canadian populations of Sclerotinia homoeocarpa in the form of latent infection. Latent infection by OMV3a was not associated with an apparent phenotype and did not significantly reduce the growth and virulence of the pathogen. In the present study, we found that isolates of S. homoeocarpa latently infected by OMV3a can change to hypovirulent isolates after storage at 4 °C, and that this attenuation of virulence was associated with increased concentration of the OMV3a virus. Recurrent observations revealed that up to 29.8% of latently infected isolates changed to hypovirulent isolates after 21 months of storage. Transmission of OMV3a dsRNA from latently infected isolates to virus-free isolates resulted in latent infection of the recipient isolates, indicating that latent infection by OMV3a was not associated with genetic differences in the fungal host. The RNA genomes of the OMV3a virus in an isogenic pair of latently infected and hypovirulent isolates were sequenced and compared. Each of the two RNAs contained an open reading frame of 726 amino acids with conserved motifs typical of RNA-dependent RNA polymerase (RdRp). The OMV3a RNA sequences in these two isolates share 95.1% nucleotide and 94.6% amino acid sequence identities. The development of hypovirulence from latent infection by OMV3a virus may provide new strategies to improve the biological control efficacy of hypovirulence in dollar spot management.  相似文献   

7.
ABSTRACT Strains of the chestnut blight fungus, Cryphonectria parasitica, have been genetically engineered to contain an integrated full-length cDNA copy of the prototypic virulence-attenuating hypovirus CHV1-EP713. Unlike natural hypovirulent C. parasitica strains, these transgenic hypovirulent strains are able to transmit virus to ascospore progeny under laboratory conditions. This ability provides the potential to circumvent barriers to cytoplasmic virus transmission imposed by the fungal vegetative incompatibility system. During July 1994, transgenic hypovirulent strains were introduced into a Connecticut forest site (Biotechnology Permit 94-010-01). Subsequent analysis of the release site confirmed hypovirus transmission from transgenic hypovirulent strains to ascospore progeny under field conditions. Additionally, it was possible to recover transgenic hypovirulent strains from the test site as long as 2 years after the limited, single-season release. Evidence also was obtained for cytoplasmic transmission of transgenic cDNA-derived hypovirus RNA, including transmission to mycelia of a virulent C. parasitica canker after treatment with conidia of a transgenic strain. Finally, a transgenic hypovirulent strain was recovered from a superficial canker formed on an untreated chestnut tree. Genetic characteristics of the recovered strain suggested that the canker was initiated by an ascospore progeny derived from a cross involving an input transgenic hypovirulent strain. The durability of a molecular marker for field-released cDNA-derived hypovirus RNA is discussed.  相似文献   

8.
The major chestnut-growing areas in Aydın Province, which yield nearly 35% of Turkey’s production, were examined for the presence of chestnut blight and bark samples were collected from the canker formations. Generally virulent type cankers were observed. Of 31 villages, 22 were found to be contaminated with the disease. A total of 97Cryphonectria parasitica (Murrill) M.E. Barr. isolates were characterized for the presence of potential hypovirulence by looking at cultural characteristics on media and virulence in cv. ‘Golden Delicious’ apple fruit. The isolates were placed into four groups based on pigmentation and abundance of pycnidia formation. Isolates produced lesions of various sizes on apple fruits but lesion size was not correlated with cultural characteristics typical to hypovirulent isolates. Among 97 isolates, ten possessing the characteristics associated with hypovirulence were assayed for the presence of dsRNA. Among these isolates only one, coded M1-3, was found to contain dsRNA. No dsRNA was detected in the single conidium isolates derived from M1-3. All of the isolates were screened for vegetative compatibility and two European vc types, EU-1 and EU-12, were detected. This low vc-type diversity in the region may indicate a high potential for spread of transmissible hypovirulence. http://www.phytoparasitica.org posting May 30, 2008.  相似文献   

9.
Zhou T  Boland GJ 《Phytopathology》1997,87(2):147-153
ABSTRACT One hundred and thirty-two isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass, were evaluated for virulence on swards and detached leaves of creeping bentgrass and for the presence of double-stranded RNA (dsRNA). In at least four isolates, the hypovirulent phenotype was associated with the presence of specific segments of dsRNA. In addition, these hypovirulent isolates often grew slowly on potato dextrose agar (PDA), formed thin colonies with atypical colony margins, and failed to produce typical black stroma. The hypovirulent phenotype and dsRNA were transmitted from hypovirulent isolate Sh12B to virulent isolate Sh48B, and the converted isolate was hypovirulent and contained dsRNA. The hypovirulent phenotype and dsRNA also were transmitted to at least four other isolates of the pathogen, including the fungicide-resistant, dsRNA isolate KY-7. Converted isolates of KY-7 developed the hypovirulent phenotype, grew on fungicide-amended medium, and contained dsRNA. Subcultures of hypovirulent isolate Sh12B that did not contain dsRNA were obtained through curative treatment using cycloheximide-containing medium and heat. Cured subcultures grew faster on PDA, had more typical colony morphologies, were more virulent on bentgrass leaves, and did not contain dsRNA. No cured subcultures were obtained from hypovirulent isolate Sh09B. Isolates regenerated from protoplasts of hypovirulent isolate Sh12B were not cured, remained hypovirulent, and contained dsRNA. Transmission of hypovirulence and dsRNA in S. homoeocarpa has potential as a novel approach to the management of dollar spot of turfgrass.  相似文献   

10.
An inoculation method using Lupinus luteus was developed for estimating virulence of isolates of the white root rot fungus, Rosellinia necatrix Prillieux. Fungal cultures grown on pieces of mulberry twigs were placed in contact with the hypocotyl of 3-week-old seedlings growing in pots of soil. Disease development was uniform and reproducible in repeated experiments. Of 24 isolates with double-stranded RNA, eight were weakly virulent. This method is useful throughout the year for estimating virulence of many isolates of the fungus and for screening for hypovirulent isolates. Received 2 March 2001/ Accepted in revised form 25 May 2001  相似文献   

11.
ABSTRACT Interspecific transmission of a hypovirulence-associated double-stranded RNA (dsRNA) and hypovirulent phenotype was attempted from hypovirulent isolate Ss275 of Sclerotinia sclerotiorum to five virulent isolates of S. minor. dsRNA and the hypovirulent phenotype were successfully transmitted to one of the five isolates, Sm10. Three putative converted isolates of Sm10 were slow growing and developed atypical colony morphologies characteristic of the hypovirulent phenotype. These isolates were assayed for virulence and produced significantly smaller lesions than isolate Sm10 on detached leaves of Romaine lettuce. One of these putative converted isolates, designated Sm10T, was tested to confirm interspecific transmission of dsRNA. In northern hybridizations, dsRNA isolated from Sm10T hybridized with a digoxigenin-labeled cDNA probe prepared from dsRNA isolated from Ss275. Random amplified polymorphic DNA analysis confirmed that isolate Sm10T was derived from Sm10 and not from Ss275 or a hybrid of the two species. The dsRNA and hypovirulent phenotype were subsequently transmitted intraspecifically from Sm10T to Sm8. To our knowledge, this is the first report of interspecific transmission of dsRNA and an associated hypovirulent phenotype between fungal plant pathogens by hyphal anastomosis.  相似文献   

12.
Zhou T  Boland GJ 《Phytopathology》1998,88(8):788-794
ABSTRACT Selected hypovirulent isolates of Sclerotinia homoeocarpa were evaluated for efficacy in suppressing dollar spot of turfgrass under growth room and field conditions. Under growth room conditions, hypovirulent isolates Sh12B, Sh09B, or Sh08D of S. homoeocarpa caused 3.4 to 30.4% diseased turf in comparison to virulent isolates Sh48B and Sh14D, which caused 80.2 to 90.2% disease. In treatments that received both virulent and hypovirulent isolates, only hypovirulent isolate Sh12B significantly reduced disease as compared with the control with virulent isolates alone. In a field experiment in 1993 on swards of creeping bentgrass artificially inoculated with a virulent isolate of the pathogen, all treatments containing hypovirulent isolate Sh12B applied as a mycelial suspension, granular mix, or alginate pellets developed significantly less disease (6.3 to 20.8% diseased turf) compared with their respective formulation controls (23.8 to 31.2%). Suppression of dollar spot by treatment with mycelial suspensions of isolate Sh12B was evident up to 45 days postinoculation, and disease suppression was still significant 1 year after application when compared with the water control. Applications of hypovirulent isolate Sh09B did not reduce dollar spot in any treatments. Significant suppression of dollar spot by isolate Sh12B was also observed in the experiment conducted in 1994. In addition, suppression of dollar spot by hypovirulent isolate Sh12B was evaluated on swards with naturally occurring inoculum during 1994. Treatments with a mycelial suspension and alginate pellets of hypovirulent isolate Sh12B significantly reduced dollar spot compared with their respective formulation controls. With few exceptions, there was no statistical difference between treatments with hypovirulent isolate Sh12B and the fungicide chlorothalonil (Daconil 2787). Multiple applications of the hypovirulent isolate did not result in greater suppression of dollar spot as compared with a single application. The results indicate that hypovirulence has potential as an effective strategy for the management of dollar spot.  相似文献   

13.
Two-hundred and forty-eight isolates of Rhizoctonia spp, were obtained from 13 locations in Gifu Prefecture in Japan using the plant debris particles isolation, colonization of bait tissue, and soil-clump plating methods. Of the isolates, 143 were binucleate Rhizoctonia spp., 60 were R. solani and 45 were R. zeae. Three isolates of R. solani and 54 of binucleate Rhizoctonia spp, were hypovirulent on radish, whilst all isolates of R. zeae were highly virulent, Hypovirulent strains were isolated most frequently by the plant debris particles isolation method, Hypovirulent isolates of R. solani belonged to anastomosis group 4, whilst the hypovirulent binucleate Rhizoctonia isolates belonged to AG A, AG Ba, AG G, and AG O.
Thirty-two isolates of Rhizoctotria spp, selected for hypovirulence on radish were tested on cucumber in vitro. Only five binucleate Rhizoctonia isolates and one R. solani isolate were hypovirulent on both species, and these isolates were also hypovirulent on seven other crop species. Cucumber showed wide variation in disease susceptibility to different isolates but hypovirulent isolates exhibited a consistent reaction on five different host cultivars, Pathogenicity tests using cucumber grown in soil also showed consistent reactions with isolates selected either for hypovirulence or virulence. The results support the use of cucumber in bioassays for identifying hypovirulent isolates of binucleate Rhizoctonia spp.  相似文献   

14.
A single 3 kb segment of double-stranded (dsRNA) was present in three of 30 Brazilian isolates of Cryphonectria cubensis . These dsRNA-containing isolates showed morphological characteristics suggestive of hypovirulence and were significantly less virulent than dsRNA-free isolates. One isolate, however, with morphological characteristics suggestive of hypovirulence, showed reduced virulence, but was free from dsRNA. Conversion of virulent isolates with normal morphology to a morphology associated with hypovirulence was achieved by pairing hypovirulent and virulent isolates of the same vegetative compatibility group (VCG). This suggests that dsRNA can be transmitted to isolates of the same vegetative compatibility group by hyphal anastomosis. Converted isolates exhibited the same hypovirulence-associated traits as those of the original dsRNA-containing hypovirulent isolates. These studies suggest that a single 3 kb segment of dsRNA alters both morphology and virulence by conferring hypovirulence on the pathogen; the first such report for Brazilian isolates of C. cubensis .  相似文献   

15.
ABSTRACT Phytophthora root rot of citrus in Florida is caused by Phytophthora nicotianae and P. palmivora. A naturally occurring isolate of P. nicotianae (Pn117) was characterized as hypovirulent on citrus roots. Pn117 infected and colonized fibrous roots, but caused significantly less disease than the virulent isolates P. nicotianae Pn198 and P. palmivora Pp99. Coincident inoculation of rootstock seedlings of Cleopatra mandarin (Citrus reticulata) or Swingle citrumelo (C. paradisi x Poncirus trifoliata) with the hypovirulent Pn117 and the virulent isolates Pn198 and Pp99 did not reduce the severity of disease caused by the virulent Phytophthora spp. When either rootstock was inoculated with the hypovirulent Pn117 for 3 days prior to inoculation with virulent isolates, preinoculated seedlings had significantly less disease and greater root weight compared with seedlings inoculated with the virulent isolates alone. Recovery of the different colony types of Phytophthora spp. from roots of sweet orange (C. sinensis) or Swingle citrumelo was evaluated on semiselective medium after sequential inoculations with the hypovirulent Pn117 and virulent Pp99. Pn117 was isolated from roots at the same level as the Pp99 at 3 days post inoculation. Preinoculation of Pn117 for 3 days followed by inoculation with Pp99 resulted in greater recovery of the hypovirulent isolate and lower recovery of the virulent compared with coincident inoculation.  相似文献   

16.
Sharon M  Freeman S  Sneh B 《Phytopathology》2011,101(7):828-838
Certain hypovirulent Rhizoctonia isolates effectively protect plants against well-known important pathogens among Rhizoctonia isolates as well as against other pathogens. The modes of action involved in this protection include resistance induced in plants by colonization with hypovirulent Rhizoctonia isolates. The qualifications of hypovirulent isolates (efficient protection, rapid growth, effective colonization of the plants, and easy application in the field) provide a significant potential for the development of a commercial microbial preparation for application as biological control agents. Understanding of the modes of action involved in protection is important for improving the various aspects of development and application of such preparations. The hypothesis of the present study is that resistance pathways such as systemic acquired resistance (SAR), induced systemic resistance (ISR), and phytoalexins are induced in plants colonized by the protective hypovirulent Rhizoctonia isolates and are involved in the protection of these plants against pathogenic Rhizoctonia. Changes in protection levels of Arabidopsis thaliana mutants defective in defense-related genes (npr1-1, npr1-2, ndr1-1, npr1-2/ndr1-1, cim6, wrky70.1, snc1, and pbs3-1) and colonized with the hypovirulent Rhizoctonia isolates compared with that of the wild type (wt) plants colonized with the same isolates confirmed the involvement of induced resistance in the protection of the plants against pathogenic Rhizoctonia spp., although protection levels of mutants constantly expressing SAR genes (snc1 and cim6) were lower than that of wt plants. Plant colonization by hypovirulent Rhizoctonia isolates induced elevated expression levels of the following genes: PR5 (SAR), PDF1.2, LOX2, LOX1, CORI3 (ISR), and PAD3 (phytoalexin production), which indicated that all of these pathways were induced in the hypovirulent-colonized plants. When SAR or ISR were induced separately in plants after application of the chemical inducers Bion and methyl jasmonate, respectively, only ISR activation resulted in a higher protection level against the pathogen, although the protection was minor. In conclusion, plant colonization with the protective hypovirulent Rhizoctonia isolates significantly induced genes involved in the SAR, ISR, and phytoalexin production pathways. In the studied system, SAR probably did not play a major role in the mode of protection against pathogenic Rhizoctonia spp.; however, it may play a more significant role in protection against other pathogens.  相似文献   

17.
Monosporascus root rot/vine decline (MRR/VD) causes root necrosis and severe stunting of muskmelon and watermelon plants in several countries around the world. MRR/VD is caused by the soilborne ascomycete fungus, Monosporascus cannonballus. Currently, there are few options available for control of MRR/VD. This research describes experiments to test the possibility of using naturally occurring M. cannonballus isolates containing double-stranded RNA (dsRNA) for the biological control of MRR/VD. These isolates often develop a degenerate phenotype characterized by slow growth and reduced ascospore production. In addition, these degenerate isolates are hypovirulent on muskmelon. Plants co-inoculated with a hypovirulent, dsRNA+ isolate (Tx93-449+) and a virulent, dsRNA- isolate (Az90-33-) at an inoculum ratio of 10:1 (hypovirulent:virulent) were indistinguishable from the uninoculated plants in greenhouse pathogenicity trials. In vitro infection assays using fluorescence microscopy on aniline-stained muskmelon roots suggested that although the hypovirulent dsRNA+ isolate Tx93-449+ penetrated and partially colonized roots of the seedlings, it was not as efficient in colonizing the roots as the virulent, dsRNA- isolate Az90-33-. While more extensive experiments are needed, these data suggest that hypovirulent dsRNA+ isolates of M. cannonballus have potential for development as biological control agents to reduce disease pressure associated with MRR/VD.  相似文献   

18.
In order to improve understanding of its diversity, 338 isolates of Cryphonectria parasitica, the causal agent of chestnut blight, were sampled from 10 chestnut populations throughout chestnut‐growing coastal and continental areas of Croatia. Eighteen vegetative compatibility (VC) types were identified. The VC type EU‐1 was the most widespread, comprising 42·9% of the isolates, followed by EU‐2 (21%) and EU‐12 (14·2%). In respect to the occurrence of the main VC types, the C. parasitica populations in Croatia combined features of both northwestern and southeastern European populations. Perithecia and mating‐type ratios of approximately 1 : 1 were found in all populations, suggesting that sexual reproduction of the fungus is common in Croatia. Natural hypovirulence was also evident in all populations, with incidence of hypovirus‐infected isolates ranging from 12·7% in Istria‐Buje to 66·6% in the continental part of the country. A total of 36 hypovirus‐infected isolates sampled throughout Croatia were analysed in ORF‐A and ORF‐B by RT‐PCR/RFLP analysis. All viral isolates belonged to the Italian subtype of Cryphonectria hypovirus 1 (CHV‐1) and were closely related to the isolates found in other European countries. The RFLP patterns found were also identical or similar to the patterns of three isolates collected in Croatia 22 years ago, suggesting a slow evolution of the hypovirus.  相似文献   

19.
Deng F  Boland GJ 《Phytopathology》2004,94(9):917-923
ABSTRACT Two genetically distinct double-stranded RNA (dsRNA) elements were identified in hypovirulent isolates of Sclerotinia homoeocarpa, the causal agent of dollar spot of turfgrass. The large dsRNA (L-dsRNA) was consistently present in all hypovirulent isolates, whereas the small dsRNA (S-dsRNA) was found only in some hypovirulent isolates. Virulence comparisons revealed that there was no significant difference between isolates containing one or both dsRNAs. Therefore, the L-dsRNA appears to be the genetic determinant of hypovirulence, while the S-dsRNA is not essential for hypovirulence in S. homoeocarpa. The L-dsRNA in hypovirulent isolate Sh12B of S. homoeocarpa was previously characterized as a fungal mitochondrial virus and designated Ophiostoma novo-ulmi mitovirus 3a-Sh12B (OnuMV3a-Sh12B) because it was conspecific with O. novo-ulmi mitovirus 3a-Ld from O. novo-ulmi, the causal agent of Dutch elm disease. In the present study, the nucleotide sequences of the S-dsRNAs (738 to 767 nucleotides) in hypovirulent isolates Sh12B, Sh279B, and Sh286B were determined. Nucleotide sequence analysis indicated that the S-dsRNA was not derived from the OnuMV3a dsRNA and it could not encode an RNA-dependent RNA polymerase. These results are consistent with biological data that the S-dsRNA was always associated with the L-dsRNA and was never found independently. Therefore, the S-dsRNA can be regarded as a satellite RNA of OnuMV3a in S. homoeocarpa. Northern blotting analysis indicated that nucleic acid extracts from isolate Sh12B of S. homoeocarpa contained more single (+) stranded RNA than dsRNA for this satellite RNA. The 5'- and 3'-terminal sequences of the positive strand of the S-dsRNA each could be folded into a stem-loop structure and the terminal 21 nucleotides were complementary to each other, potentially forming a panhandle structure.  相似文献   

20.
A 4.1 kbp positive-strand RNA virus known as Diaporthe RNA virus 1 (DRV1) occurs in hypovirulent, non-sporulating isolates of the fungal pathogen Diaporthe perjuncta. A full-length cDNA clone of DRV1 was developed and RNA transcribed from the cDNA clone used to transfect different Diaporthe spp. The transfected species included three D. ambigua isolates and an unidentified Phomopsis asexual state of a Diaporthe sp. Successful transfections were confirmed using RT-PCR. Although the in vitro-transcribed positive sense single-stranded RNA used for transfection included vector sequences at both ends, the genomes of progeny virus from DRV1-transfected isolates were free of the vector sequences. Transfection resulted in morphological changes in these fungal pathogens. However, the presence of DRV1 did not reduce growth rate in two of the three D. ambigua or the Phomopsis sp. significantly. Pathogenicity studies showed that the transfected isolates have reduced aggresiveness.  相似文献   

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