Virusand Virus-LikeDiseases of Pome andStone Fruits Editedby Ahmed Hadidi U.S.Department of Agriculture AgriculturalResearch Service Beltsville,Maryland 20705, USA MarinaBarba AgriculturalResearch Council PlantPathology Research Center 00156Rome, ltaly Thierry Candresse NationalInstitutefor AgriculturalResearch INRAResearch Center 33883Villenaved'Ornon Cedex, France WilhelmJelkmann JuliusKuehn Institute, Federal Research Center for CultivatedPlants Institutefor PlantProtection in FruitCrops and Viticulture 69221Dossenheim, Cermany f-\Vry HT'E The AmericanPhytopathological Society St.Paul. Minnesota Coverimages courtesy M. Barba,T. Candresse,J. C. Desvignes,J. Dunez, P.Gentit, A. Hadidi,T. lto, D. James,W. Jelkmann,G. Jesperson,E. Seemüller, and J. K. Uyemoto Libraryof CongressControl Number: 2011909928 InternationalStandard Book Number:978-0-89054-396-2 O 2011by the AmericanPhytopathological Society All rightsreserved. No portionof this book may be reproducedin anyform, including photocopy, microfilm,information storage and retrievalsystem, computer database, or software,or by any means,including electronic or mechanical,without writtenpermission from the publisher. Printedin the UnitedStates of Americaon acid-freepaper The AmericanPhytopathological Society 3340Pilot Knob Road St. Paul,Minnesota 55121, U.S.A. CHAPTER24 Cherry leaf roll virus C. Büttner, S. von Bargen,M. Bandte,and A. Myrta lntroduction have not yet been determined.The sizesof RNA-I and RNA-2, Cherry leaf roll virus (CLRV) was reported for the first estimated by denaturing electrophoresis of viral RNA prepa- il time in 1933 in English walnut (Juglans regia L., Schusterand rations,ranged between 1.02-8.2 (RNA-l) and 6.33-6.8 (RNA- Miller, 1933)and sweetcherry (Prunus avium L.; Posnetteand 2) kilobases(Murant et al., 1981,Pallas et al., 1991).CLRV Cropley, 1955).Since then numerous hosts have been recorded belongs to the subgroup C of nepoviruses.Species within this revealing its wide natural host range which includes 17 genera cluster are characterized by a large RNA-2 with a 3' NCR of woody plants and a variety of herbaceousplants. Some of the which is identical or nearly identical to that of RNA-I (Scott most reported and common natural hosts of CLRV are com- et al., 1992; Borja et al., 1995). The 3' NCR region is among nron birch species (Betula sp.), black elderberry (Sambucus the longest known for nepovirusesas estimated for six CLRV nigra L.), English walnut, and sweetcherry. The virus has been isolatesexhibiting lengths between 1,557and 1,602nucleotides detected worldwide, for example, throughout Europe, the for- (Langer et al., 2010). Although no evidenceof transmissionby mer USSR, North America, Chile, New Zealand, and Japan nematodes or other animal vectors has been found to date, ge- (Jones,1986). nome organization of CLRV seems to be in accordance with CLRV belongs to the Nepovirus genus within the family that of Tobacco ringspot uirzs (TRSV), the type speciesof the Secoviridae(Wellink et aI.,2000). Unlike the majority of other nepoviruses. The CLRV genome codes for a single coat protein membersof this genus,CLRV is not consideredto be transmit- (CP), the coding sequenceof which is located 3' proximal of ted by nematodes.However, reliable investigations on nematode the putative movement protein sequence on genomic RNA-2. transmissionare still lacking. CLRV belongsto the subgroupC Coat protein sequencesfor one birch isolate and for four walnut of the nepoviruses, which are characterized by a large RNA-2 isolates of CLRV respectively,have been published (Scott et with a long (1.2-1.6kb) 3' non-codingregion (3'NCR), which al., 1993, Zhou et al., 1998). Comparison of this CP coding is almost identical to that of RNA-I (Borja et al., 1995). The region with additional sequencesobtained from seven CLRV bipartite, single-stranded,positive-sense RNA genome is es- isolates varied between 1,539 and I,542 nucleotides in length timated to be about 15 kb, with RNA-1 and RNA-2 at about (Langer et al.200l ), but substantiated the serological relation- 8 and 7 kb, respectively.Both RNAs are encapsidatedsepa- ships found by Rebenstorfet al. (2006). Additionally, a719 bp rately in isometric particles 28 nm in diameter (Jones, 1986). fragment of the coding region of viral RNA-1 for a virus isolate Rebenstorfet al. (2006) assessedthe serologicaland molecular originating from ash (Fraxinus excelsior) has been sequenced diversity of CLRV using a collection of isolatesand samplesre- by Maliogka et al. (2004). Phylogenetic comparison of the de- covered fiom woody and herbaceoushost plants from different rived amino acid sequence,corresponding to part of the viral geographical origins. Serological and molecular phylogenetic RNA-dependent RNA polymerase (RdRP) with other taxa of reconstructionswere strongly correlated. Remarkably, the di- the picorna-like plant viruses, supported the taxonomic clas- versity of CLRV is defined, to a large extent, by the host plant sification of CLRV within the genus Nepovirus. from which the viral sampleswere originally obtained. Economiclmpact and DiseaseSymptoms TaxonomicPosition and NucleotideSequence As CLRVis transmissiblebyseed, it is a threatto genebank Family: Secoviridae,' genus: Nepovirus; species: Chercy contamination. Such ClRV-contaminated propagative mate- leaf roll vlrus (CLRV). CLRV is an establishedspecies within rial is of major importance for human-mediated propagation the genus Nepovirus that belongs to the family Secoviridae. and dispersal. Latent virus contamination of mother planta- In accordance with the currently acknowledged criteria for tions also has to be taken into consideration. Therefore, CLRV classificationwithin this family, CLRV consistsof two single- is included in the list of plant viruses that should be closely stranded RNAs, encapsidatedseparately in icosahedral, non- monitored during sanitary production of propagationmaterial, envelopedparticles, measuring 28 nm in diameter (Wellink et especiallyfor walnut and olive trees(Bassi and Martelli, 2003). al., 2000). Both particles are required for infectivity (Jonesand Kegler et al. (1972) reported on crop losses in sour cherry Duncan, 1980). Genomic RNAs, each coding for a polyproG (Prunus cerasus L.) of 9I to 98Va.In Italy approximately 5Vo ein, have a genome encoded protein (VPg) covalently linked of the tested olive trees grown in areas in which national and at their 5'end and are polyadenylatedat the 3' terminus (Jones local olive tree cultivars and selectionsare grown were CLRV and Mayo, 1972; Walkey et al., 1973: Hellen and Cooper, infected. The percentage of infection by CLRV in olive in 1987).The full length sequencesof the CLRV genomic RNAs Italy was similar to that in Spain (Faggioli et al., 2005). CLRV ll9 120 j Chapter 24 infection correlates with the death of grafted English walnut propagation whereas only 20vo of the cuttings froni scions (Juglans regia) propagated 11{e_rmis1 on rootstocks of Northern clRV-infected trees survived. The annual increment of-CLRv- California black walnut (J. hindsii), ,paradox, hybrids U. hind_ infected seedlingscultivated under greenhouseconditions was sii x J. regia), Chinese wingnut (pteriocarya stenoprtera)or half that of healthy birch seedlinss. other Juglans spp. (Mircetich and Rowhani, r9g4; Iridmeth et Referring to the production ofwood as raw material and to al., 1990; Grant and McGranahan, 2005). The infection re_ the ecological value of forests,the extent of lossesdr.re to virus mains symptomlessin seedlingsof many cultivars of J. regia. infection is difficult to calculate as there is a strong impact of However, if the virus invades the graft union of suitable giaft other stressfactors in forest stands in a long periöd between combinations, it induces tissue necrosis at the scion-rootstock sowing in nurseriesand wood harvesting.In any case,it is sug- junction, known as blackline or brownline, which eventually gested to prevent virus dispersal by using clean planting ma_ girdles and kills the tree (Mircetich et al., l9g0; Rowhani and terial for the production of wood and to sustain the function Mircetich, 1988). The potential monetary value of developing of forest as recreational, cultural forest parks and suburban effective measuresof cLRV in walnut ii indicated by annual forests. losses due to blackline diseaseof 3vo of the total Cälifornia CLRV symptoms vary according to plant species,virus crop, as well as a l3vo loss in coastal orchards in this state strain. and season,and have been summarized.by Bandte ancl (Brooks and Bruening, 1995). Büttner (2001). For instance,CLRV-infected birc-h,elderberry. A rapid decline over a one or two year period was described dogwood, and blackberry show yellow vein netting, chlorotic by Nömeth (1986) when clRV-infected cherry trees were mix- ringspots, mottling, and leaf roll (Fig. 24.1). Diebick is often infected with Prunus necrotic ringspot virzs (pNRSV) and observed in clRV-infected sweet cherry, birch, and black- Prune dwarf viras (PDV). Furthermore, germination the rate berry. Susceptiblewalnut leavesmay deveiop chlorosis,discol- of seedsobtained from those trees was reducä bv 20 to 50vo. ored rings, or arabesks.Blackline diseaseaffects only English when compared with seeds from healthy (LO*, trees lggr. walnuts grafted onto non-regia rootstocks, and causestermi- According to cooper and Massalski (19g4), seedlings and nal shoot dieback in some cases.chlorotic leaf mottling and cuttings from naturally infected birch trees grow less iapidly spotting is associatedwith