Cherry virus A (CVA), a member of the genus Capillovirus, has been reported in sweet cherry in Germany, Canada, and Great Britain. No data are available on the effects of CVA on fruit quality and yield of infected trees. Little cherry disease (LChD) occurs in most cherry growing areas of the world. Symptoms on sensitive cultivars include discolored fruit that remain small, pointed in shape, and tasteless. Three Closterovirus spp. associated with LChD have been described (Little cherry virus-1 [LChV-1], LChV-2, and LChV-3). Diseased local and commercial cultivars of sour cherry trees were found in a Prunus sp. germplasm collection and orchards in Poland during the 2003 growing season. The foliar symptoms included irregular, chlorotic mottling, distortion, and premature falling of leaves. Some of the diseased trees developed rosette as a result of decreased growth and shortened internodes. Severely infected branches exhibited dieback symptoms. Because the symptoms were suggestive of a possible virus infection, leaf samples were collected from 38 trees and assayed for Prune dwarf virus and Prunus necrotic ringspot virus using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). RNA extracted from leaves was used in a reverse transcription-polymerase chain reaction (RT-PCR) with the One-Step RT-PCR with Platinum Taq (Invitrogen Life Technologies) and primer sets specific for CVA (1), LChV-1 (3), and LChV-2 (3). The RNA samples were also tested using RT-PCR for detection of Cherry mottle leaf virus (CMLV), Cherry necrotic rusty mottle virus (CNRMV), and Cherry green ring mottle virus (CGRMV) with specific primer sets (2). Amplification of a 397-bp coat protein gene product confirmed infection of 15 trees with CVA. A 419-bp fragment corresponding to the coat protein gene of LChV-1 was amplified from cv. Gisela rootstock and local cv. WVIII/1. To confirm RT-PCR results, CVA amplification products from local cv. WX/5 and LChV-1 from cvs. Gisela and WVIII/1 were cloned in bacterial vector pCR 2.1-TOPO and then sequenced. The sequences were analyzed with the Lasergene (DNASTAR, Madison, WI) computer program. The alignment indicated that the nucleotide sequence of cv. WX/5 was closely related to the published sequences of CVA (Genbank Accession No. NC_003689) and had an 89% homology to the corresponding region. The nucleotide sequence similarity between the 419-bp fragment obtained from cvs. Gisela and WVIII/1 was 87% and 91%, respectively, compared with the reference isolate of LChV-1 (Genbank Accession No. NC_001836). The sampled trees tested negative for LChV-2, CGRMV, CMLV, and CNRMV using RT-PCR. Some trees tested positive for PNRSV and PDV. To our knowledge, this is the first report of CVA and LChV-1 in Poland.
References: (1) D. James and W. Jelkmann. Acta Hortic. 472:299, 1998. (2) M. E. Rott and W. Jelkmann. Eur. J. Plant Pathol. 107:411,2001. (3) M. E. Rott and W. Jelkmann. Phytopathology. 91:61, 2001.