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Title: First report of seed-borne cherry leaf roll virus in wild potato, Solanum acaule, from South America

Author
item Crosslin, James
item EASTWELL, K - Washington State University
item DAVITT, C - Washington State University
item ABAD, J - Animal And Plant Health Inspection Service (APHIS)

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2010
Publication Date: 6/1/2010
Citation: Crosslin, J., Eastwell, K.C., Davitt, C.M., Abad, J.A. 2010. First report of seed-borne cherry leaf roll virus in wild potato, Solanum acaule, from South America. Plant Disease. 94:782.

Interpretive Summary: In 2008 a virus was isolated from plants of wild potato, Solanum acaule, by personnel from the USDA Animal and Plant Health Inspection Service (APHIS). The wild potatoes originated from seed collected in Peru. The virus was easy to transmit by mechanical inoculation and was purified by standard virus procedures. Preliminary tests indicate that the virus is a new strain of cherry leaf roll virus (CLRV). CLRV has been reported in the US on walnuts and a few other hosts. This is the first report of CLRV infecting wild potato. Wild potato is used in potato breeding programs because it has some desirable traits such as frost hardiness and pathogen resistance. The fact that this virus was seed transmitted in wild potato suggests that it may pose a threat to potato breeding programs using S. acaule as a parent in crosses with potato.

Technical Abstract: A virus, designated JCM-79, was isolated from wild potato (Solanum acaule Bitt.) plants grown from true seed received at USDA-APHIS Potato Quarantine Program from Peru. JCM-79 was mechanically transmissible to Nicotiana clevelandii, N.tabacum cv. Samsun NN, and Chenopodium quinoa. Symptoms in the original S. acaule were chlorosis and necrotic lesions. Symptoms in N. tabacum and N. clevelandii included necrotic lesions on inoculated leaves and mottle or necrotic spots, respectively, on upper leaves. C. quinoa showed necrotic local lesions and systemic necrosis. Cultivated potatoes (Solanum tuberosum) infected with JCM-79 by grafting from N. clevelandii were symptomless but virus was detected by back-inoculation to N. clevelandii. Viral nucleoproteins were purified by differential centrifugation and sucrose density gradient fractionation from N. clevelandii and N. tabacum. Transmission electron microscopy of nucleoproteins revealed isometric particles approximately 25 nm in diameter. Two RNA species approximately 8,000 and 6,500 nucleotides in size were obtained from nucleoproteins digested with sodium dodecylsulfate and Proteinase K. The above characteristics suggested JCM-79 was a nepovirus or nepovirus-like in nature. RT-PCR tests for Cherry rasp leaf virus, genus Cheravirus, which was reported from potato (3), were negative. An approximately 1,600 bp cDNA clone was obtained from RNA of JCM-79 by oligo dT primed reverse transcription and second strand cDNA synthesis. Sequence analysis (GenBank GU321989) revealed the closest homology to Cherry leaf roll virus (CLRV), genus Nepovirus. Subsequent RT-PCR tests with CLRV-specific primers (4) resulted in amplification of a 417 bp product from nucleic acid extracts of infected C. quinoa, N. clevelandii, and N. tabacum. The amplified product from N. clevelandii was cloned and three clones were sequenced in both directions. The consensus sequence (GenBank GU321988) showed approximately 90% homology to the 3’ untranslated region of isolates of CLRV including those from birch, walnut, and sweet cherry (GenBank accessions S84124, Z34265, and AJ877128, respectively). JCM-79 was also detected in extracts of infected plants by enzyme linked immunosorbent assay (ELISA) using CLRV-cherry reagents (Bioreba AG, Reinach, Switzerland). These results indicate JCM-79 represents a new variant of CLRV. This is the first report of CLRV naturally infecting S. acaule. S. acaule is common in the Andean regions of South America and has been used in breeding programs for crosses with S. tuberosum due to its pathogen resistance characteristics (1). The fact that JCM-79 is seed transmitted in S. acaule suggests this virus could be a threat to potato breeding programs. Another nepo-like virus with properties similar to JCM-79, designated Potato virus U (PVU), was reported from South America, but PVU was not serologically related to CLRV (2).