First Report of Cherry mottle leaf virus Infecting Cherry in China

Cherry mottle leaf virus (CMLV) is a member of the genus Trichovirus (family Betaflexiviridae). CMLV infects several species of the genus Prunus including cherry (Prunus avium) and peach (P. persica) (2,3). It is spread via budding and grafting with infected wood and can be transmitted from infected bitter cherry (P. emarginata), or infected but symptomless peach trees to healthy sweet cherry trees by the bud mite (Eriophyes inaequalis) (1). On susceptible sweet cherry cultivars, CMLV causes symptoms such as chlorotic mottle-leaf pattern, distortion, puckering of younger leaves, and small fruits that ripen late (1), which may lead to severe economic losses in some cultivars. Cherry is one of the most important fruit tree species in North China, and Shandong Province is one of the major cherry production areas. In June 2013, a survey of possible CMLV presence was conducted in a cherry orchard planted in 1996 in Zoucheng city, Shandong. The sweet cherry cultivars in this orchard included Black Tartarian, Bing, Hongdeng (a hybrid between cvs. Napoleon and Huangyu), and others; the rootstock cultivar utilized to graft these cultivars was mountain cherry (P. tomentosa). During the survey, characteristic symptoms on leaves such as leaf mottling, distortion, and puckering similar to those caused by CMLV were observed on some trees of the cv. Hongdeng, and the symptomatic trees accounted for ~10% of the total trees of this cultivar. Five symptomatic cherry leaf samples and three healthy-looking cherry leaf samples of cv. Hongdeng were collected. Total RNA extracted from the leaf samples using RNeasy plant mini kit (Qiagen Inc., Valencia, CA) was subjected to first strand cDNA synthesis with the reverse primer CMLV-3R (5′-CTCGAGAACACAGAGATTTGTCGAGAC-3′, sequence in italics indicates restriction site XhoI) and M-MLV reverse transcriptase (Promega, Madison, WI) according to the manufacturer's instruction. The cDNA was then used as template in the PCR assay using primers CMLV-5F (5′-GGATCCATGTCGGCGCGATTGAATC-3′, sequence in italics indicates restriction site BamHI) and CMLV-3R, which amplify the genome fragment including the capsid protein gene of CMLV. The expected PCR product ~590 bp was amplified from all five symptomatic samples, while no such PCR product was amplified from the symptomless samples. The PCR products were cloned into pMD18-T vector (TaKaRa, Dalian, China). Three positive clones for each of the five amplicons were sequenced in both directions. Sequence alignment and nucleotide BLAST analysis of the sequences revealed that they were 99% to 100% identical to the corresponding capsid protein gene sequence of a cherry isolate of CMLV (GenBank Accession No. AF170028) and 85% identical with that of the peach wart strain of CMLV (KC207480). Our results confirm the infection of cherry trees by CMLV in Shandong. To our knowledge, this is the first report of CMLV on cherry in China. As the spread of CMLV by mite vector in the field is rare (1), and no bud mite outbreak had occurred in this orchard in the past years, so it is possible that virus-infected propagation materials are largely responsible for the spread of this virus. Considering the importance of cherry cultivation in China, this report prompts the need to survey the occurrence of this virus in Shandong and other provinces, and the need to develop more effective management strategies such as the use of certified virus-free nursery stocks to reduce the impact of CMLV. References: (1) J. E. Adaskaveg et al. Diseases. Page 61 in: UC IPM Pest Management Guidelines: Cherry. University of California ANR Publication 3444, 2014. (2) D. James et al. Arch. Virol. 145:995, 2000. (3) T. A. Mekuria et al. Arch. Virol. 158:2201, 2013.