First Report of Plantago asiatica mosaic virus in Imported Asiatic and Oriental Lilies (Lilium hybrids) in the United States.

Abstract

Asiatic and Oriental hybrid lilies (Lilium sp., Liliaceae) are bulbous ornamentals valued for their flowers. Bulbs of several varieties of each lily type, imported from the Netherlands, were purchased in spring 2013 from retail nurseries and grown in a cool greenhouse; additional bulbs were obtained in 2014. After flowering in 2013, but prior to leaf senescence, necrotic streaking was observed in midstem leaves of several plants. RNA extracted from leaves of several individual plants was subjected to reverse-transcription-polymerase chain reaction (RT-PCR) assay using NSNC-odT primed cDNA and PCR with primers PxDeg/BNSNC or potyS/BNSNC to amplify potexvirus/carlavirus and potyvirus products respectively (2,3,4). Sequencing of a c. 1.7-kb PCR product from one lily identified Lily symptomless virus (LSV). Mechanical inoculation of pooled lily leaf samples to Nicotiana benthamiana, N. glutinosa, and Chenopodium quinoa (not hosts of LSV) yielded chlorotic or necrotic local lesions on C. quinoa and systemic mosaic with necrotic spotting, streaking, or apical necrosis on N. benthamiana; electron microscopy revealed potexvirus-like flexuous particles. RT-PCR from C. quinoa and N. benthamiana with PxDeg/BNSNC yielded a c. 1.3-kb product, which was cloned and sequenced; the consensus sequence (KM205357) had 98.7% nucleotide identity to a Dutch isolate of Plantago asiatica mosaic virus (PlAMV, KF471012; 78.5 to 87.8% to other isolates), and 99.0% coat protein amino acid identity to KF471012 (88.9 to 93.2% to other isolates). The 2013 lilies were stored overwinter at 4°C, and RNA was extracted from roots of individual bulbs. Primers PlAMV CP-F2 (TTCGTCACCCTCAGCGG) and PlAMV CP-R3 (AAACGGTAAAATACACACCGGG) were designed based on alignment of KM205357 with all PlAMV sequences available in GenBank. RT-PCR using PlAMV CP-F2/CP-R3 yielded products of the expected 511 bp from 20 bulbs and no product from a no-template control. ELISA of root and bulbscale samples using PlAMV-lily specific antibody and conjugate (a gift of R. Miglino, BKD, The Netherlands) confirmed PlAMV in seven of 20 bulbs positive by RT-PCR. Bioassay of PCR-positive lilies on N. benthamiana, C. quinoa, and Tetragonia expansa confirmed infection in three out of eight by both symptoms and ELISA. Altogether nine out of 13 Asiatic lilies (four of four cultivars: America, Connecticut King, Grand Cru, and Pink Pixie) and 11 Oriental lilies (cvs. Stargazer and Starfighter) were found to be infected with PlAMV by RT-PCR, of which seven were confirmed by bioassay and/or ELISA. Bulbs obtained in 2014 were tested only by ELISA; five of 18 Asiatic lilies (three of six cultivars: Connecticut King, Crimson Pixie, and Yellow Electric) and three of 13 Oriental lilies (three of six cultivars: Anastasia, Casa Blanca, and Garden Party) were found to be infected. PlAMV was reported in lilies in the Netherlands in 2010, with losses of up to 80% in greenhouse cut-flower production (1). The Nandina mosaic isolate (PlAMV-NMV) has been known in the United States since 1976 (5), but PlAMV infection of lily has not previously been documented in the United States. Both RT-PCR and ELISA tests also detected PlAMV-NMV. The degree of damage observed in the Netherlands suggests that growers should seek bulb stocks free of PlAMV.