First report of plumeria mosaic virus infecting Plumeria spp. in the United States

Abstract

Plumeria (Plumeria spp.) is a small ornamental tree grown in subtropical and tropical areas, providing shade and attractive and fragrant flowers in public and private landscapes. In Hawaii, plumeria is also commercially grown, with flowers harvested for cut flower and lei production. In 2019, a total of 10 cut flower plumeria farms in Hawaii sold 7,356,702 blossoms, valued at $395,791 (USDA/NASS). In July 2021, a commercial plumeria farm in Maui County, Hawaii reported trees with flowers exhibiting color breaking, and leaves with mosaic and vein banding. To determine if a viral pathogen was present, leaf tissue from a symptomatic plant was processed using a Double-RNA Viral dsRNA Extraction Kit for plant tissue (iNtRON Biotechnology, Korea), followed by random amplification (Melzer et al. 2010). The resulting products underwent paired-end sequencing on a MiSeq platform (Illumina, CA) at the Advanced Studies in Genomics, Proteomics, and Bioinformatics laboratory at the University of Hawaii. Of the 2,913,913 paired-end 300-bp reads generated, Geneious Prime (Biomatters, New Zealand) mapped 350,686 to plumeria mosaic virus (PluMV; KJ395757.1) and 293,911 to frangipani mosaic virus (FrMV; JN555602.2), with mean coverage depths of 10,318 and 7,348 respectively. A 6,648 nt contig representing the near full-length genome of PluMV-HI (OP342599) was found to be >97% identical to PluMV isolates PluMV-DR_TW (KX881422.2) and PluMV-Plu-Ind-1 (KJ395757.1). Similarly, a 6,631 nt contig representing the near full-length genome of FrMV-HI (OP342600) was found to be >98% identical to FrMV isolates FrMV-P (Lim et al. 2010; HM026454.1) and FrMV-Fr-Ind-1 (Kumar et al. 2015; JN555602.2). Bioinformatic analyses (Olmedo-Velarde et al. 2019) of the reads that did not map to PluMV and FrMV suggested the presence of a novel ampelovirus and reovirus in the tissue. To confirm the presence of PluMV and FrMV in Hawaii, leaves were collected in June 2022 from 5 plumeria trees on the Maui County farm and 16 ornamental plumeria trees from Honolulu County. Total RNA extracted as described by Li et al. (2008) as well as non-template (water) and positive (HTS tissue sample) controls underwent RT-PCR using random primers for cDNA synthesis, followed by virus-specific primers for PluMV (1133: 5’-TGGGCAAATAATCCGGCTATAC-3’/1134: 5’CCGGAGAGAGCATCAAACAA-3’) and FrMV (1129: 5’-TGAGTTTAGGTCGCAGTTGATAG-3’/1130: 5-’AAAGACCAGAACCTCCAGAAAG-3’) in singleplex reactions. The results indicated that all 5 plumeria samples from Maui County were positive for both PluMV and FrMV, whereas 6 out of 16 plumeria samples collected from Honolulu County tested positive for PluMV only. Both PluMV and FrMV are tobamoviruses (Virgaviridae) that can be transmitted mechanically and spread through the introduction and/or movement of cuttings, the primary method of plumeria propagation. Both PluMV and FrMV cause leaf mosaic (Kumar et al. 2015; Lim et al. 2010; Lin et al. 2020) and FrMV may also cause color break or “splash” in flowers, which was observed at the Maui County farm. This represents the first report of PluMV in the USA. FrMV was detected in Florida (Dey et al. 2020), but this is the first report of the virus in Hawaii. Additional surveys are required to determine the incidence of both viruses in other counties of Hawaii. The putative discovery of a novel ampelovirus and reovirus in plumeria warrants further research to characterize these agents and determine their distribution and impact on plumeria health.