First Report of Papaya (Carica papaya) Naturally Infected With the Introduced Tomato yellow leaf curl virus-Israel
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2016, American Phytopathological Society. All rights reserved. Previously unreported virus-like disease symptoms consisting of severe mosaic and interveinal chlorosis, distortion, and brittleness were observed during the fall/spring of 2014 to 2015 in a 50-ha commercial papaya orchard planted with variety Red Maradol in the Rio Grande Valley of Texas. Populations of the silverleaf whitefly (Bemisia tabaci Genn.) and the green peach aphid (Myzus persicae Sulzer) were observed feeding and reproducing on papaya plants. Incidence of symptomatic trees increased from 40 to 100% within 6 months after the disease was first noted during fall 2014 and the most severely affected plants were stunted, with reduced or no fruit set, and poor fruit quality. To explore the papaya plant virome, a cDNA library constructed from DNase-treated total RNA extracts of leaf samples pooled from eight randomly collected symptomatic trees was subjected to high-throughput sequencing (HTS) using the Illumina NextSeq 500 platform, and the HTS data obtained were analyzed as described previously (Alabi et al. 2015). The analysis revealed the presence of only one 301-nt contig mapped to the genome of Tomato yellow leaf curl virus-Israel (TYLCV-IL) in plants also harboring two RNA viruses (data not shown). To confirm HTS results, total DNA purified from the original eight symptomatic leaf tissues was used as templates for rolling cycle amplification (RCA) using the TempliPhi 100 Amplification Kit (GE Healthcare Biosciences Corp., Cranbury, NJ). The RCA templates were used in PCR with abutting primers (TYPap-C1a_F: 5-GCTCGTAGAGGGTGACGAAG and TYPap-C1a_R: 5-GAGCCACTGTTCGCAAGTAT, and TYPap-C2a_F: 5-GATAACAGAACACAGCCAGAGG with TYPap-C2a_R: 5-TGGTTCATTAGAAATGGCCTC) designed based on the HTS sequences. The 2.7 kbp products from three papaya samples were cloned individually into the pCR2.1 TOPO-TA vector (Life Technologies, Carlsbad, CA), and the DNA sequence was determined bidirectionally for each plasmid. The 2,781-nt long complete viral genomes from three samples (KX024639, KX024643, and KX024647) shared 99 to 100% nt identity with each other, and 98 to 99% nt identity with their closest relative, a TYLCV-IL isolate from Sinaloa, Mexico (EF523478). Further analysis of the full-length genome of these papaya isolates revealed that their closest relatives in the old world, at 98% nt identity, are isolates from Morocco (EF060196) and the Netherlands (FJ439569). Unlike the TYLCV-IL isolates reported earlier on tomato plants from new world locations in Texas (EF110890), Arizona (EF210554), and Grenada (FR851297), the papaya isolates contained no deletion in the intergenic region located between the nt coordinates (2,700 and 2,728), suggesting a possible recent or previously undetected TYLCV-IL introduction in Texas from movement within or outside North America. Whether TYLCV-IL infection alone causes symptoms in papaya in the absence of the other viruses detected here is not known because all plants harbored TYLCV-IL together with other viruses. The wide host range of TYLCV includes tomato and other cultivated and noncultivated plants (Daz-Pendon et al. 2010). Here we report the first detection of TYLCV-IL infecting papaya. Papaya plants, when grown as perennials, can serve as important reservoirs of viruses that infect susceptible crops in the vicinity. Thus, this discovery presents new challenges to virus disease management in papaya, tomato, and other annual and perennial crops grown in South Texas.
