September 2014, Volume 80, Issue 5 , pp 449–453

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New natural hosts of Tomato yellow leaf curl virusidentified in and near tomato-growing greenhouses in eastern China

· Authors

· Authors and affiliations

· Gang Li

· Li-ming Zhao

· Xiang Wang

· Ying Gao

· Guo-zhen Sun

· Xiao-ping Zhu Email author

1. 1.

Viral and Viroid Diseases

First Online:

June 2014

DOI: 10.1007/s10327-014-0531-5

Cite this article as:

Li, G., Zhao, L., Wang, X. et al. J Gen Plant Pathol (2014) 80: 449. doi: 10.1007/s10327-014-0531-5

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Abstract

Tomato yellow leaf curl virus (TYLCV) causes huge losses to tomato production worldwide. In July 2011 and July–August 2012, we screened for potential TYLCV hosts in a tomato-growing area in Shandong Province, the core vegetable-producing region in China. PCR detection showed that 5 species of plants, Zinnia elegans, Acalypha australis, Gossypium hirsutum, Abutilon theophrasti, and Nicotiana tabacum, were infected. Full genomic sequences of the new TYLCV isolates were obtained and submitted for sequence analysis. Sequence alignment and similarity analysis showed that they all belonged to the TYLCV-IL strain.

Keywords

TYLCVChinaSequence analysisNew hosts

G. Li, L. Zhao have contributed equally to this research.

Electronic supplementary material

The online version of this article (doi: 10.1007/s10327-014-0531-5 ) contains supplementary material, which is available to authorized users.

Tomato yellow leaf curl virus (TYLCV; genus Begomovirus, family Geminiviridae) is transmitted by the whitefly Bemisia tabaci. The TYLCV genome consists of circular, single-stranded DNA (ssDNA). Tomato yellow leaf curl disease (TYLCD) poses a serious threat to tomato production throughout the world. The virus was first discovered in 1939 in Israel and Jordan, and in 1964 it was officially named TYLCV. Since then, the disease has spread rapidly to the Middle East and the Mediterranean coast, East Asia, South Asia, Africa, Europe, the United States, Central America, Australia, Italy and many other countries and regions (Accotto et al. 2003; Boulton 2003; Moriones and Navas-Castillo 2000 ). In recent years, the disease has broken out in many provinces and cities across a large area in China and has quickly spread from south to north. The rapid spread of TYLCD is directly related to an outbreak of the virus vector B. tabaci in China. Because B. tabaci can invade a variety of plants, the number of potential TYLCV hosts will undoubtedly expand.

In this study, we screened for potential TYLCV hosts in Shandong Province, the main tomato-growing region in China. Several plant species susceptible to TYLCV infection were identified, and the respective TYLCV isolates were sequenced and analyzed.

Leaf samples of crops and weeds with either symptoms of virus infection or no symptoms of virus infection but a large number of B. tabaci on the leaves were collected in July 2011 and July–August 2012 in the main tomato-growing regions of Shandong Province, Shouguang and Tai’an. The samples were randomly collected from 8 sites in or around tomato-growing greenhouses where severe outbreaks of TYLCD and B. tabaci had been observed. Among the samples in Table 1, only Zinnia elegans collected in Shouguang District showed typical disease symptoms such as yellowing, dwarfing, and crimpling of the leaves with their margins curling upward (Fig. 1 ).

Table 1

Results of Tomato yellow leaf curl virus (TYLCV) detection and symptom evaluation in TYLCV hosts

Tested plant	Symptoms/detection

Asteraceae

Bidens bipinnata Linn.

NS/−

Eclipta prostrata (L.) L.

NS/−

Helianthus annuus L.

NS/−

Sonchus oleraceus Linn.

NS/−

Xanthium sibiricum Patr.

NS/−

Zinnia elegans Jacq.

S, Mo, LC, CR/+

Cannabaceae

Humulus scandens (Lour.) Merr.

NS/−

Chenopodiaceae

Chenopodium album Linn.

NS/−

Convolvulaceae

Ipomoea hederacea Jacq.

NS/−

Cruciferae

Capsella bursa-pastoris (L.) Medic.

NS/−

Cucurbitaceae

Cucurbita moschata Duch.ex Poir

NS/−

Cucumis sativus Linn.

NS/−

Luffa cylindrica (Linn.) Roem.

NS/−

Momordica charantia Linn.

NS/−

Euphorbiaceae

Acalypha australis Linn.

NS/+

Euphorbia heberophylla L.

NS/−

Euphorbia pulcherrima Willd.

NS/−

Labiatae

Salvia splendens Ker-Gawler

NS/−

Leguminosae

Phaseolus vulgaris L.

NS/−

Pisum sativum Linn.

NS/−

Vigna radiata (L.)

NS/−

Vigna unguiculata (Linn.) Walp

NS/−

Malvaceae

Abutilon theophrasti Medik

NS/+

Gossypium hirsutum L.

NS/+

Hibiscus rosa-sinensis L.

NS/−

Abelmoschus moschatus Medicus Malv.

NS/−

Moraceae

Morus alba L.

NS/−

Rosaceae

Rosa chinensis Jacq.

NS/−

Solanaceae

Nicotiana tabacum L.

M, LC, CR/+

Solanum melongena L.

NS/−

Solanum nigrum L.

NS/−

“+” detected; “− ” not detected by PCR

NS no symptoms, M mild symptoms, S severe symptoms, LC leaf curling, Mo mottle or mosaic, CR leaf crinkling

Fig. 1

Symptoms of Zinnia elegans plants infected with Tomato yellow leaf curl virus. aHealthy plant, bZ. elegans plant with typical infection symptoms

Total DNA was extracted from all samples using the Plant Genomic DNA Kit (Tiangen, Beijing, China) according to the manufacturer’s instructions. In the preliminary detection, the universal degenerate primer pair PA/PB specific for begomoviruses (Deng et al. 1994 ) was used in the PCR with total DNA as a template.

After preliminary testing, positive samples were subjected to further analysis. Three pairs of overlapping primers (Online resource 1) covering all areas of virus DNA-A were designed in the conserved region based on the complete TYLCV sequence registered in NCBI. To obtain the full-length nucleotide sequence of the positive samples, the overlapping primer method for PCR amplification was used. PCR products were cloned in the pMD18-T Vector (TaKaRa, Dalian, China). The recombinant clones were sequenced at least twice in both directions by Invitrogen Biotechnology (Shanghai, China), and the fragments were assembled using DNAMAN software (Lynnon Biosoft, Pointe-Claire, QC, Canada). The complete genomic sequences of TYLCV isolates obtained in this study were deposited in the GenBank database with accession numbers KC852151 (Zinnia elegans), KC852147 (Gossypium hirsutum), KC852150 (Acalypha australis), KC852149 (Abutilon theophrasti), and JX856172 (Nicotiana tabacum). A phylogenetic tree was generated by the neighbor-joining method using the program MEGA 4.0 (Tamura et al. 2007 ). BLAST (GenBank database) and DNASTAR software (DNASTAR Inc., Madison, WI, USA) were used to analyze sequence identities and similarities.

A specific 541-bp DNA fragment was amplified by PCR from Z. elegans, G. hirsutum, A. australis, A. theophrasti, and N. tabacum DNA using the primer pair PA/PB, indicating that these plants were infected by a begomovirus. BLAST sequence analysis revealed that isolates from Z. elegans, A. australis, G. hirsutum, A. theophrasti, and N. tabacum shared high sequence similarity (> 99.0 %) with TYLCV isolates registered in GenBank. The above results revealed the presence of TYLCV in these 5 samples. The symptoms of TYLCV infection for each host are summarized in Table 1.

The expected specific fragments of 1369, 752, and 833 bp were obtained separately and used to assemble complete genomic DNA-A, which consisted of 2781 nucleotides for all isolates from positive samples. Sequence analysis of the ORFs revealed that all isolates had a genome organization similar to that of monopartite begomoviruses, with 6 ORFs corresponding to AC1, AC2, AC3, AC4, AV1, and AV2 (Navot et al. 1991 ).

Comparative analysis of sequence similarities and ORF identities between the TYLCV isolates and other begomoviruses revealed that genomes of the 5 positive isolates shared 91.6–99.8 % sequence identity with TYLCV isolates from Shandong and other provinces in China. However, the sequence homology of Z. elegans and N. tabacum TYLCV isolates with other geminiviruses from the same plants was below 75 %. The DNA-A similarity (Online resource 2) between Z. elegans, G. hirsutum, A. australis, and A. theophrasti isolates and TYLCV-SDCS (JX669541), TYLCV-SDCL (JQ038240), TYLCV-SDYT (JX669544), TYLCV-SDZB (HM627885), and TYLCV-Shouguang (JQ411237) strains ranged from 99.5 to 99.8 % and that sequence identity among the 4 positive isolates ranged from 99.6 to 99.8 %. In addition, the complete genome of an isolate from N. tabacum showed 97.2 % sequence identity with TYLCV-SDTA tomato isolates. According to the Geminiviridae classification (Fauquet et al. 2008 ), Z. elegans, G. hirsutum, A. australis, A. theophrasti, and N. tabacum isolates were identified as TYLCV isolates TYLCV-SDZi, TYLCV-SDGp, TYLCV-SDAc, TYLCV-SDAb, and TYLCV-SDTT, respectively.

To better analyze the phylogenetic relationship and taxonomic status of the isolated viruses, a phylogenetic tree was constructed based on DNA-A sequences of TYLCV and other geminiviruses isolated from Z. elegans and N. tabacum (Fig. 2 ). The results show that all TYLCV isolates form a large branch, while other geminiviruses infecting Z. elegans and N. tabacum cluster into a separate branch. The TYLCV branch was further divided into 4 phylogenetic clades representing 4 TYLCV strains, TYLCV-Gez, TYLCV-IL, TYLCV-MILD, and TYLCV-IR. The TYLCV isolates from China were all located in the clade with TYLCV-IL. The TYLCV isolates from Shandong Province were closely related to each other; they clustered together in 2 subclades within the clade of the TYLCV-IL strain from Israel. TYLCV-SDZi, TYLCV-SDGp, TYLCV-SDAc, and TYLCV-SDAb were closely related to TYLCV-SDCS (JX669541), TYLCV-SDCL (JQ038240), TYLCV-SDYT (JX669544), TYLCV-SDZB (HM627885), and TYLCV-Shouguang (JQ411237), forming one of the two subclades. TYLCV-SDTT, which was most closely related to TYLCV-SDTA (JF414236), grouped with the other subclade. These related isolates mentioned, all from tomato plants growing in or around the sampling sites, were sampled and sequenced by this team and other research groups before this study.

Fig. 2

Neighbor-joining phylogenetic tree based on complete DNA-A sequence alignments indicating the relationship between the Shandong isolates of Tomato yellow leaf curl virus in this study (marked with filled triangles) and other begomoviruses. The reliability of the analysis was subjected to a bootstrap test with 1000 replicates. Bootstrap values are shown as percentages; only values over 60 % are shown. Horizontal branch lengths represent genetic distances, as indicated by the scale bar; vertical distances are arbitrary. Representative begomovirus sequences obtained from GenBank are indicated by corresponding abbreviations, isolate names, and accession numbers. The outgroup is an isolate of Abutilon mosaic Bolivia virus (AbMBoV-Bolivia; HM585445)

These results demonstrate that Z. elegans, G. hirsutum, A. australis, A. theophrasti, and N. tabacum host TYLCV strains that may play an important role in viral epidemics in tomato fields in China.

To date, TYLCD has become one of the most damaging threats to tomato production in Shandong Province, the most important vegetable-producing region in China. According to previous reports, TYLCV can infect pepper, bean (Gharsallah Chouchane et al. 2007 ), and A. australis (Ji et al. 2013 ), and 461 samples belonging to 49 species from 15 families confirmed the presence of TYLCV (Papayiannis et al. 2011 ). However, there is no report that TYLCV infected the four new hosts.

The phylogenetic tree showed that TYLCV isolates reported around Shandong are clustered into a small branch within the branch of the TYLCV-IL strain. Sequence analysis of a full-length genome definitively placed the 5 isolates collected in this study in the TYLCV-IL group, and they were most closely associated with local or neighboring TYLCV isolates. Many studies indicate that TYCLV epidemics are linked to outbreaks of B. tabaci (Rybicki and Pietersen 1999 ). Therefore, the TYLCV isolated from Z. elegans, A. australis, G. hirsutum, A. theophrasti, andN. tabacum most likely originated from severely diseased tomato greenhouses infested with B. tabaci.

In this TYLCV-host screening study, TYLCV-positive A. australis, G. hirsutum, A. theophrasti, and N. tabacum did not manifest symptoms, and no other RNA viruses were detected (data not shown). In previous studies, the TYLCV hosts Conyza sumatrensis, Convolvulus sp., Cuscutasp., and Chenopodium murale L. were also symptomless (Jordá et al. 2001 ), as was A. australisidentified in China (Ji et al. 2013 ). Previous reports showed that some begomovirus infections in hosts to which the viruses were not well adapted were characterized by mild or no symptoms, low infection rates, and low levels of viral DNA (Hou et al. 1998; Petty et al. 1995; Pooma et al. 1996 ). Symptomless hosts may be an important TYLCV reservoir where the virus can temporarily survive and where the whiteflies can acquire TYLCV from infected leaves and transmit it to healthy plants.

With the continuous spread of TYLCV and the expansion of its host range, infection of Z. elegans and N. tabacum not only negatively affects their growth and production, but also makes prevention and control of TYLCV infection more difficult. In our investigation, the infection rates in Z. elegans were 70–80 %, depending on the field sampled, suggesting that Z. elegans may be an important reservoir of TYLCV, especially during a nontomato-planting period.

Acknowledgments

This research was supported by Grants 201003065 (Special Fund for Agro-scientific Research in the Public Interest), 30871620 (National Natural Science Foundation of China, NSFC), and KN214-ZR2012CM032 (Provincial Natural Science Foundation of Shandong).

Supplementary material

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(DOC 101 kb)

References

1. Accotto GP, Bragaloni M, Luison D, Davino S, Davino M (2003) First report of Tomato yellow leaf curl virus (TYLCV) in Italy. Plant Pathol 52: 799 CrossRef Google Scholar

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