First Report of Cucumber mosaic virus Isolated from Wild Vigna angularis var. nipponensis in Korea.

A viral disease causing severe mosaic, necrotic, and yellow symptoms on Vigna angularis var. nipponensis was prevalent around Suwon area in Korea. The causal virus was characterized as Cucumber mosaic virus (CMV) on the basis of biological and nucleotide sequence properties of RNAs 1, 2 and 3 and named as CMV-wVa. CMV-wVa isolate caused mosaic symptoms on indicator plants, Nicotiana tabacum cv. Xanthi-nc, Petunia hybrida, and Cucumis sativus. Strikingly, CMV-wVa induced severe mosaic and malformation on Cucurbita pepo, and Solanum lycopersicum. Moreover, it caused necrotic or mosaic symptoms on V. angularis and V. radiate of Fabaceae. Symptoms of necrotic local or pin point were observed on inoculated leaves of V. unguiculata, Vicia fava, Pisum sativum and Phaseolus vulgaris. However, CMV-wVa isolate failed to infect in Glycine max cvs. 'Sorok', 'Sodam' and 'Somyeong'. To assess genetic variation between CMV-wVa and the other known CMV isolates, phylogenetic analysis using 16 complete nucleotide sequences of CMV RNA1, RNA2, and RNA3 including CMV-wVa was performed. CMV-wVa was more closely related to CMV isolates belonging to CMV subgroup I showing about 85.1-100% nucleotide sequences identity to those of subgroup I isolates. This is the first report of CMV as the causal virus infecting wild Vigna angularis var. nipponensis in Korea.

CMV is the type species of the genus Cucumovirus in the family Bromoviridae (Palukaitis and Garcia-Arenal, 2003; Roossinck et al., 1999). It is one of the most widespread and economically important plant viruses in the world and has a very extremely wide host range infecting approximately 1,000 plant species in 100 families (Douine et al., 1979; Kaper and Waterworth, 1981). Some of weed species are potential virus sources for aphid transmission into crop fields. These weed species are likely to be important role in the survival of CMV (Kaper and Waterworth, 1981). The CMV genome consists of three single-stranded RNAs, i.e. RNAs 1, 2, and 3 (Ding et al., 1994; Palukaitis and Garcia-Arenal, 2003; Palukaitis et al., 1992). Many CMV isolates have been described previously and classified into two subgroups, I and II, on the basis of serological properties and nucleotide sequence identity (Owen and Palukaitis, 1998; Palukaitis and Garcia-Arenal, 2003).

Vigna angularis var. nipponensis was an annual wild species belonging to the subgenus Ceratotropis in the genus Vigna. It is widely distributed in East Asian and Southeast Asian countries including Korea, Japan, China, Nepal, and Taiwan. V. angularis var. nipponensis was formerly treated as a progenitor of Phaseolus or Azukia (Tateishi, 1984; Lumpkin and McClary, 1994; Yamaguchi, 1992). V. angularis var. nipponensis is expected to be a valuable genetic source for breeding of azuki bean (Siriwardhane et al., 1991; Kaga et al., 2008). It is also very important species for the study of origin of Azuki bean.

Several virus are known to infect Azuki bean including Alfalfa mosaic virus (AMV), Azuki bean mosaic virus (AzMV), Blackeye cowpea mosaic virus virus (BICMV), Bean common mosaic virus (BCMV), Bean yellow mosaic virus (BYMV), Cucumber mosaic virus (CMV), and Cowpea mosaic virus (CPMV) (Iizuka et al., 1990; Tsuchizaki et al., 1987). Among them, AMV (Heo et al., 1976; Jung et al., 2000), BCMV (Choi et al., 1989), and CMV (Choi et al., 1998; Heo et al., 1976) have been reported in Korea.

In this article, we report the occurrence of a CMV on Vigna angularis var. nipponensis in Korea, characterized on the basis of biological and complete nucleotide sequence-based properties, and named it as CMV-wVa. To our knowledge, this is the first report of CMV on V. angularis var. nipponensis in the world.

Vigna angularis var. nipponensis, showing severe mosaic, chlorotic spots, and yellow symptoms were collected from fields around Suwon, Korea (Fig. 1). The collected isolate was identified by conducting Double Antibody Sandwich-Enzyme Linked Immune Sorbent Assay (DAS-ELISA) and Reverse Transcription-Polymerase Chain Reaction (RT-PCR) using CMV specific forward (5′-TGGTCGTCCAACT ATTAACCAC-3′), Reverse (5′-TACTGATAAACCAGTACCGGTGA -3′) primers of the coding region of coat protein gene. Each cycle included a denaturing step at 94°C for 30 sec, an annealing step at 55°C for 30 sec, and extension step at 72°C for 90 sec, and finally kept at 72°C for 10 min. DAS-ELISA was performed using CMV polyclone antibody described by Clark and Adams (Agdia, USA). Shortly, CMV antibody and its conjugate were both diluted 1:200 and all incubations were carried out at 37°C for 1 h except for the substrate that was incubated for 30 min. Quantitative measurements were examined by absorbance at 405 nm (A405). To identify the virus isolate from V. angularis var. nipponensis, infected-leaf was macerated in 0.01 M sodium phosphate buffer, pH 7.0 and the crude sap was rubbed to the leaves of indicator plants including Chenopodium amaranticolor. Single lesions were isolated and re-inoculated on healthy Ch. quinoa three consecutive times. The isolate obtained from the third re-inoculated Ch. quinoa was designated as CMV-wVa, propagated in Nicotiana tabacum cv. ‘Xanthi-nc’, and was subjected to biological and molecular analyses.To test the infectivity of virus isolate and the symptoms on indicator plants, seedlings of test plants at the 3–5 leaf stage were inoculated by sap extracted from N. tabacum cv. ‘Xanthi-nc’. The plants were put in an insect-free greenhouse maintained at 20–25°C for 12–16 h light period. Disease symptoms were recorded four times a week for 30 days. CMV-wVa isolate caused mosaic or vein clearing symptom on the upper leaves of N. tabacum cv. ‘Xanthi-nc’, N. glutinosa, Capsicum annuum, Petunia hybrid, Cucurbita moschata, Cucumis sativus, and Cu. melo. In addition, the CMV-wVa isolate induced severe mosaic, malformation or fern leaves on upper leaves of Solanum lycopersicum (Table 1) and C. pepo (Table 1 and Fig. 2D). CMV-wVa induced necrotic local lesion on inoculated leaves and chlorotic ring local, mosaic symptoms on upper leaves of Vigna radiate (Table 1 and Fig. 2G). Local lesions were observed on Datura stramonium, Ch. amaranticolor, and Ch. quinoa. However, no symptoms were observed on Glycine max (cvs. ‘Sorok’, ‘Sodam’, and ‘Somyeong’), Brassica peckinensis L., Raphanus sativus L., and Spinacia oleracea L. (Table 1).

Fig. 1.

Natural symptoms on Vigna angularis var. nipponensis in field infected with Cucumber mosaic virus (CMV) isolate wVa. Chlorotic spots, mosaic, and leaf yellowing were observed.

Table 1.

Symptoms developed on indicator plants inoculated mechanically with Cucumber mosaic virus isolate wVa (CMV-wVa)

Indicator plants	Symptomsa on the leaves
	Inoculated	Upper
Solanaceae
Nicotiana tabacum cv. ‘Xanthi-nc’	cl	m
N. glutinosa	–	m
Capsicum annuum	–	m
Solanum lycopersicum	–	sm,f
Datura stramonium	cl	–b
Petunia hybrida	–	m
Cucurbitaceae
Cucurbita pepo	cl	sm, mal
C. moschata	cl	vc
Cucumis sativus	cl	m
Cu. melo	cl	m
Fabaceae
Glycine max cv
‘Sorok’	–	–
‘Sodam’	–	–
‘Somyeong’	–	–
Brassicaceae
Brassica peckinensis	–	–
Raphanus sativus	–	–
Chenopodiaceae
Chenopodium amaranticolor	p.p	–
Ch. quinoa	p.p	–
Spinacia oleracea	–	–

cl, chlorotic local; f, fern leaves; m, mosaic; mal, malformation; p.p, pin point; sm, severe mosaic; vc, vein clearing; –, no symptom.

Test results of symptomless leaves from ELISA was negative.

Fig. 2.

Symptoms on test plants inoculated with CMV-wVa. CMV-wVa caused mosaic symptom on the upper leaves of Nicotiana tabacum cv. ‘Xanthi-nc’ (A), Petunia hybrida (B) and N. glutinosa (C) while causing severe mosaic and/or malformation on Cucubita pepo (D), Cucumis sativus (E), and Cu. melo (F). CMV-wVa induced mosaic symptom on the upper leaves of Vigna radiate (G) and V. angularis (H). CMV-wVa caused necrotic spot symptoms on the of V. unguiculata (I), V. fava (J) and Pisum sativum (K); however, the symptoms were not prevalent on the upper leaves.

To compare the infectivity of CMV-wVa isolate with CMV isolates of various host, CMV-Z(zucchini), -RB(cone flower), -ZM(maize), -Pa(azuki bean), and CM-19(azuki bean) (Choi et al., 1998; Kim et al., 2010a, 2010b, 2011 and lizuka et al., 1990) along with CMV-wVa were inoculated onto 6 different plant species belonging to Fabaceae. Four to 30 plant seedlings of each test plant listed in Table 2 were inoculated with sap extracted from N. tabacum cv. ‘Xanthi-nc’. The CMV-wVa, -Z, -RB and -Pa induced similar chlorotic and necrotic symptoms as well as mottle and mosaic symptoms on inoculated or upper leaves of Vigna angularis. However, symptoms of necrotic local or pin point were observed on inoculated leaves of V. unguiculata, Vicia fava, Pisum sativum, and Phaseolus vulgaris with no systemic symptom. CMV-ZM isolate failed to infect in V. angularis and Phaseolus vulgaris (Table 2; Fig. 2). The experimental infectivity of CMV-wVa was similar to that reported for CMV isolates of zucchini, cone flower, maize and azuki bean in the host reaction of Solanaceae and Cucubitaceae (Choi et al., 1998 and Kim et al., 2010a, 2010b, 2011). However, Japan CMV isolate (CM-19) from azuki been did not systemically infect V. radiate (Iizuka et al., 1990), only CMV-wVa isolate infected systemically causing local chlorotic ring or necrosis and systemic mosaic on V. radiata leaves. These differences are considered as unique characteristics of CMV-wVa.

Table 2.

Comparison of the infectivity of CMV-wVa isolate with CMV isolates on test plants belonging to Fabaceae

Indicator	Symptomsa on the leaves (inoculated/upper)					Reference
	CMV-wVa		CMV-Zb	CMV-RBc	CMV-ZMd	CMV-Pae	CM-19f
Vigna angularis	cl,nl/mo	14/30g	nl/m	nl/m	–/–h	/m	/m
V. unguiculata	nl/–	20/25	nl/–	pp/–	pp/	nt	l/–
V. radiate	nl/crl,nl,m	4/6	nt	nt	nt	nt	l/–
Vicia fava	nl/–	5/15	nl/–	nl/–	nl/–	nt	l/–
Pisum sativum	nl/–	7/20	nl/–	nl/–	nl/–	nt	l/n
Phaseolus vulgaris	nl/–	4/26	nl/–	nl/–	–/–	nt	l/–

cl, chlorotic local; m, mosaic; mo, mottle; l, local; nl, necrotic local; pp, pin point; –, no symptom; nt, not tested.

CMV-Z, Cucumber mosaic virus - Zucchini (Kim et al., 2010b).

CMV-RB, Cucumber mosaic virus - Rudbeckia bicolor (Kim et al., 2010a).

CMV-ZM, Cucumber mosaic virus - Zea mays (Kim et al., 2011).

CMV-Pa isolated from Phaseolus angularis (Choi et al., 1998).

CM-19 isolated from Phaseolus angularis (Iizuka et al., 1990).

Number of plants infected/number of plant mechanically inoculated.

Test results of symptomless leaves from ELISA was negative.

CMV has one of the broadest host ranges among plant viruses, and its numerous stains have been differentially characterized (Palukaitis et al., 2003). Most CMV typically infects Solanaceae and Cucurbitaceae, but either produce local lesions or do not infect legume species (Whipple et al., 1941). CMV-wVa isolate infected not only V. angularis and V. radiate but also Solanaceae and Cucurbitaceae. Despite no ordinary occurrence of CMV in wild V. angularis var. nippensis, CMV-wVa has a broad host ranges including red bean, mung bean, tomato, pepper and cucumber. So it is very important role in CMV sources for aphid transmission into commercial fields.

Total RNAs were extracted from the N. tabacum leaves that were inoculated with CMV-wVa by easy-spin™ total RNA kit (iNtRON, Korea). Sequence specific full-length primers were designed based on previously reported genomic sequences of CMV isolates available in GenBank of National Center for Biotechnology (NCBI) (Kim et al., 2010b). RT reaction was carried out at 42°C for 30 min, and was denatured by heating at 95°C for 5 min in 5× RT buffer containing 5 μg of total RNA, 10 pmoles of the downstream primer, 2.5 mM each of four dNTPs, and 2.5 units AMV reverse transcriptase (Promega, USA). The RT reaction mixture was mixed with 1.25 units GoTaq™ DNA polymerase (Promega, USA), 5× Green PCR buffer and 2.5 mM MgCl2, and 10 pmoles of the upstream primer followed by amplification in a Bio-Rad Thermal Cycler (USA). The amplified PCR products were purified using PCR gel/direct extraction kit (iNtRON, Korea) and sequenced. End sequences of the genomes were obtained with the 5′/3′ rapid amplification of cDNA ends (RACE) protocol (Frohmant et al., 1988). cDNA clones containing the 5′ end of the genomes were obtained using Xec primers (5′ AAAGAATTCCCCCCCCCCCC-3′) and CMV 5′-RNA1 (5′-TCCTTTATCGCCGTGGGAGGCTAC-3′); for CMV 5′-RNA2 (5′-TCCTCGGGAGTGTCGACACC-3′); and for CMV 5′-RNA3 (5′-CCTACTGGTACCTTGGAAAGCCAT-3′) primers complementary to nucleotides 151–128, 159–140, and 144–121, respectively, of CMV strain. In addition, cDNA clones containing the 3′ end of the genomes were obtained using CMV 3′-RNA1 (5′-TTGCTCGTGCTT AGCGG3′); for CMV 3′-RNA2 (5′-ACAAAGTCCCAGCGAGAG-3′); for CMV 3′-RNA3 (5′-TTGATTCTACCGTGTGGGTGACAGT-3′), and anchor primers (5′-GACCACGCGTATCGATGTCGACTTTTTTTTTTTTTTTTV-3′).

The lengths of CMV-wVa RNAs 1, 2, and 3 were consisted of about 3.3 kb, 3 kb and 2.2 kb, respectively. CMV-wVa RNAs 1, 2, and 3 nucleotide sequences were deposited at the GenBank under accession codes JX014246, JX014247, and JX014248, respectively. So far full length three RNAs segment sequence of wild azuki bean of CMV have been not reported. This is the first record on Vigna angularis var. nipponensis. The sequences were then compared with corresponding regions of the other CMV isolates along with previously reported Korean CMV isolates (-Z, -RB, -ZM and -Pa) retrieved from the GenBank database (Choi et al., 1998; Kim et al., 2010a, 2010b, 2011 and Roossinck, 2002). The sequences of Japan CM-19 isolate from azuki bean have been not reported.

Multiple nucleotide/amino acid sequence alignment was performed by using Clustal W (MEGA 5.0). Comparative sequence analysis disclosed that the 1a, 2a, 2b, 3a, and CP ORFs of CMV-wVa had 89.1–98.8%, 89.7–98.6%, 85.1-100%, 91.3–97.6%, and 91.8–98.0% nucleotide sequence identity, respectively, with CMV subgroup I isolates at the nucleotide level (Table 3). In contrast, identities of 54.4 to 79.0% were observed with subgroup II isolates at the nucleotide level. Database comparisons of the deduced amino acid sequences showed 94.2 to 99.2% sequence identity with 1a ORF gene of CMV subgroup I. In CMV-wVa, 1a ORF showed highest sequence identity at nucleotide level with the CMV-ZM isolate (98.8%) and 2a and 2b ORFs of CMV-wVa RNA2 showed 98.6 and 100% sequence identity with the CMV-Mf and -RB isolates, respectively. Similarly, the 3a and CP ORFs of CMV-wVa showed 97.6 and 98.0% sequences identity with the CMVY and -Z isolates, respectively. To compare the sequence identity of CMV-wVa isolate with CMV-Pa from azuki bean in Korea showed lowest sequence identity (91.3%) of 3a ORF (Table 3). In general, nucleotide and the deduced amino acid sequences of five ORFs of CMV-wVa showed highest sequence identity with CMV subgroup I isolates. Phylogenetic analysis were performed employing the Maximum likehood method packaged in the MEGA 5.1 software and with the complete nucleotide sequences of three segments of CMV isolates from the GenBank database. The bootstrap maximum-likehood trees for these genomic regions are shown (Fig. 3A, B, and C). Phylogenetic analysis of RNAs 1, 2, and 3 showed that 17 CMV isolates were divided into two subgroups such as subgroup I and II. CMV-wVa isolate was belonged to subgroup I and was closely related to the CMV-ZM and -Rb in analysis with the RNA1 sequence. Analysis of nucleotide sequences with RNAs 2 and 3 showed that CMV-wVa was most closely related to the members of subgroup IA. Especially, CMV-wVa RNA1 was divided in subgroup I. Along with CMV-wVa RNA1, RNA2 and RNA3 of CMV-wVa were also assigned to subgroup I based on phylogenetic analysis (Fig. 3). Therefore, results of phylogenetic analyses of the RNA segments 1, 2, and 3 suggested that CMV-wVa belongs to subgroup I of CMV.

Table 3.

Nucleotide/amino acid sequence identities (%) between CMV-wVa and the other previously reported CMV strains and/or isolates

Isolate	Group	Isolatesa	Nucleotide and amino acid identity (%)
			RNA1		RNA2	RNA3
			1a	2a	2b	3a	CP
wVa	I	CMV-ZM	98.8/99.2	96.6/97.7	97.3/98.2	96.8/98.9	96.5/98.6
		CMV-RB	92.6/95.7	96.6/97.7	100/100	96.7/98.9	97.3/98.2
		CMV-Z	92.5/97.7	96.6/97.7	96.4/95.5	97.3/98.9	98.0/99.1
		CMV-Fny	91.8/97.5	96.9/97.9	97.3/97.3	97.1/98.9	97.0/98.6
		CMV-Y	91.2/95.5	97.2/98.5	97.6/96.4	97.6/99.3	96.8/97.7
		CMV-Leg	91.9/96.7	96.3/97.3	91.9/87.3	97.0/99.3	96.8/98.6
		CMV-Mf	92.4/96.6	98.6/98.8	98.8/99.1	96.7/98.9	97.3/98.2
		CMV-NT9	91.1/96.9	91.9/93.2	86.3/99.1	94.1/97.1	94.7/98.2
		CMV-Tfn	90.9/96.8	92.0/93.0	86.3/79.3	94.1/97.1	95.0/98.6
		CMV-Ix	90.8/96.1	90.0/91.4	86.3/74.4	92.5/94.6	91.8/95.4
		CMV-CTL	90.6/95.7	90.8/93.4	87.2/81.1	94.8/96.1	92.2/98.2
		CMV-IA	89.1/94.2	89.7/90.7	85.1/73.9	93.7/96.4	92.5/97.2
		CMV-Pa	–	–	–	91.3/92.2	97.0/99.1
		CM-19	–	–	–	–	–
	II	CMV-Q	77.8/84.1	71.9/73.1	54.4/47.7	79.0/83.2	77.1/82.6
		CMV-Trk7	77.9/84.6	71.9/74.4	55.0/47.7	78.8/83.9	76.1/80.4
		CMV-Ly	77.7/84.3	72.0/74.2	55.3/46.8	78.9/83.5	76.5/82.2
		CMV-Ls	77.9/85.0	71.9/74.7	55.0/47.7	78.8/83.2	76.8/81.7
	Outgroup	PSV-ER	66.7/71.7	56.9/51.9	44.3/32.7	63.4/64.9	51.2/44.8

The Genbank accession number of the reference CMV isolates : Va (JX014246, JX014247 and JX014248); ZM (JN180309, JN180310, and JN180311); RB (GU327363, GU327364, and GU327365); Z (GU327366, GU327367, and GU327368); Fny (D00356, D00355, and D10538); Y (D12537, D12538, and D12499); Leg (D16403, D16406, and D16405); Mf (AJ276479, AJ276480, and AJ276481); NT9 (D28778, D28779, and D28780); Tfn (Y16924, Y16925, and Y19626); Ix (Y20220, U20218, and U20219); CTL (EF213023, EF213024, and EF213025); IA (AB042292, AB042293, and AB042294); Pa (AB290913, and AB290152); Q (X02733, X00985, and M21464); Trk7 (AJ007933, AJ007934, and L15336); Ly (AF198101, AF198102, and AF198103); Ls (F416899, AF416900, and AF127976); PSV (NC002038, NC002039, and NC002040); – (not reported).

Fig. 3.

Phylogenetic trees derived from nucleotide sequences of the CMV RNA segments 1, 2, and 3 of CMV-wVa with the other previously reported CMV isolates (panels A, B, and C, respectively). Peanut stunt virus (PSV) was used as an outgroup. Phylogenetic analyses were performed employing the maximum likehood method packaged in the MEGA 5.1 software.

Vigna angularis var. nippensis is considered to be the wild counterpart of azuki bean (Lumpkin and McClary, 1994; Tateishi, 1984; Yamaguchi, 1992) and is distributed widely in Asian countries including Korea. Several azuki bean crops naturally infected by CMV have been reported (Choi et al., 1998; Heo et al., 1976; Iizuka et al., 1990).

However, there is no report of natural infection of V. angularis var. nippensis (wild azuki bean) by CMV in the world. CMV-wVa isolate causing severe mosaic, necrotic, and yellow symptoms on Vigna angularis var. nipponensis identified by serological test (DAS-ELISA) and reverse transcription-polymerase chain reaction (RT-PCR). Results of this study indicated that CMV-wVa isolate infected systemically causing local chlorotic ring or necrosis and systemic mosaic on V. radiata and economically plants including pepper, tomato. CMV-wVa was more closely related to CMV isolates belonging to CMV subgroup I. This is the first reported show the occurrence and identification of CMV subgroup I on V. angularis var. nippensis on the basis of biological and complete sequence analyses. Further studies of comparison analysis between CMV-wVa (wild azuki bean, Korea) and CM-19 (azuki bean, Japan) will be required for identification of gene involved in pathogen and geographical relation.