Bong-Nam Chung

Seed Transmission of Chrysanthemum stunt viroid in Chrysanthemum

The presence of Chrysanthemum stunt viroid (CSVd) in seed and pollen of diseased chrysanthemum was demonstrated. In seeds infected male parent from crosses in May, CSVd was transmitted to 6.7% of the progeny seedlings, whereas if the female parent was infected, CSVd transmission rate was between 46.9 and 75.7%. A relatively high incidence of 94.4 to 96.0% seed transmission occurred when both parents were infected. In seeds infected male parent from crosses in December, no progeny seedlings were infected with CSVd, whereas if the female parent did, CSVd transmission rate was 1.5%. When both parents were infected, 6.9% seed transmission was occurred. The seed transmission rate depended on the temperature when the crosses were made. CSVd was not detected in the non-infected female parent pollinated with infected pollen but was transmitted to the progenies. This is the first report of seed-borne transmission of CSVd in chrysanthemum.

Survey of Viral Diseases Occurrence on Major Crops in 2007

The severe damage induced by the important viruses of Rice stripe virus (RSV), Cucumber green mottle mosaic virus (CGMMV), Melon necrotic spot virus (MNSV), Tomato spotted wilt virus (TSWV) and Tomato bushy stunt virus (TBSV) was described on major crops in Korea. In 2007, the plot incidence rate of RSV was 100% on the precocious rice cultivars at the Western coastal provinces of Gyeonggido, Chungcheongnamdo, Jellabugdo and Jellanamdo, and Jejudo. RSV occurred in 2,441 ha with incidence rate of 70% over at 5 areas of Seocheon, Seosan, Boryung, Hongsung and Buyou in Chungcheongnamdo. At 4 areas of Buan, Gimje, Gunsan and Gochang in Jellabukdo, RSV occurred in 2.016 ha. CGMMV occurred on watermelon in 4.6 ha at Cheongyang area, and its outbreak was also 890 ha on oriental melon for 120 farmers with the incidence area of 23% against total cultivation areas of Seongju. MNSV was recorded firstly on watermelon in 2006 at Andong and it spread to 3 areas of Hapcheon, Gochang and Yanggu. TSWV occurred firstly at Danggin in Chungcheongnamdo in 2005. TSWV in 2006 spread to 6 areas; Taian, Hongsung and Seosan in Chungcheongnando, Namwon in Jellabukdo, and Sunchon and Kwangju in Jellanamdo. In 2007, TSWV covered 17 areas of western and southern parts; the 5 area including Taian in Chungcheongnamdo, Kwangju in Jellanamdo, Bucheon in Gyunggido, and so forth. TBSV was described firstly on table tomato at Sacheon in Kyungsangnamdo in 2004. TBSV occurred on cherry tomato at Chungju in 2006 and on table tomato at Busan area.

Viruses and Symptoms on Peppers, and Their Infection Types in Korea

The incidence of virus disease on peppers was investigated at the 52 areas in the whole country in 2002, 2004 to 2006. Among the six viruses, Cucumber mosaic virus (CMV), Pepper mottle virus (PepMoV), Pepper mild mottle virus (PMMoV), Broad bean wilt virus 2 (BBWV2), Tobacco mild green mosaic virus (TMGMV) and Tomato spotted wilt virus (TSWV), infecting peppers in Korea, the incidence of CMV, PepMoV, PMMoV and BBWV2 was 29.4%, 13.6%, 14.3%, 25.6%, orderly. TMGMV and TSWV had the same low infection rate of 1.0%. The infection rate of CMV was higher as 53.3% and 34.2% in 2002 and 2004, but it was decreased to 18.2% and 11.9% in 2005 and 2006, respectively. The infection rate of BBWV2 was lower as 1.3% in 2002 and 1.8% in 2004, but it was increased abruptly to 41.3% in 2005 and 58.2% in 2006. For the types of mixed infections of pepper viruses, the incidence of CMV+PepMoV was 62.6% in 2002 and 50.0% in 2004, and that of CMV+BBWV2 was increased suddenly from 33.3% in 2005 to 83.2% in 2006. The triplex infection of CMV+BBWV2+PepMoV was 6.4% in average. CMV caused severe mosaic and BBWV2 induced ring spots, and the two mixed virions caused chlorosis on the leaves of red peppers. TSWV induced the typical symptoms of multiple ring spots on the leaves and fruits of red peppers.

Effect of temperature on the Concentration of Chrysanthemum stunt viroid in CSVd-infected Chrysanthemum

CSVd-infected chrysanthemum plants grown under growth chamber for 2 months resulted a higher dilution endpoint of template RNA for Reverse transcription and polymerase chain reaction (RT-PCR) than those grown for 1 month: for 1 month, and for 2 months. Independent experiment, shoots cut from CSVd (Chrysanthemum stunt viroid)-in footed chrysanthemum plants grown under growth chamber for 2 months showed the same CSVd concentration as control() at 8 weeks after moving them to normal green-house condition(). From those results, it was concluded that even though the concentration of CSVd was reduced in plants grown at low temperatures, when they were moved to normal glass-house temperature CSVd concentration increased to that of untreated plants in 8 weeks. This conclusion was supported by the rapid replication of CSVd in chrysanthemum after infection.

Biological Characteristics and Nucleotide Relationships in Korean Tomato spotted wilt virus Isolates

Tomato spotted wilt virus (TSWV) was identified from seven plants at two areas, Anyang and Dangjin, in Korea. The isolates of TSWV were seven as TSWV-KATm from tomato, TSWV-KAPo from potato, TSWV-KABal from balsam, TSWV-KACTm from cherry tomato and TSWV-KAIxe from Ixeris dentata at Anyang area, and TSWV-KDSe from sesame and TSWV-KDRP from red pepper at Dangjin area. Pathogenicity of seven TSWV isolates was various on the assay plants, and could not be grouped definitely. Three isolates of TSWV-KAIxe, TSWV-KACTm and TSWV-KABal had relatively narrower host ranges among the seven isolates. Percentage of nucleotide substitution in nucleotide sequences encoding nucleocapsid protein (NCP) was 1.2-1.7% among seven TSWV isolates and TSWV-KP. Korean TSWV isolates were divided into three groups by nucleotide homology or amino acid compositions. From the analysis of nucleotide sequences of Korean TSWV isolates compared with those of TSWV reported from other 5 countries including Japan, the Korean seven isolates of TSWV was grouped with German TSWV (D13926). No Korean TSWV isolates were grouped with those from The Netherlands, Brazil and USA.

Genome analysis and characterization of a tobacco mosaic virus isolate infecting balsam (Impatiens balsamina)

The complete RNA genomic sequence of a tobacco mosaic virus isolate infecting Impatiens balsamina, designated as TMV-IM, has been determined. The genomic sequence and the predicted gene products of TMV-IM were similar to those of other members of the genus Tobamovirus. The CP ORF of TMV-IM showed sequence identities of 95.0–99.5% with the corresponding ORFs of other TMV strains. Full-length cDNA of TMV-IM was amplified by RT-PCR with a 5′-end primer harboring a T7 promoter sequence and a 3′-end TMV-specific primer. Subsequently, the full-length cDNA was cloned into plasmid vectors. Capped transcripts synthesized from the cDNA clone were highly infectious and caused characteristic symptoms in balsam plants, similar to wild-type TMV-IM and TMV-U1. These results provide definitive evidence for the natural occurrence of TMV in balsam.

Genetic variability in the coat protein genes of Cymbidium mosaic virus isolates from orchids.

The variability in the nucleotide (nt) and amino acid (aa) sequences of the coat protein (CP) of Cymbidium mosaic virus (CymMV), which naturally infects orchids worldwide, was investigated. The CP genes of 55 CymMV isolates originating from different locations in Korea were amplified using RT-PCR and sequenced. The encoded CP consists of 223 aa. The CP sequences of the Korean isolates were compared with those of previously published CymMV isolates originating from different countries at both nt and aa levels. The Korean isolates shared 74.9–98.3 and 52.7–100% CP homology with CymMV isolates from other countries at the nt and aa levels, respectively. No particular region of variability could be found in either grouping of viruses. In the deduced CymMV CP aa sequence, the C-terminal region was more divergent than the N-terminal. The phylogenetic tree analysis based on nt sequence diversity of CP genes of CymMV isolates supported the hypothesis that CymMV isolates were divided into two subgroups. However, these subgroups were not formed by phylogenetic tree analysis of CP aa sequences. There was no distinct correlation between geographical locations and specific sequence identity, while recombination analysis revealed that there were no intra-specific recombination events among CymMV isolates.

Phytoplasma-associated Shoot Proliferation and Leaf Yellowing in Lettuce

Phytoplasma was identified from leaf lettuce (Lactuca sativa) cultivated in commercial green-house in Korea. Diseased leaf lettuce revealed proliferation of shoots, and yellowing and shrinking of leaves (lettuce proliferation-K). Polymerase chain reaction (PCR) with universal primer pair P1/P6, and aster yellows (AY) specific primer pair R16F1/R1 amplified 1.5kb and 1.1kb length of DNA fragments, respectively. Nucleotide sequences of 16S rRNA gene were determined (Gen Bank accession no EF489024). Phylogenetic analysis of 16S rDNA showed the closest relationship with AY phytoplasma (GenBank accession no. AY389822 and AY389826), indicating that lettuce proliferation-K is a member of AY. Phytoplasma bodies were detected in phloem sieve tubes of diseased lettuce by transmission electron microscopy. The structures had round or pleomorphic shapes with a diameter of 130-300nm. Phylogenetic analysis of 16S rRNA gene, microscopic observation of phytoplasma bodies and symptomatology indicated that lettuce proliferation-K is caused by phytoplasma in the AY group. This is the first report of phytoplasma disease in lettuce in Korea.

Occurrence of Chrysanthemum chlorotic mottle viroid in Chrysanthemum(Dendranthema grandiflorum) in Korea

Chrysanthemum chlorotic mottle viroid(CChMVd) isolates have been identified from chrysanthemum showing yellow spots or infected without symptom. They were 399-400 nucleotides length of RNA. CChMVd-SSHA6(GenBank accession no. DQ450682) revealed a GAAA to DUUC substitution in positions 82-85 of CChMVd-MSIN34(GenBank accession no. DQ402041). In vitro RNA transcripts with the complete CChMVd sequence were infectious and induced the typical CChMVd infection symptom of yellow spots in chrysanthemum cv. Sharotte. CChMVd caused reduction in growth in some cultivars, whereas some cultivars were not affected. This is the first report on the occurrence of CChMVd in chrysanthemum in Korea.

Strawberry mild yellow edge potexvirus from Strawberry in Korea

National Academy of Agricultural Science, RDA, Suwon 441-707, Korea(Received on March 23, 2011; Accepted on April 25, 2011) Symptoms induced in the leaves of strawberry (Fragariax ananassa Duch.), ‘Seolhyang’ and ‘Eyeberry’, weremosaic, distortion and black colored edge on leaves atNonsan area, one of the important production areas inKorea. Electron microscopy by quick-dip revealed theflexuous rod-shape particles having about 550-600 nmlength. Cytoplasmic inclusion bodies composed of aggre-gated virus particles were observed frequently in meso-phyll parenchyma and epidermal cells for the leaves ofstrawberry. The specific primers amplifying products of635 bp and 729 bp were developed for RT-PCR detec-tion of Strawberry mild yellow edge virus (SMYEV).Nucleotide identity of the CP gene of SMYEV was 92.8-99.2% with those of other SMYEV isolates from Gen-Bank database.Keywords : nucleotide identity, RT-PCR, SMYEV,strawberry, ultrastructureStrawberry, the genus Fragaria, is one of the fruit veget-ables producing about 200 metric tons for the five yearsfrom 2001 in Korea (naqs.go.kr/statistics). The Koreanconsumption of strawberry is shared to 6% of world and13% of Europe production (Babini et al., 2004). More than30 kinds of virus are known to infect strawberry, but thesymptoms are not described well. Viral infection instrawberry may cause stunting under continuous croppingand a loss of vigor, and resulted up to 80% yield loss fromthe synergistic symptom expression with the mixedinfection of two or more viruses. The disease by Strawberrymild yellow edge virus (SMYEV) was first described inCalifornia in 1922 and it has occurred with an infection rateof over 30% (Converse et al., 1987). SMYEV is transmitted by the strawberry aphid in apersistent manner. Five European countries including Italy,three aphid-transmitted viruses, Strawberry mild yellowedge virus (SMYEV), Strawberry mottle virus (SMoV) andStrawberry crinkle virus (SCV) without Strawberry veinbanding virus (SVBV) occurred with the infection rate of1.3%, 1.6% and 1.2%, respectively, and SMoV occurredonly regionally in Poland and Lithuania (Babini et al.,2004; Karesova et al., 2004). The viral infection can bedetermined by the diagnostic methods of bioassay, sero-logical test of ELISA and genetic test of RT-PCR. Thebioassay using indicator plants by grafting has been usedclassically. The ELISA and RT-PCR have been developedrecently against strawberry infecting viruses (Thompsonand Jelkmann, 2004a), but those methods need to beverified for the purpose of certification or quarantine in theworld (Martin, 2004). The multiplex RT-PCR for the 4aphid transmitting viruses was proposed (Thompson, Wittzeland Jelkmann, 2004), however, three viruses (SCV, SMYEVand SMoV) could be detected in every possible combi-nation, excluding with SVBV. In Korea, there is no reportfor the viruses infecting strawberry to date in spite of massproduction of strawberry fruits from the mass multiplicationof strawberry clones. Strawberry cultivar ‘Seolhyang’ was collected from Nonsanarea and ‘Eyeberry’ cultivar was acquired at greenhousemaintaining genetic resources in Nonsan strawberry experi-ments station. Mosaic symptom was produced typically onthe newly developed leaves of strawberry ‘Seolhyang’(Fig. 1). The leaves showing mosaic symptom were develop-ed distortion later. On ‘Eyeberry’ cultivar of strawberry, thetypical symptom of black colored edge on the leaves wasproduced. Electron microscopy was conducted through LEO 902A.Quick leaf dip method was used for the observation of virusparticles after staining with 2% PTA. Potexvirus particles offlexuous rod having 550-600 nm length were observedfrequently from the leaves of strawberry showing the symp-toms of mosaic, distortion and black leaf margin (Fig. 2).For the ultrastructural studies of the infected cells, theleaves of strawberry were cut into 1 × 1-2 mm and fixedwith Karnovsky’s fixative for 30 min. The fixed specimenswere dehydrated with ethyl alcohol gradually from 30% to100% with 8 steps. For infiltration medium of the dehydratedspecimens, LR White resin was used. Hardening of theresin blocks was done at 60 for 24 hr. Sections of 80 nmthickness were stained with uranyl acetate and lead citrate