To date, fire blight, a bacterial disease in apple, pear and other Rosaceous plants, has been reported worldwide, while in Korea, this disease was not reported to date. In early May 2015, disease symptoms similar to typical blossom and shoot blight of fire blight disease were observed in young blossoms and shoots of Asian pear (Pyrus pyrifolia cv. ‘Shingo’) in 20 orchards in the regions of Anseong (37o00´30˝ N; 127o16´30˝ E) and Cheonan (36o48´55˝ N; 127o06´50˝ E). Disease incidence ((infected tree numbers/total tree numbers) x 100) varied from 0.2 to 93.2%. To isolate and identify the causal pathogen, 1 g of margins from healthy and diseased shoot was excised and homogenized in 1 ml of 10 mM MgCl2. The supernatant was spread on MGY (Mannitol Glutamic Yeast) medium and incubated at 26oC for 2 days. Based on colony morphologies, creamy white or white mucoid colonies were collected and purified. PCR with the universal primer set fD1/rP2 (Geider et al., 2008) for the partial 16 rRNA gene was performed, and t...

The fall armyworm, Spodoptera frugiperda, is an important agricultural pest native to tropical and subtropical regions of the Western Hemisphere, and has invaded Africa and further spread into most countries of Asia within two years. Here, we analyzed the genetic variation of invaded populations by comparing the nucleotide sequences of two genes: the nuclear Z-chromosome linked gene triose phosphate isomerase (Tpi) and the mitochondrial gene cytochrome oxidase subunit I (COI) of 27 specimens collected in Africa (DR Congo, Tanzania, Uganda, and Zimbabwe) and Asia (Bangladesh, Korea, Nepal, and Vietnam). The results revealed that 25 specimens were from a heterogeneous hybrid (Tpi-corn strain and COI-rice strain; Tpi-C/COI-R) of the corn strain male and rice strain female, but two specimens were from a homogenous corn strain (Tpi-corn strain and COI-corn strain; Tpi-C/COI-C). The further analysis of the fourth exon and the fourth intron sequences of the Tpi gene identified at least four subgroups of the corn strain. These four genetic subgroups were identified in Africa and Asia, suggesting no significant genetic change due to the rapid migration within two years. Our study provides essential information for understanding the genetic diversity of fall armyworm in new habitats.

Erwinia amylovora is a plant-pathogenic bacterium that causes fire blight disease in Rosaceae plants. Since fire blight is highly contagious and results in serious losses once introduced, it is regulated as a quarantine disease. Recently, for the first time in East Asia, fire blight emerged in Korea with strains of E. amylovora being isolated from lesions of infected trees. Five of those strains were selected and subjected to whole-genome shotgun sequencing. Each strain had two circular replicons, a 3.8-Mb chromosome and a 28-kb plasmid. The genome sequences were compared with those of other E. amylovora strains isolated from different hosts or geographical regions. Genome synteny was analyzed and sequence variations including nucleotide substitutions, inversions, insertions, and deletions were detected. Analysis of the population genomic structure revealed that the five strains form a distinct structural group. Phylogenomic analysis was performed to infer the evolutionary relationships among E. amylovora strains, which indicated that the Korean isolates, all descended from a common ancestor, are closely related to a lineage of North American strains. These results provide useful information for understanding the genomic dynamics of E. amylovora strains including those in Korea, developing genetic markers for surveillance of the pathogen or diagnosis of the disease, and eventually developing measures to eradicate it.

Lycorma delicatula (White) suddenly arrived in Korea where it rapidly spread out in the central region of Korea and caused serious damage to grape vineyards. To trace the source region of its invasiveness, population genetic structures were compared between the native region, China, and the introduced regions, Korea and Japan. We examined 762 individuals from 38 different population collections using 15 microsatellite loci. Both principal coordinate and structure analyses displayed that the Chinese populations were separated into three subgroups which were located significantly far apart from each other. Among them, the Shanghai population was located closest to most Korean populations. Based on the genetic relationships and structures, it was revealed that the multiple introductions into Korea occurred at least three times. In addition, the Shanghai population was strongly estimated to be a source of initial invasive populations of Korea. In addition, analysis of the approximate Bayesian computation suggested simultaneous spread from two distant locations early in the invasion by artificial transportation of the host plants bearing egg masses. Our population genetics study can provide a precedent case with regards to identifying spreads by anthropogenic outcomes in other invasive regions.

To infer the introduction sources of the oriental fruit fly, Bactrocera dorsalis, we used a mitochondrial marker to reconstruct the haplotype network and 15 microsatellite loci to reveal genetic structure and relationships between the geographically or temporally different collections from Asia. We performed Approximate Bayesian computations to infer a global origin and a source of the quarantine collections found in Korea. As a result, the 40 populations were divided into three groups, of which genetic similarity is not related to the geographic vicinity. Korean samples had a similar genetic structure to Taiwan and Thailand ones. Our results suggest that the place of origin of the B. dorsalis specimens found in Korea’s border quarantine is likely to be Taiwan or Thailand. As the global origin of B. dorsalis, we estimated that Taiwan and Thailand were most likely the global origins of Southeast Asian populations by testing hypothetical scenarios by the approximate Bayesian computation analyses. Our results will allow easier identification of the source region of the forthcoming invasion of quarantined B. dorsalis specimens.

Alcea rosea, in the family Malvaceae, is a biennial plant native to China and is grown typically for gardening in Korea (Lee 2003). Seven microcyclic Puccinia species have been reported on A. rosea: P. heterogenea, P. heterospora, P. lobata, P. malvacearum, P. platyspora, P. sherardiana, and P. modiolae (Demers et al. 2015; Aime and Abbasi 2018). In early May 2022, characteristic symptoms of rust were observed on four of ten seedlings of A. rosea purchased at a wholesale nursery (36°50′19.8″N, 128°55′28.7″E) in Bonghwa, Korea. Rust spots were present on almost 90% of the 1,000 seedlings of A. rosea in that nursery during our survey in late May. Through a distribution survey from June to July 2022, similar symptomatic leaves were additionally collected from the leaves of A. rosea grown in gardens at five sites in Gimcheon (two sites), Gumi (one), Seongju (one), and Busan (one). Spots were yellow-orange the center surrounded by chlorotic haloes on the adaxial leaf surface, and reddish-brown or dark brown pustules on the abaxial leaf surface. Over time, the spots enlarged and coalesced, causing the decay of large sections of the leaves, and heavily infected leaves fell early. Spermogonia, produced at the center of the chlorotic spot on the adaxial leaf surface, were subepidermal, obovoid, and 113.2–164.5 × 97.6–153.3 μm in size. Telia were reddish-brown to dark brown, round, mostly grouped, 0.28–0.61 mm in diameter, and mainly formed on the abaxial leaf surface but sometimes on the adaxial leaf surface also. Teliospores were two-celled, but rarely one- or three-celled, and were fusoid and 37. 6–110 × 12.4–21.5 μm in size; the wall was yellowish or almost colorless, smooth, 1.2–2.6 μm thick at the sides, and up to 7.4 μm thick at the apex. The morphological characteristics were similar to those of P. modiolae, although the teliospores in our study were longer than those observed by Aime and Abbasi (2018). For phylogenetic analysis, genomic DNA was extracted from the teliospores of each regional specimen. Partial 18S, internal transcribed spacer (ITS), and partial 28S sequences were amplified using primers NS1, ITS4, ITS5, and LR11. The PCR products were sequenced (Celemics, Seoul, Korea) and deposited in GenBank. The ITS-partial large subunit (LSU) sequence and 28S sequences had 100% homology with other P. modiolae sequences deposited in GenBank (accession numbers are shown in Fig. 2). In the phylogenetic trees of the ITS and LSU sequences, the isolates collected in this study were grouped with the reference sequences of P. modiolae, including the Korean isolate (ON631218) recently reported on Malva verticillata by Lee et al. (2022). For the pathogenicity test, the teliospores with germinating basidiospores were suspended in sterile distilled water and smeared on the upper surface of asymptomatic A. rosea leaves in August. The inoculated plants were sprayed with distilled water and kept in the dark with saturated moisture for 24 h in an isolated glass house of the Animal & Plant Quarantine Agent. After 2 weeks, typical rust spots and telia of P. modiolae were observed on the leaves of the inoculated plants, but not in the control plants, which were only sprayed with distilled, sterilized water and otherwise treated similarly to the inoculated plants. The results of this study show that the casual fungus is P. modiolae, which has been commonly found in A. rosea in Korea. To the best of our knowledge, this is the first report of P. modiolae in A. rosea in Korea.