Korean Agricultural Research Articles

First Report of Ramularia coleosporii causing Leaf Spot on Perilla frutescens in Korea.

Perilla (Perilla frutescens var. japonica), a member of the family Labiatae, is an annual herbaceous plant native to Asia. Its fresh leaves are directly consumed and its seeds are used for cooking oil. In July 2018, leaf spots symptoms were observed in an experimental field at Gangneung-Wonju National University, Gangneung, Gangwon province, Korea. Approximately 30% of the perilla plants growing in an area of about 0.1 ha were affected. Small, circular to oval, necrotic spots with yellow borders were scattered across upper leaves. Masses of white spores were observed on the leaf underside. Ten small pieces of tissue were removed from the lesion margins of the lesions, surface disinfected with NaOCl (1% v/v) for 30 s, and then rinsed three times with distilled water for 60 s. The tissue pieces were then placed on potato dextrose agar (PDA) and incubated at 25°C for 7 days. Five single spore isolates were obtained and cultured on PDA. The fungus was slow-growing and produced 30-50 mm diameter, whitish colonies on PDA when incubated at 25ºC for 15 days. Conidia (n= 50) ranged from 5.5 to 21.3 × 3.5 to 5.8 μm, were catenate, in simple or branched chains, ellipsoid-ovoid, fusiform, and old conidia sometimes had 1 to 3 conspicuous hila. Conidiophores (n= 10) were 21.3 to 125.8 × 1.3 to 3.6 μm in size, unbranched, straight or flexuous, and hyaline. The morphological characteristics of five isolates were similar. Morphological characteristics were consistent with those described for Ramularia coleosporii (Braun, 1998). Two representative isolates (PLS 001 & PLS003) were deposited in the Korean Agricultural Culture Collection (KACC48670 & KACC 48671). For molecular identification, a multi-locus sequence analysis was conducted. The internal transcribed spacer (ITS) regions of the rDNA, partial actin (ACT) gene and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene were amplified using primer sets ITS1/4, ACT-512F/ACT-783R and gpd1/gpd2, respectively (Videira et al. 2016). Sequences obtained from each of the three loci for isolate PLS001 and PLS003 were deposited in GenBank with accession numbers MH974744, MW470869 (ITS); MW470867, MW470870 (ACT); and MW470868, MW470871 (GAPDH), respectively. Sequences for all three genes exhibited 100% identity with R. coleosporii, GenBank accession nos. GU214692 (ITS), KX287643 (ACT), and 288200 (GAPDH) for both isolates. A multi-locus phylogenetic tree, constructed by the neighbor-joining method with closely related reference sequences downloaded from the GenBank database and these two isolates demonstrated alignment with R. coleosporii. To confirm pathogenicity, 150 mL of a conidial suspension (2 × 105 spores per mL) was sprayed on five, 45 days old perilla plants. An additional five plants, to serve as controls, were sprayed with sterile water. All plants were placed in a humidity chamber (>90% relative humidity) at 25°C for 48 h after inoculation and then placed in a greenhouse at 22/28°C (night/day). After 15 days leaf spot symptoms, similar to the original symptoms, developed on the leaves of the inoculated plants, whereas the control plants remained symptomless. The pathogenicity test was repeated twice with similar results. A fungus was re-isolated from the leaf lesions on the inoculated plants which exhibited the same morphological characteristics as the original isolates, fulfilling Koch's postulates. R. coleosporii has been reported as a hyperparasite on the rust fungus Coleosporium plumeriae in India & Thailand and also as a pathogen infecting leaves of Campanula rapunculoides in Armenia, Clematis gouriana in Taiwan, Ipomoea batatas in Puerto Rico, and Perilla frutescens var. acuta in China (Baiswar et al. 2015; Farr and Rossman 2021). To the best of our knowledge, this is the first report of R. coleosporii causing leaf spot on P. frutescens var. japonica in Korea. This disease poses a threat to production and management strategies to minimize leaf spot should be developed.

An Analysis of the Effect of Logistics Efficiency on the Export of Korean Agricultural Products to New Southern Countries

An Analysis of the Effect of Logistics Efficiency on the Export of Korean Agricultural Products to New Southern Countries

Implication of the Korean Agricultural Technology Group Activities during the Vietnam War

Implication of the Korean Agricultural Technology Group Activities during the Vietnam War

First report of root mat disease in a hydroponic tomato production system caused by rhizogenic Agrobacterium biovar 1 in South Korea.

In June 2019, root mat disease was observed in hydroponically cultivated tomatoes in Jinju, South Korea, which occurred in at least 30% of the plants in the greenhouse. To isolate the causal bacteria, 10 g of infested tomato root mat sample was ground with 50 mL of sterile water. A 100-µL aliquot of the homogenate was serially diluted and spread on Mannitol-Glutamate (MG) medium amended with 0.1% yeast extract (MGY) and incubated at 28°C for 48 hours. Fifteen dominant colonies that formed on the MGY medium were purified and subjected to diagnostic polymerase chain reaction (PCR) based on the virD2-ipt gene loci. Because Ti-plasmid harbors both virD2 and ipt genes, Ri-plasmid-borne Agrobacterium species with only virD2 can be differentiated using virD2-ipt PCR. To amplify virD2, the primers 5'-ATG CCC GAT CGA GCT CAA GT-3' and 5'-TCG TCT GGC TGA CTT TCG TCA TAA-3' were used; for ipt amplification, the primers 5'-GAT CG(G/C) GTC CAA TG(C/T) TGT-3' and 5'-GAT ATC CAT CGA TC(T/C) CTT-3' were used. Amplification involved an initial 94°C for 1 min and then 40 cycles at 94°C, 50°C, and 72°C for 1 min at each temperature, with a final 5-min extension at 72°C. For three strains (GNIY2, J10, and J11), virD2 PCR products, but no ipt PCR products, were identified, indicating that three strains are Ri-plasmid-borne Agrobacterium species. A pathogenicity test was performed on 2-week-old tomato plants. Bacteria isolates (GNIY2, J10, and J11) cultured overnight in LB were made into a bacterial suspension (107 cfu/mL) in 50 mM phosphate buffer. Five tomato seedling roots were cut with sterilized scissors and soaked in each bacterial suspension for 1 hour. Phosphate buffer was used as a negative control. The inoculated tomato seedlings were transplanted in new pots and placed in a greenhouse with 25°C day and 20°C night temperature set points in natural light. After 9 weeks, all inoculated tomato plants produced overgrown roots, while the negative control plants had no symptoms. To satisfy Koch's postulates, re-isolation was performed from the diseased tomato and was the re-isolated bacteria were subject to partial 16S rDNA sequencing. Biovar tests performed as previously described revealed that all three isolates were biovar 1. A representative strain (GNIY2) was deposited in the Korean Agricultural Culture Collection (KACC 21759). To confirm the identity, four housekeeping genes of KACC 21759 were sequenced (16S rRNA, trpE, rpoB, and recA) and deposited in GenBank (accession nos. MT071560, MT444428, MT444429, and MT444430). Multilocus sequence analysis performed as previously described showed that the KACC 21759 strain was grouped in Agrobacterium genomospecies 4. This is the first report on mat root disease caused by Agrobacterium biovar 1 in hydroponic tomatoes in South Korea.

First Report of Fusarium Wilt Caused by Fusarium equiseti on Cabbage (Brassica oleracea var. capitate L.) in Korea.

Cabbage (Brassica oleracea var. capitate L.) is an important vegetable crop that is widely cultivated throughout the world. In August 2019, wilting symptoms on cabbage (stunted growth, withered leaves, and wilted plants) were observed in a cabbage field of Pyeongchang, Gangwon Province, with an incidence of 5 to 10%. To identify the cause, symptomatic root tissue was excised, surface-sterilized with 70% ethanol, and rinsed thrice with sterile distilled water. The samples were dried on blotter paper, placed onto potato dextrose agar (PDA), and incubated at 25°C for 1 week. Five morphologically similar fungal isolates were sub-cultured and purified using the single spore isolation method (Choi et al. 1999). The fungus produced colonies with abundant, loosely floccose, whitish-brown aerial mycelia and pale-orange pigmentation on PDA. Macroconidia had four 4 to six 6 septa, a foot-shaped basal cell, an elongated apical cell, and a size of 20.2 to 31.8 × 2.2 to 4.1 μm (n = 30). No microconidia were observed. Chlamydospores were produced from hyphae and were most often intercalary, in pairs or solitary, globose, and frequently formed chains (6.2? to 11.7 μm, n = 10). Based on these morphological characteristics, the fungus was identified as Fusarium equiseti (Leslie and Summerell 2006). A representative isolate was deposited in the Korean Agricultural Culture Collection (KACC48935). For molecular characterization, portions of the translation elongation factor 1-alpha (TEF-1α) and second largest subunit of RNA polymerase II (RPB2) genes were amplified from the representative isolate using the primers pair of TEF-1α (O'Donnell et al. 2000) and GQ505815 (Fusarium MLST database), and sequenced. Searched BLASTn of the RPB2 sequence (MT576587) to the Fusarium MLST database showed 99.94% similarity to the F. incarnatum-equiseti species complex (GQ505850) and 98.85 % identity to both F. equiseti (GQ505599) and F. equiseti (GQ505772). Further, the TEF-1α sequence (MT084815) showed 100% identity to F. equiseti (KT224215) and 99.85% identity to F. equiseti (GQ505599), respectively. Therefore, the fungus was identified as F. equiseti based on morphological and molecular identification. For pathogenicity testing, a conidial suspension (1 × 106 conidia/ml) was prepared by harvesting macroconidia from 2-week-old cultures on PDA. Fifteen 4-week-old cabbage seedlings (cv. 12-Aadrika) were inoculated by dipping roots into the conidial suspension for 30 min. The inoculated plants were transplanted into a 50-hole plastic tray containing sterilized soil and maintained in a growth chamber at 25°C, with a relative humidity of >80%, and a 12-h/12-h light/dark cycle. After 4 days, the first wilt symptoms were observed on inoculated seedlings, and the infected plants eventually died within 1 to 2 weeks after inoculation. No symptoms were observed in plants inoculated with sterilized distilled water. The fungus was re-isolated from symptomatic tissues of inoculated plants and its colony and spore morphology were identical to those of the original isolate, thus confirming Koch's postulates. Fusarium wilt caused by F. equiseti has been reported in various crops, such as cauliflower in China, cumin in India, and Vitis vinifera in Spain (Farr and Rossman 2020). To our knowledge, this is the first report of F. equiseti causing Fusarium wilt on cabbage in Korea. It This disease poses a threat to cabbage production in Korea, and effective disease management strategies need to be developed.

한국 농어업인 무릎 퇴행성관절염의 라이프 케어를 위한 유병률과 관련 요인에 대한 조사

본 연구는 국민건강영양조사 제5기(2010-2012) 원시자료를 이용하여 한국 농어업종사자의 무릎 OA 유병률을 파악하고 관련요인을 알아보기 위해 시행하였다. 국민건강영양조사 제5기(2010-2012) 원시자료 중 50세 이상 농어업에 종사하는 50세 이상 성인 1,264명(2010년 440명, 2011년 448명, 2012년 376명)을 연구대상자로 선정하였다. 연구대상자 중 X-ray 판독결과 Kellgren Lawrence grade가 2 이상이고 최근 3개월 동안 30일 이상 무릎관절통이 있었다고 응답한 215명과 X-ray 판독 결과 Kellgren Lawrence grade가 1 이하이고 최근 3개월 동안 30일 이상 무릎관절통이 없었다고 응답한 601명, 총 816명을 최종 연구대상자로 선정하였고 무릎 OA 유병률과 인구사회학적 또는 건강관련 요인별 유병교차비를 분석하였다. 연구결과 무릎 OA 유병률은 26.3%였고, 인구사회학적 측면에서 여성, 연령이 증가할수록, 교육수준이 낮을수록, 월소득이 적을수록 무릎 OA 유병률은 증가하였다. 건강관련 요인에서는 비흡연군, BMI가 높을수록 무릎 OA 유병률이 증가하였다.

First report of bacterial shot-hole disease caused by Xanthomonas arboricola pv. pruni on plumcot in South Korea.

Plumcot is an interspecific hybrid product between Japanese plums (Prunus salicina) and apricots (Prunus armeniaca) obtained by the NIHHS, Korea in 1999 [1]. At the early of 2017, black spots-like symptoms were observed on plumcot fruits and leaves at cultivation areas in Naju (34.965595, 126.665853) province. Further investigation shows that approximately 60% of the plumcot leaves in the affected orchard were infected, which caused 40% total production loss. At the early stage of infection, disease symptoms appear as small, angular and water-soaked spots and develop into circular brown spots at the later stages of infection. As the disease progresses, the leaf tissues around the spots became yellow and the lesions enlarged. When the adjacent lesions merged and the necrotic tissues fall off, shot-hole symptoms appear on the leaves. To identify the causal agent of this disease, infected leaf tissues were excised and surface-sterilized with 1% NaOCl for 30 secs prior to rinsing with sterile water, thrice . Tissue samples were then placed in sterile water (0.5 mL) for 5 min before its aliquots were streaked onto Luria-Bertani (LB) agar. Plates then were incubated at 28°C. To obtain pure colonies, bacteria were re-streak into a new LB agar and colonies showing typical Xanthomonas spp. morphology (i.e. convex, smooth, yellow, and mucoid) were subjected to Gram staining assay. For molecular identification, 16S ribosomal DNA (16S-rDNA) and gyrase B (gyrB) genes were amplified using a 9F/1512r and UP-1/UP-2Sr primers [2,3] respectively from 5 gram-negative isolates. PCR products were sequenced and analysed using BLASTN. Result shows that 16S-rDNA and gyrB genes are 99-100% identical to a similar genomic region of Xanthomonas arboricola pv. pruni (Xap) isolated in almond (MK156163), peach (MG049922) and apricot (KX950802) respectively [4,5,6]. 16S-rDNA and gyrB gene sequences were deposited in the GenBank (LC485472 and LC576824), whereas pathogen isolate was deposited into Korean Agricultural Culture Collection (KACC19949). Pathogenicity test was performed using Xap bacterial suspension (108 cfu/mL) inoculated on the abaxial and adaxial surface of plumcot detached leaves. For inoculation, 10 healthy young leaves were used whereas, 5 young leaves mock-inoculated with sterile LB broth were used as a control. Both leaf samples were kept in a closed container to maintain 100% humidity before being incubated at 25°C. The water-soaked symptoms were observed visually on the inoculated leaves 2 to 3 days post-inoculation. No water-soaked symptoms were observed on the control leaves. Morphology and sequences of molecular markers used showed that the 3 bacterial colonies re-isolated from the inoculated leaves were identical to the original isolate, fulfilling Koch's postulate. Pathogenicity tests were repeated twice and the results obtained were consistent with the first experiment. As a new variety of stone fruit cultivated in Korea, information about pathogens and registered agrochemicals to control disease outbreak in plumcot are still limited. Therefore, the identification of Xap as a causal agent to the black spot disease is critical for the development of disease management strategies and to identify appropriate agrochemicals to control the occurrence of this disease in the field. To our knowledge, this is the first report of Xap as a causal agent to the shot-hole disease on the plumcot in Korea.

Diversity, Pathogenicity, and Fungicide Sensitivity of Colletotrichum Species Associated with Apple Anthracnose in South Korea.

Apple fruits with anthracnose symptoms were collected from commercial apple orchards in different regions of the Republic of Korea, and isolations were made on potato dextrose agar to isolate the causal agents. The fungal isolates were identified based on their morphological characteristics, growth rates, and multigene sequences. Nine isolates were identified via phylogenetic analysis: three Colletotrichum fructicola, two C. fioriniae, one C. gloeosporioides sensu stricto (s.s.), two C. nymphaeae, and one C. siamense isolates. The pathogenicity of the Colletotrichum isolates was tested using detached apple fruits under laboratory conditions. This study also reidentified six Colletotrichum isolates responsible for apple anthracnose, which were deposited in the Korean Agricultural Culture Collection. Among the six isolates, three were identified as C. siamense (deposited as C. gloeosporioides s.s.), and three were C. nymphaeae (deposited as C. acutatum s.s.). All the Colletotrichum species identified in this study were highly sensitive to tebuconazole in terms of inhibition of mycelial growth (EC50 value of 0.12 to 2.1 μg/ml).

Fusarium fujikuroi causing Fusarium wilt of Lactuca serriola in Korea.

Lactuca serriola L. (syn. L. scariola L.) is an annual Asteraceae plant, native to Europe, and accidentally introduced to Korea in the late 1970s (Yim and Jeon, 1981). The Korean Ministry of Environment designated this weed as a harmful plant, which may disturb the balance of ecosystems (Kim et al., 2013). In July 2019, wilting symptoms of prickly lettuce were found among a roadside in Sangju (36°26'15'' N, 128°07'35'' E), Korea, with a disease incidence of 60%. Initial symptoms appeared pale to dark brown lesions on the basal stem and leaves of the plant, and over time the lesions expanded to the upper parts of the plant, resulting in extensive rot. Ultimately, the plants wilted and died. Symptomatic vascular tissues (5 x 5 mm2) of two diseased plants were surface sterilized in 2% NaClO solution for 1 min, followed by 70% ethanol for 1min, and rinsed two times in sterile distilled water. The pieces were placed on potato dextrose agar (PDA) and incubated at 25°C in the dark for a week. Each single spore isolate was obtained from the hypha tip growing on PDA and examined for morphological and molecular analysis. A representative isolate has been deposited at the Korean Agricultural Culture Collection (KACC49588). Macroconidia were slender, straight, and measured 20.4 to 59.6 × 2.5 to 3.9 μm (n=50), with three to five septa. Microconidia were clavate and measured 6.1 to 13 × 2.5 to 3.3 μm (n=50). Chlamydospores were absent. The colonies developed white aerial mycelium and turned pale purple after a week on PDA. Both morphological and cultural characteristics of the Korean isolate were close to Fusarium fujikuroi (Leslie and Summerell, 2006). Also, DNA sequence-based identification was carried out using primer sets of ITS1-F/ITS4 for the internal transcribed spacer (ITS) rDNA region, Btu-F-F01/Btu-F-R01 for β-tubulin (TUB) gene (Watanabe et al., 2011), and EF-1/EF-2 for translation elongation factor 1-alpha (TEF) gene. The resulting sequences were deposited in GenBank with accession numbers MT102938 for ITS, MT182734 for TUB, and MT625962 for TEF. On a BLASTn search, the Korean isolate revealed 100% sequence identity with the verified sequences of F. fujikuroi MF984413.1 for ITS, 99.79% (1 out of 368 bp is different) with U34415.1 for TUB, and 99.85% (1 out of 675 bp) with MN193860.1 for TEF. Pathogenicity was tested by dipping the roots of five healthy prickly lettuce seedlings in the spore suspension (1 × 106 conidia/ml) for 1 hour. Inoculated plants were transplanted into pots and maintained in a growth chamber at 90% relative humidity and 20°C. Five non-inoculated plants served as controls. After four weeks, wilt symptoms accompanied by expanding brown spots were observed on the basal stem and leaves of all inoculated seedlings, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical to one of the original infections, fulfilling Koch's postulates. Based on the morphological characteristics, sequencing data, and pathogenicity test, the pathogen was identified as F. fujikuroi. Bakanae (foolish seedling) disease caused by F. fujikuroi is one of the most serious rice diseases in Asia, but also this pathogen has been recorded on Lactuca sativa in Thailand (Farr and Rossman 2020). To our knowledge, this is the first report of F. fujikuroi causing Fusarium wilt on L. serriola in Korea.

Molecular Markers for Detecting a Wide Range of Trichoderma spp. that Might Potentially Cause Green Mold in Pleurotus eryngii

In Pleurotus sp., green mold, which is considered a major epidemic, is caused by several Trichoderma species. To develop a rapid molecular marker specific for Trichoderma spp. that potentially cause green mold, eleven Trichoderma species were collected from mushroom farms and the Korean Agricultural Culture Collection (KACC). A dominant fungal isolate from a green mold-infected substrate was identified as Trichoderma pleuroticola based on the sequences of its internal transcribed spacer (ITS) and translation elongation factor 1-α (tef1) genes. In artificial inoculation tests, all Trichoderma spp., including T. atroviride, T. cf. virens, T. citrinoviride, T. harzianum, T. koningii, T. longibrachiatum, T. pleurotum, and T. pleuroticola, showed pathogenicity to some extent, and the observed symptoms were soaked mycelia with a red-brown pigment and retarded mycelium regeneration. A molecular marker was developed for the rapid detection of wide range of Trichoderma spp. based on the DNA sequence alignment of the ITS1 and ITS2 regions of Trichoderma spp. The developed primer set detected only Trichoderma spp., and no cross reactivity with edible mushrooms was observed. The detection limits for the PCR assay of T. harzianum (KACC40558), T. pleurotum (KACC44537), and T. pleuroticola (CAF-TP3) were found to be 500, 50, and 5 fg, respectively, and the detection limit for the pathogen-to-host ratio was approximately 1:10,000 (wt/wt).

Evaluation of Farming Practices for Reduction of Greenhouse Gas Emission in Korean Agricultural Sector

This study was conducted to provide low carbon farming technique for greenhouse gases(GHGs) emission reduction in agriculture sector. It reviewed literatures on the characteristic of cultivation technique and its effects on carbon emission reduction. The effects of GHGs emission reduction were evaluated in agricultural land with several farming practices. In the rice cultivation technique, the irrigation water management showed good effect on GHGs emission reduction in paddy field. It also evaluated reduction efficiency of source of nitrogen supply and soil improvement. The intermittent irrigation showed 25.1% carbon reduction efficiency as compared to continuously flooded treatment. Slow release fertilizer and ammonium sulphate decreased carbon emission by 19.8% and 7.9% compared to urea, respectively. With soil amendments treatment, silicate fertilizer and zeolite reduced carbon emission 14.1% and 21.7% compared to rice straw treatment. In the upland crop cultivation technique, the efficiency of tillage management, green manure, livestock compost and nitrification inhibitor application were estimated. Substitution of 50% of nitrogen with hairy vetch showed 65.6% carbon reduction efficiency. It also showed 20.4% emission reduction with nitrification inhibitor treatment. However, GHGs emission were increased with livestock compost application. It provided basic data for reducing the GHGs emission in agriculture sector by accomplishing low carbon farming technique and policy project. Effect of farming practices on GHG emission reduction in paddy field.

First Report of Web Blight on Lavender Caused by Rhizoctonia solani AG-1-IB in Korea

Lavender (Lavandula officinalis L.) is an annual or short-lived perennial herb belonging to the mint family (Lamiaceae) that originates from eastern Africa, the Mediterranean, southwest Asia, to southeast India. Lavenders are cultivated extensively as ornamental plants for garden and landscape uses, for usage as culinary herbs, and commercially for the extraction of essential oils. In June 2017, approximately 5 to 10% of plants showed web blight symptoms in a private garden located near Gangneung, Gangwon Province, Korea. Specifically, leaf tissues were blighted, and white mycelial growth was seen on the stems. Symptomatic tissues were surface sterilized with 1% NaOCl, washed twice in sterilized water, blotted on sterile filter paper, and plated on 2% water agar at 25°C. After 2 days, hyphal tips were transferred to potato dextrose agar (PDA) to obtain pure cultures. A total of five morphologically similar fungal isolates (LWB001 to LWB005) were obtained from diseased samples; isolate LWB002 was selected for identification. The fungus produced a white mycelium when young but produced a brown mycelium with dark brown sclerotia on PDA at 20 ± 2°C for 10 days. Mature sclerotia (n = 20) were dark, spheroidal, with diameters ranging from 0.2 to 2.2 mm (average 0.7 mm). The young hyphae had acute angular branching near the distal septum of the multinucleated cells, and mature hyphal branches showed approximately 90° angles. Morphological characteristics were consistent with those of Rhizoctonia solani (Sneh et al. 1991). A representative isolate (LWB002) was deposited in the Korean Agricultural Culture Collection (KACC), National Institute of Agricultural Science, Rural Development Administration, Wanju, South Korea (KACC48671), to be used for further studies. The identification of the anastomosis group of the R. solani isolate was carried out on sterilized glass slides coated with 2% water agar medium placed on Petri dishes. The representative isolate was paired with tester strains of R. solani (AG-1-IA, AG-1-IB, AG-1-IC, AG 2-2-IIIB, AG 4, AG 7, and AG 11), which were collected from KACC (Ogoshi 1987) and examined microscopically. The fungal isolate anastomized only with tester strain AG-1-IB. To obtain a DNA sequence-based identification, a total DNA was extracted directly from the mycelium with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). Following DNA extraction, the internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and sequenced (White et al. 1990). BLASTn analysis of the 706 bp showed a 100, 99.71, and 99.86% similarity with sequences of R. solani AG-1-IB (teleomorph Thanatephorus cucumeris) in GenBank (JQ692293.1, GU585667.1, and KF907717.1, respectively). The nucleotide sequence has been assigned GenBank number MH122653. To confirm pathogenicity, three fungal mycelial discs (14 days old, 6.5 mm) were placed onto three wounded young plant stems on the soil line. Another three plants served as controls, for which only an agar plug was used on wounded plant stems. Then all the plants were incubated in a growth chamber (at 28 ± 2°C, 90% relative humidity, with 12/12-h light/dark). After 10 days, blight symptoms were similar to the original symptoms developed on inoculated plant leaves and stems, whereas no symptoms were observed on control plants. Five fungal isolates were reisolated from disease lesions of inoculated plants on PDA with the same morphological characters as before, and the identity was confirmed by microscopic studies, which fulfilled Koch’s postulates. Lavender web blight caused by R. solani AG-1-IB has been recorded in Italy (Garibaldi et al. 2013). To our knowledge, this is the first disease report of web blight on lavender caused by R. solani AG-1-IB in Korea, which poses a potential threat to lavender production, and our findings will be useful for the development of effective control strategies and further research.

The Impact of the U.S.-China Trade Dispute on the Korean Agricultural Market Using Computational General Equilibrium Model

The Impact of the U.S.-China Trade Dispute on the Korean Agricultural Market Using Computational General Equilibrium Model

Korean Agricultural ODA and Its Economic Impacts: System，Performance，and Some Issues

Korean Agricultural ODA and Its Economic Impacts: System，Performance，and Some Issues

First Report of Cercospora malayensis Causing Leaf Spot on Okra in Korea

In Korea, okra (Abelmoschus esculentus [L.] Moench) is cultivated on small family farms and experimental plots (0.5 ha). In August 2014 and 2015, okra plants of cultivar ‘Green Hope’, grown in the farms of Iksan, Korea, were observed for leaf spot symptoms. Leaf spots were circular to irregular-shaped, initially brown, and subsequently turned reddish-brown with a yellowish margin. On leaves, stromata were brown, small, and composed of a few swollen hyphal cells. The conidiophores were fasciculate, olivaceous to brown, paler toward the apex, straight to minimally curved, geniculate, 30 to 250 µm long, 3.5 to 5.0 µm wide, one- to five-septate, and with conspicuous conidial scars. Conidia (n = 50) were hyaline, acicular, subacute to obtuse at the apex, truncate to obconically truncate at the base, 2- to 20-septate, 34 to 280 × 3.4 to 6.5 µm, and with a thickened, darkened hilum at the base. The morphological characteristics were consistent with Cercospora malayensis F. Stevens & Solheim (Chupp 1953). To obtain a pure conidial suspension, conidia were collected from 50 infected leaves using sterile forceps, placed in an Eppendorf tube containing sterile water, streaked onto the surface of 2% water agar plates supplemented with 100 mg/liter of streptomycin sulfate, and transferred onto potato dextrose agar (PDA). After 7 days of incubation, fungal colonies (10 isolates) appeared off-white and flat with aerial mycelia. Voucher specimens were housed in the Korea University herbarium (KUS-F28701), and one isolate was deposited in the Korean Agricultural Culture Collection (KACC47769). Additional fungal confirmation was conducted using the internal transcribed spacer (ITS), translation elongation factor 1-α (EF), and actin (ACT) gene sequences (Groenewald et al. 2013). A BLASTn search using ITS and ACT sequences showed >99% identity with C. malayensis ITS and ACT sequences (KM489070 and KY082664), whereas EF sequences showed 97.8% identity with C. malayensis EF gene (KY082663). The ITS, EF, and ACT sequences of the isolate were deposited in GenBank (MH129519, MH129517, and MH129515). Five 4-month-old okra plants (Green Hope) were spray-inoculated with C. malayensis (KACC47769) hyphal suspensions obtained from 2-week-old colonies grown on PDA at 25°C and transferred to a greenhouse (25°C) with a 12-h photoperiod. Five control plants were inoculated with sterile water. Symptoms observed on the C. malayensis inoculated plants were 100% identical with infected field conditions. C. malayensis was reisolated from symptomatic leaf tissues, and the identity was confirmed by microscopic studies. The pathogenicity test was repeated twice. Okra leaf spots associated with C. malayensis have previously been reported from several countries but not Korea (Farr and Rossman 2019). To our knowledge, this is the first report of C. malayensis on okra in Korea. Because okra hectares may increase, the disease poses a threat to okra cultivation in Korea.

Constructing County-Level Data for Agricultural Inputs and Analyzing Agricultural Productivity, 1951-1980

Constructing County-Level Data for Agricultural Inputs and Analyzing Agricultural Productivity, 1951-1980

Proper Plant Density for Mechanical Transplanting of Several Leafy Vegetables Under Korean Agricultural Condition

This study surveyed the information for development of mechanical transplanting of leafy vegetables. The priority production area of each crop, cultivation season, primary cultivar, transplanting method, and cultivation practice, in terms of furrow, ridge, and planting distance, were determined. The cultivation region, cultivation period, seedling, transplanting method, and size of furrow and ridge for cultivation of kimchi cabbage, cabbage, broccoli, and head lettuce were determined. These activities were carried out on commercial farms in the main producing region of leafy vegetables. Regarding kimchi cabbage, the standard sizes of furrow and ridge were 63 and 13 cm, respectively. The suitable wheel distance of the transplanting machine was 112–136 cm and the planting distance of kimchi cabbage was 65 × 45 cm. For cabbage transplanted in a single row, the furrow and ridge sizes were 76–90 and 13–15 cm, and the wheel distance and planting distance ranged from 152–180 and 76–90 × 45 cm, respectively. For broccoli and head lettuce, respectively, the furrow size range indicated 50–78 and 63–69 cm, with corresponding ridges of 10–20 and 12–13 cm, and the suggested wheel distances were 100–156 and 126–138 cm. In addition, the planting distance of broccoli and head lettuce represented 76–90 × 45 cm and 63–69 × 30 cm, respectively. Results indicated the optimal density for mechanized transplanting of various types of leafy vegetables and the information provided could be applied to develop the specification of the machine’s end effects.

실제이익조정과 농협조합 최고경영자 교체와의 관련성

실제이익조정과 농협조합 최고경영자 교체와의 관련성

First Report of Leaf Spot Caused by Septoria lactucae on Lactuca serriola in Korea

Lactuca serriola L. (syn. L. scariola L.), called prickly lettuce, has become naturalized globally in temperate regions. Because the plant was accidentally introduced to Korea in the late 1970s (Yim and Jeon 1980), they are now distributed throughout the country, threatening native plant communities. Thus, prickly lettuce has been designated as one of the 12 harmful nonindigenous plants by the Korean Ministry of Environment (Kim et al. 2013). In June 2019, leaf spot symptoms on this weed were found at a public garden in Gunsan (35°57′59″N, 126°43′28″E), Korea. Leaf lesions were 2 to 10 mm in diameter, mostly angular, vein-limited, dark brown, and exhibited numerous black pycnidia with a hyaline cirrhus. A representative specimen was deposited in the Kunsan National University Herbarium (KSNUH379). Pycnidia were amphigenous, globose, dark brown to blackish, and measured 70 to 90 μm in diameter. Ostioles were 15 to 22 μm in diameter, with a hyaline, slender cirrhus. Conidia were hyaline, filiform, slightly curved to straight, aguttulate, uniseptate, subtruncate at the base, tapering to a rounded apex, and measured 20 to 32 × 1.5 to 2.0 μm. Single-conidial isolations on potato dextrose agar formed dark grayish colonies and grew slowly (10 mm 5 weeks after inoculation at 25°C). On the basis of morphological and cultural characteristics, the fungus was identified as Septoria lactucae Pass. (Verkley et al. 2013). An isolate was deposited in the Korean Agricultural Culture Collection (KACC48731). To confirm the morphological identification, genomic DNA was extracted from a diseased leaf of KSNUH379. Three DNA regions were sequenced: internal transcribed spacer (ITS rDNA) with primers ITS1-F and ITS4, large subunit (LSU) rDNA with LSU1Fd and LR5 (Verkley et al. 2013), and actin gene region (ACT) with ACT512F and ACT783R (Carbone and Kohn 1999). The resulting sequences were deposited in GenBank (accession nos. MN267567 for ITS, MN267564 for LSU, and MN284910 for ACT). A BLASTn search revealed that the Korean sample is identical with the sequences of S. lactucae parasitic to Lactuca sativa (KF251439 and KF251440 for ITS, KF251943 and KF251944 for LSU, and KF253743 and KF253744 for ACT). Pathogenicity was confirmed by inoculating the leaves of three 4-week-old lettuce plants with a conidial suspension (∼1 × 10⁶ conidia/ml). Three noninoculated plants served as controls. For 72 h after inoculation, the plants were incubated in a growth chamber at 100% relative humidity and darkness at 25°C and then kept in an outdoor greenhouse at 80% relative humidity and 25 to 30°C. After 3 weeks, typical leaf spots, identical to those observed in the field, developed on the inoculated leaves. No symptoms were observed on the control plants. The fungus was successfully reisolated from the symptomatic plants, fulfilling Koch’s postulates. Based on the morphological characteristics, sequencing data, and pathogenicity test, the pathogen was identified as S. lactucae. Previously, the association of L. serriola with Septoria leaf spot has been known in Australia, the Canary Islands, Ethiopia, and the United States (Farr and Rossman 2019). To our knowledge, this is the first report of S. lactucae on prickly lettuce in Asia. Because of its potential as a biocontrol agent, further studies are needed.

Variation in pathogenicity of different strains of Xenorhabdus nematophila; Differential immunosuppressive activities and secondary metabolite production

Xenorhabdus nematophila, an entomopathogenic bacterium, is mutualistic with the nematode Steinernema carpocapsae. The bacterium produces secondary metabolites to inhibit target insect phospholipase A2 (PLA2) and induce immunosuppression, which is required for the pathogenicity of this bacterium-nematode complex. However, it was unclear if immunosuppressive intensity of the bacteria was correlated with their insecticidal potency. We compared six different X. nematophila strains inhibiting the immune responses of the beet armyworm (Spodoptera exigua) to explain their virulence variations. In addition to four known strains obtained from the Korean Agricultural Culture Collection, we identified two new strains (SK1 and SK2) of X. nematophila from two different isolates of S. carpocapsae. Although all six strains were virulent, they showed significant variation in median lethal bacterial dosage (LD50). The LD50 of most strains was 15–30 CFU/larva, however, the LD50 of the SK1 strain was more than two-fold higher against S. exigua larvae. Immunosuppressive activities of the six strains were measured by comparing hemocyte-spreading behavior and nodule formation; the SK1 strain was significantly less potent than other bacterial strains. These suppressed hemocyte behaviors were recovered by adding arachidonic acid (a catalytic product of PLA2) into all six strains. Bacterial culture broth was fractionated with different organic solvents and the ability to inhibit immune response and PLA2 activity were assessed. All organic extracts had immunosuppressive activities and PLA2-inhibitory activities. GC-MS analysis showed that these organic extracts possessed a total of 87 different compounds. There were variations in chemical components among the six bacterial strains. Organic extracts of SK1 strain, which exhibited the lowest virulence, contained the least number of secondary metabolites.