The population shifts of Monilinia fructicola isolates which were resistant to the fungicide benzimidazoles were investigated in four regions of Korea from 1998 to 2000. The isolation frequency of benzimidazole-resistant isolates ranged from 18.8% to 29.6% in Chongdo and from $22.0\%$ to $26.8\%$ in Gyeongsan during the same period. However, the frequency of benzimidazoleresistant isolates was less than $4.0\%$ in Chochiwon and Youngduk during the same period. Benzimidazoleresistant isolates showed cross-resistance among benzimidazoles. On the other hand, none of the isolates showed cross-resistance to diethofencarb and carbendazim. Regardless of the year, the benzimidazole-resistant isolates of $EC_{50}$ higher than 500 $\mug%$ a.i./ml were isolated more frequently in mid and late season than in early season. In an orchard of Gyeongsan that had not been exposed to any fungicides for several years, the population of benzimidazole-resistant isolate had persisted without much fluctuation for three years. These results suggest that benzimidazole resistance of M. fructicola is becoming a problem in controlling brown rot and blossom blight of peach in regions like Chongdo and Gyeongsan.

Anthracnose severely occurred on begonia (Begonia semperflorens Link.) nurseries in Gyeongju, Gyeongbuk in July, 2004. More than $80\%$ of begonia seedlings were diseased in the greenhouse surveyed and diseased leaves per plant were $12.1\%$ in average. Yellowish spots occurred on the leaves of begonia as initial symptoms, and they coalesced irregularly to form large brown pleomorphic lesions. Severely infected leaves were defoliated, resulting in abnormal growth of the entire plant. Colletotrichum sp. was repeatedly isolated from the diseased plants and was identified as Colletotrichum acutatum on the basis of the mycological characteristics on potato dextrose agar and RAPD analysis. Pathogenicity of the fungus was also confirmed by artificial inoculation on healthy plants. The optimum temperature for mycelial growth of C. acutatum was around $25^{\circ}C$. The fungus was sensitive to azoxystrobin, bitertanol, diethofencarb-carbendazim, difenoconazole and tebuconazole. This is the first report on the anthracnose of begonia caused by C. acutatum in Korea.

Five seed samples of carrot were tested to detect Alternaria spp. by blotter method. A. alternata and A. radicina were detected from all the seed samples as high as $25.8-70.5\%$ and $37.5-63.5\%$, respectively. A. dauci was detected from four seed samples as low as $0.5-7.5\%$. The three Alternaria spp. were detected from the pericarp and the seed coat and endosperm of the carrot seeds but not from the embryo by component plating test. A. alternata and A. radicina were much more detected from the pericarp than the seed coat and endosperm. A. dauci was detected from the pericarp and the seed coat and endosperm at similar rate. The seed sample which was most severely infected with A. radicina showed the lowest rate of germination in the test on top of paper (TP). In the TP test, differences in total infection rate of A. radicina and A. dauci of the seed samples were very closely correlated with those in incidence of seedling rot on the seed samples. However, there was no correlation between infection rate of A. alternata and rate of germination or seedling rot of the seed samples. Soil test for seedling growth revealed that there was no correlation between differences in total infection rate of A. radicina and A. dauci and those in rate of normal seedlings of the seed samples.

Four leguminous crops grown in greenhouses and fields in Korea were surveyed from 2000 through 2002. Sclerotinia rot most severely occurred up to $60\%$ in Phaseolus vulgaris grown in greenhouses but occurred as low as $0-0.5\%$ in that grown in fields. Incidence of the disease in Pisum sativum grown in greenhouses ranged $1-5\%$, and that in Vicia Java and Vigna sinensis grown in fields was $0.8\%$ and $2\%$, respectively. Symptoms of Sclerotinia rot commonly developed on stems and pods of the crops. A total of 59 isolates of Sclerotinia species were obtained from diseased stems and pods of the crops. All of the isolates were identified as Sclerotinia sclerotiorum based on their morphological characteristics. Eight isolates of the fungus were tested for their pathogenicity to four host crops by artificial inoculation. All of the isolates induced rot symptoms on stems of the host crops tested, which were similar to those observed in the fields. The pathogenicity tests revealed that there was no significant difference in the susceptibility to the isolates among the leguminous crops tested This is the first formal report that S. sclerotiorum causes the Sclerotinia' rot of the four leguminous crops in Korea.

We immunized BALB/c mice with purified Cucumber green mottle mosaic virus isolate HY1 (CGMMV-HY1). Through the selection of positive clones that were grown on the HAT medium, four sensitive monoclonal clones (CG99-01, CG99-02, CG99-03, and CG99-04) were selected from 500 Hypoxanthine-guanine phosphoribosyltransferase positive hybridoma cells. Four sensitive clones of CGMMV-HYI were determined as IgM type of the subclass of mouse immunoglobulins Ig group. The titer of monoclonal antiserum against CGMMVHY1 was estimated 1:12,800 by the indirect ELISA. Although monoclonal antibodies (MAbs) from CG99-01 and from CG99-04 cross-reacted with Zucchini green mottle mosaic virus and Kyuri green mottle mosaic virus, MAb from the cell line CG99-03 was highly specific to CGMMV. No MAbs cross-reacted with Cucumber mosaic virus-Fny. Only CG99-04 reacted with Pepper mild mottle virus weakly and CG99-02 reacted with both CGMMV and KGMMV. CGMMV was detected from the rind of watermelon fruit by DAS-ELISA of CGMMV-HY1, but not from the flesh of watermelon. Average seed transmission rate of CGMMV in watermelon was $24\%$ from symptomatic watermelon collected from 5 regions of Gyeongnam province. CGMMV was detected by DAS-ELISA with specific MAb of CGMMVHY1 periodically from root stock, during the sequential process for nursery seedling in Haman. Necrotic spots on cotyledons of root stock seedling progressed to reveal the typical symptomatology on the primary leaves of scion upon grafting. Here, we have established MAb based ELISA system, which could accurately detect CGMMV from watermelon seeds, nursery seedlings, transplants and field samples from greenhouse or open out door field as well.

Virulence and genetic diversity were studied using 21 isolates of Sclerospora graminicola, the pearl millet downy mildew pathogen collected from major pearl millet growing areas of India. Variability for virulence was determined by inoculating a set of 10 differential hosts with the S. graminicola isolates in a greenhouse. The isolates varied for latent period (6.4 to 11 days), disease incidence (0 to $98\%$), virulence index (0 to 18.7) and oospore-production potential (1 to 4). Among the 21 isolates, Sg 139 (Rajasthan) was the most virulent and Sg 110 (Tamil Nadu) the least virulent. Based on virulence index (disease incidence$\time$slatent $period^{-1}$), the 21 isolates were classified into eight virulence groups. Genetic diversity among isolates was studied using AFLP markers. Based on similarity index of banding pattern, the 21 isolates were clustered into eight genotypic groups. The AFLP groupings, however, did not match with that of the virulence groupings, and these two were found independent. The isolate Sg 139 that remained distinct in both pathogenic and genetic groupings indicated its highly virulent nature. Implications of these results in downy mildew resistance breeding are discussed.

Twenty isolates of Didymella bryoniae were isolated from infected cucurbit plants in various growing areas of southern Korea in 2001 and 2002. Random Amplified Polymorphic DNA (RAPD) group [RG] I of D. bryoniae was more virulent than RG IV to watermelon. Virulence of the RG I isolate was strong to moderate to cucumber, whereas that of the RG IV varied from strong, moderate to weak. Two hundred seventy-three amplified fragments were produced with 40 primers, and were analyzed by a cluster analysis using UPGMA method with an arithmetic average program of NTSYSPC. At the distance level of 0.7, two major genomic DNA RAPD groups were differentiated among 20 isolates. The RG I included 7 isolates from watermelon and one isolate from melon, whereas the RG IV included 12 isolates from squash, cucumber, watermelon and melon. Amplification of internal transcribed spacer (ITS) region and small subunit rRNA region from the 20 isolates yielded respectively a single fragment. Restriction pattern with 12 restriction enzymes was identical for all isolates tested, suggesting that variation in the ITS and small subunit within the D. bryoniae were low. Amplification of the genomic DNAs of the tested isolates with the sequence characterized amplified regions (SCAR) primer RG IF-RG IR specific for RG I group resulted in a single band of 650bp fragment for 8 isolates out of the 20 isolates. Therefore, these 8 isolates could be assigned into RG I. The same experiments done with RG IIF-RG IIR resulted in no amplified PCR product for the 20 isolates tested. An about 1.4 kb-fragment amplified from the RG IV isolates was specifically hybridized with PCR fragments amplified from genomic DNAs of the RG IV isolates only, suggesting that this PCR product could be used for discriminating the RG IV isolates from the RG I isolates as well other fungal species.

A virus causing chlorotic ringspot, yellow mosaic and vein clearing symptoms was prevalent on mungbean plants around Taean, Korea. The isolate caused mosaic on Chenopodium quinoa, Nicotiana benthamiana, Phaseolus vulgaris and Vida laba but no symptoms on peanut plants. Inclusion bodies such as scroll, pinwheel and laminated aggregates induced by the virus in the host cells were similar to those produced by members of the Potyvirus subdivision III. Multiple alignment as well as cluster dendrograms of the 709 nucleotide region comprising part of the coat protein gene and 3'untranslated region (UTR) showed that the isolate belongs to the BCMV-PSt subgroup. Altogether, these results support the identification of the causal virus as peanut stripe strain of Bean common mosaic virus (BCMV-PSt).

Three strains of Cucumber mosaic virus (CMV) have been found to cause a lethal disease, referred to as fern leaf syndromes and mild mosaic symptoms in tomato (Lycopersicon esculentum Mill.) crops grown in Kuwait. CMV strains were detected and identified based on host range, symptomatology, serology, electron microscopy, and ribonucleic acid (RNA) electrophoresis in polyacrylamide gels. A high degree of viral genomic heterogeneity was detected among CMV strains isolated in Kuwait, with no apparent correlation to symptomatology in tomato host plants. Two different virus satellites of 'CMV associated RNA 5', designated CARNA 5, were detected in two virus strains that caused both lethal disease and mild symptoms, designated CMV-D1 and CMV-S1 respectively. CARNA5 was not detected in the third CMV strain that caused fern leaf syndromes designated CMV-F. All the three isolated strains were serologically indistinguishable from each other and may belong to one serotype according to Ouchterlony gel diffusion tests. These strains transmitted via aphids (Myzus persicae Sulz) in a non-persistent manner. Physical properties of the virus strains were very similar where thermal inactivation test showed that virus withstood heating for 10 min at $70^{/circ}$, dilution end point was $10^{-4}$, and the longevity in vitro at room temperature was less than 5 days for all virus strains. CMV-D1 and CMV-F were the most devastating diseases spreading in both greenhouse and field-grown tomato where aborted flower buds failed on fruit setting due to the viral infection. This is the first report to isolate three different strains of CMV in Kuwait.

Apple scar skin, one of the most destructive diseases affecting apple, is caused by Apple scar skin viroid (ASSV d). Fruit dappling appeared on several cultivars in Korea and has been distributed to major cultivated areas since 2001. ASSVd was identified from infected fruits by using nucleic acid sequence-based amplification with electrochemiluminescence (NASBA-ECL). NASBA-ECL method was faster and hundredfold more sensitive than reverse transcription-polymerase chain reaction (RT-PCR) for ASSVd detection in apple leaves/ stems. ASSVd was rapidly transmitted to the entire tree in the second year after artificial inoculation. The ASSVd could be transmitted efficiently by using contaminated pruning scissors to both lignified stems (60 to $70\%$) and green shoots (20 to $40\%$) of apple tree and young plants. Dipping of contaminated scissors in $2\%$ sodium hypochlorite solution effectively prevented viroid transmission. In the ASSV d-infected fruits, the viroid was easily detected from fruit skin, seed coat, and embryo. Moreover, embryo and endosperm separately excised from the ASSVd-infected seeds were ASSVd positive in NASBA-ECL assay. Seedlings germinated from ASSVd-positive seeds showed $7.7\%$ infection rate., which indicated that ASSVd is seed-borne.

A new virus with a dsRNA genome was isolated and characterized from the Suhan-:neutari strain (ASI 2504) of Pleurotus ostreatus, which was characterized as long and slightly bent with small caps on the stipe of fruit body. Thirty nm isometric viruses with three dsRNA segments (approximately 2.0, 1.84 and 1.82 kb in sizes) were isolated by ultracentrifugation in sucrose gradients. Western analysis of protein extracted purified viruses with anti-virus polyclonal antibody confirmed that viruses have two specific proteins (36 and 68 kDa). Computer analysis of 2.0 kb segment shows that high. sequence identity with RNA-dependent RNA polymerase (RdRp) of partitiviruses, respectively. When compared to other dsRNA mycoviruses in a phylogenetic analysis, OMDV was most related to Pleurotus ostreatus virus 1.

The actinomycete strain JK-1 that showed strong inhibitory activity against some plant pathogenic fungi and oomycetes was isolated from Jung-bal Mountain in Ko-yang, Korea. The strain JK-1 produced spores singly borne on sporophores and the spores were spherical and 0.9-1.2 11m in diameter. The cell wall of the strain JK-1 contained meso-diaminopimelic acid. The actinomycete strain JK-1 was identified as the genus Micromonospora based on the morphological, physiological, biochemical and chemotaxonomic characteristics. From the 168 rDNA analysis, the strain JK-1 was assigned to M aurantiaca. The antibiotic MA-1 was purified from the culture broth of M aurantiaca JK-1 using various purification procedures, such as Diaion HP20 chromatography, C18 flash column chromatography, silica gel flash column chromatography and Sephadex LH-20 column chromatography. $^{1}H-$, $^{13}C-NMR$ and EI mass spectral analysis of the antibiotic MA-1 revealed that the antibiotic MA-1 is identical to phenylacetic acid. Phenylacetic acid showed in vitro inhibitory effects against fungal and oomycete pathogens Alternaria mali, Botrytis cinerea, Magnaporthe grisea, Phytophthora capsici and yeast Saccharomyces cerevisiae at < 100 $\mug$ $ml^{-1}$. In addition, phenylacetic, acid completely inhibited the growth of Sclerotinia sclerotiorum, Bacillus subtilis, Candida albicans, Xanthomonas campestris pv. vesicatoria at < $\mug$ $ml^{-1}$. Phenylacetic acid strongly inhibited conidial germination and hyphal growth of M grisea and C. orbiculare. Phenylacetic acid showed significantly high levels of inhibitory' effect against rice blast and cucumber anthracnose diseases at 250 $\mug$ $ml^{-1}$. The control efficacies of phenylacetic acid against the two diseases were similar to those of commercial compounds tricyclazole, iprobenfos and chlorothalonil .n the greenhouse.

Innate defence mechanism in plants can be triggered and enhanced by certain agents, referred as inducers against broad range of pathogens. In the present study, Dravya (a sea weed extract) was highly compatible with commonly available synthetic fungicides, Bavistin and Dithane M-45. Incidence of Alternaria padwickii and Bipolaris oryzae was also reduced to a greater extent in the paddy seed samples in Dravya treatment. Dravya also enhanced the seed germination and seedling vigour. Seedlings of treated samples also showed enhanced activity of peroxidase upon challenge inoculation with Alternaria padwickii. The enzyme activity was two fold high after the inoculation of pathogen. The suppression in disease incidence in growing plants indicated the promising effect of Dravya and Dithane M-45 under green-house condition.

In a search for plant extracts with potent in vivo antifungal activity against various plant pathogenic fungi, the methanol extract of the Curcuma longa rhizomes effectively controlled the development of rice blast catised by Magnaporthe grisea and tomato late blight caused by Phytophthora infestans. Three curcuminoids such as curcumin, demethoxycurcumin, and bisdemethoxycurcumin were purified from the methanol extract of C. longa rhizomes as antifungal principles. Among the three curcuminoids, demethoxycurcumin was the most active to both rice blast and tomato late blight, followed in order by curcumin and bisdemethoxycurcumin. However, they all exhibited no or little in vivo antifungal activity against other fungal pathogens causing rice sheath blight (Corticium sasaki), tomato gray mold (Botrytis cinerea), wheat leaf rust (Puccinia recondita), or barley powdery mildew (Blumeria graminis f. sp. hordel).

A virus causing vein banding, sometimes yellow mosaic and rugose symptoms on peanut was prevalent around Suwon, Korea. A survey conducted in the area found disease incidence, depending on cultivar, to range from 79 to $100\%$. The virus was found to be seed-transmissible in all the five peanut cultivars tested with transmission rates ranging from 2 to $16\%$. Host range analysis failed to differentiate 9 field isolates collected from different peanuts cultivars showing various symptoms. Inclusion bodies such as scroll, pinwheel and long laminated aggregates induced by the virus in host plant cells were similar to those induced by members of the Potyvirus subdivision III. The virus showed < $95\%$ homology with Bean common mosaic virus (BCMV), BCMV-BICMV/AzMV strains and only < $91\%$ with Desmodium mosaic virus. Based on biological characterization, electron microscopy and molecular analyses of a Korean isolate (Daewon 1), the virus was identified as peanut stripe strain of BCMV.

In this biocontrol research, we evaluated disease suppressive effects of antagonistic bacterial strains ISE13 and KJ1R5 against Korean ginseng root rot caused by P. eaetorum. We also examined the effects of nutrient solution in the hydroponic culture system for Korean ginseng on biological activity of the bacterial strains. As results of dual culture tests of the bacterial strains on $V_{8}$ juice agar, the strain ISE13 showed antifungal activity against P. eaetorum and other plant pathogenic fungi, but the strain KJ1R5 did not. When their inhibitory effects against infection of P. eaetorum on the roots grown in either nutrient solution or water were tested, the strains ISE13 and KJ1R5 inhibited the disease severity of Korean ginseng roots only grown with water, compared to buffer-treated, inoculated controls. However, the nutrient solution used for hydroponic cultures of ginseng in pots caused higher levels of disease severity by the strains ISE13 and KJ1R5 from 418.8\%$ to 40.0\%$ and from 24.3\%$ to 45.0\%$, respectively. In this study, the bacterial strains ISE13 and KJ1R5 could be potentially biocontrol agents to suppress Korean ginseng root rot caused by P. eaetorum. However, more attention using nutrient solution in hydroponic cultures for Korean ginseng production should be applied in biocontrol of plant diseases using the antagonistic microorganisms.