About 300 actinomycetes were isolated from two forest and one sea-shore soil and tested for inhibitory effects on mycelial growth of six plant pathogenic fungi Magnaporthe grisea, Alternaria mali, Colletotrichum gloeosporioides, Phytophthora capsici, Fusarium oxysporum f. sp. cucumerinum, and Rhizoctonia solani. Among 300 actinomycetes tested, only 16 actinomycetes showed the antifungal activity against the test fungi. Isolate NH 50 was selected for production and purification of antifungal antibiotic substances. Actinomycete isolate NH 50 displayed the broad antifungal spectra against 11 plant pathogenic fungi. To identify actinomycete isolate NH 50, cultural characteristics on various agar media, diaminopimelic acid type, and morphological characteristics by scanning electron microscopy were examined. As a result, actinomycete isolate NH 50 was classified as a rare actinomycete that had LL-DAP type and did not produce spores. After incubation of isolate NH 50 in yeast extract-malt extract-dextrose broth, antifungal compound NH-B1 that inhibited mycelial growth of some plant pathogenic fungi was purified from the methanol eluates of XAD-16 resins by a series of purification procedures, i.e., silica gel flash chromatography, C18 flash chromatography, Sephadex LH-20 column chromatography, silica gel medium pressure liquid chromatography (MPLC), C18 MPLC, and high pressure liquid chromatography (HPLC). UV spectrum and 1HNMR spectrum of antifungal compound NH-B1 dissolved in methanol were examined. The antibiotic NH-B1 showed the major peaks at 230 and 271.2nm. Based on the data of 1H-NMR spectrum, NH-B1 was confirmed to be an extremely complex polymer of sugars called polysaccharides. The antibiotic NH-B1 showed strong antifungal activity against Alternaria solani and Cercospora kikuchi, but weak activity against M. grisea.

We isolated and characterized an antifungal peptide from the seeds of Phytolacca americana. Growth inhibition assay with Botrytis cinerea was used to screen inhibitory proteins from 60 different plant species. A 4 kDa antifungal peptide (Pa-AFP) inhibitory to hyphal growth of B. cinerea was found in the seeds of P. americana. The peptide Pa-AFP was purified to homogeneity by chromatographies of Sephadex G-50, DEAE-Sepharose, Sephacryl S-300, and C18 reverse-phase HPLC. Western blot analysis showed that a polyclonal antibody raised against the purified peptide cross-reacted with a 4 kDa protein in seeds but not in root and leaf tissues of P. americana. Pa-AFP inhibited the hyphal growth of Botrytis cinerea, Rihzoctonia solani, Fusarium oxysporum, and Magnaporthe grisea. Pa-AFP exhibited growth inhibition of Saccharomyces cerevisiae strain BWG7a, which was sensitive to osmotin.

Black dot root rot occurred severely in greenhouse tomatoes in jangseong area of Korea in April, 1996. The causal fungus of the disease was identified as Colletotrichum coccodes based on the morphological and cultural characteristics. Pathogenicity tests revealed that isolates of the fungus were responsible for the disease, and two cultivars of cherry tomato were less susceptible to the disease than other cultivars of tomato and cherry tomato tested.

Capsicum pepper selections fro PI163192, PI241670, PI244670, PI271322, PI308787, PI322719, and PI369994 were confirmed to be non-hypersensitively resistant to race 3 of Xanthomonas campestris pv. vesicatoria. A resistant cultivar,‘SR’, was shown to be hypersensitive. Four Koran local cultivars, a cytoplasmic male sterile line (A-line) and its maintainer (B-line) were highly susceptible. The resistant selections and cultivars were crossed with a male sterile A-line (Smsms) and fertility of their F1 hybrids was examined by observing he pollen production, testing pollen germination, and quantifying the amount of pollen produced per anther to identify the genotype interacting with the male sterile cytoplasm. The seven resistant PI selections turned out to be restorers (N(S)MsMs) and‘SR’to be a maintainer (Nmsms).

Of over 100 accessions of pepper tested, MC 4 and MC 5, PBC631, PI322727, PI358812, PBC066, Kerting, PI322726, PI369994, PI377688, CMS-B, PI322728, and Jatilaba showed similarly high level of resistance to bacterial wilt (Ralstonia solanacearum).

In 1995, we collected stock (Matthiola incana) plants causing mosaic symptoms on leaves and color breakings on flowers in Daekwallyong, Korea. Two viruses were isolated from the infected plants, and identified as cucumber mosaic virus (CMV) and turnip mosaic virus (TuMV) by experiments of host range, serology and electron microscopy. Each of the virus did not produce the same symptoms on the stock seedlings as naturally infected plants caused. When the viruses were coinoculated to the stock seedlings, however, severe mosaic symptoms were observed on leaves, and then the color breakings were expressed on flowers.

Turnip mosaic virus)TuMV-Ca) was isolated from a Chinese cabbage showing severe mosaic and black necrotic spots symptoms in Korea. The virus was identified as a strain of TuMV by its host range test, particle morphology, serology, double stranded RNA analysis. For detection of the virus, reverse transcription and polymerase chain reaction(RT-PCR) was performed with a set of 18-mer TuMV-specific primers to amplify a 876 bp DNA fragment The virus was rapidly detected from total nucleic acids of virus infected tissues as well as native viral RNA of purified virion particles by RT-PCR. Detection limit of the viral RNA by RT-PCR was 10 fg.

Antibodies were raised against fusion proteins of the N-terminus and a region containing the GDNQ (Gly-Asp-Asn-Gln) polymerase motif of the L (polymerase) protein of sonchus yellow net virus (SYNV). Immunoblot analyses using these antibodies revealed the presence of the L protein in purified SYNV preparations and in nuclear extracts from infected tobacco. The serological analyses and detection in a polyacrylamide gels suggested that the L protein is present in at least a 20 fold lower abundance than the G, N, M1 and M2 proteins, and has size corresponding to a molecular weight of over 200 kDa as predicted from nucleotide sequence data. Electron microscopy with gold-labelled antibodies was used to localize the N, M2, and G proteins of SYNV in thin sections of infected tissue. When sections of SYNV-infected tissue were treated with antisera against total SYNV proteins and N protein, gold label could be detected in both the viroplasms and in virus particles. With the anti-M2 protein antiserum, the gold label was strongly localized in the viroplasms but only limited labelling of the virus particle sonly. Limited labelling of the L protein was observed in the viroplasms and the virus particles, presumably because of the low abundance of L protein in the tissues.

A cDNA encoding desiccation-related protein was isolated from a flower bud cDNA library of Chinese cabbage (C-DH) and its nucleotide sequence was characterized. It contains 679 bp nucleotides with 501 bp open reading frame. The amino acid sequence of the putative protein showed the highest amino acid sequence homology (79 % identity) to dehydrin protein in Gossypium hirsutum. Also, the C-DH shares 48-52% amino acid sequence identity with the other typical dehydrin proteins in plant cells. When the amino acid sequence of their proteins were aligned, several peptide motifs were well conserved, of which function has to be solved. Particularly the C-DH contains 15 additional amino acids at its N-terminus. Genomic Southern blot analysis using the coding region of C-DH showed that the C-DH consists of a single copy gene in Chinese cabbage genome. The C-DH mRNA, whose transcript size is 0.7 kb, was expressed with a tissue-specific manner. It was highly expressed in seed, flower buds and low expression as detected in root, stem or leaf tissues of Chinese cabbage. And the transcript level of C-DH was significantly induced by the treatment of plant hormone, abscisic acid and water-deficit conditions.

A series of greenhouse test was conducted to evaluate infection of Calonectria ilicicola on soybean plants of different ages at time of inoculation. Lesion length and number of perithecia were determined on cultivars Braxton, Deltapine 726, and Riverside 699 that were 10∼40 days old and 4-10 days old at time of inoculation. Quadratic and linear relationships were described between plant age at inoculation and lesion length or perithecia production in greenhouse studies. Soybean seedlings exhibited low susceptibility to C. ilicicola regardless of cultivar susceptibility. On 8- or 1-0-days-old Braxton, lesion lenght and perithecia numbers were reduced. Lesion lengths were longest on plants 30 days old whereas perithecia production was greatest on plants 20∼30 days old at time of inoculation. Differences in lesion length and perithecia production that were observed on young plants (4∼10 days old) were similar to relative levels of susceptibility in soybean cultivars in greenhouse and field tests, suggesting that reaction to C. ilicicola in soybean cultivars may be determined early in plant development.

Effects of soil disinfection, fungicide application, and narrow ridge cultivation on ginger rhizome rot development were examined in two naturally-infested fields at Seosan, Choongnam province. Soil disinfection treatments were assigned to main plots, and fungicide and ridge treatments to sub-plots in a split plot design with three replications. The rhizome rot started in late July, and progressed rapidly until late September with the peak incidence in mid-august to early September. Soil disinfection by dazomet application showed the most prominent inhibition effects in both fields, where the disease was reduced by the treatment from 17.5% to 4.8% in one field, and from 51.0% to 2.2% in the other field. Three to five applications of fungicide metalaxyl-copper during the growing season inhibited the disease by 89.7% in one field, but less effectively in the other field. Narrow ridge cultivation reduced the disease effectively by 78.1% and 63.9%, compared to the unridged control plots in each field, respectively. Germination rate of seed-rhizomes and growth of ginger plants were similar between treatments, except when the plots received improper aeration after applying dazomet, and then the germination rate was significantly reduced. The greatest yields were obtained in the disinfected plots, regardless of rhizome rot incidence, except one control plot with very little disease. Ginger yield was negatively correlated with disease severity. However, the yield of ridge plots averaged 58∼59% compared to those of the unridged plots, due mainly to the half planting rate of the ridge plots. In spatial progress, the disease in the disinfected plots started from a single focus of the inoculum, and spread into the adjacent areas only, whereas in the untreated plots, the disease started from many foci that were distributed over the plot, and rapidly progressed to make an epidemic during the season. The soil density of P. myriotylum in the disinfected plots was not changed or, if not, increased slightly during the season. However, in the untreated plots it increased rapidly to reach the density 3 to 5 times greater by the end of the season.

This study was undertaken to find a new formulation of soil amendment, and selection of antogonists and to effectively control brown and large patch of turfgrasses caused by Rhizoctoniz solani AG1-1 and AG 2-2. Fourteen inorgainc chemicals (1%, w/w) were added individually in vitro, and some chemicals showed suppressiveness to R. solani. Alum suppressed effectively mycelial growth of R. solani in the range of 17 to 77% as compared with control. The four chemicals such as Al2(SO4)3, alum, CaO, and NH4NO3 were finally selected. Out of three organic compounds, composted pine bark (CPB) showed prominent suppressive effect as compared with milled alfalfa and pine leaves. After inoculation of R. solani isolates AG-1 and AG2-2 on the turf seedlings, water soaked lesions and blight symptoms were developed on the whole seedlings. According to inhibition zone method, mycelial growth of the fungus were greatly suppressed by culture filterates of the antagonists, Gliocladium virens (Gl1-) and Pseudomonas sp. (P713). CPB soil amendment mixed with antagonists (1% w/w) controlled not only brown and large patch of turfgrasses, but also promote the good growth of the seedlings. In addition, the controlling effect was maintained more than 30 days. Especially, the controlling effect of two antagonists was similar to Cㅖㅠ soil amendment with the antagonists and also stimulated a favorable growth of the seedlings. Therefore, its is expected that continuous control of Rhizoctonia blight of turfgrasses can be obtained in field by subsequent applications of the antagonists.

The production of Korean ginseng, one of the most important medicinal root crops, is limited by many factors including soil sickness, root rots in fields as well as during storage prior to consumption. Although much research has been conducted on the diseases in field condition, little information is available on the control of postharvest roots rots. To obtain better management strategy of postharvest root rots in ginseng, biological control using antagonistic bacteria was attempted. Of 208 bacteria obtained form suppressive soil samples, 4 were selected based on the inhibitory effect on mycelial growth of two major causal fungi for postharvest root rots in ginseng, Botrytis cinerea and Fusarium solani. The culture filtrates of these bacterial antagonists greatly inhibited the conidial germination of both pathogenic fungi and produced abnormal morphology such as swollen germ tubes in F. solani and vacuolation of nongerminated conidia in B. cinerea. The population levels of bacterial antagonists on the ginseng roots were gradually increased up to 8 days of incubation. Postharvest root rots of ginseng caused by f. solani and B. cinerea were controlled in dipping tests in the ranges of 60∼80% by antagonistic Bacillus spp. obtained from suppressive soil. These results suggest that biological control using these antagonistic bacteria would be an alternative strategy to control postharvest root rots in ginseng.

Effects of chitosan on growth of tomato plant, and suppression of Fusaruim wilt caused by Fusarium oxysporum f. sp. lycopersici and late blight casued by Phytophthora infestans, were examined. Both late blight and fusarium wilt were suppressed by spray and irrigation of chitosan, respectively. Inhibition of mycelial growth was not greatly affected by molecular size of chitosan but, concentration dependent effects was observed. Ninty percent of P. infestans and 80% of F. oxysporum f. sp. lycopersici of mycelial growth was inhibited by 1,000 ppm of chitosan (MW 30,000~50,000) when amended in plate media. Induction of defense-related gene expression in plant by chitosan treatments were observed when chitosan treated tobacco and tomato RNA samples were hybridized with several defense-related genes as probes. The results revealed that $\beta$-1,3-glucanase and chitinase genes were strongly induced, while pathogenesis-related protein-1, 3-hydroxy-3-methylglutaryl coenzyme A reductase, anionic peroxidase, phenylalanine ammonia lyase genes were weakly induced by chitosan treatment. These results suggest that chitosan have dual effects on these host-pathogen interactions. Possible roles of chitosan in suppression of tomato diseases by inhibition of mycelial growth and activation of plant defense responses are discussed.