• Korean journal of applied entomology
• /
• v.23 no.1 s.58
• /
• pp.22-27
• /
• 1984

The effects of solarization on the suppression of soilborne plant pathogen and the growth promotion of cucumber plants were examined in artificially infested soil by vinyl mulching and not mulching from July 25 to August 25, 1983. During the solarization period, the highest temperatures were $58^{\circ}C,\;45^{\circ}C,\;and\;42^{\circ}C$, at 5cm, 15cm, and 25cm of soil depth respectively. The inoculum of cucumber wilt pathogen, Fusarium oxysporum f. sp. cucumerinum, was mixed with soil 30cm deep and saturated with water. The pathogen was completely killed after 30dys of solarization in 5cm soil depth and 98 percent of inoculum was eliminated in 15cm soil depth. But the survival rate of the fungi in 25cm soil depth of solarized plot did not show significant differences compared with those in nontreated plot in 5cm and 15cm depth. Although some of the pathogenic fungi might survive from solarized soil in 15cm and 25cm depth, the ability of microconidia production was reduced significantly The number of microconidia grown on Komada's medium in isolates the primary colonies from solarized soil was less than that in isolates from nontreated soil approximately by one fourth. The first subcultured solates from the solarized soil grown on potato dextrose agar also produced a small amount of microc. onidia compare with that of subcultured isolates from nontreated soil. Cucumber seedlings planted in the soil collected from solarized plot grew much better than that in the soil from nontreated plot at any of soil loved, especially in 5cm of soil depth. And the fruits harvested from cucumber plants grown in the solarized plot were more in number and leavier in weight than that from nontreated plot. Besides the typical symptom development, significant growth suppression wvas recognized with increase of inoculum density of F. oxysporum f. sp. cucumerinum at early stage of cucumber seedlings in steam sterilized soil.

• Mycobiology
• /
• v.28 no.4
• /
• pp.190-192
• /
• 2000

Antifungal bacteria for biological control of plant diseases or production of novel antibiotics to plant pathogens were isolated in 1997 from various soils of Ansung, Chunan, Koyang, and Paju in Korea. Sixty-four bacterial strains pre-screened from approximately 1,400 strains were tested on V-8 juice agar against eight plant pathogenic fungi using in vitro bioassay technique for inhibition of mycelial growth. Test pathogens were Alternaria mali, Colletotrichum gloeosporioides, C. orbiculare, Fusarium oxysporum f. sp. cucumerinum, F. oxysporum f. sp. lycopersici, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. A wide range of antifungal activity of bacterial strains was found against the pathogenic fungi, and strain RC-B77 showed the best antifungal activity. Correlation analysis between inhibition of each fungus and mean inhibition of all eight fungi by 64 bacterial strains revealed that C. gloeosporioides would be best appropriate for detecting bacterial strains producing antibiotics with potential as biocontrol agents for plant pathogens.

• Korean Journal Plant Pathology
• /
• v.11 no.4
• /
• pp.287-291
• /
• 1995

Biocontrol agents, Gliocladium virens G872B and Pseudomonas putida Pf3, were compatible each other in colonizing cucumber rhizosphere, which contributed to a long-term inhibition of cucumber Fusarium wilt. G872B colonized successfully on the cucumber root system, irrespective of the introduction of Pf3. Pf3 also colonized well in the cucumber rhizosphere regardless of the presence of G872B. The individual strains effectively suppressed cucumber wilt up to 56 days after transplanting. The combined treatment of G872fB and Pf3 provided a long-term protection of about 80 days with the efficacy greater than that obtained by any individual strains under greenhouse conditions. These results suggest that the colonization of the biological control agents in the rhizosphere could be correlated directly to Fusarium wilt-suppressive potentials.

• The Plant Pathology Journal
• /
• v.21 no.3
• /
• pp.244-251
• /
• 2005

The induction of growth promotion on numerous crops by rhizobacteria is a well documented phenomenon. In case of tomato (Lycopersicon esculentum), fruit yield is higher in replant soil than that in fresh soil. To investigate what kind of rhizobacterium is involved, microbial community in rhizosphere and on rhizoplane of tomato plants from each soil was analyzed by dilution plating on selective media. Many Gram-negative bacteria and actinomycetes were isolated from tomato in replant soil. One Gram-negative rhizobacterium isolated was identified as Pseudomonas putida based on its biochemical characteristics, fatty acid methyl ester analysis and 16S rDNA sequence. This bacterium designated strain 17 inhibited the growth of Pseudomonas corrugata, and increased growth of tomato seedlings. In addition, its culture filtrate inhibited conidial germination of plant-pathogenic fungi such as Fusarium oxysporum f. sp. radicis-lycopersici, F. oxysporum f. sp. cucumerinum, and Nectria radicicola. Scanning electron microscopy revealed strain 17 colonized and persisted on the epidermal surfaces of tomato radicles and roots. These results suggest that P. putida strain 17 may serve as a biological control agent to suppress multiple soil-borne diseases for tomato plants. Increased microbial populations that suppress deleterious microorganisms including pathogens could be one of the major factors in increased tomato yield in replant soil.

• The Plant Pathology Journal
• /
• v.31 no.2
• /
• pp.140-151
• /
• 2015

Bacillus subtilis B006 strain effectively suppresses the cucumber fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (Foc). The population dynamics of Foc, strain B006 and its surfactin over-producing mutant B841 and surfactin-deficient mutant B1020, in the rhizosphere were determined under greenhouse conditions to elucidate the importance of the lipopeptides excreted by these strains in suppressing Foc. Results showed that B. subtilis strain B006 effectively suppressed the disease in natural soil by 42.9%, five weeks after transplanting, whereas B841 and B1020 suppressed the disease by only 22.6% and 7.1%, respectively. Quantitative PCR assays showed that effective colonization of strain B006 in the rhizosphere suppressed Foc propagation by more than 10 times both in nursery substrate and in field-infected soil. Reduction of Foc population at the cucumber stems in a range of $0.96log_{10}ng/g$ to $2.39log_{10}ng/g$ was attained at the third and the fifth weeks of B006 treatment in nursery substrate. In field-infected soil, all three treatments with B. subtilis suppressed Foc infection, indicated by the reduction of Foc population at a range of $2.91log_{10}ng/g$ to $3.36log_{10}ng/g$ at the stem base, one week after transplanting. This study reveals that the suppression of fusarium wilt disease is affected by the effective colonization of the surfactin-producing B. subtilis strain in the rhizosphere. These results improved our understanding of the biocontrol mechanism of the B. subtilis strain B006 in the natural soil and facilitate its application as biocontrol agent in the field.

• The Plant Pathology Journal
• /
• v.19 no.3
• /
• pp.129-132
• /
• 2003

Fusarium wilt of cucumber caused by Fusarium oxy-sporum f. sp. cucumerinum is a serious vascular disease worldwide. Biological control of Fusarium wilt in several crops has been accomplished by introducing non-pathogenic Fusarium sup. and other biocontrol agents in soil or in infection courts. In this study, quantitative models were used to determine the biocontrol efficacy of inundatively applied antagonist formulations and the length of their effectiveness in controlling Fusarium wilt of cucumber. Quantitative model of the form [Y=L (1${-exp}^{-kx}$)] best described the relationship between disease incidence (Y, %) and inoculum density (X) of isolates F51 and F55. Isolate F51 was selected as a more virulent isolate based on the extent of its effectiveness in causing the wilt disease. The degree of disease control (Xi/X) obtained with the density of the biocontrol agent (Z), was described by the model [Xi/X=A (1${-exp}^{-cz}$)]. The zeolite-based antagonist formulation amended with chitosan (ZAC) was better at lower rates of application and peaked at around 5 g/ kg of the potting medium, whereas the peat-based antagonist formulation (PA) peaked at around 10 g/kg of the potting medium. ZAC formulation provided significantly better suppression of Fusarium wilt as described by the curvilinear relationship of the type Y= a+bX+c$X^2$, where Y represents percent disease incidence and X represents sustaining effect of the biocontrol agent.

• Korean journal of applied entomology
• /
• v.24 no.2 s.63
• /
• pp.85-95
• /
• 1985

It has been tried to find effective biological control measures involved in nature of soil suppressiveness to fusarium wilt of cncumber caused by Fusarium oxysporum f. sp. cucumerinum Owen. Total 28 soil samples were obtained from Jinju, Haman, Namji, Milyang and Suncheon vinyl house area. The disease response of test soil was quantified in terms of DI50 value which caculated from log-probit transformation of diseases response curves. Soils designated 5 from Jinju, 7 from Suncheon, 22 from Namji were recognized as suppressive to fusarium wilt of cucumber. This suppressiveness was completely nullified after autoclave. The disease suppressiveness of tested soil did not indicate any consistency according to either chemical property or texture of soil. Conidial germination, induction and germination of chlamydospore were markedly inhibited in supprerssive soil compared to those in intermediate or conducive soils, however, mycelial lysis did not appear to have direct relationship with disease suppressiveness of given soil. Population density of fluorescent Pseudomonads and Bacillus spp. in the soil originated from different degree of suppressiveness were not different significantly but the number of lytic bacterial plaques measured by triple layer agar method was remarkably higher in suppressive soil than that in intermediate or conducive soil.

• Journal of Microbiology and Biotechnology
• /
• v.5 no.6
• /
• pp.324-334
• /
• 1995

The actinomycete strain A 11 was antagonistic to plant pathogenic fungi Phytophthora capsid and Magnaporthe grisea. Based on the diaminopimelic acid (DAP) type and morphological characteristics examined by scanning electron microscopy, the strain A 11 was confirmed to belong to the genus Streptomyces. Based on Willcox probability and similarity level, the strain A 11 was numerically identified as Streptomyces flaveus using TAXON program of Ward and Goodfellow. Antibiotic production of S. flaveus strain A 11 was most favorable when cultured on glycerol yeast extract peptone (GYP) agar for 20 days at $28^{\circ}C$. The crude antibiotics from solid GYP agar cultures of the strain A 11 were most effective against Phytophthora capsici and Sclerotinia sclerotiorum among the fungi tested. Antifungal activity of the antibiotics against Alternaria solani, Botryosphaeria dothidea, Cercospora capsici, Magnaporthe grisea, and Rhizoctonia solani was somewhat high, whereas Colletotrichum gloeosporioides and Fusarium oxysporum f. sp. cucumerinum were rarely inhibited even at high concentrations.

• Applied Biological Chemistry
• /
• v.41 no.8
• /
• pp.600-604
• /
• 1998

Methanol extracts from 53 species of oriental medicinal plants in 34 families were tested for their fungicidal activities against Pyricularia grisea, Rhizoctonia solani, Phytophthora capsici, Phytophthora infestans, Collectotrichum dematium, Botryospaeria dothidea, Fusarium oxysporum f. sp. cucumerinum, Botrytis cinerea, Puccinia recondita, and Erysiphe graminis. In in vitro study using impregnated paper disc method, the efficacy varied with both plant pathogen and plant species tested. Methanol extracts of Asarum sieboldii roots, Sinomenium acutum roots, Pinus densiflora leaves, Rheum undulatum root barks, Coptis japonica roots, and Phellodendron amurense barks showed potent fungicidal activities against the various pathogens when treated with 10 mg/disc. In a whole plant test, methanol extracts of P. densiflora leaves and roots and C. japonica roots were highly effective against a variety of plant pathogens. As a naturally occurring fungicide, P. densiflora- and C. japonica-derived materials could be useful as new fungicidal products against various plant diseases induced by plant pathogenic fungi.

• The Plant Pathology Journal
• /
• v.16 no.4
• /
• pp.189-199
• /
• 2000

To search for the antifungal substances, various actino-mycete isolates were obtained from various soils of Korea using plate dilution method on the humic acid vitamin agar plates. In the screening procedures using a dual culture method, 32 actionomycete isolates were selected, which showed the inhibitory activity against mycelial growth of plant pathogenic fungi Altirnaria mali, Colletotrichum gloeosporides, Fusarium oxysporum f.sp. cucumerinum, Magnaporthe grisea, Phytophthora capsici, and Rhizoctonia solani. Bioassay of the crude extracts from culture filtrates and mycelial mets revealed that 12 antagonistic actionomycetes produced highly active antifungal substances. Actinomycete strain S5-55 which showed the substantial antifungal activity against the tested fungi was selected for production of the antifungal substances. Based on the cytochemical and morphological characteristics, strain S5-55 was identified as a Streptomyces species. The results of the numerical identification using the TAXON program confirmed that Streptomyces strain S5-55 was identical with Streptomyces humidus including in TAXON major cluster 19. The production of antifungal substance was most favorable when S. humidus strain S5-55 was cultivated for 10 dats on soluble starch broth supplemented with $K_2$HPO$_4$. The antifungal substances active against the plant pathogenic fungi P. capsici and M. grisea were partially purified using $\textrm{C}_{18}$ reversed-phase column chromatography.