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A novel butanoic acid, thiobutacin (1), 4-(2-aminophenyl)-4-oxo-2-methylthiobutanoic acid (C11H13NO3S), was isolated from the culture broth of a soil actinomycete, Lechevalieria aerocolonigenes strain VK-A9. The structure of thiobutacin (1) was elucidated on the basis of the extensive 2D NMR spectral data including 1H-1H COSY, HMBC, HMQC, ROESY, and NOESY. Thiobutacin (1) showed antioomycete and antifungal activity against phytopathogenic Phytophthora capsici and Botrytis cinerea and the yeast Saccharomyces cerevisiae.

The methanol extract of Anemarrhena asphodeloides rhizomes exhibited strong antifungal activity against the plant pathogenic fungi Magnaphothe grisea, Rhizoctonia solani, and the plant pathogenic oomycete Phytophthora capsici. The antifungal substance isolated from the rhizomes of A. asphodeloides was identified to be nyasol, (Z)-1,3-bis(4-hydroxyphenyl)-1,4-pentadiene by NMR and mass spectral analysis. Nyasol effectively inhibited the mycelial growth of Colletotrichum orbiculare, P. capsici, Pythium ultimum, R. solani, and Cladosporium cucumerinum in a range of 1-50 mug/ml, but did not affect the growth of bacteria and yeast. In a greenhouse test, treatment with the antifungal compound nyasol was significantly effective in suppressing the Phytophthora blight on pepper plants.

The bacterial strain GC-B26, which showed strong antifungal and anti-oomycete activity against some plant pathogens, was isolated from a grassland soil in Korea. Based on morphological, physiological and biochemical characteristics, GC-B26 was identical to Pseudomonas aeruginosa (Schroeter) Migula. The antibiotic G26A, active against Phytophthora capsici Leonian and Colletotrichum orbiculare (Berk & Mont) van Arx, was isolated from the culture filtrates of Ps aeruginosa strain GC-B26 using various chromatographic procedures. The EI mass and UV spectral results indicated that G26A is an analogue of phenazines, having molecular formula C13H8N2O2 (M+, m/z 224.0664). On the basis of NMR spectral data, G26A was confirmed as phenazine-1-carboxylic acid. C orbiculare, P capsici and Pythium ultimum Trow were most sensitive to G26A, with MIC values of approximately 5 microg ml(-1). However, no antimicrobial activity was found against yeasts and bacteria, even at a concentration of over 100 microg ml(-1). Treatment with the antibiotic gave highly significant protective activity against the development of Phytophthora disease on pepper and anthracnose on cucumber plants. The disease control efficacy was only slightly less than that of the commercial fungicides metalaxyl and chlorothalonil.

The bacterial strain MM-B16, which showed strong antifungal and antioomycete activity against some plant pathogens, was isolated from a mountain forest soil in Korea. Based on the physiological and biochemical characteristics and 16S ribosomal DNA sequence analysis, the bacterial strain MM-B16 was identical to Pseudomonas fluorescens. An antibiotic active against Colletotrichum orbiculare and Phytophthora capsici in vitro and in vivo was isolated from the culture filtrates of P. fluorescens strain MM-B16 using various chromatographic procedures. The molecular formula of the antibiotic was deduced to be C(10)H(11)NO(2)S (M(+), m/z 209.0513) by analysis of electron impact mass spectral data. Based on the nuclear magnetic resonance and infrared spectral data, the antibiotic was confirmed to have the structure of a thiazoline derivative, aerugine [4-hydroxymethyl-2-(2-hydroxyphenyl)-2-thiazoline]. C. orbiculare, P. capsici, and Pythium ultimum were most sensitive to aerugine (MICs for these organisms were approximately 10 micro g ml(-1)). However, no antimicrobial activity was found against yeasts and bacteria even at concentrations of more than 100 micro g ml(-1). Treatment with aerugine exhibited a significantly high protective activity against development of phytophthora disease on pepper and anthracnose on cucumber. However, the control efficacy of aerugine against the diseases was in general somewhat less than that of the commercial fungicides metalaxyl and chlorothalonil. This is the first study to isolate aerugine from P. fluorescens and demonstrate its in vitro and in vivo antifungal and antioomycete activities against C. orbiculare and P. capsici.

Diversity of actinomycetes and their antifungal activities against some plant pathogenic fungi were examined in various vegetative soils from 14 different sites in the western part of Korea. Actinomycete counts ranged from 1.17 × 10[sup 6] to 4.20 × 10[sup 6] cfu·g[sup -1] dried soil. A total of 1510 actinomycetes were isolated from the soil samples. Streptomyces was predominant in soils with a pH range of 5.1-6.5, 9.1-13.0% moisture, and 9.1-11.0% organic matter. Most Micromonospora, Dactylosporangium, and Streptosporangium were distributed in soils with pH 4.0-5.0, 2.0-9.0% moisture, and 4.0-7.0% organic matter. Actinomadura and nocardioform actinomycetes were abundant in soils with pH 4.0-5.0 and 13.1-20.0% moisture and with 9.1-11.0 and 4.0-7.0% organic matter, respectively. Populations of Streptomyces were predominant in all the soils, but were highest in grassland and lowest in mountain-forest soils. Micromonospora was most abundant in pepper-field soil and nocardioform actinomycetes were highest in rice paddy field soil. Dactylosporangium was predominant in lake-mud sediments and pepper-field soil, Streptosporangium in lake-mud sediments, and Actinomadura in mountain-forest soil. Antifungal actinomycetes were abundant in orchard soil and lake mud. More than 50% of antifungal isolates from most soils were classified as genus Streptomyces. Actinomycete isolates that showed strong antifungal activity against Alternaria mali, Colletotrichum gloeosporioides, Fusarium oxysporum f.sp. cucumerinum, and Rhizoctonia solani were predominant in pepper-field soils, whereas those against Magnaporthe grisea and Phytophthora capsici were abundant in radish-field soils.Key words: actinomycetes, antifungal activity, plant pathogenic fungi, vegetative soils.Nous avons examiné la diversité des actinomycètes qui provenaient de différents sols sous couvert végétal prélevés à 14 sites localisés dans l'ouest de la Corée et avons évalué leur activité antifongique envers certains champignons phytopathogènes. Les dénombrements d'actinomycètes ont varié de 1,17 × 10[sup 6] à 4,20 × 10[sup 6] ufc·g[sup -1] de sol sec. Au total, 1510 actinomycètes ont été isolés de ces échantillons de sol. Les Streptomyces prédominaient dans les sols dont le pH était de 5,1 à 6,5, l'humidité de 9,1 à 13% et qui contenaient 9,1-11% de matière organique. La majorité des Micromonospora, Dactylosporangium et des Streptosporangium se retrouvaient dans les sols où le pH était 4,0-5,0, avec une humidité de 2,0 á 9,0% et qui contenaient 4,0-7,0% de matière organique. Les Actinomadura et les actinomycètes nocardioformes étaient abondants dans les sols à pH 4,0-5,0, dont l'humidité était de 13,1 à 20,0% et qui contenaient respectivement 9,1-11,0 et 4,0-7,0% de matière organique. Les populations de Streptomyces prédominaient dans tous les sols, mais les valeurs les plus élevées s'observaient dans les sols récoltés dans les prairies et les plus faibles dans les sols forestiers montagneux. Micromonospora était le plus abondant dans le sol de plantations de poivriers et la concentration la plus élevée des actinomycètes nocardioformes a été observée dans le sol des rizières. Les Dactylosporangium étaient retrouvés en prédominance dans les sédiments boueux des lacs et dans le sol des plantations de poivriers, les Streptosporangium dans les sédiments boueux des lacs et les Actinomadura dans les sols forestiers en montagne. Les actinomycètes antifongiques étaient abondants dans les sols des vergers et des sédiments boueux des lacs. Plus de 50% des isolats antifongiques présents dans la plupart des sols ont été classés dans le genre Streptomyces. Les isolats d'actinomycètes qui démontraient une forte activité antifongique contre Alternaria mali, Colletotrichum gloeosporioides, Fusarium oxysporum f.sp. cucumerinum et Rhizoctonia solani se retrouvaient en prédominance dans les sols de plantations de poivriers tandis que les isolats actifs envers Magnaporthe grisea et Phytophthora capsici étaient abondants dans les sols de plantations de radis.Mots clés : actinomycètes, activité antifongique, champignons phytopathogènes, sols sous couvert végétal. [ABSTRACT FROM AUTHOR]