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Introduction: Phenazines are nitrogen-containing heterocyclic molecules produced by fluorescent Pseudomonas. These compounds have broad-spectrum antibiotic properties including antimicrobial activity against phytopathogenic fungi and pathogenic bacteria. Several mechanisms of action have been proposed, including inhibition of DNA replication, uncoupling of electron, transport and energy production, and disruption of normal membrane functions resulting in the generation of toxic intracellular oxygen species. Methods: Production of antimicrobial metabolites in vitro was assayed in NBY supplemented with glucose to a final concentration of 2%. Results: Extracts of supernatants from liquid cultures completely inhibited phytopathogenic fungi when incorporated into agar culture at a rateof 20 and 40 µ g/ml, this crude extracts was active against all tested fungi. In a disc assay, extracts equivalent to 20 µ g gave zones of inhibition of 15 mm and 25 mm for the Gram positive bacteria Bacillus subtilis and Paracoccus paratrophus, respectively with disc diffusion technique. The purified extracts were analyzed by UV spectroscopy and GC/MS. [ABSTRACT FROM AUTHOR]

Fourteen bacterial isolates from the rhizosphere of potato plants growing near Sétif, (Algeria) were characterised as fluorescent Pseudomonads by phenotypical methods and one was identified as Pseudomonas chlororaphis by sequencing ribosomal DNA. In dual culture, this isolate inhibited the growth of the phytopathogenic fungi Fusarium oxysporum f. sp. lycopersici, F. oxysporum f. sp. albedinis, F. solani and Rhizoctonia solani and the oomycete Pythium ultimum. Extracts of supernatants from liquid cultures of the Ps. chlororaphis isolate completely inhibited these organisms when incorporated into potato dextrose agar at a rate equivalent to 0.31 ml culture filtrate/ml, or greater. In a disc assay, extracts equivalent to 0.31 ml supernatant gave inhibition zones of 15 mm and 25 mm for the Gram-positive bacteria Bacillus subtilis and Paracoccus paratrophus, respectively. Fractionation of extracts of supernatants by TLC and HPLC with diode array detection allowed the identification of phenazine carboxylic acid as one of the antimicrobial compounds and the tentative identification of two others as 2-hydroxy phenazine carboxylic acid and 2-hydroxy phenazine. [ABSTRACT FROM AUTHOR]

El-KassasR, KaramEl-DinZ, BealeMH, WardJL&StrangeRN (2005) Bioassay-led isolation ofMyrothecium verrucariaand verrucarin A as germination inhibitors ofOrobanche crenata.Weed Research45, 212–219.A total of 188 fungal isolates was obtained from the rhizosphere ofVicia fabagrown in an Egyptian soil heavily infested withOrobanchespecies. Agar cultures of 58 isolates inhibited the germination of conditioned seed ofOrobanche crenataexposed to the germination stimulant, GR24. Filtrates of inhibitory fungi grown in liquid medium for 9–15 days were also assayed and those of five isolates, which were morphologically similar, inhibited germination even when diluted 16-fold. The fungus was identified asMyrothecium verrucaria(Alb.&Schwein.) Ditmar by its morphology and the nucleotide sequence of the ITS1 and ITS2 regions of the ribosomal repeat unit. Purification of the inhibitor to homogeneity was accomplished by solvent partitioning, flash chromatography on silica gel, semi-preparative HPLC on a reversed phase C18 column, solid phase extraction and tlc on silica gel. The inhibitor was identified as verrucarin A by nuclear magnetic resonance spectroscopy and comparison of the spectra with those of an authentic sample of the compound. A preliminary experiment demonstrated that infection ofV. fababyO. crenatacould be prevented by addition of spores of the fungus to soil infested by the parasite. [ABSTRACT FROM AUTHOR]

When zoospores of Phytophthora drechsleri were added to a hydroponic medium in which roots of cucurbit plants were immersed, marrow and pumpkin (Cucurbita spp.) remained symptomless but cantaloup, melon and cucumber (Cucumis spp.) wilted. Symptom development was proportional to the logarithm of day number after inoculation and approximately proportional to the logarithm of zoospore number in cantaloup and melon but not cucumber which was also less susceptible. The fungus became established preferentially in the hypocotyls of cantaloups. Ten times as many chlamydospores differentiated on infected cantaloup hypocotyls as on lupin roots when both tissues were buried in moist soil. [ABSTRACT FROM AUTHOR]

Groundnut leaves, naturally infected in the field with Cercospora arachidicola or artificially infected in the greenhouse with C arachidicola or Puccinia arachidis, accumulated isoflavonoid phytoalexins. Major compounds included medicarpin, formononetin. demethylmedicarpin, three isoflavanones and the isoflavone, daidzein. In both greenhouse and field experiments cv. Egret was less susceptible than cv. P84/5/244 to both pathogens, and accumulated phytoalexin (medicarpin) concentrations which were up to three times greater. Higher concentrations and greater variation of phytoalexins were detected when both cultivars were infected with C. arachidicola than when they were infected with P. arachidis. [ABSTRACT FROM AUTHOR]

The production of ascochitine by seven isolates of Ascochyta fabae accounted for the toxicity of culture filtrates of the fungus to cells isolated from leaves of Vicia faba. The LID50 value for cells from cultivars that were susceptible, tolerant or resistant to the fungus was similar i.e. 3·0× 10-5 M, 3·8×10-5 M and 2·9×10-5 M, respectively. Ascochitine affected neither the germination of seeds nor the growth of mature plants at 5·17×10-4M but caused necrosis and wilting of plant cuttings at 2·5×10-4 M and 5 × 10-4M. There was no association between virulence of 16 isolates of A. fabae for three cultivars of V. faba and the production of ascochitine in vitro. One isolate produced no ascochitine in vitro and yet was the most virulent for two of three cultivars. The toxin could not be extracted from infected plants. [ABSTRACT FROM AUTHOR]

Production of the solanapyrone toxins by Ascochyta rabiei is nutrient dependent. When grown on a medium consisting entirely of expressed sap from the aerial parts of young chickpea plants (PSM), only low concentrations of the solanapyrones were produced (< 24 μM). However, toxicity of 4-day-old culture filtrates to isolated cells of chickpea leaflets was comparable with that obtained from 12-day-old culture filtrates on Czapek Dox nutrients supplemented with chickpea seed extract or cations-media that are conducive to solanapyrone production. The additional toxic component which peaked at 4 days in culture was heat labile, losing about 50% of its activity on boiling for 10 min. Affinity for solid-phase extraction media, precipitation with ammonium sulphate and acetone, ionization properties and UV absorption characteristics suggested that the toxin was a polypeptide. The toxin was purified by solid-phase extraction, acetone precipitation and high performance liquid chromatography (HPLC) on a C2 column. Hydrolysis of the purified toxin yielded 14 amino acids, and calculation of the numbers of residues of each amino acid suggested a molecular mass of 7,551 Da. A band corresponding to this molecular mass was present on SDS-PAGE gels. However, both the native peptide and its hydrolysate contained a compound that reacted with p-anisaldehyde suggesting the possibility of a glycosidic moiety. [ABSTRACT FROM AUTHOR]

Nine isolates of Ascochyta rabiei from Pakistan were grown in still culture on Czapek Dox liquid medium supplemented with aqueous extracts of the seed of-one or two cultivars, a desi (6153)or a kabufi (Cypressa). Toxicity of the culture filtrates from both media was assayed with calls isolated from the leaves of both cultivars and concentrations of the phytotoxins, solanapyrone A and solanapyrone C, in the filtrates were determined by high-performance liquid chromatography (HPLC). For eight of the fungal isolates, toxicity and solanapyrone concentration were correlated, r varying from 0.383 to 0.859 according to medium and assay cultivar, but culture filtrates of another isolate, which was the most active by more than an order of magnitude, contained cytochalasin D but neither of the solanapyrones. [ABSTRACT FROM AUTHOR]

The phytotoxic solanapyrones A, B and C, were produced by Ascochyia rabiei when grown on Czapek Dox nutrients supplemented with an aqueous extract of chickpea seed but not when grown on Czapek Dox nutrients alone. Addition of amino acids, vitamins and inorganic ions to Czapek Dox nutrients allowed the production of the solanapyrones in good yields. By systematic elimination of components of this medium, the constituents essential for toxin production were identified as the divalent metal cations Zn2+, Ca2+, Mn2+ and Cu2+. When these ions were added to Czapek Dox nutrients in the same concentrations as those found in chickpea extract, concentrations of the phslotoxins similar to those found in Czapek Dox nutrients supplemented with chickpea extract were detected. Removal of cations from the chickpea supplement by a cation exchange resin did not affect the growth of the fungus compared with growth on the medium containing the complete supplement, but no toxin was produced. A defined medium and cultural conditions suitable for solanapyrone production by A. rabiei are described. [ABSTRACT FROM AUTHOR]

The affinity of various lectins for protoplasts from isolines of wheat differing in their reaction to Puccinia graminis Pers. f. sp. tritici, Ericks and E. Henn, race 21 and for infection structures of the fungus was studied. Protoplasts of both isolines were agglutinated by concanavalin A and soybean lectin and lysed by wheat germ agglutinin. Pokeweed mitogen and wheat germ agglutinin bound to fungal germ tubes and appressoria but not to uredospore walls, substomatal vesicles or infection hyphae. Viability of protoplasts from either isoline was not affected when they were incubated with uredospores, germlings with and without infection structures or with an extract of the susceptible line, heavily infected by the fungus. No differences between polypeptide fractions prepared from protoplasts of the isolines were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis. [ABSTRACT FROM AUTHOR]

A fungus with morphological features corresponding to the group species Colletotrichum gloeosporioides was consistently isolated from cassava with shoots showing dieback symptoms in Ghana. When four locally-grown cultivars were inoculated with isolates of the fungus, they developed disease symptoms, which consisted of discrete dark brown lesions on the stems followed by defoliation. Koch's postulates were completed by re-isolating the fungus from the inoculated plants. The relatedness of the isolates lo other members of the genus Colletotrichum, whose identities were well established, was investigated by comparison of the nucleotide sequence of domain 2 of their ribosomal DNA. The cassava isolates differed from authentic isolates of C. gloeosporioldes by only one nucleotide among the 193 analysed. The causal agent of cassava stem tip dieback (STDB) is thus identified as a form of C. gloeosporioides. [ABSTRACT FROM AUTHOR]

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Fluorescent Pseudomonad spp. were isolated from the rhizosphere of potato plants (Algeria) by serial dilutions of rhizosphere soils on Kings B medium and were tested for their antifungal activity. The antifungal activity of the Pseudomonas isolated from Potatoes rhizosphere was tested against Pythium ultimum, Rhizoctonia solani and Fusarium oxysporum in dual culture with bacteria on PDA. The Petri dish was divided into tow, on one the bacteria was spread and on the opposite side fungal plugs were inoculated and incubated for one week. Fourteen bacteria were isolated; only one isolate inhibited the growth of Pythium ultimum, Rhizoctonia solani, Fusarium solani; Fusarium oxysporum f.sp. albedinis and Fusarium oxysporum f. sp. Lycopersici with inhibition zones of 39.9, 33.7, 30.8, 19.9 and 22.5 mm respectively.