Showing papers on "Phytoalexin published in 1975"

Specific elicitors of plant phytoalexin production: detenninants of race specificity in pathogens?

Abstract: Race 1 cultures of the phytopathogenic fungus Phytophthora megasperma var. sojae produced a specific elicitor of the soybean phytoalexin hydroxyphaseollin that resulted in higher production of the phytoalexin on disease-resistant Harosoy 63 soybeans than in the near-isogenic susceptible cultivar Harosoy. Race 3 of the fungus, which gives susceptible reactions on both soybean cultivars, did not produce the race I specific elicitor.

Host-Pathogen Interactions: VIII. Isolation of a Pathogen-synthesized Fraction Rich in Glucan That Elicits a Defense Response in the Pathogen's Host.

Abstract: A polysaccharide from the fungal pathogen Colletotrichum lindemuthianum causes browning and phytoalexin production when applied to the cut surfaces of bean (Phaseolus vulgaris) cotyledons and hypocotyls. The application of an amount of polysaccharide equivalent to less than 100 ng of glucose will elicit this response in the bean tissues. The polysaccharide has been isolated both from culture filtrates and from the mycelial walls of the fungus. Purification of the polysaccharide involved anion and cation exchange chromatography and gel filtration. The polysaccharide has an apparent molecular weight between 1,000,000 and 5,000,000 daltons, and consists predominantly of 3- and 4-linked glucosyl residues.

Ozone Injury in Soybeans Isoflavonoid Accumulation Is Related to Necrosis

Abstract: Fumigation of soybean leaves (Glycine max [L.] Merr. with ozone caused stippling and silvering at the same time that large accumulations of the isoflavonoid compounds daidzein, coumestrol, and sojagol occurred. Nitrogen dioxide and sulfur dioxide caused lesser accumulation of the isoflavonoids, and peroxyacetyl nitrate did not result in significant accumulation. Visible toxicity and chemical changes in ozone-fumigated leaves were similar to the hypersensitive disease defense reaction of soybean leaves to the pathogen Pseudomonas glycinea, except that the phytoalexin hydroxyphaseollin was not produced in the ozone-treated leaves.

Phytoalexin Activity in Barley Powdery Mildew

Abstract: Phytoalexin activity was detected in an obligate parasitic host-parasite combination, barley and Erysiphe graminis. There are two phases of phytoalexin production in the pathogenesis. In the first phase, phytoalexin activity was found 12hr after inoculation and was more prominent in incompatible cultivar-race interactions than in compatible ones. Both resistance and the ability to accumulate phytoalexin activity in leaves of the incompatible cultivar during the first phase were lost by heat treatment at 50C for 5min. In the second phase, phytoalexin activity was detected around the fungal colonies formed on leaves of the compatible hosts. The antifungal activity of the second phase phytoalexin was almost the same against several races. The role of phytoalexin in the pathogenesis in powdery mildew of barley are discussed.

Viii. isolation of a pathogen-synthesized fraction rich in glucan that elicits a defense response in the pathogen's host'

Abstract: A polysaccharide from the fungal pathogen Colletotrichum lindemuthianum causes browning and phytoalexin production when applied to the cut surfaces of bean (Phaseolus vulgaris) cotyledons and hypocotyls. The application of an amount of polysaccharide equivalent to less than 100 ng of glucose will elicit this response in the bean tissues. The polysaccharide has been isolated both from culture filtrates and from the mycelial walls of the fungus. Purification of the polysaccharide involved anion and cation exchange chromatography and gel filtration. The polysaccharide has an apparent molecular weight between 1,000,000 and 5,000,000 daltons, and consists predominantly of 3- and 4-linked glucosyl residues.

Induced conversion of the phytoalexin maackiain to dihydromaackiain by the alfalfa pathogen Stemphylium botryosum

Abstract: The conversion of maackiain (3-hydroxy-8,9-methylenedioxypterocarpan), a proposed phytoalexin of red clover, by the alfalfa pathogen Stemphylium botryosum occurred readily in vitro, and was detected in vivo. The initial product of maackiain conversion was identified as dihydromaackiain (7,2′-dihydroxy-4′,5′-methylenedioxyisoflavan) by spectrophotometric, chromatographic (t.l.c., g.l.c.) and mass spectrometric comparisons with authentic dihydromaackiain. Dihydromaackiain, as well as maackiain, was inhibitory to germ tube growth of S. botryosum but the concentration of dihydromaackiain in culture filtrates declined relatively rapidly. The conversion of maackiain to dihydromaackiain could be induced by the presence of maackiain, phaseollin (a phytoalexin from beans) or medicarpin (a phytoalexin from alfalfa and red clover). Maackiain could induce the conversion of phaseollin or medicarpin to their respective 2′-hydroxyisoflavan derivatives, phaseollinisoflavan and vestitol. Conversion of all three of these phytoalexins was prevented or delayed when cycloheximide was added at the same time as the inducer but conversion did occur normally if cycloheximide was added after induction had occurred. The results are discussed in relationship to the pathogenicity of S. botryosum on alfalfa and its lack of pathogenicity on beans and red clover.

Orchid phytoalexins. ii. isolation and characterization of possible sterol companions

Abstract: Four sterols have been isolated from extracts of Cymbidiumn pseudobulbs infected with Rhizoctonzia repenis M 32. One of them, ergosterol peroxide, is most probably an artifact of extraction. The other three, sitosterol, stigmasterol, and campesterol, occur in a 70:25:5 ratio. Appearance of phytoalexin(s) in pseudobulb extracts coincides with increase of sterol production. This raises the question whether Cymbidium phytoalexins are related, biosynthetically or structurally, to sterols. Since the same three sterols occur (free or conjugated) in Cattleya and Arundinia, but in different ratios to each other than in Cymbidillin, they may be of value in chemotaxonomy.

Phytoalexin production by lucerne (Medicago sativa L.) in response to infection by Verticillium

Abstract: The diffusate obtained when excised lucerne leaves were inoculated with drops of spore suspension of strains of Verticillium contained antifungal compounds in significant quantity only if the strain was nonpathogenic. If spores of the pathogenic strains were also present in the inoculum this ability of the non-pathogenic strain to induce phytoalexins was markedly reduced. Bioassays showed that pathogenic strains were relatively insensitive to these compounds. It is suggested that the differential pathogenicity of the strains is closely related to phytoalexin accumulation.