Gaeumannomyces

Abstract: Four ascomycete species of the genus Gaeumannomyces infect roots of monocotyledons. Gaeumannomyces graminis contains four varieties, var. tritici, var. avenae, var. graminis, and var. maydis. G. graminis varieties tritici, avenae, and graminis have Phialophora-like anamorphs and, together with the other Gaeumannomyces and Phialophora species found on cereal roots, constitute the Gaeumannomyces-Phialophora complex. Relatedness of a number of Gaeumannomyces and Phialophora isolates was assessed by comparison of DNA sequences of the 18S rRNA gene, the 5.8S rRNA gene, and the internal transcribed spacers (ITS). G. graminis var. tritici, G. graminis var. avenae, and G. graminis var. graminis isolates can be distinguished from each other by nucleotide sequence differences in the ITS regions. The G. graminis var. tritici isolates can be further subdivided into R and N isolates (correlating with ability [R] or inability [N] to infect rye). Phylogenetic analysis of the ITS regions of several oat-infecting G. graminis var. tritici isolates suggests that these isolates are actually more closely related to G. graminis var. avenae. The isolates of Magnaporthe grisea included in the analysis showed a surprising degree of relatedness to members of the Gaeumannomyces-Phialophora complex. G. graminis variety-specific oligonucleotide primers were used in PCRs to amplify DNA from cereal seedlings infected with G. graminis var. tritici or G. graminis var. avenae, and these should be valuable for sensitive detection of pathogenic isolates and for diagnosis of take-all.

Abstract: The ability of phytopathogenic fungi to overcome the chemical defense barriers of their host plants is of great importance for fungal pathogenicity. We studied the role of cyclic hydroxamic acids and their related benzoxazolinones in plant interactions with pathogenic fungi. We identified species-dependent differences in the abilities of Gaeumannomyces graminis var. tritici, Gaeumannomyces graminis var. graminis, Gaeumannomyces graminis var. avenae, and Fusarium culmorum to detoxify these allelochemicals of gramineous plants. The G. graminis var. graminis isolate degraded benzoxazolin-2(3H)-one (BOA) and 6-methoxy-benzoxazolin-2(3H)-one (MBOA) more efficiently than did G. graminis var. tritici and G. graminis var. avenae. F. culmorum degraded BOA but not MBOA. N-(2-Hydroxyphenyl)-malonamic acid and N-(2-hydroxy-4-methoxyphenyl)-malonamic acid were the primary G. graminis var. graminis and G. graminis var. tritici metabolites of BOA and MBOA, respectively, as well as of the related cyclic hydroxamic acids. 2-Amino-3H-phenoxazin-3-one was identified as an additional G. graminis var. tritici metabolite of BOA. No metabolite accumulation was detected for G. graminis var. avenae and F. culmorum by high-pressure liquid chromatography. The mycelial growth of the pathogenic fungi was inhibited more by BOA and MBOA than by their related fungal metabolites. The tolerance of Gaeumannomyces spp. for benzoxazolinone compounds is correlated with their detoxification ability. The ability of Gaeumannomyces isolates to cause root rot symptoms in wheat (cultivars Rektor and Astron) parallels their potential to degrade wheat allelochemicals to nontoxic compounds.

Abstract: This invention relates to 4,5-dimethyl-N-2-propenyl-2-(trimethyl silyl)-3-thiophenecarboxamide, a method for the control of Take-All disease (Gaeumannomyces species) in plants by the use of this compound, and to fungicidal compostions for carrying out the method.

Abstract: Examination of the type and other specimens of Gaeumannomyces graminis (Sacc.) Arx & Olivier and of Ophiobolus oryzinus Sacc. has shown that they are identical, and should be known under the name G. graminis var. graminis. This fungus produces on its hosts a mycelium with abundant lobed brown hyphopodia. The fungus causing take-all of wheat differs from G. graminis var. graminis in having simple unlobed hyphopodia and is named G. graminis var. tritici var. nov. The oat take-all fungus, G. graminis var. avenae (E. M. Turner) Dennis, also has simple unlobed hyphopodia, with larger ascospores than the other two varieties. A group of Gaeumannomyces species with hyphopodiate mycelia on Carex spp. is recognized. The significance of these results on identification of cereal take-all fungi and on their host ranges is discussed. Type specimens of several species described earlier than G. graminis were also examined. The names Sphaeria cariceti Berk. & Br. and S. eucrypta Berk. & Br. cannot be applied to the cereal take-all group of fungi. S. helicospora Berk. & Br. is transferred to Acanthophiobolus and S. chaetophora Crouan is reduced to synonymy under this name. Several other species are considered.