Showing papers on "Phialophora gregata published in 2003"
Journal Article•
TL;DR: Using ITS and 28S rDNA sequences, members of the genus Cadophora are shown to be anamorphs of the Helotiales (discomycetes) and distinct from the morphologically similar anamorph genus Phialophora.
Abstract: Using ITS and 28S (LSU) rDNA sequences, members of the genus Cadophora are shown to be anamorphs of the Helotiales (discomycetes) and distinct from the morphologically similar anamorph genus Phialophora. The rDNA sequences of Cadophora spp. were similar to those of the teleomorph genera Mollisia, Pyrenopeziza, and Tapesia (which have anamorphs in Ramulispora) and to the anamorph genera Phialocephala and Rhynchosporium. The type species of Cadophora is C. fastigiata, and C. malorum is another common species in the genus. Also included are C. finlandia comb. nov., the soybean pathogen C. gregata comb. nov., C. lagerbergii, C. luteo-olivacea comb. nov., and C. melinii. Phialophora atra and C. heteroderae are synonymized with C. malorum. Phialophora goidanichii is synonymized with C. luteo-olivacea.
111 citations
TL;DR: Findings indicate that H. glycines can increase the incidence and severity of BSR in soybean regardless of resistance or susceptibility to either pathogen.
Abstract: Tabor, G. M., Tylka, G. L., Behm, J. E., and Bronson, C. R. 2003. Heterodera glycines infection increases incidence and severity of brown stem rot in both resistant and susceptible soybean. Plant Dis. 87:655-661. Growth chamber experiments were conducted to investigate whether parasitism by Heterodera glycines, the soybean cyst nematode, increases incidence and severity of brown stem rot (BSR) of soybean, caused by Phialophora gregata, in both resistant and susceptible soybean cultivars. Soybean genotypes with various combinations of resistance and susceptibility to both pathogens were inoculated with P. gregata alone or P. gregata plus H. glycines. In most tests of H. glycines-susceptible genotypes, incidence and severity of internal stem discoloration, characteristic of BSR, was greater in the presence than in the absence of H. glycines, regardless of susceptibility or resistance to BSR. There was less of an increasing effect of H. glycines on stem symptoms in genotypes resistant to both BSR and H. glycines; however, P. gregata colonization of these genotypes was increased. Stems of both a BSR-resistant and a BSRsusceptible genotype were colonized earlier by P. gregata in the presence than in the absence of H. glycines. Our findings indicate that H. glycines can increase the incidence and severity of BSR in soybean regardless of resistance or susceptibility to either pathogen. Additional keywords: BSR, pathogen interaction, Phialophora gregata, SCN
39 citations
TL;DR: Genetic variation and variation in aggressiveness in Phialophora gregata f.
Abstract: Genetic variation and variation in aggressiveness in Phialophora gregata f. sp. sojae, the cause of brown stem rot of soybean, was characterized in a sample of 209 isolates from the north-central region. The isolates were collected from soybean plants without regard to symptoms from randomly selected soybean fields. Seven genotypes (A1, A2, A4, A5, A6, M1, and M2) were distinguished based on DNA fingerprinting with microsatellite probes (CAT)5 and (CAC)5, with only minor genetic variation within the A or M genotypes. Only the A1, A2, and M1 genotypes were represented by more than one isolate. The A genotypes dominated in the eastern Iowa, Illinois, and Ohio samples, whereas the M genotypes were dominant in samples from western Iowa, Minnesota, and Missouri. In growth chamber experiments, isolates segregated into two pathogenicity groups based on their aggressiveness toward soybean cvs. Kenwood and BSR101, which are relatively susceptible and resistant, respectively, to brown stem rot. In both roo...
33 citations
TL;DR: Brown stem rot (BSR), caused by Phialophora gregata f.
Abstract: Brown stem rot (BSR), caused by Phialophora gregata f. sp. sojae, is an important yield-limiting disease of soybean (Glycine max) in the midwestern United States. Midwestern populations of P. gregata are separated into genotypes A and B based on intergenic spacer sequences of nuclear ribosomal DNA. Genotype A causes both leaf and stem symptoms, and genotype B typically causes internal stem symptoms only. Data are limited on the geographic distribution of genotypes A and B. It is not well understood whether cultivars may be infected preferentially by a genotype. Field plots were established at five sites in Illinois, three sites in Wisconsin, and two sites in Minnesota in two different years. Soybean cvs. Bell, BSR101, Dwight, Sturdy, Williams 82, LN92-12033, and LN92-12054 were sown with two to four replications at each field site. From each plot, 5 to 10 stems were harvested arbitrarily at the R8 growth stage and assayed by polymerase chain reaction to detect the A and B genotypes. Both pathogen...
19 citations
TL;DR: It is suggested that stem inoculation methods may be useful for assessing resistance to P. gregata and internal stem discoloration was not as useful as colonization and foliar symptoms in discriminating resistant from susceptible genotypes.
Abstract: Growth chamber experiments were conducted to determine if resistance to Phialophora gregata, the causal agent of brown stem rot (BSR) of soybean, is expressed in the stems of resistant soybean genotypes. Upon introduction of the pathogen into the base of stems of 2-week-old seedlings, the fungus advanced with the growing tips of plants of susceptible genotypes but lagged behind in resistant genotypes. Five weeks after introduction of the pathogen, both mean percent stem length colonized by P. gregata and mean percentage of symptomatic trifoliate leaflets were significantly less for resistant than for susceptible genotypes. These results indicate that resistance can be expressed in the stems of resistant soybean plants and suggest that stem inoculation methods may be useful for assessing resistance to P. gregata. Also, in our experiments, internal stem discoloration was not as useful as colonization and foliar symptoms in discriminating resistant from susceptible genotypes.
14 citations
TL;DR: A new set of soybean accessions from south-central China were added to the USDA germplasm collection in 1996 and ten accessions were identified that had BSR resistance equal to or greater than the current resistant sources.
Abstract: A new set of soybean accessions from south-central China were added to the USDA germplasm collection in 1996. Previous studies have shown that accessions with high levels of resistance to brown stem rot (BSR) can be found in germplasm collected from central and southern China. The objective of this study was to screen these accessions and identify those with resistance to BSR. In a preliminary study, 85 of 623 accessions tested were identified as resistant to BSR. In the second study, these 85 accessions were challenged with multiple biotypes of Phialophora gregata f. sp. sojae to identify those accessions with the strongest resistance. From these two studies, ten accessions were identified that had BSR resistance equal to or greater than the current resistant sources.
7 citations