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An Epidemiological Comparison Of The Us And Canadian Plum Pox Virus Eradication Programs, Andrew Gougherty Jan 2011

An Epidemiological Comparison Of The Us And Canadian Plum Pox Virus Eradication Programs, Andrew Gougherty

Graduate Theses and Dissertations

Plum pox virus (PPV) is one of the most damaging viral diseases of Prunus spp. worldwide. The virus was first detected in North America in Pennsylvania in 1999, and in Ontario, Canada in 2000. Following the detection of PPV in Pennsylvania and Ontario, both countries implemented PPV survey and eradication programs. The eradication program was successful in Pennsylvania, as PPV was officially declared eradicated in 2009. However, PPV remains present in Ontario. The US and Canadian eradication programs had differing effects on the epidemiology of PPV in their respective countries. The objectives of this research, therefore, were to: (i) quantify ...


A Negative Regulator Of Ribosomal Rna Processing Specifies R-Gene-Independent Cell Death In Barley - Powdery Mildew Interactions, Liu Xi Jan 2008

A Negative Regulator Of Ribosomal Rna Processing Specifies R-Gene-Independent Cell Death In Barley - Powdery Mildew Interactions, Liu Xi

Retrospective Theses and Dissertations

Programmed Cell Death (PCD) plays a pivotal role in plant development and defense. Pathogen dependent cell-death mutants were used to investigate the complex regulatory pathways between PCD and R-gene mediated resistance. Time-course expression profiles of Blumeria graminis f. sp. hordei (Bgh) challenged C.I. 16151 (harboring the Mla6 powdery mildew resistance allele) and its fast-neutron-derived "Bgh-induced tip cell death1" mutant, bcd1, were compared using the 22K Barley1 GeneChip. Contrasts were made to identify genes associated with the cell death phenotype as opposed to R-gene mediated resistance. One hundred eighty-two genes were found in the intersection of these contrasts at a ...


Soybean Mosaic And Stem Canker In Iowa Soybean Fields, Xin Lu Jan 2008

Soybean Mosaic And Stem Canker In Iowa Soybean Fields, Xin Lu

Retrospective Theses and Dissertations

A statewide soybean disease survey was carried out during the 2005 to 2007 growing seasons in Iowa to determine the relative risks for soybean diseases in Iowa. Soybean plants were collected from almost 1,000 fields in each growing season. A systematic design was used to collect 30 plants from 3-5 fields in each county at four growth stages, V2-V3, R1-R2, R4-R5, and R6-R7. The survey provided a unique opportunity to study the spatial and temporal prevalence and incidence of several soybean diseases in Iowa. This thesis will focus on soybean mosaic and stem canker.;Soybean mosaic virus (SMV) is ...


Epidemiological Studies Of Shading Effects On Asian Soybean Rust, Ana Paula Da Silva Dias Jan 2008

Epidemiological Studies Of Shading Effects On Asian Soybean Rust, Ana Paula Da Silva Dias

Retrospective Theses and Dissertations

Asian soybean rust (ASR), caused by the fungus Phakopsora pachyrhizi, is considered to be the most threatening disease in major soybean production regions worldwide. Leaf infection usually results in premature defoliation, which reduces soybean yield components related to pod number, seed number, and size. Among other environmental factors, sunlight intensity negatively affects P. pachyrhizi biology with possible effects on disease epidemiology. Field observations suggest that higher disease severity occurs in shaded environments, such as on soybean leaves in the lower canopy and kudzu leaves under trees, compared with open ground. In this thesis, investigations have been carried out with the ...


Alternative Hosts Of Phakopsora Pachyrhizi In The Americas: An Analysis Of Their Role In The Epidemiology Of Asian Soybean Rust In The Continental U.S., Oscar Pérez-Hernández Jan 2007

Alternative Hosts Of Phakopsora Pachyrhizi In The Americas: An Analysis Of Their Role In The Epidemiology Of Asian Soybean Rust In The Continental U.S., Oscar Pérez-Hernández

Retrospective Theses and Dissertations

Role of susceptible hosts of Phakopsora pachyrhizi in the occurrence of epidemics of Asian soybean rust (ASR) in the U.S. was assessed. Phenology of kudzu (Pueraria montana var. lobata) along a ∼800 km transect in the U.S. was characterized in 2003 and 2004 to assess the potential for kudzu to serve as an inoculum source for occurrence of ASR and subsequent spread to the north central soybean growing regions. Also, the occurrence, distribution, and growing periods of six potential hosts of P. pachyrhizi (including kudzu and soybean), in Central America, the Caribbean, and Mexico, were delineated. Sampling data ...


Soybean Rust In The United States: Assess Its Potential Epidemic Ranges And Frequency Based On Disease Limiting Factors, Disease Attributes, And Comparative Epidemiology, Xun Li Jan 2007

Soybean Rust In The United States: Assess Its Potential Epidemic Ranges And Frequency Based On Disease Limiting Factors, Disease Attributes, And Comparative Epidemiology, Xun Li

Retrospective Theses and Dissertations

No abstract provided.


Sooty Blotch And Flyspeck Of Apple: Assessment Of An Rflp-Based Identification Technique And Adaptation Of A Warning System For The Upper Midwest, Katrina Beth Duttweiler Jan 2007

Sooty Blotch And Flyspeck Of Apple: Assessment Of An Rflp-Based Identification Technique And Adaptation Of A Warning System For The Upper Midwest, Katrina Beth Duttweiler

Retrospective Theses and Dissertations

Sooty blotch and flyspeck (SBFS) of apple, a disease caused by more than 30 species of fungi, reduces crop value by blemishing the fruit surface. This study investigated two research tools designed to improve identification of SBFS fungi and management of the disease.;The first objective was to validate a PCR-based method to identify SBFS pathogens. Members of the sooty blotch and flyspeck (SBFS) disease complex are challenging to identify by traditional mycological methods that rely on agar-plate isolation and morphological description. Identification using a PCR-RFLP assay was investigated as an alternative to culturing. The method involved amplification of the ...


Phytophthora Root And Stem Rot Of Soybean In Iowa: Minimizing Losses Through An Improved Understanding Of Population Structure And Implementation Of Novel Management Strategies, Sarah Marie Cerra Jan 2007

Phytophthora Root And Stem Rot Of Soybean In Iowa: Minimizing Losses Through An Improved Understanding Of Population Structure And Implementation Of Novel Management Strategies, Sarah Marie Cerra

Retrospective Theses and Dissertations

Phytophthora root and stem rot (PRR), caused by the oomycete Phytophthora sojae, is an economically important soybean disease in the North Central Region of the United States, including Iowa. Management of PRR includes the use of specific resistance (Rps genes), partial resistance, and seed treatment fungicides. We had three objectives specific to PRR in Iowa; (i) to determine the within field population diversity of P. sojae in fields with a history of PRR, (ii) to screen 32 PI lines identified with unique resistance to P. sojae with isolates from Iowa and determine their value for future breeding efforts and (iii ...


Genomics And Molecular Biology Approaches To Plant-Parasitic Nematode Biology And Parasitism , Axel Armin Elling Jan 2006

Genomics And Molecular Biology Approaches To Plant-Parasitic Nematode Biology And Parasitism , Axel Armin Elling

Retrospective Theses and Dissertations

The plant-parasitic nematodes Pratylenchus penetrans and Heterodera glycines are of major economic importance worldwide. Here, we present a survey of over 1,900 expressed sequence tags (ESTs) for P. penetrans and of almost 22,000 ESTs for H. glycines. Furthermore, we conducted microarray expression profiling for over 6,800 H. glycines genes throughout the life cycle. We identified over 600 H. glycines genes that encode secretory proteins and provide microarray data for all known H. glycines parasitism genes as well as for H. glycines genes with similarity to known plant and microbe sequences. In order to extend these studies, we ...


Epidemiology And Disease Management Of Stewart's Disease Of Corn In Iowa , Paul David Esker Jan 2005

Epidemiology And Disease Management Of Stewart's Disease Of Corn In Iowa , Paul David Esker

Retrospective Theses and Dissertations

Research was conducted from 2001 to 2003 in Iowa to determine ideal sampling methods, as well as the effect of planting date with/without seed insecticides to reduce corn flea beetle vector (CFB) (Chaetocnema pulicaria) feeding and Stewart's disease (Pantoea stewartii) of corn. Sampling for CFB's was conducted at Ames, Crawfordsville, and Sutherland in 2001 and Crawfordsville and Johnston in 2002. Yellow sticky cards were placed at 15 combinations (five replications) of height (0.15, 0.3, 0.45, 0.6, 0.9 m) and orientation (vertically, horizontally, or 30° angles) at each location. The 0.3 m ...


Sooty Blotch And Flyspeck On Apple: Expansion Of The Fungal Complex, Post-Harvest Removal And Heterogeneity Of Apple Canopy Wetness And Its Impact On The Outcome Of A Disease-Warning System , Jean Carlson Batzer Jan 2005

Sooty Blotch And Flyspeck On Apple: Expansion Of The Fungal Complex, Post-Harvest Removal And Heterogeneity Of Apple Canopy Wetness And Its Impact On The Outcome Of A Disease-Warning System , Jean Carlson Batzer

Retrospective Theses and Dissertations

Sooty blotch and flyspeck (SBFS) fungi blemish the cuticle of apples. Previous studies reported that the SBFS complex is comprised of four species. This is study surveyed the SBFS complex from nine orchards in four Midwestern states (USA). The LSU analyses of the rDNA inferred that 30 species were Dothideomycetes; one species was within the Pleosporales, 27 were within Dothideales, and two species could not be placed at the ordinal level. The LSU sequences of 17 Dothideales species clustered with LSU sequences of known species of Mycosphaerella. Post-harvest dips in commercial disinfestants were used to remove SBFS signs. Apples were ...


Translational Control Of Gene Expression Mediated By The 3' Untranslated Region Of Barley Yellow Dwarf Virus , Elizabeth Lynn Pettit Jan 2005

Translational Control Of Gene Expression Mediated By The 3' Untranslated Region Of Barley Yellow Dwarf Virus , Elizabeth Lynn Pettit

Retrospective Theses and Dissertations

The 869 nt 3' untranslated region (3' UTR) of Barley yellow dwarf luteovirus (BYDV) RNA facilitates cap-independent and poly(A) tail-independent translation. A 105 nt cap-independent translation element (BTE, or BYDV TE) within the 3' UTR was previously defined using wheat germ translation extracts (Guo et al., 2000), but additional 3' UTR sequence is required for translation in plant cells. One domain, nt 4918--5008, confers cap-independent translation in vivo in a discrete and strong manner. Some of this extra sequence places the BTE on a phylogenetically conserved, long double-stranded "stalk", making it more accessible to cellular translational machinery. Another sequence ...


Host Specialization, Intersterility, And Taxonomy Of Populations Of Ceratocystis Fimbriata From Sweet Potato, Sycamore, And Cacao , Christine Jeanette Baker Engelbrecht Jan 2004

Host Specialization, Intersterility, And Taxonomy Of Populations Of Ceratocystis Fimbriata From Sweet Potato, Sycamore, And Cacao , Christine Jeanette Baker Engelbrecht

Retrospective Theses and Dissertations

Ceratocystis fimbriata is a large complex of fungal species that cause wilt-type diseases on a variety of temperate and tropical plants. Within the Latin American clade of C. fimbriata, isolates from sweet potato (Ipomoea batatas), sycamore ( Platanus spp.), and cacao (Theobroma cacao) form monophyletic lineages and are specialized to these three hosts. The sweet potato and sycamore lineages correspond to intersterility groups, and there are two intersterility groups within the cacao lineage, corresponding to a sublineage in western Ecuador and a second sublineage in Brazil, Colombia, and Costa Rica. The cacao lineage is described as a new species, C. cacaofunesta ...


Use Of Remote Sensing, Geographic Information Systems, And Spatial Statistics To Assess Spatio-Temporal Population Dynamics Of Heterodera Glycines And Soybean Yield Quantity And Quality , Antonio Jose De Araujo Moreira Jan 2004

Use Of Remote Sensing, Geographic Information Systems, And Spatial Statistics To Assess Spatio-Temporal Population Dynamics Of Heterodera Glycines And Soybean Yield Quantity And Quality , Antonio Jose De Araujo Moreira

Retrospective Theses and Dissertations

Soybean, Glycine max (L.) Merr., is an important source of oil and protein worldwide, and soybean cyst nematode (SCN), Heterodera glycines, is among the most important yield-limiting factors in soybean production worldwide. Early detection of SCN is difficult because soybean plants infected by SCN often do not exhibit visible symptoms. It was hypothesized, however, that reflectance data obtained by remote sensing from soybean canopies may be used to detect plant stress caused by SCN infection. Moreover, reflectance measurements may be related to soybean growth and yield.;Two field experiments were conducted from 2000 to 2002 to study the relationships among ...


Identification, Characterization, And Cloning Of Arabidopsis Rhd1-4: A Udp-Glucose-4-Epimerase Mutant That Exhibits Hypersusceptibility To The Sugar Beet Cyst Nematode And Altered Root Ethylene Responses , Martin John Evers Wubben Ii Jan 2004

Identification, Characterization, And Cloning Of Arabidopsis Rhd1-4: A Udp-Glucose-4-Epimerase Mutant That Exhibits Hypersusceptibility To The Sugar Beet Cyst Nematode And Altered Root Ethylene Responses , Martin John Evers Wubben Ii

Retrospective Theses and Dissertations

Cyst nematodes (genus Heterodera) constitute an economically important class of plant pathogens that induce the formation of a complex feeding site, i.e., a syncytium, within host plant roots. Cyst nematode-induced modulations in host cell gene expression and signal transduction, via the activity of nematode esophageal gland secretions, are likely required in order to bring about syncytium formation. However, the identities of these host genes and signaling pathways targeted by the nematode remain obscure. In an effort to identify host genes pertinent to successful cyst nematode parasitism, a forward genetics mutant screen was implemented based on the Arabidopsis thaliana-Heterodera schachtii ...


Epidemiology And Predictive Management Of Gray Leaf Spot Of Maize , Pierce Anderson Paul Jan 2003

Epidemiology And Predictive Management Of Gray Leaf Spot Of Maize , Pierce Anderson Paul

Retrospective Theses and Dissertations

Models were developed to assess the risk and predict the severity of gray leaf spot of maize, and to describe relationships between environmental variables and the rate of lesion expansion and sporulation of the causal organism, Cercospora zeae-maydis. Environmental, genotype, and site-specific data were collected from 50 locations in Iowa between 1998 and 2002 and used as input variables for model development, while disease severity at the R4/R5 growth stage of maize was used as the response variable. Pre-planting data were used to develop risk assessment models using ordinal logistic regression and classification and regression tree (CART) modeling approaches ...


Ecology And Epidemiology Of Colletotrichum Acutatum On Symptomless Strawberry Leaves , Leonor Frazão Da Silva Leandro Jan 2002

Ecology And Epidemiology Of Colletotrichum Acutatum On Symptomless Strawberry Leaves , Leonor Frazão Da Silva Leandro

Retrospective Theses and Dissertations

Germination, appressorial production and secondary conidiation of Colletotrichum acutatum were investigated on symptomless strawberry (cv. Tristar) foliage under a range of environmental conditions, and in the presence of strawberry plant extracts. Germination started within 3 h after inoculation and melanized appressoria were formed within 9 h after inoculation on detached strawberry leaves inoculated with a conidial suspension and incubated at 26°C under continuous wetness. Secondary conidia were formed on conidial and hyphal phialides within 6 h after inoculation, resulting in up to threefold increases in conidial populations on leaf surfaces without the development of symptoms or fruiting structures. Under ...


Ecological And Quantitative Studies Of Occurrence Of Soybean Sclerotinia Stem Rot, Caused By Sclerotinia Sclerotiorum, In The North-Central Region Of The United States , Asimina Leonidas Mila Jan 2002

Ecological And Quantitative Studies Of Occurrence Of Soybean Sclerotinia Stem Rot, Caused By Sclerotinia Sclerotiorum, In The North-Central Region Of The United States , Asimina Leonidas Mila

Retrospective Theses and Dissertations

Since the early 90's, Sclerotinia stem rot of soybeans (SSR), caused by Sclerotinia sclerotiorum (Lib.) de Bary, has emerged as a serious problem in the north-central soybean production region of the United States. Understanding the epidemiology of Sclerotinia sclerotiorum and developing models that explain, and eventually may forecast, the risk of SSR occurrence in the region may help extension specialists and growers manage the disease. Regional prevalence of soybean SSR was modeled using historical data collected between 1995 and 1998 from 4 states of the North-Central Region of the United States (Illinois, Iowa, Minnesota and Ohio). Tillage practices, soil ...


Effects Of Herbicides On Growth And Survival, And Influence Of Latitude On Anastomosis Group Diversity In Rhizoctonia Solani , Harikrishnan Ramasubramaniam Jan 2001

Effects Of Herbicides On Growth And Survival, And Influence Of Latitude On Anastomosis Group Diversity In Rhizoctonia Solani , Harikrishnan Ramasubramaniam

Retrospective Theses and Dissertations

Studies were conducted to investigate the direct effects of herbicides on Rhizoctonia solani, effects of herbicides on damping-off and root rots caused by R. solani on glyphosate-tolerant and glyphosate non-tolerant soybeans, and distribution of different anastomosis groups (AGs) of R. solani across the soybean growing regions of the USA.;Effects of three commonly applied soybeans herbicides (glyphosate, imazethapyr, and pendimethalin) were evaluated on the mycelial growth, sclerotial production, and viability of Rhizoctonia solani isolates (anastomosis groups AG-1, AG-2-2, and AG-4) under controlled conditions. Only pendimethalin significantly reduced mycelial growth of all three R. solani isolates investigated. Sclerotial production was affected ...


Molecular Mechanisms Of Cap And Poly(A) Independent Translation Of Barley Yellow Dwarf Virus Rna , Edwards M. Allen Jan 2001

Molecular Mechanisms Of Cap And Poly(A) Independent Translation Of Barley Yellow Dwarf Virus Rna , Edwards M. Allen

Retrospective Theses and Dissertations

Barley yellow dwarf virus RNA contains a translation element (3 'TE) that confers efficient cap-independent initiation at the 5 proximal AUG. Direct end-labeling of RNAs verified the absence of a 5 ' modification on virion RNA. Thus BYDV differs from related viruses by having neither a genome-linked protein nor a 5 ' cap. To function in the 3' UTR, the 3 'TE must recruit ribosomes and associated translation factors, and communicate with the 5' end of the mRNA where translation initiates. The communication function is mediated by direct base pairing between the 3'TE and the 5' UTR. We propose that protein ...


Structural Genomics Of The Barley Mla Powdery Mildew Resistance Complex , Fusheng Wei Jan 2001

Structural Genomics Of The Barley Mla Powdery Mildew Resistance Complex , Fusheng Wei

Retrospective Theses and Dissertations

Powdery mildew of barley, caused by Blumeria ( Erysiphe) graminis f. sp. hordei, is a model system for investigating the mechanism of gene-for-gene interaction between large-genome cereals and obligate-fungal pathogens. We used AFLP markers to saturate the Mla region in a high-resolution mapping population. These tightly linked genetic markers were used to develop a physical contig of YAC and BAC clones spanning the Mla cluster. A lowpass and BAC-end sequencing strategies revealed three distinct NBS-LRR resistance-gene homologue (RGH) families in the contig. Genetic and physical mapping delimited the RGH families to a 240-kb interval. Recombination suppression was found within the RGH ...


Effects Of Liquid Swine Manure And Its Components On Heterodera Glycines Population Densities And Soybean Growth And Yield , Dean Alan Reynolds Jan 2000

Effects Of Liquid Swine Manure And Its Components On Heterodera Glycines Population Densities And Soybean Growth And Yield , Dean Alan Reynolds

Retrospective Theses and Dissertations

The effects of application of swine manure and a comparable rate of inorganic fertilizer to corn on soybean cyst nematode, Heterodera glycines, population densities and soybean growth and yield the following year were studied in two two-year corn and soybean rotations. Soybean heights and yields were increased by manure and inorganic fertilizer that were applied the previous year in corn. Heterodera glycines egg population densities were reduced 48 to 64% in the two experiments after a year of corn. Egg population densities at corn harvest in both experiments were the same where manure or fertilizer was applied and in the ...


Assessing Disease Stress And Modeling Yield Losses In Alfalfa , Jie Guan Jan 2000

Assessing Disease Stress And Modeling Yield Losses In Alfalfa , Jie Guan

Retrospective Theses and Dissertations

Alfalfa is the most important forage crop in the U.S. and worldwide. Fungal foliar diseases are believed to cause significant yield losses in alfalfa, yet, little quantitative information exists regarding the amount of crop loss;Different fungicides and application frequencies were used as tools to generate a range of foliar disease intensities in Ames and Nashua, IA. Visual disease assessments (disease incidence, disease severity, and percentage defoliation) were obtained weekly for each alfalfa growth cycle (two to three growing cycles per season). Remote sensing assessments were performed using a hand-held, multispectral radiometer to measure the amount and quality of ...


Fusarium Ear Rot And Fumonisins In Bt And Conventional Corn Hybrids, 1998, Gary P. Munkvold, Richard L. Hellmich, K. S. Gillette, L. G. Rice Jan 2000

Fusarium Ear Rot And Fumonisins In Bt And Conventional Corn Hybrids, 1998, Gary P. Munkvold, Richard L. Hellmich, K. S. Gillette, L. G. Rice

Entomology Publications

Fusarium ear rot and fumonisin concentrations were compared within five pairs of Bt and near-isogenic conventional hybrids in a replicated field plot at the Iowa State University Johnson Research Farm in Story Co., IA. For each of the five commercially available Bt transformation events, a representative commercial hybrid and its near-isogenic conventional counterpart were included. The 17-ft, four-row plots were planted on 13 May with 30 in row spacing and 120 seeds per plot. The experimental design was a randomized complete block with eight replications. The previous crop was soybeans.


Replication Of Barley Yellow Dwarf Virus Rna And Transcriptional Control Of Gene Expression , Guennadi Koev Jan 1999

Replication Of Barley Yellow Dwarf Virus Rna And Transcriptional Control Of Gene Expression , Guennadi Koev

Retrospective Theses and Dissertations

Barley yellow dwarf virus (BYDV) is an important pathogen of cereal crops. It has a single-stranded positive sense genomic RNA (gRNA), 5.7 kilobases. During infection of a plant cell, BYDV generates a nested set of three subgenomic mRNAs (sgRNAs) for expression of its 3'-proximal genes. The goal of this study was to map and characterize cis-acting RNA signals involved in transcription and replication of BYDV RNA. Three sgRNA promoters and the 3' origin of replication were characterized. The sgRNA1 promoter was mapped to a 98 nt region that contains two stem-loop structures. A combination of primary and secondary ...


Relationships Among Tillage, Spatial Patterns Of Heterodera Glycines, And Soybean Yield , Walber Luiz Gavassoni Jan 1999

Relationships Among Tillage, Spatial Patterns Of Heterodera Glycines, And Soybean Yield , Walber Luiz Gavassoni

Retrospective Theses and Dissertations

Heterodera glycines spatial patterns were studied under different tillage systems in naturally infested soybean fields from 1994 to 1997. The tillage treatments were conventional tillage, reduced tillage, ridge tillage, and no tillage. Results of geostatistical analysis of both cyst and egg population densities showed that no tillage and ridge tillage promoted aggregation of the nematode population, but conventional and reduced tillage resulted in a more uniform spatial pattern. The relationship of soil properties and H. glycines population densities were investigated in the no-tillage plots. Nematode population densities were positively correlated with soil pH, and negatively correlated with organic matter content ...


Genetic Analysis And Dissection Of Crown Rust Resistance In Diploid Avena , Gong-Xin Yu Jan 1999

Genetic Analysis And Dissection Of Crown Rust Resistance In Diploid Avena , Gong-Xin Yu

Retrospective Theses and Dissertations

Disease resistance genes provide an effective way to prevent disease. They confer resistance specificity to a variety of plant pathogens, however, they share conserved mechanisms of pathogen recognition and resistance induction. Resistance genes are often organized as clusters in individual plant genomes. The gene clusters are predicted to be a source of genetic diversity for new resistance specificity. A series of 5 tightly linked genes; Pc81, Pc82, Pc83, Pc84 and Pc85 were authenticated within the Pca crown rust resistance cluster by recombination analysis. They conferred resistance specificity to six different crown-rust isolates. Three markers, Agx4, Agx7 and Agx9 were identified ...


Biological Control Of Sclerotinia Stem Rot Of Soybean With Sporidesmium Sclerotivorum , Luis Enrique Del Rió Mendoza Jan 1999

Biological Control Of Sclerotinia Stem Rot Of Soybean With Sporidesmium Sclerotivorum , Luis Enrique Del Rió Mendoza

Retrospective Theses and Dissertations

A single soil infestation with 2 and 20 macroconidia/cm 2 of soil of the mycoparasite Sporidesmium sclerotivorum was conducted in the fall of 1995 or the spring of 1996 at three Iowa locations. Soil infestation with the mycoparasite resulted in 50 to 60% reductions (P < 0.05) of Sclerotinia stem rot (SSR) of soybean in one location in 1996, and two locations in 1998. SSR was completely suppressed at a third location in 1998. In some instances the 2 spores/cm2 infestation rate provided disease control equal to the higher rate. S. sclerotivorum was retrieved from all infested plots using sclerotia of S. sclerotiorum as bait, two years after infestation, and from all control plots in the location where SSR was suppressed. Infestation of S. sclerotivorum into 100 m2 macroplots in commercial fields provided from 50 to 100% control of SSR two years later. Optimum conditions for germination of S. sclerotivorum macroconidia in the presence of sclerotia of S. sclerotiorum are pH 5.0 to 6.5, temperatures from 20 to 30°C, CO2 concentrations of 1% (v/v) or lower and O2 concentrations 1% and above. Almost no germination occurred when spores were incubated at 10 or 35°C. CO2 concentrations of 3 to 6% (v/v) reduced germination by half (P < 0.05). Baiting of 810 soil samples from 55 Iowa counties with sclerotia of Sclerotinia sclerotiorum resulted in Sporidesmium sclerotivorum isolates from soil samples from ten counties. This is the first report on the presence of this mycoparasite in Iowa. Trichoderma hamatum, T. harzianum, T. koningii, T. longibrachiatum, T. polysporum, T. pseudokoningii, and T. viride were also isolated from the sclerotial baits. Pathogenicity tests confirmed the parasitic activity of T. polysporum on the sclerotia of S. sclerotiorum. This is the first report on this association. Gliocladium roseum and G. virens were also retrieved from sclerotial baits. Coniothyrium minitans was isolated from soil samples from 12 counties, most of them located in northern Iowa.


Comparison Of Fumonisin Concentrations In Kernels Of Transgenic Bt Maize Hybrids And Nontransgenic Hybrids, Gary P. Munkvold, Richard L. Hellmich, Larry G. Rice Jan 1999

Comparison Of Fumonisin Concentrations In Kernels Of Transgenic Bt Maize Hybrids And Nontransgenic Hybrids, Gary P. Munkvold, Richard L. Hellmich, Larry G. Rice

Entomology Publications

Maize hybrids genetically engineered with genes from the bacteriumBacillus thuringiensis (Bt maize) express CryIA(b) and other Cry proteins that are toxic to certain insects, particularly the European corn borer (Ostrinia nubilalis). Maize kernel feeding by O. nubilalis often leads to infection by fungi in the genus Fusarium, including the fumonisin-producing species F. verticillioides and F. proliferatum. In field experiments in 1995, 1996, and 1997, transgenic maize hybrids and near-isogenic, nontransgenic hybrids were manually infested with neonatal European corn borer larvae. Manual infestation increased Fusarium ear rot severity and fumonisin concentrations in kernels of nontransgenic hybrids. Transgenic hybrids with ...


The Poplar-Leaf Rust Pathosystem: Inheritance Of Resistance And Pathogenic Variability , Girma Melesse Tabor Jan 1998

The Poplar-Leaf Rust Pathosystem: Inheritance Of Resistance And Pathogenic Variability , Girma Melesse Tabor

Retrospective Theses and Dissertations

Among diseases that cause serious yield reduction on Populus deltoides is leaf rust caused by Melampsora medusae. The objectives of this project were to study the pathogenic variability of M. medusae, the genetic basis of inheritance of M. medusae resistance in a family of P. deltoides; and to identify molecular markers linked to a leaf-rust resistant locus. Three pathotypes of M. medusae were identified on the basis of their differential reaction to three Populus clones. Pathotypes D-93, F-93, and IL-48 were compatible with clone 1-488 (P. X euramericana). F-93 and IL48 were also compatible with clone 57-276 (P. deltoides X ...