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2004

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Plant Pathology

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Full-Text Articles in Life Sciences

Expression Of The Tobacco Β- 1,3-Glucanase Gene, Pr-2d, Following Induction Of Sar With Peronospora Tabacina, Deanna L. Funnell, Christopher B. Lawrence, Jeffrey F. Pedersen, Christopher L. Schardl Dec 2004

Expression Of The Tobacco Β- 1,3-Glucanase Gene, Pr-2d, Following Induction Of Sar With Peronospora Tabacina, Deanna L. Funnell, Christopher B. Lawrence, Jeffrey F. Pedersen, Christopher L. Schardl

Papers in Plant Pathology

Systemic acquired resistance (SAR) is induced following inoculation of Peronospora tabacina sporangia into the stems of Nicotiana tabacum plants highly susceptible to the pathogen. Previous results have shown that accumulation of acidic P-1,3-glucanases (PR-2's) following induction of SAR by P. tabacina may contribute to resistance to P. tabacina. We showed that up-regulation of the PR-2 gene, PR-2d, following stem inoculation with P. tabacina, is associated with SAR. Studies using plants transformed with GUS constructs containing the full length promoter from PR-2d or promoter deletions, provided evidence that a previously characterized regulatory element that is involved in response to ...


Knowing The Risk Of Soybean Rust By Comparison With Brazil, X. B. Yang, Emerson M. Del Ponte, Ana Paula Dias Dec 2004

Knowing The Risk Of Soybean Rust By Comparison With Brazil, X. B. Yang, Emerson M. Del Ponte, Ana Paula Dias

Integrated Crop Management News

One of the common questions we receive is whether to move away from soybean because of the risk of soybean rust (SBR). Although studies indicate that the U.S. soybean production region is suitable to this disease, many experts believe outbreaks of the disease are likely to be sporadic.


Renewed Interest In Foliar Fungicide Use On Field Crops, Laura E. Sweets Dec 2004

Renewed Interest In Foliar Fungicide Use On Field Crops, Laura E. Sweets

Proceedings of the Integrated Crop Management Conference

Although the use of chemicals or fungicides to control plant diseases can be traced back as far as 1000 B.C., it was not until the 1930's- 1960's that substantial efforts were devoted to the development of non-corrosive and non-phytotoxic fungicides. Among the first of the "modern" fungicides were the dithiocarbamate fungicides such as thiram, maneb, and zineb. These materials have broad-spectrum activity but are contact, protectant fungicides. Dithiocarbamate fungicides were used for control of field crop diseases and there still are several formulations labeled for use on field crops. Their use has declined because they are protectants ...


Ecology And Management Of Diseases Of Soybean That Occurred In Iowa During The 2004 Season. Part Ii: Stem And Root Diseases, Alison Robertson, X. B. Yang Dec 2004

Ecology And Management Of Diseases Of Soybean That Occurred In Iowa During The 2004 Season. Part Ii: Stem And Root Diseases, Alison Robertson, X. B. Yang

Proceedings of the Integrated Crop Management Conference

The 2004 season growing season had cooler than normal temperatures associated with frequent rainfalls. The weather conditions were favorable for the occurrence of many soybean diseases. This season, we saw the worst ever outbreaks of white mold and sudden death syndrome, which resulted in considerable damage for many soybean producers. Both diseases were reported in two-to-three weeks earlier in the growing season than usual. Severe white mold outbreaks were found in eastern Iowa, especially from Interstate 80 north. Our quick-and-dirty survey indicates about 20% of soybean fields were affected with white mold in that region, and some fields were up ...


Managing Scn With Resistant Soybean Varieties: It's Not Just About This Year's Yield, Greg Tylka Dec 2004

Managing Scn With Resistant Soybean Varieties: It's Not Just About This Year's Yield, Greg Tylka

Proceedings of the Integrated Crop Management Conference

Soybean cyst nematode (SeN), Heterodera glycines, is a widespread pest of soybeans in Iowa. The nematode is estimated to be present in three out of every four fields in Iowa (Workneh et al., 1999). The nematode is a serious threat to soybean production because it reproduces very quickly, survives in the soil for many years in the absence of a soybean crop, and can cause substantial yield losses, particularly in dry years. Resistance is a very effective strategy for managing SeN, producing acceptable yields yet suppressing reproduction of the nematode. The number of soybean varieties with genetic resistance to SeN ...


Iowa's Plans And Preparations For The Possible Arrival Of Asian Soybean Rust In 2005, Greg Tylka, Alison Robertson Dec 2004

Iowa's Plans And Preparations For The Possible Arrival Of Asian Soybean Rust In 2005, Greg Tylka, Alison Robertson

Proceedings of the Integrated Crop Management Conference

Asian soybean rust, caused by the fungus Phakopsora pachyrhizi, can seriously reduce soybean yields and/or significantly increase the cost of soybean production when the disease occurs with high incidence and severity Until most recently, the continental United States was the only major soybean-producing area of the world where the disease was not known to exist. But on November 10, 2004, all that changed. On that date, the United States Department of Agriculture (USDA) and subsequently the Iowa Department of Agriculture and Land Stewardship announced that Asian soybean rust had been confirmed near Baton Rouge, Louisiana. The fields where the ...


Management Of Soybean Foliar Diseases Which Were Prevalent In Iowa During The 2004 Growing Season, Alison Robertson, X. B. Yang Dec 2004

Management Of Soybean Foliar Diseases Which Were Prevalent In Iowa During The 2004 Growing Season, Alison Robertson, X. B. Yang

Proceedings of the Integrated Crop Management Conference

The 2004 growing season was cool and wet, and therefore favorable for the development of a number of soybean foliar diseases. Many of the diseases occurred together in the same area and often on the same plant. Some diseases showed up early in the season, some later in the season and some were present throughout the season. The diseases which showed up early in, and remained present throughout the growing season were brown spot and bacterial blight. Cercospora leaf blight, frogeye leaf spot and downy mildew started in middle of the season and continued until the end of season. Powdery ...


Biology, Distribution, And Management Of Glyphosate-Resistant Horseweed (Aka Marestail), Bill Johnson, Vince Davis Dec 2004

Biology, Distribution, And Management Of Glyphosate-Resistant Horseweed (Aka Marestail), Bill Johnson, Vince Davis

Proceedings of the Integrated Crop Management Conference

The adoption of Roundup Ready crops and no-till practices and reliance on glyphosate has resulted in a serious concern for long-term use of this valuable weed management tool. Glyphosate rates used in Roundup Ready soybean have increased steadily since its introduction in 1996 suggesting that biotypes with greater tolerance have been selected for in a number of weed species. Within the North Central region, populations of field bindweed resistant to glyphosate in Indiana were reported in the 1980's, and populations of horseweed resistant to glyphosate were confirmed in 2002. In addition, there is substantial evidence that common waterhemp, common ...


Mutations In Pmr5 Result In Powdery Mildew Resistance And Altered Cell Wall Composition, John P. Vogel, Ted K. Raab, Chris R. Somerville, Shauna C. Somerville Dec 2004

Mutations In Pmr5 Result In Powdery Mildew Resistance And Altered Cell Wall Composition, John P. Vogel, Ted K. Raab, Chris R. Somerville, Shauna C. Somerville

Ted K. Raab

Powdery mildews and other obligate biotrophic pathogens are highly adapted to their hosts and often show limited host ranges. One facet of such host specialization is likely to be penetration of the host cell wall, a major barrier to infection. A mutation in the pmr5 gene rendered Arabidopsis resistant to the powdery mildew species Erysiphe cichoracearum and Erysiphe orontii, but not to the unrelated pathogens Pseudomonas syringae or Peronospora parasitica. PMR5 belongs to a large family of plant-specific genes of unknown function. pmr5-mediated resistance did not require signaling through either the salicylic acid or jasmonic acid/ ethylene defense pathways, suggesting ...


Seasonal Abundance Of Mosquitoes (Diptera: Culicidae) At A High And Low Prevalence Site For La Crosse Encephalitis In Eastern Tennessee, Nathan David Caldwell Dec 2004

Seasonal Abundance Of Mosquitoes (Diptera: Culicidae) At A High And Low Prevalence Site For La Crosse Encephalitis In Eastern Tennessee, Nathan David Caldwell

Masters Theses

La Crosse (LAC), a California (CAL) serogroup bunyavirus, is the most prevalent pediatric arboviral disease in the United States and accounts for virtually all encephalitis cases associated with CAL serogroup arboviruses. In Tennessee, USA, prior to the drastic increase of confirmed La Crosse (LAC) encephalitis cases in 1997, the sum of documented cases reported to the Tennessee Department of Health totaled 9. During subsequent years in Tennessee (1997 to 2003), an average of 12 cases has been reported annually. Approximately 62% of these reported cases have occurred in the months of July and August. The native, container-inhabiting mosquito Ochlerotatus triseriatus ...


Scn-Resistant Soybean Varieties Listed In Updated Publication, Gregory L. Tylka Nov 2004

Scn-Resistant Soybean Varieties Listed In Updated Publication, Gregory L. Tylka

Integrated Crop Management News

Soybean cyst nematode (SCN) is a serious and widespread pest of soybean throughout Iowa and the Midwest. Fortunately, SCN-resistant soybean varieties have been developed and are an effective management tool. To assist growers in choosing SCN-resistant varieties, Iowa State University Extension annually compiles and publishes a list of public and private SCN-resistant soybean varieties in maturity groups I, II, and III.


Soybean Rust First Detector Training Session Announced, Gregory L. Tylka, Brent A. Pringnitz Nov 2004

Soybean Rust First Detector Training Session Announced, Gregory L. Tylka, Brent A. Pringnitz

Integrated Crop Management News

Asian soybean rust is a topic of great interest among Iowa soybean growers and agribusiness. The Iowa Department of Agriculture and Land Stewardship, the Iowa Soybean Association and Promotion Board, and Iowa State University have formed the Iowa Soybean Rust Team and have developed a system in Iowa whereby soybean samples that are suspected of possibly being infected with soybean rust can be examined and passed through a sequence of trained personnel to offer Iowa soybean growers rapid and accurate identification of the disease.


Asian Soybean Rust Confirmed In The Continental United States, Alison E. Robertson Nov 2004

Asian Soybean Rust Confirmed In The Continental United States, Alison E. Robertson

Integrated Crop Management News

On November 10, 2004, the United States Department of Agriculture (USDA) and the Iowa Department of Agriculture and Land Stewardship announced that Asian soybean rust has been confirmed near Baton Rouge, LA. The fields where the rust was found are located on research farms belonging to Louisiana State University. No information was given on the stage of plant growth in the fields. Most of the commercial fields in Louisiana have been harvested. X.B. Yang, Iowa State University plant pathologist, is one of the leading experts in the world and has flown down to Louisiana as a member of the ...


Necrotic Lesion Resistance Induced By Peronospora Tabacina On Leaves Of Nicotiana Obtusifolia, E.P. Heist, D. Zaitlin, Deanna L. Funnell, W.C. Nesmith, C.L. Schardl Oct 2004

Necrotic Lesion Resistance Induced By Peronospora Tabacina On Leaves Of Nicotiana Obtusifolia, E.P. Heist, D. Zaitlin, Deanna L. Funnell, W.C. Nesmith, C.L. Schardl

Papers in Plant Pathology

Infection of Nicotiana obtusifolia plant introduction (PI) #555573 by the downy mildew pathogen Peronospora tabacina resulted in a compatible interaction, in which P. tabacina penetrated and freely colonized host leaf tissue. This interaction became incompatible 5 to 6 days later, with the appearance of necrotic lesions (NLs) and inhibition of pathogen growth and subsequent sporulation. NL development depended upon the presence of P. tabacina in host tissue, was not due to the effects of other microbes, and occurred co-incident in time with the pathogen’s ability to produce asexual sporangia on a susceptible N. obtusifolia genotype. Inhibition of the necrotic ...


Corn Ear Molds And Mycotoxins In Fall 2003, Gary P. Munkvold Oct 2004

Corn Ear Molds And Mycotoxins In Fall 2003, Gary P. Munkvold

Integrated Crop Management News

There has been elevated concern again this year about mycotoxins in grain, especially aflatoxins. Aflatoxins are not a common problem in Iowa, but the dry weather that occurred in some parts of the state caused stress on the plants, which lead to aflatoxin problems. Corn plants that experience drought stress are more susceptible than usual to the fungus that produces aflatoxins, Aspergillus flavus.


Check Seed Quality At Harvest, X. B. Yang Oct 2004

Check Seed Quality At Harvest, X. B. Yang

Integrated Crop Management News

This growing season, diseases caused by Cercospora fungi were widespread in Iowa. There were twoCercospora species, one causing frogeye leaf spot and another causing Cercospora leaf blight. Frogeye leaf spot occurred locally in southern Iowa and Cercospora leaf blight was widely spread throughout Iowa. In some cases, Cercospora leaf blight has been called "sunburn." Because fungi of both diseases can infect seeds at harvest, it is likely that soybean from some fields show seed discoloration, which happened two years ago in northern Iowa. This article addresses the seed quality issue of this fall.


Stinkhorns Spotted In Fields, Paula Flynn Oct 2004

Stinkhorns Spotted In Fields, Paula Flynn

Integrated Crop Management News

John Holmes, extension field crop specialist, reported that farmers are finding lots of stinkhorn mushrooms in soybean fields as they harvest. These fungi do not cause disease to plants or animals, but instead live a harmless existence on dead organic matter such as crop debris. They also are commonly found on decaying mulch. A stinkhorn begins life as an egg-like structure.


Fall Is Prime Time To Sample Fields For Scn, Gregory L. Tylka Oct 2004

Fall Is Prime Time To Sample Fields For Scn, Gregory L. Tylka

Integrated Crop Management News

The soybean cyst nematode (SCN) is an extremely damaging and widespread pest of soybean in Iowa. The nematode infests approximately 70 percent of the fields statewide. However, SCN usually causes no obvious aboveground symptoms for many years after being introduced into a field. Consequently, many SCN-infested fields in Iowa have not been diagnosed. The lack of symptoms and subsequent missed diagnosis are unfortunate because the key to effective management of SCN is early detection, before large nematode population densities develop.


Corn Ear Rots, Alison E. Robertson Oct 2004

Corn Ear Rots, Alison E. Robertson

Integrated Crop Management News

This year does not appear to be a particularly bad year for ear rots. The season has been cooler than normal, and the weather has been fairly dry since silking. However, some field crop specialists have noticed ear rot problems, in particular, Diplodia ear rot. The incidence of corn ear rot should be determined before harvest for a number of reasons. First, ear rot diseases can reduce yield and quality of the corn harvest. Second, some of the fungi that infect corn ears may produce mycotoxins, which are harmful, and can be fatal, to livestock. Finally, ear rots can continue ...


Check Seed Quality At Harvest, X. B. Yang Oct 2004

Check Seed Quality At Harvest, X. B. Yang

Integrated Crop Management News

This growing season, diseases caused by Cercospora fungi were widespread in Iowa. There were twoCercospora species, one causing frogeye leaf spot and another causing Cercospora leaf blight. Frogeye leaf spot occurred locally in southern Iowa and Cercospora leaf blight was widely spread throughout Iowa. In some cases, Cercospora leaf blight has been called "sunburn." Because fungi of both diseases can infect seeds at harvest, it is likely that soybean from some fields show seed discoloration, which happened two years ago in northern Iowa. This article addresses the seed quality issue of this fall.


Phomadidacte: A Computer-Aided Training Program For The Severity Assessment Of Phoma Stem Canker Of Oilseed Rape, Jean-Noel Aubertot, Yassine Sohbi, Hortense Brun, Annette Penaud, Forrest W. Nutter Jr. Oct 2004

Phomadidacte: A Computer-Aided Training Program For The Severity Assessment Of Phoma Stem Canker Of Oilseed Rape, Jean-Noel Aubertot, Yassine Sohbi, Hortense Brun, Annette Penaud, Forrest W. Nutter Jr.

Plant Pathology Presentations and Posters

Phoma stem canker (caused by Leptosphaeria maculans) is one of the main diseases that affect oilseed rape world-wide. The disease is usually characterised by the visual assessment of the severity of cankers created by the pathogen at the crown level of infected plants. In order to avoid arbitrary categories and to maintain stsndardisation of assessment keys, a rating scale based on the percentage severity estimates of cross-section cankered crowns has been recently proposed in France. 1bis scale consists in 6 severity classes, defined as a function of the percentage of the discoloured cross-section: 1, healthy plant, no visible lesions; 2 ...


Remember To Scout For Corn Stalk Rots, Alison E. Robertson Sep 2004

Remember To Scout For Corn Stalk Rots, Alison E. Robertson

Integrated Crop Management News

Stalk rot occurs to some extent in every cornfield in Iowa each year because as corn stalks mature, they naturally decay. However, stalk rot can occur prior to physiological maturity and is considered a disease problem, which reduces yields in two ways. First, affected plants die prematurely (Fig. 1) and therefore produce lightweight ears with poorly filled kernels. Second, and this is more common, plants with stalk rot easily lodge (Fig. 2), which makes harvesting difficult, and many ears are left in the field.


Note For Fall Soybean Diseases, X. B. Yang, Shrishail S. Navi Sep 2004

Note For Fall Soybean Diseases, X. B. Yang, Shrishail S. Navi

Integrated Crop Management News

It is well established that outbreaks of plant diseases are associated with extreme weather. This year's extreme weather created favorable conditions for several soybean diseases. Sudden death syndrome(SDS) was severe in southern Iowa, and severe outbreaks of white mold occurred in eastern Iowa. The two diseases also occurred in other parts of Iowa, and an article will address the management of the two diseases later this year. Besides these two diseases, several other diseases are prevalent in fall causing early defoliation, such as brown spot, Cercospora leaf blight, and brown stem rot. In this article, we will discuss ...


Note For Fall Soybean Diseases, X. B. Yang, Shrishail S. Navi Sep 2004

Note For Fall Soybean Diseases, X. B. Yang, Shrishail S. Navi

Integrated Crop Management News

It is well established that outbreaks of plant diseases are associated with extreme weather. This year's extreme weather created favorable conditions for several soybean diseases. Sudden death syndrome(SDS) was severe in southern Iowa, and severe outbreaks of white mold occurred in eastern Iowa. The two diseases also occurred in other parts of Iowa, and an article will address the management of the two diseases later this year.


Interaction-Dependent Gene Expression In Mla-Specified Response To Barley Powdery Mildew, Rico A. Caldo, Dan Nettleton, Roger P. Wise Sep 2004

Interaction-Dependent Gene Expression In Mla-Specified Response To Barley Powdery Mildew, Rico A. Caldo, Dan Nettleton, Roger P. Wise

Statistics Publications

Plant recognition of pathogen-derived molecules influences attack and counterattack strategies that affect the outcome of host–microbe interactions. To ascertain the global framework of host gene expression during biotrophic pathogen invasion, we analyzed in parallel the mRNA abundance of 22,792 host genes throughout 36 (genotype × pathogen × time) interactions between barley (Hordeum vulgare) and Blumeria graminis f. sp hordei (Bgh), the causal agent of powdery mildew disease. A split-split-plot design was used to investigate near-isogenic barley lines with introgressed Mla6, Mla13, and Mla1 coiled-coil, nucleotide binding site, Leu-rich repeat resistance alleles challenged with Bgh isolates 5874 (AvrMla6 and AvrMla1) and ...


Disabling Surveillance: Bacterial Type Iii Secretion System Effectors That Suppress Innate Immunity, Avelina Espinosa, James R. Alfano Aug 2004

Disabling Surveillance: Bacterial Type Iii Secretion System Effectors That Suppress Innate Immunity, Avelina Espinosa, James R. Alfano

Faculty Publications from the Center for Plant Science Innovation

Many Gram-negative bacterial pathogens of plants and animals are dependent on a type III protein secretion system (TTSS). TTSSs translocate effector proteins into host cells and are capable of modifying signal transduction pathways. The innate immune system of eukaryotes detects the presence of pathogens using specific pathogen recognition receptors (PRRs). Plant PRRs include the FLS2 receptor kinase and resistance proteins. Animal PRRs include Tolllike receptors and nucleotide-binding oligomerization domain proteins. PRRs initiate signal transduction pathways that include mitogen-activated protein kinase (MAPK) cascades that activate defencerelated transcription factors. This results in induction of proinflammatory cytokines in animals, and hallmarks of defence ...


Diseases Show Up Earlier In 2004, X. B. Yang Aug 2004

Diseases Show Up Earlier In 2004, X. B. Yang

Integrated Crop Management News

Since the third week of July, a few diseases (white mold, sudden death syndrome, and downy mildew) started to show up in Iowa soybean fields. These diseases normally aren't seen until early August. This season's cool weather has promoted their unusually early occurrence.


Mesa, A Novel Fungal Protein Required For The Stabilization Of Polarity Axes In Aspergillus Nidulans, Claire L. Pearson, Kaimei Xu, Kathryn E. Sharpless, Steven D. Harris Aug 2004

Mesa, A Novel Fungal Protein Required For The Stabilization Of Polarity Axes In Aspergillus Nidulans, Claire L. Pearson, Kaimei Xu, Kathryn E. Sharpless, Steven D. Harris

Papers in Plant Pathology

The Aspergillus nidulans proteome possesses a single formin, SepA, which is required for actin ring formation at septation sites and also plays a role in polarized morphogenesis. Previous observations imply that complex regulatory mechanisms control the function of SepA and ensure its correct localization within hyphal tip cells. To characterize these mechanisms, we undertook a screen for mutations that enhance sepA defects. Of the mutants recovered, mesA1 causes the most dramatic defect in polarity establishment when SepA function is compromised. In a wild-type background, mesA1 mutants undergo aberrant hyphal morphogenesis, whereas septum formation remains unaffected. Molecular characterization revealed that MesA ...


Examining Varroa-Resistant Honey Bee Queens From Commercial Breeders: Colony Productivity, Hygienic Behavior, Suppression Of Mite Reproduction, And The Relationship Of Juvenile Hormone Iii To Mite Abundance, Laura L. Bryant Aug 2004

Examining Varroa-Resistant Honey Bee Queens From Commercial Breeders: Colony Productivity, Hygienic Behavior, Suppression Of Mite Reproduction, And The Relationship Of Juvenile Hormone Iii To Mite Abundance, Laura L. Bryant

Masters Theses

This research was conducted to assess the performance of commercially bred honey bee queens sold as resistant to the parasitic mite, Varroa destructor. The study’s objectives were to: 1) Compare honey and pollen stores and V. destructor infestation in colonies established with hybrid Russian, SMR, and control queens, 2) Determine levels of hygienic behavior and mite non-reproduction in the same colonies, and 3) Determine the relationship between juvenile hormone III in honey bee larvae and V. destructor reproduction.

In Part One, when honey, pollen, and V. destructor levels were measured, no significant differences were found among types of queens ...


Soybean Cercospora Diseases Show Up, X. B. Yang Jul 2004

Soybean Cercospora Diseases Show Up, X. B. Yang

Integrated Crop Management News

Since the planting season, weather in Iowa has been cooler and wetter than normal with frequent rainfall. The unusual weather has resulted in the prevalence of foliar diseases. Several diseases have shown up earlier than usual this season. Two weeks ago, we reported that bacterial blight and brown spot were prevalent in Iowa soybean fields. In our early planted research plots, soybean sudden death syndrome started to show foliar symptoms in the second week of July, more than two weeks earlier than normal.