Life Sciences Commons^™

The Coat Protein And Nia Protease Of Two Potyviridae Family Members Independently Confer Superinfection Exclusion, Satyanarayana Tatineni, Roy French

Department of Plant Pathology: Faculty Publications

Superinfection exclusion (SIE) is an antagonistic virus-virus interaction whereby initial infection by one virus prevents subsequent infection by closely related viruses. Although SIE has been described in diverse viruses infecting plants, humans, and animals, its mechanisms, including involvement of specific viral determinants, are just beginning to be elucidated. In this study, SIE determinants encoded by two economically important wheat viruses, Wheat streak mosaic virus (WSMV; genus Tritimovirus, family Potyviridae) and Triticum mosaic virus (TriMV; genus Poacevirus, family Potyviridae), were identified in gain-of-function experiments that used heterologous viruses to express individual virus-encoded proteins in wheat. Wheat plants infected …

Mapping Quantitative Trait Loci For Resistance To Goss’S Bacterial Wilt And Leaf Blight In North American Maize By Joint Linkage Analysis, Amritpal Singh, Aaron P. Andersen, Tamra A. Jackson-Ziems, Aaron J. Lorenz

Department of Plant Pathology: Faculty Publications

Goss’s wilt and leaf blight is a bacterial disease of maize (Zea mays L.) caused by the Gram-positive bacterium Clavibacter michiganensis subsp. nebraskensis. Goss’s wilt has reemerged as an important disease in the western United States and is spreading to other areas. Although the reasons for this reemergence are not completely known, it is important to understand the genetic basis of resistance to Goss’s wilt. The objective of this study was to map the quantitative trait loci (QTL) underlying resistance to Goss’s wilt. To achieve this objective, joint linkage and linkage mapping in 3 of the 25 nested …

Corn Yield Loss Estimates Due To Diseases In The United States And Ontario, Canada From 2012 To 2015, Daren S. Mueller, Kiersten A. Wise, Adam J. Sisson, Tom W. Allen, Gary C. Bergstrom, D. Bruce Bosley, Carl A. Bradley, Kirk D. Broders, Emmanuel Byamukama, Martin I. Chilvers, Alyssa Collins, Travis R. Faske, Andrew J. Friskop, Ron W. Heiniger, Clayton A. Hollier, David C. Hooker, Tom Isakeit, Tamra A. Jackson-Ziems, Douglas J. Jardine, Heather M. Kelly, Kasia Kinzer, Steve R. Koenning, Dean K. Malvick, Marcia Mcmullen, Ron F. Meyer, Pierce A. Paul, Alison E. Robertson, Gregory W. Roth, Damon L. Smith, Connie A. Tande, Albert U. Tenuta, Paul Vincelli, Fred Warner

Department of Plant Pathology: Faculty Publications

Annual decreases in corn yield caused by diseases were estimated by surveying members of the Corn Disease Working Group in 22 corn-producing states in the United States and in Ontario, Canada, from 2012 through 2015. Estimated loss from each disease varied greatly by state and year. In general, foliar diseases such as northern corn leaf blight, gray leaf spot, and Goss’s wilt commonly caused the largest estimated yield loss in the northern United States and Ontario during nondrought years. Fusarium stalk rot and plant-parasitic nematodes caused the most estimated loss in the southern-most United States. The estimated mean economic loss …

Bacterial Leaf Streak Of Corn Confirmed In Nebraska, Other Corn Belt States August 26, 2016, Tamra Jackson-Ziems, Kevin A. Korus, Tony Adesemoye, Julie Van Meter

Department of Plant Pathology: Faculty Publications

Bacterial leaf streak disease of corn, caused by Xanthomonas vasicola pv. vasculorum, has now been confirmed in Nebraska, as well as in Colorado, Illinois, Iowa, and Kansas. The disease had not been previously identified in the U.S., but had been reported on corn in South Africa. Surveys are currently underway across the Corn Belt to identify the disease distribution. Initial observations and survey results suggest that it may be widely distributed throughout the Corn Belt. Unusual symptoms were first reported on corn samples received by the University of Nebraska Plant and Pest Diagnostic Clinic. Over the last two years, the …

Validation Of Reference Genes For Robust Qrt-Pcr Gene Expression Analysis In The Rice Blast Fungus Magnaporthe Oryzae, Sarena Che Omar, Michael A. Bentley, Giulia Morieri, Gail M. Preston, Sarah J. Gurr, Richard Wilson (Editor)

Department of Plant Pathology: Faculty Publications

The rice blast fungus causes significant annual harvest losses. It also serves as a genetically- tractable model to study fungal ingress. Whilst pathogenicity determinants have been unmasked and changes in global gene expression described, we know little about Magnaporthe oryzae cell wall remodelling. Our interests, in wall remodelling genes expressed during infection, vegetative growth and under exogenous wall stress, demand robust choice of reference genes for quantitative Real Time-PCR (qRT-PCR) data normalisation. We describe the expression stability of nine candidate reference genes profiled by qRT-PCR with cDNAs derived during asexual germling development, from sexual stage perithecia and from vegetative mycelium …

Antiviral Rna Silencing Suppression Activity Of Tomato Spotted Wilt Virus Nss Protein, Tania Ocampo Ocampo, Sergio M. Gabriel Peralta, Nicole Bacheller, Stella Uiterwaal, Aaron Knapp, Alanna Hennen, Daniel Leobardo Ochoa-Martínez, Hernan Garcia-Ruiz

Department of Plant Pathology: Faculty Publications

In addition to regulating gene expression, RNA silencing is an essential antiviral defense system in plants. Triggered by double-stranded RNA, silencing results in degradation or translational repression of target transcripts. Viruses are inducers and targets of RNA silencing. To condition susceptibility, most plant viruses encode silencing suppressors that interfere with this process, such as the Tomato spotted wilt virus (TSWV) NSs protein. The mechanism by which NSs suppresses RNA silencing and its role in viral infection and movement remain to be determined. We cloned NSs from the Hawaii isolate of TSWV and using two independent assays show for the first …

Description Of Mesocriconema Ericaceum N. Sp. (Nematoda: Criconematidae) And Notes On Other Nematode Species Discovered In An Ericaceous Heath Bald Community In Great Smoky Mountains National Park, Usa, Thomas O. Powers, Peter Mullin, Rebecca Higgins, Timothy Harris, Kirsten S. Powers

Department of Plant Pathology: Faculty Publications

A new species of Mesocriconema and a unique assemblage of plant-parasitic nematodes was discovered in a heath bald atop Brushy Mountain in Great Smoky Mountains National Park. Mesocriconema ericaceum n. sp., a species with males, superficially resembles M. xenoplax. DNA barcoding with the mitochondrial COI gene provided evidence of the new species as a distinct lineage. SEM revealed significant variability in arrangement of labial submedian lobes, plates, and anterior and posterior annuli. Three other nematodes in the family Criconematidae were characterized from the heath bald. Ogma seymouri, when analyzed by statistical parsimony, established connections with isolates from north-eastern Atlantic …

Microbe-Id: An Open Source Toolbox For Microbial Genotyping And Species Identification, Javier F. Tabima, Sydney E. Everhart, Meredith M. Larsen, Alexaandra J. Weisberg, Zhian N. Kamvar, Mathew A. Tancos, Christine D. Smart, Jeff H. Chang, Niklaus J. Grünwald

Department of Plant Pathology: Faculty Publications

Development of tools to identify species, genotypes, or novel strains of invasive organisms is critical for monitoring emergence and implementing rapid response measures. Molecular markers, although critical to identifying species or genotypes, require bioinformatic tools for analysis. However, user-friendly analytical tools for fast identification are not readily available. To address this need, we created a web-based set of applications called Microbe-ID that allow for customizing a toolbox for rapid species identification and strain genotyping using any genetic markers of choice. Two components of Microbe-ID, named Sequence-ID and Genotype-ID, implement species and genotype identification, respectively. Sequence-ID allows identification of species by …

First Report Of Pythium Ultimum, P. Irregulare, Rhizoctonia Solani Ag4, And Fusarium Proliferatum From Arrowleaf Clover (Trifolium Vesiculosum): A Disease Complex, I. J. Pemberton, G. R. Smith, G. L. Philley, F. M. Rouquette, G. Y. Yuen

Department of Plant Pathology: Faculty Publications

Poor stand establishment, failure to recover after grazing, and premature plant death have reduced the utilization of arrowleaf clover (Trifolium vesiculosum Savi) as a forage crop in the southeastern United States in recent years. Clover plants collected from poor stands in east Texas pastures during the 1995 to 1996 and 1996 to 1997 seasons first exhibited root disease symptoms as young seedlings in the fall. Symptoms consisted of one or more of the following: tan discoloration of lateral roots and taproot; root pruning; and small, tan, sunken lesions on the taproot and crown. Many Rhizobium nodules were brown and …

Corn Disease Profiles: Diseases Favored By Wet Conditions, Tamra A. Jackson-Ziems, Anthony O. Adesemoye, Loren J. Giesler, Robert M. Harveson, Kevin A. Korus, Stephen N. Wegulo

Department of Plant Pathology: Faculty Publications

Extension Circular 1909 (EC1909)

Extreme weather events are predicted to become increasingly common and could bring periods of more intense rainfall. Wet conditions are favorable for many plant pathogens and the development of diseases. Seasonal timing when these conditions occur, as well as other factors such as temperature, impact which diseases develop and when. Listed, described, and illustrated are some common corn diseases favored by wet conditions: Pythium Root Rot, Eyespot, Northern Corn Leaf Blight, Gray Leaf Spot, Physoderma Brown Spot, Rust Diseases (Puccinia spp.), Stalk and Crown Rot Diseases (such as those caused by Fusarium and Diplodia spp.), …

Northern Corn Leaf Blight, Tamra A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

Northern corn leaf blight (NCLB) is a disease of corn caused by a fungus, Exserohilum turcicum (sexual stage Setosphaeria turcica). Its development is favored by cool to moderate temperatures and high relative humidity. Historically, NCLB has been more common and severe in states in the eastern Corn Belt, but its incidence has increased in Nebraska and the western Corn Belt in recent years. The disease is distributed throughout most of the corn-growing areas of the United States. The disease also occurs sporadically throughout other humid corn-producing areas of the world. In Nebraska, the disease has been most serious in …

Association Of Neonectria Macrodidyma With Dry Root Rot Of Citrus In California, A. O. Adesemoye, J. S. Mayorquin, B. B. Peacock, K. Moreno, S. Hajeri, R. Yokomi, A. Eskalen

Department of Plant Pathology: Faculty Publications

During yearly surveys that started in 2010 to identify pathogens associated with dry root rot disease of citrus in California, samples with root rot symptoms were collected in Tulare County. Small pieces of tissue from root samples were plated onto potato dextrose agar amended with 0.01% tetracycline and incubated at 25°C. Pure cultures of fungal isolates were identified by morphology and sequence analysis of the Internal Transcribed Spacer and Beta Tubulin regions. Neonectria macrodidyma (Cylindrocarpon macrodidymum) was first recovered in 2011 and has subsequently been recovered multiple times from citrus samples. The pathogen appeared to be widely distributed …

Identification Of Erwinia Rhapontici As The Causal Agent Of Crown And Shoot Rot And Pink Seed Of Pea In Nebraska, Anthony O. Adesemoye, Hsin-Ho Wei, Robert M. Harveson

Department of Plant Pathology: Faculty Publications

Over the last five years, the production of dry yellow peas (Pisum sativum L.) has been increasing in Nebraska and other areas of the Central High Plains, according to a USDA report (Jasa 2013). Dry pea is a short-season crop with a low water requirement, making it a good rotational crop for the high plains. We have noted bacterial pathogens, potentially a disease complex, that may negatively impact the production of pea in this region, and one of the emerging pathogens is Erwinia rhapontici. This pathogen is a gram-negative bacterium that has been reported from soil, seed, and …

Dry Edible Bean Disease Diagnostic Series, Samuel G. Markell, Robert M. Harveson, Julie Pasche

Department of Plant Pathology: Faculty Publications

Root Diseases

Fusarium root rot...................................PP1820-1

Pythium diseases..................................PP1820-2

Rhizoctonia root rot...............................PP1820-3

Soybean cyst nematode (SCN).............PP1820-4

Soybean cyst nematode sampling.........PP1820-5

Stem and Wilt Diseases

Bacterial wilt..........................................PP1820-6

Fusarium yellows (wilt)..........................PP1820-7

Stem rot.................................................PP1820-8

White mold.............................................PP1820-9

Foliar Diseases

Anthracnose........................................PP1820-10

Bacterial brown spot............................PP1820-11

Bean common mosaic virus................PP1820-12

Common bean rust..............................PP1820-13

Common bacterial blight .....................PP1820-14

Halo blight............................................PP1820-15

Incidence Of Wheat Streak Mosaic Virus, Triticum Mosaic Virus, And Wheat Mosaic Virus In Wheat Curl Mites Recovered From Maturing Winter Wheat Spikes, E. Byamukama, S. Tatineni, G. Hein, J. Mcmechan, S. N. Wegulo

Department of Plant Pathology: Faculty Publications

Wheat curl mites (WCM; Aceria tosichella) transmit Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and Wheat mosaic virus (WMoV) to wheat (Triticum aestivum L.) in the Great Plains region of the United States. These viruses can be detected in single, double, or triple combinations in leaf samples. Information on incidence of viruses inWCM at the end of the growing season is scant. The availability of this information can enhance our knowledge of the epidemiology ofWCM-transmitted viruses. This research was conducted to determine the frequency of occurrence of WSMV, TriMV, and WMoV in WCM populations on fieldcollected maturing …

Morphological And Molecular Characterization Of Gracilacus Wuae N. Sp. (Nematoda: Criconematoidea) Associated With Cow Parsnip (Heracleum Maximum) In Ontario, Canada, Qing Yu, Weimin Ye, Thomas O. Powers

Department of Plant Pathology: Faculty Publications

Gracilacus wuae n. sp. from soil associated with cow parsnip in Ontario, Canada is described and illustrated. Morphologically, females have a long stylet ranging from 80 to 93 mmlong, the lip region not offset from the body contour, without lateral lips but with large and flat submedian lobes, the mouth opening slit-like elongated laterally and surrounded by lateral flaps, the excretory pore is anterior to the knobs of the stylet; males without stylet and the pharynx degenerated. The fourth-stage juveniles lack a stylet, the pharynx degenerated, and can be differentiated into preadult females and males based on the position of …

Developing The Framework For A Risk Map For Mite Vectored Viruses In Wheat Resulting From Pre-Harvest Hail Damage, Anthony L. Nguy-Robertson, Arthur Zygielbaum, Anthony J. Mcmechan, Gary L. Hein, Stephen N. Wegulo, Abby R. Stilwell, Travis M. Smith

Department of Plant Pathology: Faculty Publications

There is a strong economic incentive to reduce mite-vectored virus outbreaks. Most outbreaks in the central High Plains of the United States occur in the presence of volunteer wheat that emerges before harvest as a result of hail storms. This study provides a conceptual framework for developing a risk map for wheat diseases caused by mite-vectored viruses based on pre-harvest hail events. Traditional methods that use NDVI were found to be unsuitable due to low chlorophyll content in wheat at harvest. Site-level hyperspectral reflectance from mechanically hailed wheat showed increased canopy albedo. Therefore, any increase in NIR combined with large …

Cryptic Species: A Leitmotif Of Contemporary Mycology Has Challenges And Benefits For Plant Pathologists, Frank M. Dugan, Sydney Everhart

Department of Plant Pathology: Faculty Publications

Multiple traditional species names for plant pathogenic fungi have been supplemented with new names that delimit formerly cryptic species. In separate instances, isolates within a species are clearly differentiated by both phylogeny and distinctive pathogenic traits and are assigned sub-specific designations. These new species names and the sub-specific designations are both cases of cryptic species that are, in some instances, relevant and/or critical for plant disease management. Here we provide examples of such instances in which newly described taxa differ from the original (“parent”) in phenotypic traits of importance to plant disease management: host range, fungicide sensitivity, environmental niche, metabolite …

Sequence Variation In Two Genes Determines The Efficacy Of Transmission Of Citrus Tristeza Virus By The Brown Citrus Aphid, S. J. Harper, N. Killiny, Satyanarayana Tatineni, S. Gowda, S. J. Cowell, T. Shilts, W. O. Dawson

Department of Plant Pathology: Faculty Publications

Vector transmission is an important part of the viral infection cycle, yet for many viruses little is known about this process, or how viral sequence variation affects transmission efficacy. Here we examined the effect of substituting genes from the highly transmissible FS577 isolate of citrus tristeza virus (CTV) in to the poorly transmissible T36-based infectious clone. We found that introducing p65 or p61 sequences from FS577 significantly increased transmission efficacy. Interestingly, replacement of both genes produced a greater increase than either gene alone, suggesting that CTV transmission requires the concerted action of co-evolved p65 and p61 proteins.

Field Damage Of Sorghum (Sorghum Bicolor) With Reduced Lignin Levels By Naturally Occurring Insect Pests And Pathogens, Patrick F. Dowd, Deanna L. Funnell-Harris, Scott E. Sattler

Department of Plant Pathology: Faculty Publications

Sorghum (Sorghum bicolor (L.) Moench) brown midrib (bmr) mutant lines have reduced levels of lignin, which is a potentially useful trait for bioenergy production, but the effects of this trait on insect and plant pathogen interactions are unknown under field conditions. Field-grown bmr6, bmr12, and wild-type (WT) plants were examined for insect and disease damage. In most cases, observed frequency, population, or leaf area damage caused by insects or pathogens on bmr6 or bmr12 plants were not greater than those observed on WT plants in the field or laboratory assays. European corn borers [Ostrinia nubilalis (Hübner)(Lepidoptera: …

Triticum Mosaic Virus Exhibits Limited Population Variation Yet Shows Evidence Of Parallel Evolution After Replicated Serial Passage In Wheat, Melissa S. Bartels, Roy French, Robert A. Graybosch, Satyanarayana Tatineni

Department of Plant Pathology: Faculty Publications

An infectious cDNA clone of Triticum mosaic virus (TriMV) (genus Poacevirus; family Potyviridae) was used to establish three independent lineages in wheat to examine intra-host population diversity levels within protein 1 (P1) and coat protein (CP) cistrons over time. Genetic variation was assessed at passages 9, 18 and 24 by single-strand conformation polymorphism, followed by nucleotide sequencing. The founding P1 region genotype was retained at high frequencies in most lineage/passage populations, while the founding CP genotype disappeared after passage 18 in two lineages.We found that rare TriMV genotypes were present only transiently and lineages followed independent evolutionary trajectories, …

What's New In Plant Pathology, Anthony O. Adesemoye, Loren Giesler, Robert M. Harveson, Tamra A. Jackson-Ziems, Kevin Korus, Stephen N. Wegulo

Department of Plant Pathology: Faculty Publications

Changes to the Disease Management Section of the 2016 Guide for Weed, Disease, and Insect Management in Nebraska

Biological control Products

Trivapro Fungicide

Priaxor D. Fungicide

Table 1. Foliar products for disease control that were updated in the 2016 Guide for Weed, Disease and Insect Management in Nebraska.

Table 2. Seed treatment products for disease control that were updated in the 2016 Guide for Weed, Disease and Insect Management in Nebraska.

Table 3. Seed treatment nematicide product that was updated in the 2016 Guide for Weed, Disease and Insect Management in Nebraska.

Corn Disease Update, Tamra A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

The 2015 corn crop was impacted by several corn diseases from the beginning to the end of the season and in all areas of Nebraska. The increased severity and incidence of some diseases was largely due to the extended periods of favorable weather conditions in varying parts of the state that supported the increase in some diseases. In particular, frequent rainfall and high relative humidity were especially favorable for several fungal diseases. Unfortunately, almost all diseases of corn (except rusts) are caused by pathogens that can successfully overwinter in Nebraska. For this reason, making detailed notes on disease development and …

Trivapro A + Trivapro B Application Timing And Disease Efficacy In Field Corn In Nebraska, 2015, J. D. Harbour, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

The objective of the trial was to evaluate foliar fungicides and application timings for crop response and foliar disease efficacy. Irrigated corn was grown based on Nebraska Extension irrigation recommendations at the South Central Ag Lab near Clay Center, NE. Soils were a silt loam with 6.7 pH and 1.8 % OM and the previous crop was soybean. Reduced tillage was performed to the field prior to planting. Corn (DKC 65-79 RIB, tolerant to grey leaf spot (GLS)) was planted at approximately 34,000 seed/A on 26 May. Seven treatments were arranged in a randomized complete block design with six replications. …

Foliar Fungicide Comparison For Southern Rust Management, Stay Green, Push Lodging, And Yield In Nebraska, 2015, J. D. Harbour, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

The objective of the trial was to compare foliar fungicides for southern rust (SR) efficacy. Irrigated corn was grown based on Nebraska Extension irrigation recommendations at the South Central Ag Lab near Clay Center, NE. Soils were a silt loam with 6.7 pH and 1.8 % OM and the previous crop was soybean. Reduced tillage was performed to the field prior to planting. Corn (DKC 65-79 RIB, tolerant to gray leaf spot (GLS)) was planted at approximately 34,000 seed/A on 26 May. Eight treatments were arranged in a randomized complete block design with six replications. . . . Stalk lodging …

Deposition Aid Adjuvants Plus A Fungicide For Southern Rust Management, Stay Green, Push Lodging, And Yield Comparisons In Field Corn In Nebraska, 2015, J. D. Harbour, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

The objective of the trial was to compare foliar fungicides for southern rust (SR) efficacy. Irrigated corn was grown based on Nebraska Extension irrigation recommendations at the South Central Ag Lab near Clay Center, NE. Soils were a silt loam with 6.7 pH and 1.8 % OM and the previous crop was soybean. Reduced tillage was performed to the field prior to planting. Corn (DKC 65-79 RIB, tolerant to gray leaf spot (GLS)) was planted at approximately 34,000 seed/A on 26 May. Eleven treatments were arranged in a randomized complete block design with six replications. . . . Phytotoxicity was …

Fungicide Application Timing With Effects On Grey Leaf Spot And Southern Rust In Nebraska Field Corn, 2015, J. D. Harbour, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

The objective of the trial was to compare foliar fungicides applied to three growth stages of corn for grey leaf spot (GLS) and southern rust (SR) efficacy. Irrigated corn was grown based on Nebraska Extension irrigation recommendations at the South Central Ag Lab near Clay Center, NE. Soils were a silt loam with 6.7 pH and 1.8% OM and the previous crop was soybean. Reduced tillage was performed to the field prior to planting. Corn (DKC 65-79 RIB, tolerant to gray leaf spot) was planted at approximately 34,000 seed/A on 26 May. Eight treatments were arranged in a randomized complete …

Root-Lesion Nematodes, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

Root-lesion nematodes, Pratylenchus spp., are among the most commonly encountered plant-parasitic nematodes, with one or more species occurring in almost every field. Their small size (0.4-0.7 mm long) relative to most other plant-parasitic nematodes enables them to survive in almost any soil texture. Their wide host range and distribution make them one of the most damaging nematodes worldwide, ranging from cool temperate to tropical environments. At least eight species of root-lesion nematodes have been associated with sunflower.

Root-Knot Nematodes, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

Root-knot nematodes, Meloidogyne spp., are some of the most damaging plant pathogens. Several of the most common species of root-knot nematodes have been confirmed to reproduce and cause damage on sunflower, including M. arenaria, M. hapla, M. incognita, M. javanica, and M. hispanica.

Meloidogyne spp. occur worldwide but are especially common in temperate, subtropical, and tropical regions. Countries where Meloidogyne spp. have been confirmed to affect sunflower include the United States and the African nations of Egypt, Mozambique, South Africa, and Zambia. Root-knot nematodes tend to cause the most damage to plants grown in sandy …

Diseases Caused By Parasitic Nematodes, T. A. Jackson-Ziems

Department of Plant Pathology: Faculty Publications

Some plant-parasitic nematodes occur in every [sunflower] production field. Nematode populations likely include multiple species, although not all species cause notable disease. Symptoms depend on the species, the population density, and the crop's interaction with environmental factors. Several nematode species are known to cause disease in sunflower, although little research has focused on their impact or management in the crop. The highest population densities of plant-parasitic nematodes often occur in isolated areas that are randomly distributed in fields, as do the most severe plant symptoms. Symptoms are not necessarily diagnostic for nematodes, and the problem may be misdiagnosed. The most …