Neil Gudmestad - Academia.edu (original) (raw)

Papers by Neil Gudmestad

Plant Disease, Apr 1, 2015

Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato... more Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato (Solanum tuberosum), intermittent outbreaks of a foliar blight and tuber rot have been reported in the United States over the past 75 years. Due to the sporadic nature of these reports, little is known about the etiology of the disease in potato. However, foliar disease and tuber rots caused by this pathogen are usually centered near areas of standing water in the field and along pivot tracks. Moreover, soil particles adhering to the foliage of infected potato plants suggest that water splash is involved in P. nicotianae dissemination and infection. Soil infestation and water splash dissemination studies were conducted under greenhouse conditions to examine the role that zoospores of P. nicotianae may play in disease on potato. In the soil infestation study, inoculum of P. nicotianae was added to soil at four rates (0.0, 1.0 × 10 3 , 5.0 × 10 3 , and 4.0 × 10 4 zoospores/ml) and three timings (at planting and 7 and 14 days after planting). Direct infection of aboveground plant tissues was achieved via splash dissemination of inoculum onto potato foliage. All soil infestations significantly reduced emergence, with the exception

European Journal of Plant Pathology, Feb 23, 2018

Although early blight is among the most damaging foliar diseases of potato, the information avail... more Although early blight is among the most damaging foliar diseases of potato, the information available on the disease-yield relationship is scarce. Twenty-three field trials were conducted from 2003 to 2016 across North Dakota and Minnesota potato growing regions to study the relationships among disease severity estimated from tuber initiation (TI) to early bulking (growth stage III to IV) and late bulking/tuber maturation (growth stage IV to V) and yield. The strength of the association and the functional relationships between crop and disease variables were assessed based on estimates of the Fisher's Z transformation of Pearson correlation r, the intercept (β 0 ) and slope(β 1 ) for each trial, which were combined and analyzed using meta-analytic models. At TI to early bulking stage, random-effect model estimated a slope of 0.20 mt/ha/ % -1 for an expected yield (intercept) of 61.88 mt/ha. Each unit increase in percent severity at this growth stage would result in a 32 percentage point (pp) yield reduction. During late bulking/tuber maturation crop growth stage, the random-coefficients β 0 and β 1 were 65.89 mt/ha and 0.13 mt/ha/% -1 , respectively. In relative terms, yield would be reduced by 19 pp. for each unitary percentage increase in early blight severity. Based on these meta-analysis results, growers are able to predict potential yield loss for each percentage increase of early blight severity at two growth stages, which can be useful for crop-loss assessments.

Plant Disease, Jun 1, 2016

Pink rot is an important disease of potato with worldwide distribution. Severe yield and quality ... more Pink rot is an important disease of potato with worldwide distribution. Severe yield and quality losses have been reported at harvest and in postharvest storage. Under conditions favoring disease development, pink rot severity can continue to increase from the field to storage and from storage to transit, causing further losses. Prediction of pink rot disease development in storage has great potential for growers to intervene at an earlier stage of disease development to minimize economic losses. Pink rot disease is estimated as percent rot confined on the interval (0 or 1, corresponding to 0% as no disease and 100% as maximum disease). In this study, beta regression is considered over the traditional ordinary least squares regression (linear regression) for fitting continuous response variables bounded on the unit interval (0,1). This method is considered a good alternative to data transformation and analysis by linear regression. The percentages of

American Journal of Potato Research, Feb 22, 2018

Metam sodium is a widely used soil fumigant for Verticillium wilt management in most potato produ... more Metam sodium is a widely used soil fumigant for Verticillium wilt management in most potato production regions of the United States. Environmental concerns regarding volatilization losses have led to restrictions on the use of metam sodium. The potato industry adapted to these restrictions by replacing metam sodium applications through sprinkler irrigation with shank injection applications of the fumigant. Previous research established parameters for effective shank application of metam sodium based on soil temperature, injection depth and rate of fumigation. However, these recommendations were based on research conducted under coarse-textured soil conditions with a low organic matter (OM) content (<1.3%). However, many potato production soils in North Dakota and Minnesota have a finer silt loam texture and OM contents of >2.5%. Therefore, it is important to know whether metam sodium fumigation recommendations for coarse-textured soils can be adapted to fine-textured soils. Two field trials were conducted using a split strip-block design for studying metam sodium efficacy in managing wilt. In both years, metam sodium injection depth and soil temperature at the time of injection did not result in significant differences in any study variable evaluated. All metam sodium fumigation rates significantly (P < 0.05), lowered Verticillium microsclerotia, reduced wilt severity, and improved tuber yield compared to non-treated plots. However, significant differences among fumigation rates were not observed across any variable evaluated. A relatively low rate of 373 l/ha is as effective as higher metam sodium rates for effective control of Verticillium wilt. Results presented here suggest that current metam sodium recommendations for shank injection applications in coarse-textured soils can be implemented in field soils with a fine texture and higher OM content.

Journal of Economic Entomology, Jun 1, 1997

An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valle... more An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valley of Minnesota and North Dakota was the reason we began a study to determine which aphid species were found in traps placed near potato fields. Knowledge of which aphid species are present and which of these are known vectors of PVY is needed to develop management strategies that minimize virus spread. The spread of PVY to healthy indicator plants and captures of alate aphids in tile traps were monitored weekly for 3 yr consecutively (1992)(1993)(1994) throughout the Red River Valley. Thirty-four aphid species were identified from green and yellow tile traps in 1992, 25 in 1993, and 26 in 1994. Yellow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Capitophorus elaeagni (del Guercio), and RllOpalosiphum l1widis (Fitch). Intervals of greatest aphid capture in green traps were generally between mid-July and mid-August at all sites in all 3 yr. Aphid captures at all sites were 3-25 times greater in 1992 and 1994 than in 1993. PVY infection of indicator plants exposed at the trapping sites also was greater in 1992 (25 plants) and 1994 (18 plants) than in 1993 (2 plants). Eighty-nine percent of PVY spread to indicator plants occurred between 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indicator plants: Acyrthosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R. maidis, com leaf aphid; R. padi (L.), bird cheny-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitohion avenae (F.), English grain aphid. Seven of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse conditions. The 8 most common aphid species were associated with crops and weeds common in the Red River Valley. Our data suggest that although the relative importance of individual PVY vectors varies from year to year and location by location, total aphid captures may be the best indicator of the risk of PVY spread.

Canadian journal of plant pathology, Sep 1, 1999

Page 1. 213 Managing fungal diseases of potato1 Gary A. Secor and Neil C. Gudmestad ... Recommend... more Page 1. 213 Managing fungal diseases of potato1 Gary A. Secor and Neil C. Gudmestad ... Recommended seed treatments in clude mancozeb, TOPS-MZ, and Maxim. Maxim has shown suppression of silver scurf even into the storage season. ...

Plant Disease, Feb 1, 2004

Potato early blight occurs worldwide and is prevalent wherever potatoes are grown. Alternaria sol... more Potato early blight occurs worldwide and is prevalent wherever potatoes are grown. Alternaria solani Sorauer has long been recognized as a foliar pathogen of potato (Solanum tuberosum L.) and is considered to be a difficult pathogen to control (3), largely because few cultivars possess resistance (2). The most effective early blight control measure is frequent application of protectant fungicides from early in the growing season until vine desiccation (12).

Crop Protection, 2019

Water rots are a group of important potato tuber rot diseases such as pink rot, Phytophthora tube... more Water rots are a group of important potato tuber rot diseases such as pink rot, Phytophthora tuber rot, and leak caused by the oomycete pathogens Phytophthora erythroseptica, P. nicotianae, and Pythium ultimum, respectively. If not managed, these diseases either alone or in combination, can cause severe yield loss and substantial reductions in quality. Growers continue to rely on fungicides for water rot management in the field and during post-harvest storage. Previous and ongoing breeding attempts have failed to identify and develop commercially acceptable potato cultivars resistant to all three diseases. This is mainly due to the complex, expensive, and timeconsuming methodologies required to screen for susceptibility to water rot pathogens. Currently, potato genotypes are assessed for susceptibility to individual water rot pathogens which is labor intensive. Considerable savings in time and effort would be realized if potato genotypes could be evaluated for susceptibility to one water rot pathogen and then statistical analysis applied to determine the probability of the reaction of a genotype to the other rot pathogens. A proportional odds model was fitted to examine the risk of genotype screening outcome (ordinal) to understand the relationships among water rot causing oomycetes in potato. Compared to P. erythroseptica, P. ultimum infected genotypes having susceptibility risk was high (2.6) versus other cultivar susceptibility categories. Potato genotypes screened for P. nicotianae have a significant susceptibility risk decreased by 38% when compared to P. erythroseptica.

Plant Disease, Mar 1, 2019

Four trichodorid species, Paratrichodorus allius, P. minor, P. porosus, and Trichodorus obtusus, ... more Four trichodorid species, Paratrichodorus allius, P. minor, P. porosus, and Trichodorus obtusus, were found in multiple states in the United States. Traditional diagnosis based on morphology and morphometrics is laborious and requires an experienced taxonomist. Additionally, end-point diagnosis using PCR was only available for P. allius. To increase diagnostic efficiency and reduce costs, a one-step multiplex PCR assay was developed to simultaneously identify these four species using one PCR reaction. Available sequences of 18S ribosomal DNA and internal transcribed spacer 1 (ITS1) region of these species were aligned and five primers were designed. The conserved forward primer located in the 18S region, in combination with the species-specific antisense primer in the ITS1 region, amplified a single distinctive PCR fragment for each species (421/425 bp for

Plant Disease, Nov 1, 2018

Stubby root nematodes (SRN) are important plant parasites infecting many crops and widely distrib... more Stubby root nematodes (SRN) are important plant parasites infecting many crops and widely distributed in many regions of the United States. SRN transmit Tobacco rattle virus, which causes potato corky ringspot disease, thereby having a significant economic impact on the potato industry. In 2015 to 2017, 184 soil samples and 16 nematode suspensions from

American Journal of Potato Research, Jun 22, 2019

Bacterial ring rot caused by Clavibacter sepedonicus is a zero-tolerance disease in seed potato c... more Bacterial ring rot caused by Clavibacter sepedonicus is a zero-tolerance disease in seed potato certification and can cause crop loss and substantial economic damage for affected growers. To address symptom expression and time of expression, 28 cultivars and advanced breeding lines were inoculated with C. sepedonicus and grown in North Dakota and Idaho. Cultivars included russet, chip, and specialty types. Foliar ratings were taken, and first symptoms were observed as early as 91 days after planting in Idaho and 55 days in North Dakota. Symptom characteristics were noted for each cultivar. This information is useful to growers and certification officials. Samples of stems, petioles, stolons, and tubers were also collected at different pre-harvest intervals to determine if C. sepedonicus can be reliably detected in the lab. The ability to detect C. sepedonicus before harvest allows an affected grower to make harvest and management decisions that limit damage caused by bacterial ring rot. La pudrición anular bacteriana (BRR) causada por Clavibacter sepedonicus (Cs) es una enfermedad de cero tolerancia en la certificación de papa-semilla, y puede causar pérdida del cultivo y daño económico substancial a los productores afectados. Para ver la expresión de síntomas y tiempo de expresión, se inocularon 28 variedades y líneas avanzadas de mejoramiento con Cm y se cultivaron en Dakota del Norte y Idaho. Las variedades incluyeron tipos russet, de freído, y de especialidad. Se tomaron lecturas foliares y se observaron los primeros síntomas tan temprano como a los 91 días después de la siembra en Idaho, y 55 días en Dakota del norte. Se notaron las características del síntoma para cada variedad. Esta información es útil para productores y oficiales de certificación. También se colectaron muestras de tallos, pecíolos, estolones y tubérculos, a diferentes intervalos de pre-cosecha, para determinar si Cm puede ser detectada confiablemente. La habilidad para detectar Cm antes de la cosecha le permite a un productor afectado hacer decisiones de cosecha y manejo que limiten el daño causado por BRR.

Plant Disease, Jun 1, 2018

Potato mop-top virus (PMTV) causes mop top disease in potato. This disease can result in a declin... more Potato mop-top virus (PMTV) causes mop top disease in potato. This disease can result in a decline in tuber quality causing economic losses to growers due to the production of necrotic lesions and discolored tissue in infected tubers. Due to the soilborne nature of PMTV, identifying and developing host resistance against the virus is considered the best disease management option. Very little is known about the sensitivity of U.S. potato cultivars to PMTV-induced tuber necrosis. The current study is aimed at investigating the sensitivity of a large number of potato cultivars to PMTV-induced tuber necrosis. Sixty-three cultivars representing all market-types were evaluated in North Dakota over a 2-year period for virus-induced tuber necrosis incidence and severity. PMTV-induced tuber necrosis (P < 0.0001) and severity (P < 0.0001) were significantly different among cultivars. Cultivars were categorized into sensitive, insensitive, and moderately sensitive/insensitive groups based on the virus-tuber induced necrosis data from both years. Based on data from ND trials, six cultivars (Red Endeavor, Viking, Dakota Jewel, Dark Red Norland, Nicolet, and Modoc) were rated as sensitive and 43 were rated as insensitive to PMTV-induced tuber necrosis. Four cultivars, including Bannock Russet, Gemstar Russet, Lelah, and Waneta showed zero PMTV incidence over 2 years. These results will help growers in making individual or coordinated decisions for the management of PMTV-induced tuber necrosis under field and storage conditions.

Plant Disease, Mar 1, 2018

Resistance to chemistries of the succinate dehydrogenase inhibiting (SDHI) and quinone outside in... more Resistance to chemistries of the succinate dehydrogenase inhibiting (SDHI) and quinone outside inhibiting (QoI) fungicides has developed rapidly in populations of Alternaria solani, the cause of early blight of potato. Reduced sensitivity to the anilinopyrimidine (AP) fungicide pyrimethanil has also been identified recently, determining that resistance to three chemical classes of fungicides is present within the A. solani population. Although no mutations have been characterized to confer resistance to APs, in A. solani five point mutations on three AsSdh genes have been determined to convey resistance to SDHIs, and the substitution of phenylalanine with leucine at position 129 (F129L) in the cytb gene confers resistance to QoIs. The objective of this study was to investigate the parasitic fitness of A. solani isolates with resistance to one or more of these chemical classes. A total of 120 A. solani isolates collected from various geographical locations around the United States were chosen for in vitro assessment, and 60 of these isolates were further evaluated in vivo. Fitness parameters measured were (i) spore germination in vitro, (ii) mycelial expansion in vitro, and (iii) aggressiveness in vivo. No significant differences in spore germination or mycelial expansion (P = 0.44 and 0.51, respectively) were observed among wild-type and fungicideresistant isolates in vitro. Only A. solani isolates possessing the D123E mutation were shown to be significantly more aggressive in vivo (P < 0.0001) compared with wild-type isolates. These results indicate that fungicide-resistant A. solani isolates have no significant fitness penalties compared with sensitive isolates under the parameters evaluated regardless of the presence or absence of reduced sensitivity to multiple chemical classes. Results of these studies suggest that A. solani isolates with multiple fungicide resistances may compete successfully with wild-type isolates under field conditions.

Nematology, 2017

The ectoparasitic stubby root nematode, Paratrichodorus allius, transmits tobacco rattle virus, w... more The ectoparasitic stubby root nematode, Paratrichodorus allius, transmits tobacco rattle virus, which causes corky ringspot disease resulting in significant economic losses in the potato industry. A diagnostic method for direct quantification of P. allius from soil DNA using TaqMan probe and SYBR Green real-time PCR assays was developed to assist the potato industry in management of this important vector. Specificity of primers/probe designed from the internal transcribed spacer of ribosomal DNA of P. allius was demonstrated by in silico analysis and experimental PCR tests with no cross reactions using non-target nematode species and nematode communities. The SYBR Green method was more sensitive than the TaqMan probe method during detection using serial diluted DNA templates. Standard curves were generated from serial dilutions of DNA extracted from autoclaved soil with artificially inoculated P. allius individuals and were validated by high correlations between the numbers of target nematodes quantified by the assays and added to the soil. Moreover, the numbers of P. allius determined by the real-time PCR assays and estimated by the microscopic method in 17 field soil samples presented positive correlation relationships (R 2 = 0.80 and 0.86). Although the quantification using TaqMan probe overestimated the target nematodes compared to using SYBR Green in eight out of ten field soil samples, results of the two methods correlated well (R 2 = 0.92). This is the first report of P. allius quantification from soil DNA extracts using real-time PCR, providing a rapid and sensitive diagnostic method obviating time-consuming manual nematode extraction from soil and microscopic identification and quantification.

Plant Disease, 2016

Foliar fungicides continue to be the primary means of early blight management on potato in the Un... more Foliar fungicides continue to be the primary means of early blight management on potato in the United States. Both premium-priced, single-site mode-of-action "specialty" fungicides and standard protectant multisite fungicides are applied, either alone or incorporated into fungicide rotation programs to combat early blight. Individual participant data meta-analysis was conducted to compare overall fungicide efficacy against early blight on potato, quantify tuber yields, and identify the most efficacious timing for fungicide applications. In this study, the specialty fungicide-based applications were compared against the standard fungicides chlorothalonil and mancozeb applied alone. Type 3 fixed effects

American Journal of Potato Research, 2003

Page 1. Amer J of Potato Res (2003) 80:33-40 33 Short Communication Temporal Sensitivity of Alter... more Page 1. Amer J of Potato Res (2003) 80:33-40 33 Short Communication Temporal Sensitivity of Alternaria solani to Foliar Fungicides Amy L. Holm, Viviana V. Rivera, Gary A. Secor, and Neil C. Gudmestad* Department of Plant ...

Plant Disease, Jul 1, 2018

Tobacco rattle virus (TRV) causes the economically important corky ring spot disease in potato. C... more Tobacco rattle virus (TRV) causes the economically important corky ring spot disease in potato. Chemical control is difficult due to the soilborne nature of the TRV-transmitting nematode vector, and identifying natural host resistance against TRV is considered to be the optimal control measure. The present study investigated the sensitivity of 63 cultivars representing all market types (evaluated at North Dakota and Washington over 2 years) for the incidence of TRV-induced tuber necrosis and severity. This article also investigates the cultivar-location interaction (using a mixed-effects model) for TRV-induced necrosis. TRVinduced tuber necrosis (P < 0.0001) and severity (P < 0.0001) were significantly different among cultivars evaluated separately in North Dakota and Washington trials. Mixed-effects model results of pooled data (North Dakota and Washington) demonstrated that the interaction of cultivar and location had a significant effect (P = 0.03) on TRVinduced necrosis. Based on the virus-induced tuber necrosis data from both years and locations, cultivars were categorized into sensitive, moderately sensitive, insensitive, and moderately insensitive groups. Based on data from North Dakota, 10 cultivars, including Bintje, Centennial Russet, Ciklamen, Gala, Lelah, Oneida Gold, POR06V12-3, Rio Colorado, Russian Banana, and Superior, were rated as insensitive to TRVinduced tuber necrosis. Similar trials assessing TRV sensitivity among cultivars conducted in Washington resulted in a number of differences in sensitivity rankings compared with North Dakota trials. A substantial shift in sensitivity of some potato cultivars to TRV-induced tuber necrosis was observed between the two locations. Four cultivars (Centennial Russet, Oneida Gold, Russian Banana, and Superior) ranked as insensitive for North Dakota trials were ranked as sensitive for Washington trials. These results can assist the potato industry in making cultivar choices to reduce the economic impact of TRV-induced tuber necrosis.

American potato journal, Dec 1, 1986

NorKing Russet is an oblong to slightly blocky, russet-skinned potato cultivar with medium-early ... more NorKing Russet is an oblong to slightly blocky, russet-skinned potato cultivar with medium-early maturity and a strong vine. It has resistance to verticillium wilt but is susceptible to most viruses and to early and late blight. It is generally medium to high yielding and high in total solids. Norking Russet es un cultivar de papa de forma oblonga a ligeramente adoquinada, piel escamosa, tallos robustos, y maduraci6n medianamente temprana. Es resistente a la marchitez por Verticillium, pero susceptible a la mayorfa de los virus y a los tizones temprano y tardio. Sus rendimientos son generalmente medios a altos, y su contenido en s61idos totales es normalmente alto.

American Journal of Potato Research, Dec 30, 2016

The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the ... more The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the development of powdery scab, formation of root galls and tuber yield was investigated in seven field trials conducted in Minnesota and North Dakota. Sixteen potato cultivars, with different levels of susceptibility to disease on roots and tubers, were planted in plots treated with chloropicrin at rates ranging from zero to 201.8 kg a.i. ha -1 . The amount of S. subterranea DNA in soil was determined using qPCR. Bioassays were conducted to further assess the effect of chloropicrin fumigation on root colonization by S. subterranea in two potato cultivars with contrasting disease susceptibility. In the field, chloropicrin applied at rates between 70.1 to 201.8 kg a.i. ha -1 significantly decreased S. subterranea initial inoculum in soil but increased the amount of disease observed on roots and tubers of susceptible cultivars. The effect of increasing disease was confirmed in controlled conditions experiments. Although the amount of S. subterranea DNA in roots of bioassay plants increased with increasing chloropicrin rates, it remained similar among potato cultivars. Chloropicrin fumigation significantly increased tuber yield which in cultivars such as Shepody and Umatilla Russet were associated with the amount root galls (r = 0.30; P < 0.03). Results of these studies contradict earlier reports on the use of chloropicrin fumigation for the control of powdery scab. Factors other than inoculum level, such as environmental conditions that affect inoculum efficiency and host susceptibility, may be significant contributors to the development of powdery scab and root gall formation.

Plant Disease, Mar 1, 2018

Succinate dehydrogenase-inhibiting (SDHI) fungicides have been widely applied in commercial potat... more Succinate dehydrogenase-inhibiting (SDHI) fungicides have been widely applied in commercial potato (Solanum tuberosum L.) fields for the control of early blight, caused by Alternaria solani Sorauer. Fivepoint mutations on three AsSdh genes in A. solani have been identified †

Plant Disease, Apr 1, 2015

Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato... more Although Phytophthora nicotianae is not normally considered to be an important pathogen of potato (Solanum tuberosum), intermittent outbreaks of a foliar blight and tuber rot have been reported in the United States over the past 75 years. Due to the sporadic nature of these reports, little is known about the etiology of the disease in potato. However, foliar disease and tuber rots caused by this pathogen are usually centered near areas of standing water in the field and along pivot tracks. Moreover, soil particles adhering to the foliage of infected potato plants suggest that water splash is involved in P. nicotianae dissemination and infection. Soil infestation and water splash dissemination studies were conducted under greenhouse conditions to examine the role that zoospores of P. nicotianae may play in disease on potato. In the soil infestation study, inoculum of P. nicotianae was added to soil at four rates (0.0, 1.0 × 10 3 , 5.0 × 10 3 , and 4.0 × 10 4 zoospores/ml) and three timings (at planting and 7 and 14 days after planting). Direct infection of aboveground plant tissues was achieved via splash dissemination of inoculum onto potato foliage. All soil infestations significantly reduced emergence, with the exception

European Journal of Plant Pathology, Feb 23, 2018

Although early blight is among the most damaging foliar diseases of potato, the information avail... more Although early blight is among the most damaging foliar diseases of potato, the information available on the disease-yield relationship is scarce. Twenty-three field trials were conducted from 2003 to 2016 across North Dakota and Minnesota potato growing regions to study the relationships among disease severity estimated from tuber initiation (TI) to early bulking (growth stage III to IV) and late bulking/tuber maturation (growth stage IV to V) and yield. The strength of the association and the functional relationships between crop and disease variables were assessed based on estimates of the Fisher's Z transformation of Pearson correlation r, the intercept (β 0 ) and slope(β 1 ) for each trial, which were combined and analyzed using meta-analytic models. At TI to early bulking stage, random-effect model estimated a slope of 0.20 mt/ha/ % -1 for an expected yield (intercept) of 61.88 mt/ha. Each unit increase in percent severity at this growth stage would result in a 32 percentage point (pp) yield reduction. During late bulking/tuber maturation crop growth stage, the random-coefficients β 0 and β 1 were 65.89 mt/ha and 0.13 mt/ha/% -1 , respectively. In relative terms, yield would be reduced by 19 pp. for each unitary percentage increase in early blight severity. Based on these meta-analysis results, growers are able to predict potential yield loss for each percentage increase of early blight severity at two growth stages, which can be useful for crop-loss assessments.

Plant Disease, Jun 1, 2016

Pink rot is an important disease of potato with worldwide distribution. Severe yield and quality ... more Pink rot is an important disease of potato with worldwide distribution. Severe yield and quality losses have been reported at harvest and in postharvest storage. Under conditions favoring disease development, pink rot severity can continue to increase from the field to storage and from storage to transit, causing further losses. Prediction of pink rot disease development in storage has great potential for growers to intervene at an earlier stage of disease development to minimize economic losses. Pink rot disease is estimated as percent rot confined on the interval (0 or 1, corresponding to 0% as no disease and 100% as maximum disease). In this study, beta regression is considered over the traditional ordinary least squares regression (linear regression) for fitting continuous response variables bounded on the unit interval (0,1). This method is considered a good alternative to data transformation and analysis by linear regression. The percentages of

American Journal of Potato Research, Feb 22, 2018

Metam sodium is a widely used soil fumigant for Verticillium wilt management in most potato produ... more Metam sodium is a widely used soil fumigant for Verticillium wilt management in most potato production regions of the United States. Environmental concerns regarding volatilization losses have led to restrictions on the use of metam sodium. The potato industry adapted to these restrictions by replacing metam sodium applications through sprinkler irrigation with shank injection applications of the fumigant. Previous research established parameters for effective shank application of metam sodium based on soil temperature, injection depth and rate of fumigation. However, these recommendations were based on research conducted under coarse-textured soil conditions with a low organic matter (OM) content (<1.3%). However, many potato production soils in North Dakota and Minnesota have a finer silt loam texture and OM contents of >2.5%. Therefore, it is important to know whether metam sodium fumigation recommendations for coarse-textured soils can be adapted to fine-textured soils. Two field trials were conducted using a split strip-block design for studying metam sodium efficacy in managing wilt. In both years, metam sodium injection depth and soil temperature at the time of injection did not result in significant differences in any study variable evaluated. All metam sodium fumigation rates significantly (P < 0.05), lowered Verticillium microsclerotia, reduced wilt severity, and improved tuber yield compared to non-treated plots. However, significant differences among fumigation rates were not observed across any variable evaluated. A relatively low rate of 373 l/ha is as effective as higher metam sodium rates for effective control of Verticillium wilt. Results presented here suggest that current metam sodium recommendations for shank injection applications in coarse-textured soils can be implemented in field soils with a fine texture and higher OM content.

Journal of Economic Entomology, Jun 1, 1997

An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valle... more An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valley of Minnesota and North Dakota was the reason we began a study to determine which aphid species were found in traps placed near potato fields. Knowledge of which aphid species are present and which of these are known vectors of PVY is needed to develop management strategies that minimize virus spread. The spread of PVY to healthy indicator plants and captures of alate aphids in tile traps were monitored weekly for 3 yr consecutively (1992)(1993)(1994) throughout the Red River Valley. Thirty-four aphid species were identified from green and yellow tile traps in 1992, 25 in 1993, and 26 in 1994. Yellow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Capitophorus elaeagni (del Guercio), and RllOpalosiphum l1widis (Fitch). Intervals of greatest aphid capture in green traps were generally between mid-July and mid-August at all sites in all 3 yr. Aphid captures at all sites were 3-25 times greater in 1992 and 1994 than in 1993. PVY infection of indicator plants exposed at the trapping sites also was greater in 1992 (25 plants) and 1994 (18 plants) than in 1993 (2 plants). Eighty-nine percent of PVY spread to indicator plants occurred between 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indicator plants: Acyrthosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R. maidis, com leaf aphid; R. padi (L.), bird cheny-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitohion avenae (F.), English grain aphid. Seven of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse conditions. The 8 most common aphid species were associated with crops and weeds common in the Red River Valley. Our data suggest that although the relative importance of individual PVY vectors varies from year to year and location by location, total aphid captures may be the best indicator of the risk of PVY spread.

Canadian journal of plant pathology, Sep 1, 1999

Page 1. 213 Managing fungal diseases of potato1 Gary A. Secor and Neil C. Gudmestad ... Recommend... more Page 1. 213 Managing fungal diseases of potato1 Gary A. Secor and Neil C. Gudmestad ... Recommended seed treatments in clude mancozeb, TOPS-MZ, and Maxim. Maxim has shown suppression of silver scurf even into the storage season. ...

Plant Disease, Feb 1, 2004

Potato early blight occurs worldwide and is prevalent wherever potatoes are grown. Alternaria sol... more Potato early blight occurs worldwide and is prevalent wherever potatoes are grown. Alternaria solani Sorauer has long been recognized as a foliar pathogen of potato (Solanum tuberosum L.) and is considered to be a difficult pathogen to control (3), largely because few cultivars possess resistance (2). The most effective early blight control measure is frequent application of protectant fungicides from early in the growing season until vine desiccation (12).

Crop Protection, 2019

Water rots are a group of important potato tuber rot diseases such as pink rot, Phytophthora tube... more Water rots are a group of important potato tuber rot diseases such as pink rot, Phytophthora tuber rot, and leak caused by the oomycete pathogens Phytophthora erythroseptica, P. nicotianae, and Pythium ultimum, respectively. If not managed, these diseases either alone or in combination, can cause severe yield loss and substantial reductions in quality. Growers continue to rely on fungicides for water rot management in the field and during post-harvest storage. Previous and ongoing breeding attempts have failed to identify and develop commercially acceptable potato cultivars resistant to all three diseases. This is mainly due to the complex, expensive, and timeconsuming methodologies required to screen for susceptibility to water rot pathogens. Currently, potato genotypes are assessed for susceptibility to individual water rot pathogens which is labor intensive. Considerable savings in time and effort would be realized if potato genotypes could be evaluated for susceptibility to one water rot pathogen and then statistical analysis applied to determine the probability of the reaction of a genotype to the other rot pathogens. A proportional odds model was fitted to examine the risk of genotype screening outcome (ordinal) to understand the relationships among water rot causing oomycetes in potato. Compared to P. erythroseptica, P. ultimum infected genotypes having susceptibility risk was high (2.6) versus other cultivar susceptibility categories. Potato genotypes screened for P. nicotianae have a significant susceptibility risk decreased by 38% when compared to P. erythroseptica.

Plant Disease, Mar 1, 2019

Four trichodorid species, Paratrichodorus allius, P. minor, P. porosus, and Trichodorus obtusus, ... more Four trichodorid species, Paratrichodorus allius, P. minor, P. porosus, and Trichodorus obtusus, were found in multiple states in the United States. Traditional diagnosis based on morphology and morphometrics is laborious and requires an experienced taxonomist. Additionally, end-point diagnosis using PCR was only available for P. allius. To increase diagnostic efficiency and reduce costs, a one-step multiplex PCR assay was developed to simultaneously identify these four species using one PCR reaction. Available sequences of 18S ribosomal DNA and internal transcribed spacer 1 (ITS1) region of these species were aligned and five primers were designed. The conserved forward primer located in the 18S region, in combination with the species-specific antisense primer in the ITS1 region, amplified a single distinctive PCR fragment for each species (421/425 bp for

Plant Disease, Nov 1, 2018

Stubby root nematodes (SRN) are important plant parasites infecting many crops and widely distrib... more Stubby root nematodes (SRN) are important plant parasites infecting many crops and widely distributed in many regions of the United States. SRN transmit Tobacco rattle virus, which causes potato corky ringspot disease, thereby having a significant economic impact on the potato industry. In 2015 to 2017, 184 soil samples and 16 nematode suspensions from

American Journal of Potato Research, Jun 22, 2019

Bacterial ring rot caused by Clavibacter sepedonicus is a zero-tolerance disease in seed potato c... more Bacterial ring rot caused by Clavibacter sepedonicus is a zero-tolerance disease in seed potato certification and can cause crop loss and substantial economic damage for affected growers. To address symptom expression and time of expression, 28 cultivars and advanced breeding lines were inoculated with C. sepedonicus and grown in North Dakota and Idaho. Cultivars included russet, chip, and specialty types. Foliar ratings were taken, and first symptoms were observed as early as 91 days after planting in Idaho and 55 days in North Dakota. Symptom characteristics were noted for each cultivar. This information is useful to growers and certification officials. Samples of stems, petioles, stolons, and tubers were also collected at different pre-harvest intervals to determine if C. sepedonicus can be reliably detected in the lab. The ability to detect C. sepedonicus before harvest allows an affected grower to make harvest and management decisions that limit damage caused by bacterial ring rot. La pudrición anular bacteriana (BRR) causada por Clavibacter sepedonicus (Cs) es una enfermedad de cero tolerancia en la certificación de papa-semilla, y puede causar pérdida del cultivo y daño económico substancial a los productores afectados. Para ver la expresión de síntomas y tiempo de expresión, se inocularon 28 variedades y líneas avanzadas de mejoramiento con Cm y se cultivaron en Dakota del Norte y Idaho. Las variedades incluyeron tipos russet, de freído, y de especialidad. Se tomaron lecturas foliares y se observaron los primeros síntomas tan temprano como a los 91 días después de la siembra en Idaho, y 55 días en Dakota del norte. Se notaron las características del síntoma para cada variedad. Esta información es útil para productores y oficiales de certificación. También se colectaron muestras de tallos, pecíolos, estolones y tubérculos, a diferentes intervalos de pre-cosecha, para determinar si Cm puede ser detectada confiablemente. La habilidad para detectar Cm antes de la cosecha le permite a un productor afectado hacer decisiones de cosecha y manejo que limiten el daño causado por BRR.

Plant Disease, Jun 1, 2018

Potato mop-top virus (PMTV) causes mop top disease in potato. This disease can result in a declin... more Potato mop-top virus (PMTV) causes mop top disease in potato. This disease can result in a decline in tuber quality causing economic losses to growers due to the production of necrotic lesions and discolored tissue in infected tubers. Due to the soilborne nature of PMTV, identifying and developing host resistance against the virus is considered the best disease management option. Very little is known about the sensitivity of U.S. potato cultivars to PMTV-induced tuber necrosis. The current study is aimed at investigating the sensitivity of a large number of potato cultivars to PMTV-induced tuber necrosis. Sixty-three cultivars representing all market-types were evaluated in North Dakota over a 2-year period for virus-induced tuber necrosis incidence and severity. PMTV-induced tuber necrosis (P < 0.0001) and severity (P < 0.0001) were significantly different among cultivars. Cultivars were categorized into sensitive, insensitive, and moderately sensitive/insensitive groups based on the virus-tuber induced necrosis data from both years. Based on data from ND trials, six cultivars (Red Endeavor, Viking, Dakota Jewel, Dark Red Norland, Nicolet, and Modoc) were rated as sensitive and 43 were rated as insensitive to PMTV-induced tuber necrosis. Four cultivars, including Bannock Russet, Gemstar Russet, Lelah, and Waneta showed zero PMTV incidence over 2 years. These results will help growers in making individual or coordinated decisions for the management of PMTV-induced tuber necrosis under field and storage conditions.

Plant Disease, Mar 1, 2018

Resistance to chemistries of the succinate dehydrogenase inhibiting (SDHI) and quinone outside in... more Resistance to chemistries of the succinate dehydrogenase inhibiting (SDHI) and quinone outside inhibiting (QoI) fungicides has developed rapidly in populations of Alternaria solani, the cause of early blight of potato. Reduced sensitivity to the anilinopyrimidine (AP) fungicide pyrimethanil has also been identified recently, determining that resistance to three chemical classes of fungicides is present within the A. solani population. Although no mutations have been characterized to confer resistance to APs, in A. solani five point mutations on three AsSdh genes have been determined to convey resistance to SDHIs, and the substitution of phenylalanine with leucine at position 129 (F129L) in the cytb gene confers resistance to QoIs. The objective of this study was to investigate the parasitic fitness of A. solani isolates with resistance to one or more of these chemical classes. A total of 120 A. solani isolates collected from various geographical locations around the United States were chosen for in vitro assessment, and 60 of these isolates were further evaluated in vivo. Fitness parameters measured were (i) spore germination in vitro, (ii) mycelial expansion in vitro, and (iii) aggressiveness in vivo. No significant differences in spore germination or mycelial expansion (P = 0.44 and 0.51, respectively) were observed among wild-type and fungicideresistant isolates in vitro. Only A. solani isolates possessing the D123E mutation were shown to be significantly more aggressive in vivo (P < 0.0001) compared with wild-type isolates. These results indicate that fungicide-resistant A. solani isolates have no significant fitness penalties compared with sensitive isolates under the parameters evaluated regardless of the presence or absence of reduced sensitivity to multiple chemical classes. Results of these studies suggest that A. solani isolates with multiple fungicide resistances may compete successfully with wild-type isolates under field conditions.

Nematology, 2017

The ectoparasitic stubby root nematode, Paratrichodorus allius, transmits tobacco rattle virus, w... more The ectoparasitic stubby root nematode, Paratrichodorus allius, transmits tobacco rattle virus, which causes corky ringspot disease resulting in significant economic losses in the potato industry. A diagnostic method for direct quantification of P. allius from soil DNA using TaqMan probe and SYBR Green real-time PCR assays was developed to assist the potato industry in management of this important vector. Specificity of primers/probe designed from the internal transcribed spacer of ribosomal DNA of P. allius was demonstrated by in silico analysis and experimental PCR tests with no cross reactions using non-target nematode species and nematode communities. The SYBR Green method was more sensitive than the TaqMan probe method during detection using serial diluted DNA templates. Standard curves were generated from serial dilutions of DNA extracted from autoclaved soil with artificially inoculated P. allius individuals and were validated by high correlations between the numbers of target nematodes quantified by the assays and added to the soil. Moreover, the numbers of P. allius determined by the real-time PCR assays and estimated by the microscopic method in 17 field soil samples presented positive correlation relationships (R 2 = 0.80 and 0.86). Although the quantification using TaqMan probe overestimated the target nematodes compared to using SYBR Green in eight out of ten field soil samples, results of the two methods correlated well (R 2 = 0.92). This is the first report of P. allius quantification from soil DNA extracts using real-time PCR, providing a rapid and sensitive diagnostic method obviating time-consuming manual nematode extraction from soil and microscopic identification and quantification.

Plant Disease, 2016

Foliar fungicides continue to be the primary means of early blight management on potato in the Un... more Foliar fungicides continue to be the primary means of early blight management on potato in the United States. Both premium-priced, single-site mode-of-action "specialty" fungicides and standard protectant multisite fungicides are applied, either alone or incorporated into fungicide rotation programs to combat early blight. Individual participant data meta-analysis was conducted to compare overall fungicide efficacy against early blight on potato, quantify tuber yields, and identify the most efficacious timing for fungicide applications. In this study, the specialty fungicide-based applications were compared against the standard fungicides chlorothalonil and mancozeb applied alone. Type 3 fixed effects

American Journal of Potato Research, 2003

Page 1. Amer J of Potato Res (2003) 80:33-40 33 Short Communication Temporal Sensitivity of Alter... more Page 1. Amer J of Potato Res (2003) 80:33-40 33 Short Communication Temporal Sensitivity of Alternaria solani to Foliar Fungicides Amy L. Holm, Viviana V. Rivera, Gary A. Secor, and Neil C. Gudmestad* Department of Plant ...

Plant Disease, Jul 1, 2018

Tobacco rattle virus (TRV) causes the economically important corky ring spot disease in potato. C... more Tobacco rattle virus (TRV) causes the economically important corky ring spot disease in potato. Chemical control is difficult due to the soilborne nature of the TRV-transmitting nematode vector, and identifying natural host resistance against TRV is considered to be the optimal control measure. The present study investigated the sensitivity of 63 cultivars representing all market types (evaluated at North Dakota and Washington over 2 years) for the incidence of TRV-induced tuber necrosis and severity. This article also investigates the cultivar-location interaction (using a mixed-effects model) for TRV-induced necrosis. TRVinduced tuber necrosis (P < 0.0001) and severity (P < 0.0001) were significantly different among cultivars evaluated separately in North Dakota and Washington trials. Mixed-effects model results of pooled data (North Dakota and Washington) demonstrated that the interaction of cultivar and location had a significant effect (P = 0.03) on TRVinduced necrosis. Based on the virus-induced tuber necrosis data from both years and locations, cultivars were categorized into sensitive, moderately sensitive, insensitive, and moderately insensitive groups. Based on data from North Dakota, 10 cultivars, including Bintje, Centennial Russet, Ciklamen, Gala, Lelah, Oneida Gold, POR06V12-3, Rio Colorado, Russian Banana, and Superior, were rated as insensitive to TRVinduced tuber necrosis. Similar trials assessing TRV sensitivity among cultivars conducted in Washington resulted in a number of differences in sensitivity rankings compared with North Dakota trials. A substantial shift in sensitivity of some potato cultivars to TRV-induced tuber necrosis was observed between the two locations. Four cultivars (Centennial Russet, Oneida Gold, Russian Banana, and Superior) ranked as insensitive for North Dakota trials were ranked as sensitive for Washington trials. These results can assist the potato industry in making cultivar choices to reduce the economic impact of TRV-induced tuber necrosis.

American potato journal, Dec 1, 1986

NorKing Russet is an oblong to slightly blocky, russet-skinned potato cultivar with medium-early ... more NorKing Russet is an oblong to slightly blocky, russet-skinned potato cultivar with medium-early maturity and a strong vine. It has resistance to verticillium wilt but is susceptible to most viruses and to early and late blight. It is generally medium to high yielding and high in total solids. Norking Russet es un cultivar de papa de forma oblonga a ligeramente adoquinada, piel escamosa, tallos robustos, y maduraci6n medianamente temprana. Es resistente a la marchitez por Verticillium, pero susceptible a la mayorfa de los virus y a los tizones temprano y tardio. Sus rendimientos son generalmente medios a altos, y su contenido en s61idos totales es normalmente alto.

American Journal of Potato Research, Dec 30, 2016

The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the ... more The effect of chloropicrin fumigation on the soil populations of Spongospora subterranea and the development of powdery scab, formation of root galls and tuber yield was investigated in seven field trials conducted in Minnesota and North Dakota. Sixteen potato cultivars, with different levels of susceptibility to disease on roots and tubers, were planted in plots treated with chloropicrin at rates ranging from zero to 201.8 kg a.i. ha -1 . The amount of S. subterranea DNA in soil was determined using qPCR. Bioassays were conducted to further assess the effect of chloropicrin fumigation on root colonization by S. subterranea in two potato cultivars with contrasting disease susceptibility. In the field, chloropicrin applied at rates between 70.1 to 201.8 kg a.i. ha -1 significantly decreased S. subterranea initial inoculum in soil but increased the amount of disease observed on roots and tubers of susceptible cultivars. The effect of increasing disease was confirmed in controlled conditions experiments. Although the amount of S. subterranea DNA in roots of bioassay plants increased with increasing chloropicrin rates, it remained similar among potato cultivars. Chloropicrin fumigation significantly increased tuber yield which in cultivars such as Shepody and Umatilla Russet were associated with the amount root galls (r = 0.30; P < 0.03). Results of these studies contradict earlier reports on the use of chloropicrin fumigation for the control of powdery scab. Factors other than inoculum level, such as environmental conditions that affect inoculum efficiency and host susceptibility, may be significant contributors to the development of powdery scab and root gall formation.

Plant Disease, Mar 1, 2018

Succinate dehydrogenase-inhibiting (SDHI) fungicides have been widely applied in commercial potat... more Succinate dehydrogenase-inhibiting (SDHI) fungicides have been widely applied in commercial potato (Solanum tuberosum L.) fields for the control of early blight, caused by Alternaria solani Sorauer. Fivepoint mutations on three AsSdh genes in A. solani have been identified †