Russet Norkotah Research Articles

Fresh Market Evaluation of Six Russet-Type Potato Varieties and Four Russet Norkotah Strains

In 2016, Russet Norkotah was the second most widely grown potato variety in the US; however, recent research has identified alternatives with excellent production economics. During 2011–2013, fresh market variety research was conducted in the Columbia Basin of central Washington, a long-season production region. Russet Norkotah was compared to five varieties–Classic Russet, Mountain Gem Russet, Russet Burbank, Targhee Russet, and Teton Russet–and four sub-clonal strains–CO-3, CO-8, TX-278, and TX-296–derived from Russet Norkotah. Each variety was evaluated for early- (104 days between planting and vine kill) and late- (150 days between planting and vine kill) harvest tuber size profile, grade, and yield, grower economic value, susceptibility to blackspot bruise and shatter bruise, emergence, stem and at-harvest tuber numbers, tuber length-to-width ratios, and quality. When harvested early, Classic Russet and Mountain Gem Russet produced 30% and 15% more gross revenue than Russet Norkotah, respectively. All other varieties and Russet Norkotah strains except CO-3 produced as much early-harvest gross revenue as Russet Norkotah. CO-3 early-harvest revenue was close to 50% lower than that of Russet Norkotah. All varieties and Russet Norkotah strains produced significantly greater late-harvest yields and gross returns than Russet Norkotah. Late-harvest gross revenue for Targhee Russet and Mountain Gem Russet was 38% and 34% higher than Russet Norkotah, respectively. Classic Russet, Mountain Gem Russet, Targhee Russet, and Teton Russet had significantly more shatter bruise following the late harvest than Russet Norkotah and all Russet Norkotah strains. Russet Burbank was among the most susceptible to blackspot and Targhee Russet the least, with 32% and 2.1%, respectively. If bruising is mitigated, Mountain Gem Russet, Classic Russet, and Teton Russet may be suitable alternatives to Russet Norkotah and Russet Norkotah strains for both early and late harvests.

Sage Russet: a New High Yielding Russet Potato Variety with Cold-Sweetening Resistance, High Vitamin C and Protein Contents and Excellent Fresh Pack and Processing Potential

Sage Russet was released in 2009 by Oregon State University, in cooperation with the USDA-ARS and the Agricultural Experiment Stations of Idaho and Washington. It is a product of the Northwest Potato Variety (Tri-State) Development Program. Sage Russet has a medium-early maturity and produces long, somewhat flattened tubers with medium russeting of the skin. Total yields of Sage Russet are similar to those of Russet Burbank and Ranger Russet, but are significantly higher than those of Russet Norkotah. Sage Russet has significantly higher U.S. No.1 yields than Russet Burbank, Russet Norkotah, and Ranger Russet. It can be grown as an early or late crop with high U.S. No.1 yields and minimal internal defects. It achieved very high merit scores in processing and fresh market in Western Regional trials and can be considered for both markets. Sage Russet has a medium to high fertility requirements with high nitrogen use efficiency and medium storage capability. Sage Russet has moderate specific gravity and produces lighter fry color than the industry standard varieties. The color of fried strips following tuber storage at 4.4 °C and 7.2 °C is significantly lighter for Sage Russet than the control varieties, indicating good cold sweetening resistance. Chemical analyses have shown that Sage Russet has higher protein and vitamin C content than control varieties. Sage Russet is moderately resistant to early dying, early blight, and common scab, is resistant to tuber late blight, but susceptible to Fusarium wilt and is prone to shatter bruise.

Biological and molecular characterization of a tomato isolate of potato virus Y (PVY) of the PVYC lineage.

An isolate of potato virus Y (PVY), PVY-H14, was collected on the island of Oahu, Hawaii, from tomato plants exhibiting stunting and necrotic lesions on leaves. PVY-H14 triggered the hypersensitive resistance response in potato cultivars King Edward and Maris Bard, typical of a PVYC strain, and was unable to infect systemically the four tested cultivars, Desiree, Maris Bard, King Edward, and Russet Norkotah. Phylogenetic analysis of H14 and the whole genomes of 31 PVY isolates of non-recombinant strains of PVY placed PVY-H14 in the same clade with PVYC and several unclassified PVY isolates from tomato and tobacco.

Aerial multispectral imaging for crop hail damage assessment in potato

Crop loss assessment after an event of hailstorm can be inaccurate, subjective, and time consuming with the conventional method. Low-altitude, high-resolution aerial imaging using an unmanned aerial vehicle can be utilized for rapid assessment of target crops in a large scale, which can potentially improve the evaluation procedure. The goal of this study was to evaluate the feasibility of rapid and accurate assessment of crop damage due to simulated hailstorms using aerial multispectral imaging. Field experiments were conducted during two seasons in two potato varieties (Russet Norkotah, Ranger Russet) with three levels of mechanical defoliation (33%, 66%, and 99%) at three growth stages (tuber initiation, early bulk, and late bulk). All defoliation treatments were compared to the non-treated control plots (0% defoliation). Aerial multispectral images were collected between 77 and 108days after planting (0–60days after damage). Vegetation indices such as green normalized difference vegetation index (GNDVI), normalized difference vegetation index, and soil-adjusted vegetation index were calculated from replicate plots of different treatments. Results from two seasons showed similar trends in GNDVI values, with maximum effect of hail damage observed in early bulk stages. The mean GNDVI value was significantly lower in crops with the severe damage (99% defoliation) than others upon hail damage at the early bulk stage, with imaging after 10days after damage. The difference in GNDVI for crops with 33–66% damage could be detected within 10days after damage, and crop regrowth after that time period removed the effects of defoliation. The 99% defoliation damage at the early bulk stage also affected the crop yield significantly. Correlation analysis between vegetation indices and yield data indicated a strong relationship (r=0.77–0.90) for damage at the early bulk stage than other stages.

Variations in Zebra Chip Disease Expression and Tuber Biochemistry in Response to Vector Density.

Zebra chip (ZC) disease, caused by 'Candidatus Liberibacter solanacearum', which is transmitted by the potato psyllid, has negatively affected potato production in the United States for over a decade. The present study was conducted to evaluate the affect of the number of bacteriliferous psyllids on 'Ca. L. solanacearum' titer, levels of amino acids, carbohydrates, phenolics, and, subsequently, symptom severity in potato tubers. 'Red La Soda' and 'Russet Norkotah' potato were planted in the field and later inoculated with 'Ca. L. solanacearum' using 5, 10, and 30 bacteriliferous potato psyllids. In both cultivars, the increase in the number of psyllids resulted in elevated 'Ca. L. solanacearum' titer and symptom severity. In the cases of amino acids and reducing sugars, responses to vector density appeared to be cultivar specific. Overall, phenolic compounds showed a consistent increase following infection, a response that, in most cases, was positively correlated with the number of infective psyllids. Results quantified the impact of the number of infective psyllids on 'Ca. L. solanacearum' titer and biochemical content of infected tubers previously shown to be correlated with the degree of symptom expression. Managing vector numbers is currently the only effective approach for minimizing losses to ZC in grower's fields. However, our findings on physiological responses to vector density suggest that, in combination with chemical control, development of more tolerant or resistant potato genotypes, with emphasis on interrupting pathways that are associated with increased phenolic activity levels, may lead to more sustainable management of ZC in the future.

Pathogenicity and Aggressiveness of Three Alternaria spp. on Potato Foliage in the U.S. Northwest.

Alternaria spp. were collected from potato foliage showing symptoms of early blight and brown spot in the Columbia Basin, WA and Bonners Ferry and Rupert, ID between 2009 and 2011. The aggressiveness of three Alternaria spp. on potato was quantified on nonwounded and wounded detached leaves of 'Russet Norkotah' potato; wounded detached leaves of 'Alturas', 'Ranger Russet', 'Russet Burbank', and 'Umatilla Russet'; and whole plants of Russet Norkotah. Mean infection frequencies (MIF) and area under the lesion expansion curve (AULEC) were significantly greater for Alternaria solani (P = 0.0072 and 0.0002, respectively) than for A. arborescens or A. arbusti on nonwounded leaves. Wounding of tissue significantly increased MIF and AULEC for A. arbusti (P = 0.008 and 0.0047, respectively) and AULEC for A. arborescens (P = 0.01) relative to nonwounded tissue. AULEC did not differ significantly among the three Alternaria spp. when inoculated onto wounded foliage of whole plants (P = 0.34); the AULEC of whole plants was positively and significantly correlated with AULEC on detached leaves (P = 0.03). Umatilla Russet was the most susceptible and Russet Burbank was the least susceptible based on MIF and AULEC for all three pathogen species. Results indicate that A. solani was the more aggressive pathogen of potato in the Columbia Basin, because both A. arborescens and A. arbusti require wounds and A. arbusti lesions do not expand significantly in comparison with A. solani or A. arborescens following inoculation.

A Mutant eIF4E Confers Resistance to Potato Virus Y Strains and is Inherited in a Dominant Manner in the Potato Varieties Atlantic and Russet Norkotah

Potato Virus Y (PVY) is one of the most important pathogens affecting potato production worldwide. Here we tested the efficacy of engineered resistance against PVY in two popular susceptible potato varieties, Russet Norkotah and Atlantic. This resistance is based on the expression of a modified potato eIF4E gene containing mutations homologous to those in the recessive resistant allelic variant found in pepper. The expression of this eIF4E variant conferred differential resistance responses against three prevalent PVY strains including PVYO, PVYN:O and PVYNTN in the five tested transgenic lines. When resistance was established, the virus was not detectable in the inoculated leaves, the newly emerged leaves, nor in the sprouted tubers. Some strains were restrained to a low but detectable level in some of the potato lines. Crosses between transformed and wild type lines demonstrated that the engineered resistance gene was inherited in a dominant manner.

Mountain Gem Russet: a Potato Variety with High Early and Full Season Yield Potential and Excellent Fresh Market and Early Processing Characteristics

Mountain Gem Russet is a potato variety notable for having both high early and full-season yields of oblong-long, medium-russeted tubers with higher protein content than those of standard potato varieties. Mountain Gem Russet has greater resistance to soft rot, tuber late blight, growth cracks and second growth than Russet Burbank. Mountain Gem Russet produced greater total and U.S. No. 1 yields than Ranger Russet and Russet Norkotah in early-season trials conducted in Idaho, Oregon and Washington over a 3 year period. In full-season trials conducted in five western states over a 4 year period, average total and U.S. No. 1 yields for Mountain Gem Russet were almost always higher than Ranger Russet and Russet Burbank, with specific gravities averaging between these two standard cultivars. It maintains acceptable reducing sugar concentrations and fry quality when stored at 8.9 °C and has displayed a high level of fry color uniformity from tuber stem to bud end providing good potential for early processing. High fresh merit ratings and taste panel sensory scores comparable to Russet Burbank indicate good fresh market potential for Mountain Gem Russet. It was released in 2015 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon, and Washington, and is a product of the Pacific Northwest Potato Variety (Tri-State) Development Program.

Control of Early Blight in the San Luis Valley, Colorado

Early blight of potatoes caused by Alternaria solani is a disease that growers in Colorado often do not consider a major problem. However, past and this current research suggest that judicious use of a well-managed fungicide program can significantly reduce disease and increase yields. Additionally, wide spread use of fungicides in various rotations (azoxystrobin, pyraclostrobin, chlorothalonil, dithiocarbamate, mancozeb and boscalid) was shown to substantially decrease the disease levels of plants in treated versus untreated plots. Field trials evaluating fungicide rotations and application scheduling were conducted using the cultivar Russet Norkotah Selection 8. Treatments were first applied to either coincide with the dates as indicated by the early blight degree day model currently used in the San Luis Valley (~60 days after planting - DAP), or starting later in the season (~80 DAP). While significant differences (P < 0.05) in disease reduction were noted each year using fungicides, there was no corresponding yield advantage of fungicide treated versus the control (un-treated) plots. However, when data were analyzed over three years, a significant higher (P < 0.05) foliar disease control and subsequent yield increase among treatments was observed when a strobilurin product was used first in the fungicide rotation at 78 DAP. Results indicate that for a cost of $100–125/ha, growers can use fungicides with an appropriate rotation of active ingredients to control early blight and potentially increase yields.

Evaluation of sugar content in potatoes using NIR reflectance and wavelength selection techniques

Near-infrared (NIR) diffuse reflectance has been extensively and successfully applied on quality assurance for fruits, vegetables, and food products. This study is principally aimed to extract the primary wavelengths related to the prediction of glucose and sucrose for potato tubers (of Frito Lay 1879 (FL), a chipping cultivar, and Russet Norkotah (RN), a table use cultivar, and investigating the potential of classification of potatoes based on sugar levels important to the frying industry. Whole tubers, as well as 12.7mm slices, were scanned using a NIR reflectance spectroscopic system (900–1685nm). To extract the most influential wavelength in the studied range, interval partial least squares (IPLS), and genetic algorithm (GA) were utilized. Partial least squares regression (PLSR) was applied for building prediction models. Prediction models for RN showed stronger correlation than FL with r(RPD) (correlation coefficient (ratio of reference standard deviation to root mean square error of the model)) values for whole tubers for glucose being as high as 0.81(1.70), and 0.97(3.91) for FL and RN; in the case of sliced samples the values were 0.74(1.49) and 0.94(2.73) for FL and RN. Lower correlation was obtained for sucrose with r(RPD) for whole tubers as high as 0.75(1.52), 0.92(2.57) for FL and RN; and the values for sliced samples were 0.67(1.31) and 0.75(1.41) for FL and RN respectively. Classification of potatoes based on sugar levels was conducted and training models were built using different classifiers (linear discriminant analysis (LDA), K-nearest neighbor (Knn), partial least squares discriminant analysis (PLSDA), and artificial neural network (ANN)), in addition to classifier fusion. To obtain more robust classification models for the training data, 4-fold cross validation was used and results were tested using separate sets of data. Classification rates of the testing set for whole tubers, based on glucose, were as high as 81% and 100% for FL and RN. For sliced samples, the rates were 83% and 81% for FL and RN. Generally, lower classification rates were obtained based on sucrose with values of whole tubers of 71%, and 79% for FL and RN, and for sliced samples the rates were 75%, and 82% which follows a similar trend as PLSR results. This study presents a potential of using selected wavelengths and NIR reflectance spectroscopy to effectively evaluate the sugar content of potatoes and classify potatoes based on thresholds that are crucial for the frying industry.

First Report of Late Blight Caused by Phytophthora infestans Clonal Lineage US-23 on Potato in Idaho.

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is a destructive disease of potato (Solanum tuberosum) and tomato (S. lycopersicum) in the United States. Prior to 2007, the US-8 clonal lineage was the predominant genotype in the United States (4). Since 2007, a significant genetic change in the population of P. infestans occurred in the eastern United States with the appearance of new isolates with unique genotypes and epidemiological characteristics (3). These new genotypes US-22, US-23, and US-24 are sensitive to metalaxyl and represent mating types A2, A1, and A1, respectively (1,2). Prior to 2012, only US-8 had been documented in Idaho (5). In 2013, late blight was discovered in late August on potato crops (cv. Russet Norkotah) in Bingham and Madison counties, ID. Infected foliage (four samples from Bingham County and five from Madison) was sent to Michigan State University and the University of Wisconsin for confirmation of P. infestans and characterization of the isolates. Five sections from the leading edge of lesions were excised with a sterilized scalpel and placed on potato tuber slices ('Dark Red Norkotah'). Pathogen sporulation on the excised lesions was enhanced by incubation in plastic boxes lined with moistened paper towels for 5 days at 18°C in the dark. The sporulating lesions were transferred onto pea agar medium (160 g peas, 5 g sucrose, 15 g agar, 700 ml distilled water) amended with 50 mg/ml vancomycin. Ten pure cultures were obtained for each of 4 isolates per county by hyphal tipping. Cellulose acetate electrophoresis was conducted to determine Gpi allozyme genotype of the 4 isolates (4). The allozyme banding patterns were 100/100 at the Gpi locus, consistent with previously reported analyses of the US-23 genotype (1,2). Genomic DNA was extracted from 10 pure cultures using the DNeasy Plant Mini Kit (Qiagen, Germantown, MD), and SSR analyses were performed. Microsatellite markers Pi02, Pi4B, Pi63, PiG11, and D13 were used in SSR analyses. Pi02, Pi4B, and Pi63 had alleles of 162/164, 213/217, and 270/279 bp in size, respectively which is consistent with the reference US-23 genotype (1). However, heterozygosity was detected at locus D13 in the Idaho genotype with allele size of 134/210 bp and an additional allele of 140/155/176 bp at locus PiG11. This is different from the standard US-23 genotype (homozygous alleles 134/134 at locus D13 and two alleles 140/155 at locus PiG11). These allele changes indicate the isolates may be variants of US-23 isolates as all other phenotypic characteristics were similar to those of reference US-23 isolates. The Idaho genotypes were sensitive to metalaxyl both in vitro on rye A agar medium amended with metalaxyl at <0.1 ppm, and in vivo on Ridomil treated foliage tests at <0.1 ppm (1,2). Mating type assays confirmed the pathogen to be the A1 mating type. In the 2009 and 2010 late blight epidemics in the eastern United States, US-23 was the predominant genotype, but to our knowledge this genotype has never been reported previously in Idaho. Thus, this is the first known report of P. infestans genotype US-23 causing late blight on potato in Idaho, indicating a change in the population of P. infestans. In Idaho, the source of this genotype remains unknown, although infected tomatoes have been implicated in the widespread dissemination of this genotype of P. infestans in the eastern United States.

Evaluation of Sugar Content of Potatoes using Hyperspectral Imaging

Visible/near-infrared (VIS/NIR) hyperspectral reflectance imaging was evaluated as a technique toward rapid prediction of the glucose and sucrose percentages in two common fresh use and chipping potato cultivars. Tubers were sampled and held in multiple storage temperatures in an attempt to develop uniform and broad constituent distributions. Each tested sample was a 12.7-mm-thick slice cut uniformly from all tubers. Multiple features were extracted from samples including mean reflectance spectra and curve feature parameters yielded from an exponential model. Both glucose and sucrose ratios were measured using the Megazyme sucrose/D-glucose assay procedure as reference values. Partial least squares regression (PLSR), feed forward neural networks (FFNN), radial basis functions neural networks (RBFNN), and exact design radial basis functions (RBFNNE) neural networks were used for building calibration and prediction models. PLSR results demonstrated strongly correlated models built using mean reflectance spectra for glucose for Russet Norkotah (RN) with R (RPD) (or correlation coefficient (ratio of sample standard deviation to standard error of prediction)) values as high as 0.97 (3.58), whereas those values were 0.81 (1.70) for Frito Lay 1879 (FL). Sucrose models showed less correlation performance with R (RPD) values as high as 0.60 (1.14) for FL and 0.38 (1.00) for RN. Wavelength selection/prediction using interval partial least squares (IPLS) and genetic algorithm (GA) was conducted on the data, and PLSR and NN results were close to the full-wavelength models for the glucose and sucrose of both cultivars with a preference given to IPLS as it yields less selected variables than GA. Applying K-nearest neighbor (Knn) and partial least squares discriminant analysis (PLSDA) on mean reflectance spectra resulted in glucose misclassification errors of 14 % and 18 % for FL and RN, respectively. However, classification errors were higher for sucrose indicating lower accuracy for this sugar (34 and 30 % for FL and RN). The results in this study give promise to the possibility of measuring each of these sugars rapidly for quality control and monitoring in the potato industry.

Mechanical Transmission of Potato Virus Y (PVY) Through Seed Cutting and Plant Wounding

The transmission of PVY strains, PVYO, PVYN:O, and PVYNTN via tuber cutting and plant wounding was investigated in PVY susceptible cultivars Shepody and Russet Norkotah. For the tuber cutting experiment, after one infected tuber was cut with a knife, four uninfected tubers were cut sequentially with the same knife without disinfecting it between the cuts. In the plant wounding experiments, wounds were induced in the healthy and infected plants of Shepody by bouncing, brushing, hammering, squeezing, and Carborundum rubbing treatments. These treatments allowed exchange of sap between the healthy and infected plants. Results demonstrated that seed cutting did not transmit PVY, whereas plant wounding treatments caused varying levels of PVY transmission, depending on the wounding treatment. Plant bouncing was the least effective whereas hammering was the most effective.

Utilization of visible/near-infrared spectroscopic and wavelength selection methods in sugar prediction and potatoes classification

VIS/NIR spectroscopic systems have been extensively and successfully applied on quality assurance for fruits, vegetables, and food products. This study uniquely focused on the efficacy of selected wavelengths on predicting glucose and sucrose for potato tubers of Frito Lay 1879 (FL) and Russet Norkotah (RN) cultivars, and in turn the potential of classification of potatoes based on sugar levels important to the frying industry. Whole tubers, as well as 12.7 mm slices, were scanned using a VIS/NIR interactance spectroscopic system (446–1,125 nm). Interval partial least squares, and genetic algorithm were utilized for wavelength selection. Partial least squares regression (PLSR), and artificial neural networks were applied for building prediction models. Results showed that R(RPD) [correlation coefficient (ratio of reference standard deviation to root mean square error of the model)] for prediction models of glucose were as high as 0.78 (1.61), and 0.95 (3.02) for FL, and RN for slice samples, and 0.81 (1.72), and 0.97 (3.89) for FL and RN respectively in the case of whole tubers. For sucrose models, R(RPD) values were 0.71 (1.43), and 0.78 (1.57) for FL and RN for slice samples, and 0.80 (1.64), and 0.94 (2.82) for whole tubers. Classification of potatoes based on sugar levels was conducted and training models were built and validated using linear discriminant analysis, K-nearest neighbor, partial least squares discriminant analysis, and classifier fusion. Classification errors of the testing set for whole tubers, based on glucose, were as low as 18 and 0 % for FL and RN. For sliced samples, the errors were 16 and 13 % for FL and RN. Generally, higher classification errors were obtained based on sucrose with values of whole tubers as low as 26 and 14 % for FL and RN, and for sliced samples the errors were 23 and 18 % which follows a similar trend as PLSR results. This study presents a potential of using selected wavelengths in the VIS/NIR interactance range of 446–1,125 nm to effectively predict sugars and classify potatoes based on thresholds that are crucial for the frying industry.

Hairy Nightshade Critical Interference Period in Potatoes

Field research trials were conducted in Idaho at the Aberdeen Research and Extension Center in 2006 and 2007 to determine the critical interference period of hairy nightshade in potatoes. ‘Russet Norkotah’ variety was planted both years in plots three rows wide by 12 m long. When the potatoes had emerged, one- to two-leaf hairy nightshade plants that had been germinated and grown in the greenhouse were transplanted at a 2 m−1row density and allowed to grow for 10, 20, 30, or 40 d after emergence (DAE) before removal, or the potatoes were maintained weed-free for 0, 10, 20, 30, or 40 DAE before transplanting. Potatoes were harvested from the center row at the end of each growing season and yield and grade was determined. Russet Norkotah is a small-canopied potato variety and often does not completely close canopy in Idaho. Russet Norkotah U.S. No. 1 and total tuber yield were similar to weed-free yield when hairy nightshade transplanting was delayed up to 22 or 24 DAE, respectively, or planted at emergence and allowed to remain for only 6 or 11 d, respectively. Otherwise, yield decrease was 5% or greater. Therefore, the critical weed-free period for Russet Norkotah potato U.S. No. 1 or total tuber yields was 6 to 22 or 11 to 24 DAE, respectively.

Screening Potato Cultivars for new Sources of Resistance to Potato virus Y

Potato virus Y (PVY) strains have been defined based on genetic reactions in potato indicators expressing hypersensitive reaction (HR) response due to the presence of three different N genes, and also based on genomic information. Nine strains are known currently, with five PVY strains defined biologically, PVYO, PVYC, PVYZ, PVYN, and PVYE. The genetic background of the majority of North American potato cultivars has so far been poorly characterized for the presence of N genes inducing HR towards different PVY strains. Here, the HR response was studied in eight potato cultivars, elicited by five strains of PVY circulating in North America. These PVY isolates included representative isolates of PVYN-Wi, PVYNA-N, PVYO, PVYZ, and PVYN strains. Potato cultivars tested included Russet Burbank, Russet Norkotah, Shepody, Ranger Russet, Western Russet, Alturas, Rio Grande Russet, and Yukon Gem, grown in the U.S., and standard indicators Desiree and Maris Bard with the known genetic background. Three additional strains, PVYN:O, PVY-NE11, and PVYE, were tested on Yukon Gem. Virus-free potato plants were mechanically inoculated with PVY inoculum, and local and systemic foliar symptoms were observed for 8 weeks post-inoculation under different climate-controlled conditions. Virus status of the inoculated plants was tested starting at 3 weeks post-inoculation, by serotype-specific ELISA and RT-PCR, in order to monitor successful infections and confirm the identity of the inoculated PVY isolate. This systematic approach allowed us to identify Nytbr and Nztbr genes present in several North American cultivars. Two more new, putative N genes were postulated to be expressed in the cultivar Yukon Gem, and one additional putative N gene was postulated to be expressed in two cultivars, Yukon Gem and Rio Grande Russet. These N genes may represent valuable sources of resistance against multiple strains of PVY.

Evidence of a Monogenic Nature of the Nz Gene Conferring Resistance Against Potato virus Y Strain Z (PVYZ) in Potato

Hypersensitive resistance (HR) to Potato virus Y (PVY) in potato (Solanum tuberosum) is conferred by strain-specific N genes. Two such genes have been identified in potato so far, Ny tbr conferring HR to PVYO, and Nc tbr conferring HR to PVYC. A third, putative gene Nz tbr was proposed to confer HR against a distinct strain PVYZ. However, due to the scarcity of the PVYZ isolates of PVY, no formal proof of the monogenic nature of this new gene, Nz tbr , was available until now. Here, we report on a genetic study of the Nz tbr inheritance in three crosses between cultivars Maris Bard (Ny:Nz) and King Edward (ny:nz), and Maris Bard (Ny:Nz) and Russet Norkotah (ny:nz). A fully-sequenced PVYZ isolate, L26, was used to screen the parents and progeny for a virus-induced HR phenotype in foliage. Based on the phenotypic analysis of 203 progeny, segregation of HR phenotype in the PVYZ-infected plants was found to be 1:1, indicating a monogenic, dominant nature of the Nz tbr gene. Since the PVYZ strain includes PVYNTN isolates associated with tuber necrotic ringspot disease (PTNRD) in susceptible potato cultivars, the Nz tbr gene represents a valuable source of HR against PTNRD-inducing PVY isolates. This is the first demonstration that Nz tbr is a single, dominant N gene in potato conferring resistance to the PVYZ-NTN strain.

First Report of Fusarium proliferatum Causing Dry Rot in Michigan Commercial Potato (Solanum tuberosum) Production

Fusarium dry rot of potato (Solanum tuberosum L.) is a postharvest disease caused by several Fusarium spp. Thirteen Fusarium spp. have been implicated in dry rot of potatoes worldwide. Among them, 11 species have been reported causing potato dry rot of seed tubers in the northern United States (1). Historically, Fusarium sambucinum was the predominant species in Michigan potato production (3). Dry rot symptomatic tubers (n = 972) were collected from Michigan commercial potato storage facilities in 2011 and 2012 to determine the composition of Fusarium spp. Sections were cut from the margins of necrotic tissue with a sterile scalpel and surface disinfested in 0.6% sodium hypochlorite for 10 s, rinsed twice in sterile distilled water, and dried on sterile filter paper. The tissue sections were plated on half-strength potato dextrose agar (PDA) amended with 0.5 g/liter of streptomycin sulfate. Dishes were incubated at 23°C in the dark for 7 days. Putative Fusarium isolates were transferred onto water agar and hyphal tips from the margin of actively growing cultures were removed with a sterile scalpel and plated to carnation leaf agar (CLA) and half-strength PDA to generate pure cultures. Seven hundred and thirty Fusarium isolates were collected using these techniques. Preliminary identification of the 730 isolates was based on colony and conidial morphology on PDA and CLA, respectively. While F. oxysporum and F. sambucinum were isolated as expected from prior reports (3), three isolates of F. proliferatum were also identified. On CLA, macroconidia of F. proliferatum were sparse, slender, and mostly straight, with three to five septae (4). Microconidia were abundant, usually single celled, oval or club-shaped in short chains or false heads on monophialides and polyphialides (4), and chlamydospores were absent. On PDA, abundant white mycelium was produced and turned violet with age. Koch's postulates were confirmed through pathogenicity testing on disease-free potato tubers cvs. Atlantic and Russet Norkotah. Tubers were surface disinfested for 10 min in 0.6% sodium hypochlorite and rinsed twice in distilled water. Three tubers of each cultivar per isolate were wounded at the apical end of the tuber to a depth of 4 to 10 mm with a 4 mm diameter cork-borer. Tubers were inoculated by inserting a mycelial plug from a 7-day-old culture grown on PDA into the wound and incubating the tubers at 20°C for 21 days. All Fusarium isolates were tested. Control tubers were inoculated by inserting a water agar plug. Pathogenicity and virulence testing were replicated three times and repeated. Tubers inoculated with F. proliferatum developed typical potato dry rot symptoms but no dry rot symptoms were observed on control tubers. Fusarium proliferatum was re-isolated from symptomatic tubers, confirming Koch's postulates. To our knowledge, this is the first report of F. proliferatum causing potato dry rot in Michigan.

The potential use of visible/near infrared spectroscopy and hyperspectral imaging to predict processing-related constituents of potatoes

Near-infrared (NIR) transmittance spectroscopy, visible/NIR interactance spectroscopy, and visible/NIR hyperspectral imaging modes were used to determine the potential for rapid electronic estimation of glucose, sucrose, specific gravity, primordial leaf count, and soluble solids of (FL) (chipping) and Russet Norkotah (RN) (table) potato cultivars. Whole tubers and 0.5inch (12.54mm) slices were evaluated. Partial least squares regression (PLSR) was used to obtain the prediction models. Models for leaf counts and glucose were promising for all modes with the optimum model obtained for leaf count from interactance with sliced samples resulting in R (RPD) values of 0.95(3.29) for FL, and 0.90(2.19) for RN. For glucose, interactance also yielded the best model with R (RPD) values of 0.90(2.14) for FL, and 0.95(3.12) for RN. Models of other constituents were inconsistent between systems. Interactance mode with sliced samples showed best performance for soluble solids for FL with R (RPD) values of 0.55(1.18). Also, interactance mode demonstrated optimal performance for sucrose estimation with R (RPD) values of 0.81(1.63) for FL obtained from sliced samples, and 0.81(1.64) from whole tubers. Transmittance mode with sliced samples showed the best prediction models for RN with R (RPD) values of 0.63(1.30) for sucrose. Finally, specific gravity under interactance and transmittance modes with sliced samples for FL and RN respectively yielded R (RPD) values of 0.61(1.27), and 0.59(1.22).

Similarities and Differences in Physiological Responses to ‘Candidatus Liberibacter solanacearum’ Infection Among Different Potato Cultivars

Zebra chip disease (ZC), putatively caused by the fastidious bacterium 'Candidatus Liberibacter solanacearum', is a threat to potato growers worldwide. However, little is known about biochemical shifts in different potato genotypes in response to 'Ca. L. solanacearum' infection. To address this, 'Red La Soda', 'Russet Norkotah', and 'FL 1867' potato were infected with 'Ca. L. solanacearum' 4, 3, 2, and 1 weeks before harvest to observe variability in cultivar responses to 'Ca. L. solanacearum' infection. ZC symptoms, 'Ca. L. solanacearum' titers, and tuber biochemistry were assessed. Red La Soda tubers exhibited greater symptoms when infected for 4 weeks than Russet Norkotah or FL 1867 tubers. 'Ca. L. solanacearum' titers did not vary among cultivars. Tuber levels of amino acids, carbohydrates, and phenolics varied among cultivars but no consistent trends were observed. Individual amino acids and phenolics were greater in FL 1867 than Red La Soda, whereas others were greater in Red La Soda or Russet Norkotah than FL 1867. Most amino acids, carbohydrates, and phenolics were positively associated with infection duration and symptoms regardless of cultivar. Associations between most of the evaluated compounds and 'Ca. L. solanacearum' titer were positive in Red La Soda. However, no associations between 'Ca. L. solanacearum' quantity and compounds were observed in FL 1867 and Russet Norkotah.