Boutsika, K, VC Blok, MS Phillips & DJF Brown.  "Molecular Diagnostics of Virus-Vector Trichodorid Nematodes and their Associated Tobacco Rattle Virus (TRV)." [Vol. 78, 444] 

TRV occurs worldwide but is particularly prevalent in Europe and North America. The virus is transmitted from plant to plant by soil-inhabiting ectoparasitic nematodes belonging to the genera Paratrichodorus and Trichodorus. A RT-PCR assay, utilizing primers that reliably distinguish TRV and also serologically distinguishable strains of TRV, was developed that reliably detects the presence of TRV in individual trichodorids. Furthermore, the ribosomal DNA repeats unit is one of the most informative genomic regions for evolutionary and diagnostic purposes, of a wide range of organisms. It has been successfully used to distinguish nematode species. A PCR method utilizing ribosomal DNA primers derived from nematode 18S, 5.8S and 26S genes has been developed which reliably and consistently distinguishes individual P. pachydermus, T. similis and T. primitivus. Amplification products were sequenced and the complete sequence of the 18S gene and ITS1 and 2 regions from several trichodorid species have been obtained. Species specific primers have been successfully designed.

Boydston, Rick A, Corey V Ransom, & Pamela JS Hutchinson. "Crop Tolerance and Weed Control with Flumioxazin and Sulfentrazone in Pacific Northwest Potato Production."  [Vol. 78, 445]

Sulfentrazone and flumioxazin were tested for weed control in potatoes near Aberdeen, ID, Ontario, OR, and Paterson, WA. Herbicides were applied after the final hilling and preemergence to potato and weeds. Flumioxazin applied at 0.05 to 0.13 lb/a controlled hairy nightshade and common lambsquarters well, but redroot pigweed control was marginal in Idaho and Oregon. Redroot pigweed control improved as flumioxazin rate increased in Oregon. Flumioxazin did not control tame oats, barnyardgrass, or large crabgrass. Little or no potato injury was observed when treating with flumioxazin in Idaho and Oregon, but flumixoxazin slightly injured potatoes when applied at 0.13 lb/a in Washington. Sulfentrazone applied at 0.06 to 0.25 lb/a controlled common lambsquarters, redroot pigweed, and hairy nightshade greater than 90%at all locations. Sulfentrazone controlled barnyardgrass greater than 90% at 0.19 and 0.25 lb/a in Oregon. Tame oats and large crabgrass were not controlled by sulfentrazone. Sulfentrazone visually injured potatoes at 0.19 lb/a or more in Oregon and Washington, but potato tuber yield was not reduced compared to potatoes treated with herbicide standards. Tank mixes of sulfentrazone or flumioxazin with standard preemergence applied herbicides improved control of annual grass weeds and redroot pigweed.

Chen, Q, L Robertson, JT Jones, VC Blok, MS Philips & DJF Brown. "Magnetic Capture of Nematodes Using Antiserum and Lectin Coated Dynabeads."  [Vol. 78, 447]

Effective integrated management strategies require simple, rapid and reliable identification and quantification of plant parasitic nematodes present in soil. However, these nematodes are small and extremely difficult to identify. A new approach was developed using polyclonal antibody or lectin coated magnetic beads (Dynabeads) to recover target nematodes from samples. Lectins and antisera that bound specifically and reproducibly to the whole surface of Globodera rostochiensis and Meloidogyne arenaria were identified and were bound to Dynabeads to extract nematodes from test solutions. When using antisera, the efficiency of extraction was related to strength of binding of the antisera to the nematode (as determined by immunofluorescence microscopy), and several factors affected the extraction efficiency when using lectincoated beads. A panel of monoclonal antibodies against a virus vector nematode, Xiphinema index is being used to develop this technique. This study expands the use of Dynabeads from cell and molecular biology to parasitology and revealed that Dynabeads coated with a probe of suitable specificity can be used to extract target nematodes. The technique is being developed for use in a "non-expert system" for identifying virus-vector trichodorid species. 

Currie Vanessa & JA Sullivan. "Potato Variety Trials in Ontario 2000."  [Vol. 78, 450]  

In 2000, potato variety trials were conducted at the University of Guelph Cambridge Research Station to identify promising new varieties for the Ontario market. Trials included new commercial cultivars, advanced clone and adaptation tests from AAFC Fredericton and the North Central Regional Potato Variety Trial (NCRPVT). Plots were 5m - 7.6m long, 1 row wide, planted in a RBD with 4 replications. Cultivars are evaluated for yield and processing qualities. Envol, Adora, and Agata yielded 125%, 75% and 92%,of Eramosa , respectively. Salem and Eva were considered midseason maturity. Eva was scab susceptible. Fabula yielded 124% of Yukon Gold. Caesar yielded 90% of Yukon Gold. MSE149-5Y yielded 121% of Yukon Gold. Calwhite and Aquilon yielded 174% and 129% of Shepody. MSE228-1 yielded 138% of Shepody. All chipping varieties yielded higher than Snowden. Roselys was more attractive than Bris du Nord and Chieftain. AAFC Fredericton advanced selection trial included 9 clones, mostly suited for chipping. All yielded higher than Snowden. F94032 and F94036 produced high quality chips. Adaptation trial results showed good potential for F96028, F96040, F96001, and F96015. G9314-14, G9335-110 both yielded higher than Snowden. G9206-2R yielded 47% of Chieftain. In the NCRPVT, ND4093-4Rus performed well. V0168-3 yielded 103% of Russet Burbank. ND3196-1R was very attractive. MSA091-1, W1355-1, MSE018-1 show promise and will be evaluated for storage chipping quality.

Deahl, Kenneth L, MC Pagnani, FM Perez, B Moravec & LR Cooke. "Characterization of Late Blight in Uruguay."   [Vol. 78, 450]

Isolates of Phytophthora infestans were obtained from late blighted plants from several potato-growing regions of Uruguay in 1998 and 1999. Of these, 25 representative isolates were characterized in terms of allozyme genotype, mating type, mitochondrial haplotype, pathotype and metalaxyl resistance. Allozyme analyses revealed that the Uruguayan isolates were monomorphic and homozygous at the loci coding for glucose-6-phosphate isomerase and peptidase (Gpi 100/100, Pep 100/100). All isolates were of the A2 mating type and mitochondrial haplotype IIa. Metalaxylresistant isolates constituted 93% of the total. Most of the isolates displayed broadspectrum virulence and five carried virulence to 10 of the 11 R-genes tested. Despite the absence of R-genes in commercially-grown potato cultivars, virulence phenotypes were extremely complex. It was concluded that the Uruguayan P. infestans isolates resemble isolates from neighboring South American countries, notably Brazil, in terms of mating type and allozyme genotype and belong to the new populations of the pathogen now predominant in many countries.

Drake, GE & ND McKinley. "Vydate ® C-LV 'over and under' Control of Nematodes and Insects in Potatoes."  [Vol. 78, 453]  

Vydateâ is the registered trade name for oxamyl, an oxime N-methyl carbamate, introduced by E. I. du Pont de Nemours Inc. in 1969 as a nematicide with insecticidal and acaricidal properties. Oxamyl effectively controls most nematode species and a wide range of sucking and piercing insects and mites on many fruits, field crops, and vegetables including potatoes. Oxamyl has pronounced and unique systemic characteristics. Applied to the soil in irrigation water, it is absorbed and translocated upward; sprayed on the foliage it is moved downwards into the root system for plant protection. This feature allows the use of oxamyl for the combined control of nematodes and foliar feeding pests via drip and overhead irrigation systems. Vydate ® C-LV is a new formulation currently being introduced into the potato market in the Pacific Northwest including the states of Oregon, Washington, Idaho, and Colorado. Vydate C-LV can be applied through low-pressure irrigation systems including drip (trickle) systems. Application rates are at 1,1.5, and 2 lb ai/A. Nematode species include root-knot, (including Columbia root-knot nematode), sting, pin, lesion and ring. Insects controlled include Colorado potato beetle, flea beetles, potato leafhopper, and tarnished plant bug, and aphid species (including green peach aphid). Field and laboratory data have shown that oxamyl does not rapidly kill green peach aphid but inhibits feeding, slowly killing the insect and thus preventing the spread of potato leaf roll virus. At the use rates recommended through center pivot irrigation mite suppression is also achieved.

Farran, Inma & Angel M Mingo-Castel.  "Human Serum Albumin Production in Transgenic Potato Tubers."   [Vol. 78, 453]

Among all proteins of clinical relevance, human serum albumin (HSA) is the most extensively used human protein world-wide. In order to express HSA in tubers of transgenic potato plants, cDNA of mature HSA was obtained and later cloned under the B33 promoter of patatin (a specific tuber promoter). The recombinant albumin (rHSA) amino terminal was fused to a tuber signal peptide (protease inhibitor II). An Agrobacterium tumefaciens transformation of potato (cv. Desiree) leaves was performed. Transgene insertion was assessed through PCR. Transcription and expression in greenhouse potato tubers were verified by Northern and Western blots, and the levels of HSA were measured using ELISA. A total of 81 transgenic lines (PCR +) were scored for HSA. Most of them (near 80%) stored rHSA in its tubers, the higher content reaching 0.2% of tuber soluble protein. SDS-PAGE relative mobility of rHSA was identical to HSA. Recombinant HSA was localized in the apoplast of potato leaves. Tuber rHSA was purified through FPLC (fast performance liquid chromatography) and the right processing of rHSA signal peptide was verified by amino terminal sequencing. The possible influence of cultivar patatin levels on the transgene expression was also studied. Transgenic line Pas58 (cv. Desiree), which showed a 90% decrease in patatin levels (Hofgen, R. & Willmitzer L., 1992), was transformed. Surprisingly, the levels of recombinant HSA were significantly lower than the original levels of cv. Desiree.

Goyer, Claudia, Patrice Audy, Henry De Jong, Russ King, Agnes Murphy, George Tai, & Richard Tarn.  "Substractive Hybridization for the Isolation of Common Scab Resistance Genes from the Potato."     [Vol. 78, 454] 

Common scab is characterized by shallow, raised or deep-pitted brownish lesions on the tubers. This disease causes important economical losses every year in temperate regions of North America. Although several approaches have been developed to limit common scab damages on potato crop such as crop rotation, irrigation and soil acidification, breeding for resistance is still the most valuable strategy for managing potato scab. The present genetic base for scab resistance in North American varieties is very narrow. Preliminary genetic studies using scab resistant diploid S. chacoense and S. phureja in early 70’s proposed two independent loci for scab resistance, one locus with one or more dominant allele(s), the second when it is homozygous recessive. Recent genetic studies supported the hypothesis that scab resistance is relatively simply inherited. The aim of this research project is to cloned common scab resistance gene(s). Potato lines with high contrast for scab resistance has been identified, crosses were performed and the progeny was tested in greenhouse and in the field. Resistant and susceptible individuals were selected and mRNA was isolated. Subtractive hybridization enriching differentially expressed genes between susceptible and resistant plants are currently carried out. Common scab resistance gene(s) could be used to evaluate parental breeding lines and hybrids for disease resistance and could be transferred to available commercial cultivars. 

Harrison, W. Edd, Douglas C Lisk & Harvey A Yoshida.  "Gavel 75 DF Fungicide for Control of Potato Late Blight."  [Vol. 78, 456]   

Gavel 75 DF is a new protectant fungicide, developed by Rohm and Haas Company, that has shown excellent control of late blight on potatoes, as well as control of early blight. Registration for use on potatoes is expected in time for the 2001 season. In addition to the U.S., Canada and Mexico are expected to grant simultaneous registrations as part of a joint NAFTA review. Gavel fungicide contains the new active ingredient zoxamide along with mancozeb. Zoxamide belongs to the benzamide class of chemistry, and controls diseases caused by oömycetes, a class of fungi that includes Phytophthora infestans, the late blight fungus. It stops fungal growth by inhibiting cell division, preventing the fungus from reproducing. This unique mode of action for late blight control makes Gavel fungicide an excellent resistance management tool. The product also provides rainfastness due to its ability to adhere to the waxy cuticle of plant foliage. Gavel is best used as a protectant spray starting at the first signs of disease or reports of disease in a locality. Research determined that Gavel should be used in a 5 to 7 day schedule when late blight is present and conditions favor disease; it can be used in a 7 to 10 day schedule when disease pressure is low and environmental conditions do not favor disease development. Potato trials have not shown any adverse effects to foliage or tubers following season-long application.

Haynes, KG, CA Thill, G Secor, WE Fry, DS Douches, WR Stevenson & DP Weingartner.  "Foliar Resistance to Late Blight in Potato Clones Evaluated in National Trials in 2000."  [Vol. 78, 457] 

With the emergence of new and more aggressive strains of Phytophthora infestans and the release of new potato cultivars, an evaluation of potato clones for resistance to late blight is necessary. Thirty-three potato clones (19 cultivars, 14 selections) were evaluated in 2000 for late blight resistance at six U.S. locations, along with eight late blight differentials. The US-8 strain of P. infestans was present at all locations except NY, which had the US-11 strain. Percent infected foliage was recorded at approximately weekly intervals following the onset of disease at each location. Area under the disease progress curve (AUDPC) was calculated. Clones were ranked for mean AUDPC within location and the non-parametric stability statistics, mean absolute rank differences and variance of the ranks, were analyzed for phenotypic stability. There were significant genotype x environment interactions on the variance of the ranks of these clones. Only one clone, Q237-25, made a significant contribution to this interaction. The most late blight resistant clones were B0767-2, Q237-25, B0692-4, and A90586-11. AUDPC was minimal in the late blight differential LBR(8) across all locations except ND. In agreement with results from previous years, genotype x environment interactions on the rankings of AUDPC appear to be minimal for most clones evaluated: where significant, only a few clones account for the interaction.

Holeva, RC, Q Chen, R, Neilson, JT Jones & DJF Brown. "Lectin Attachment to Paratrichodorus anemones (Nematoda)."  [Vol. 78, 458] 

Lectins of Arachis hypogaea (PNA), Bauhinia purpurea (BPA), Canavalia ensiformis (ConA), Dolichos biflorus (DBA), Glycine max (SBA), Griffonia simplicifolia (GS-I, GS-II), Lycopersicon esculentum (LEA), Maclura pomifera (MPA), Solanum tuberosum (STA), Triticum vulgare (WGA) and Ulex europaeus (UEA-I) were screened for binding to surface glycoconjugates of Paratrichodorus anemones. The lectins were labelled with fluorochrome (FITC), and the fluorescence examined using incident fluorescence microscopy. Binding specificity was shown by inhibition with the appropriate sugars. All lectins, except PNA, DBA, GS-I and UEA-I, bound to the head region, indicating that specific binding sites were not present or accessible along the entire nematode cuticle. Furthermore, LEA and STA were the only lectins that produced a strong fluorescence on the entire surface coat of P. anemones. Consequently, they were selected as probes for the magnetic capture of target nematodes from mixed soil samples using Dynabeads. Polyclonal antisera is being produced to be used as an alternative probe for immuno-magnetic capture. Currently, these two approaches are being investigated for their applicability in detecting Paratrichodorus and Trichodorus nematodes, and for use in a "non-expert system" for detection, identification and quantification of virus-vector trichodorid species. 

Hutchinson, Chad M & DP Weingartner.  "Utilization of Controlled Release Fertilizers in Chip Potato Production."   [Vol. 78, 459]  

Best management practices (BMP) are being implemented to reduce potential nitrate run-off from 23,000 potato acres in St. Johns, Flagler, and Putnam counties of Florida. A BMP under consideration is the use of controlled release fertilizers (CRF). A field experiment was conducted at the Hastings REC to determine if a chip potato crop could be produced using CRFs. Treatments included a non-fertilized control and fertilizer treatments of Osmocote 19-6-12 (NPK); Osmocote Plus 15-9-12; Scott’s Topdress Special 22-5-6, and a standard 14-2-12 non-CRF. All fertilizers were applied at 168, 224, and 280 kg N/ha with standard fertilizer treatments applied in a split application. Solanum tuberosum var. Atlantic was planted February 25 and harvested and graded June 2, 2000. Total and marketable yields in all treatments were significantly higher than the non-fertilized control. Potatoes fertilized with 168 kg/ha CRF produced an average marketable yield of 32 MT/ha, 73% more than the nonfertilized control. Total nitrogen in leaf tissue ranged from 6.3% in the standard fertilizer treatment to lows of 4.8% in the Osmocote Plus treatment and 2.9% in the non-fertilized treatment. All nitrogen values from fertilized plants fell within state recommended limits. The positive results justify the further refinement of CRF use and the quantification of nitrate leaching with CRF fertilization. 

Jones, Richard W.  "Bioproduction of Stable Protein/Antimicrobial Peptides for Disease Control."  [Vol. 78, 461] 

Effective control of foliar potato diseases has relied principally upon use of resistant varieties and fungicide applications. New methods for developing resistant varieties have come through engineered resistance. New sources of fungicidal compounds are being developed in our laboratory using antimicrobial peptides produced through engineering of micro-organisms. An antimicrobial peptide was overexpressed in the bacterium E. coli as a fusion protein, coupled to the carboxy terminal region of prosystemin protein. In laboratory experiments the protein/peptide completely inhibited Phytophthora infestans zoospore and sporangial germination at 150 nanograms per microliter. The same concentration led to elimination of lesion formation on detached leaf assays. Optimizing expression of this protein/peptide combination can lead to new compounds for application in disease control. 

Karanastasi, E, SA, MacFarlane, U Wyss & DJF Brown.  "Acquisition, Retention, and Transmission of Tobravirus Particles by Trichodorid Nematodes."  [Vol. 78, 462]   

Tobacco rattle (TRV) and pea early-browning (PEBV) tobraviruses are naturally transmitted by plant parasitic nematodes belonging to the Trichodorus and Paratrichodorus genera. It was presumed that trichodorids acquire virus particles while ingesting sap from virus infected root cells. After acquisition, the particles are retained by the nematodes, adsorbed on the cuticle lining the wall of the pharyngeal lumen, and subsequently are released into further root cells, along with secretions emanating from the pharyngeal glands. The present study revealed how tobraviruses are acquired by trichodorids, and that differences exist amongst the sites of retention of distinct tobravirus strains in the pharyngeal tract of different trichodorid species. Furthermore, immunogold labelling of the coat protein of several tobravirus strains provided unequivocal evidence of the identity of tobravirus-like particles present within the pharynx of vector and non-vector trichodorid species. Subsequently, it was elucidated how tobraviruses successfully establish an infection in cells fed upon by nematodes, despite the fact that trichodorids customarily kill cells from which they withdraw cytoplasm and/or organelles. These results provide new insight of vector trichodorid-tobravirus-plant interactions. 

Kirk, William, Kimberly Felcher, David Douches, J Stein & R Hammerschmidt. "Combining Host Plant Resistance with Managed Fungicide Applications to Control Potato Late Blight (Phytophthora infestans)."  [Vol. 78, 462] 

Field experiments were conducted over four years with commercial potato cultivars and advanced breeding lines differing in susceptibility to late blight to determine their response to managed fungicide applications. Reduction of total fungicide was achieved by application of fungicides with less active ingredient, reduced application rates or a combination of these approaches. When environmental conditions were most favorable for the development of late blight, the lowest application rate of fungicides [33 % MRAR] provided unsatisfactory disease control. Under less conducive conditions effective control of late blight was achieved from 33 to 66% MRAR. RAUDPC values for Snowden (susceptible) and MSG274-3 (resistant) varied from year to year and tended to increase as disease severity values (DSV) increased. Therefore, an arbitrary scale of resistance based on RAUDPC values will not be satisfactory for predicting the efficacy of different fungicide application programs. The advanced selection, MSG274-3, was the most resistant line tested requiring minimal chemical protection. A companion experiment was conducted over two years to determine the response to reduction of total fungicide input, achieved by applying reduced amounts of fungicide at increased application intervals. In Snowden 10 and 15-day application intervals did control late blight even at 100% MRAR. At 5-day application intervals, all application rates of fungicide reduced foliar late blight in Snowden to RAUDPC<10. The advanced selection MSG274-3 was highly resistant and required minimal chemical protection.

Knowles, NR, Lisa Knowles & GNM Kumar.  "Physiological and Biochemical Markers of Seed-Tuber Productivity."  [Vol. 78, 464]

While the productivity of seed potatoes is greatly influenced by differences in tuber physiological age, our inability to define the physiological/biochemical bases of ’old’ and ’young’ remains a major obstacle to predicting and perhaps even controlling the yield potential of seed potatoes. With funding from the Washington State Potato Commission and Alberta Agricultural Research Institute, we are identifying markers of age and determining their efficacy for predicting productivity in short- and long-season growing areas. Seed-tubers possessing a broad range in growth and yield potential were produced in storage to facilitate the identification of productivity markers. Storage degree-days (DD) interacted with storage temperature, seed source (region of production) and cultivar to affect plant establishment and overall productivity. For example, yield of U.S. No. 1 tubers from seed-tubers that had accumulated 900 DD above 4 C at the beginning of storage fell from 6 to 38%, depending on these treatments. Hence, storage DD alone did not adequately describe seed age and productive potential. Seed Source (WA or Alberta) affected tuber physiological status at harvest, which in turn altered the responses to aging treatments during storage. By the end of storage, aging treatments had effected significant changes in tuber respiration, soluble sugars, indices of lipid peroxidation, tuber volatiles, proteinases, proteinase inhibitors, and enzymes associated with oxidative stress. Changes in these potential markers will be discussed in relation to age-induced differences in growth and yield potential.

Knowles, NR, RE Thornton, N Fuller & L Knowles.  "Evaluation of Clonal Susceptibility to Variation in Tuber Shape, French Fry Yield, and After-Storage Processing Quality Across Production Regions."     [Vol. 78, 464]  

In the Pacific Northwest, clones from the early and late Tri-State and Regional Variety Trials are evaluated for postharvest quality and storage potential with a focus on identifying varieties for the ’out-of-field’ and ’after-storage’ processing windows, respectively. Variable growing environments across WA, ID and OR interact with genotype to affect tuber morphology and storability. Among other attributes, a low degree of variation in tuber morphology and after-storage processing quality is desirable in a variety developed for the Tri-state area; however, measures of clonal plasticity in these characteristics are lacking. Methodologies have been developed to estimate the impact of region of production and tuber shape on yield of French fries. Number and fresh weight of fries (7.6 cm long or greater) can be estimated based on curvilinear relationships with length to width (L/W) ratios of 227- to 284-g tubers, a premium size desired for processing. Based on these models, yield of French fries (percent by no.) ranged from 67 to 78% across 16 clones, when averaged over production sites. In the 2000 trials, Russet Burbank had the most resistance to change in L/W ratio, resulting in fry yields that varied only 1.2% (by no.) across production sites. At the other extreme, A89384-10 had the greatest variation in usable fry yield, ranging from 57 to 78% across tri-state production sites. Clonal susceptibility to loss of processing quality after 60 days storage at 7 and 9 C was evaluated as a percentage of that at harvest. Analysis of the spread of variation in processing quality (after storage at 7 C) for clones produced across production sites provides an objective assessment of clonal stability during storage.

Kumar, GNM, L Knowles & NR Knowles. "Ethylene Generation from Potato Tissue is Free Radical-Mediated, Dependent on Tuber Age, and Correlated with Loss in Wound-Healing Ability."   [Vol. 78, 465]

Freshly-cut discs of tuber tissue failed to generate detectable levels of C(2)H(4) unless 1-aminocyclopropane-1-carboxylic acid (ACC) was supplied exogenously. Moreover, the ability of discs to convert exogenous ACC to C(2)H(4) declined with advancing tuber age. The conversion of ACC to C(2)H(4) was not affected by 1- aminocyclobutane-1-carboxylic acid (ACBC), a specific inhibitor of ACC oxidase (ACCO). ACBC effectively inhibited ACC-induced C(2)H(4) synthesis in apple tissue however. The free-radical (FR) scavenger, n-propyl gallate, inhibited the ability of tuber tissue to convert ACC to C(2)H(4) by as much as 80% but was completely ineffective on apple tissue. These results indicate that C(2)H(4) production from exogenously supplied ACC is primarily FR-mediated in potato tissue, in contrast to the enzymatically-mediated (via ACCO) conversion of ACC to C(2)H(4) in apple tissue. The ability of freshly wounded potato tubers to produce FRs on the wound surface declined with advancing tuber age, along with the ability to convert exogenous ACC to C(2)H(4), providing further evidence of a FR-mediated mechanism for C(2)H(4) generation from ACC in potato discs. The loss in FR-producing ability of tissue with tuber age was concomitant with a decline in wound-healing ability and we speculate that the two may be related, as FRs facilitate the polymerization of phenolics during wound periderm formation. Differences in the ability of tuber tissue to produce C(2)H(4) from ACC may thus provide a sensitive, indirect marker of wound-induced FR production and perhaps wound-healing potential. 

Miller, J Creighton, Jr., Jeff W Koym, Douglas C Scheuring, Gretta Schuster, & George JC Fernandez.  "Comparative Growth Analysis of Russet Norkotah and Russet Norkotah Strains."  [Vol. 78, 469]

Several Russet Norkotah mutant strains released by Texas A&M University and Colorado State University are rapidly replacing standard Russet Norkotah. In 2000, 38% of the "Norkotah" seed acreage in the United States was planted to one or more of these strains. It is well established that the strains can potentially, and usually do, outyield standard Russet Norkotah. The strains are somewhat later in maturity and thought to require lower inputs of nitrogen than standard Russet Norkotah. However, the developmental physiology of the strains relative to each other and Russet Norkotah is not well understood. To accomplish this, a two-year study which included standard Russet Norkotah, TXNS102, TXNS112, TXNS223, TXNS278, TXNS296, CORN-3, and CORN-8 was conducted to investigate the temporal patterns of development of individual plant parts (stolons/roots, tubers, stems, stem leaves, branches, and branch leaves). The number of plant parts and allocation of dry matter was monitored over the entire growing season. Significant differences in the temporal allocation of dry matter were found between standard Russet Norkotah and the strains and between CORN-3 and the other strains. These and other differences will be presented.

Norikane, Joey H, William W Kirk & Roger Brook. "The Corrosive Effects of Purogene and Oxidate."    [Vol. 78, 473] 

Purogene, a chlorine dioxide solution (Bio-Cide International, Norman, OK), and OxiDate, a hydrogen peroxide solution (BioSafe Systems, Glastonbury, CT), are used to control potato storage pathogens. These chemicals are strong oxidizers, but they are also corrosive. A series of tests were conducted to evaluate the corrosive effects of Purogene and Oxidate on seven common construction and application materials. Stainless steel, low carbon steel, copper, brass, polyvinyl chloride (PVC), and galvanized sheet metal were cut into 38mm square samples with an 8 mm hole in the middle of one side for mounting. The samples were suspended in Erlenmyer flasks from hooked glass rods and immersed in 700 ml of test solution. There were five treatments for the Purogene test, de-ionized water (control), 0.001M citric acid, and 100, 200, and 400 PPM total available chlorine dioxide Purogene solutions. There were also three Oxidate treatments, which were de-ionized water (control) and solutions of 50:1 and 100:1 mixing ratios. There were five replicates of each material in each of the test treatments. The samples were weighed on an analytical balance to determine rates of material loss. The 400 PPM Purogene solution was the most corrosive of the chlorine dioxide treatments, but according to the literature, the annual loss rates for all materials tested were low enough for a "good" corrosion resistance ratings. The preliminary results of the Oxidate tests show that there is corrosion, but at lower levels than the Purogene tests.

Norikane, Joey, H, Roger C Brook & William W Kirk. "Efficacy of Purogene and Oxidate Disinfectants Added to Potato Storage Humidity Water for Pathogen Control."   [Vol. 78, 473]  

Potato storage pathogens can cause serious economic losses in potatoes stored for seed, table stock or processing markets. Humidification systems are commonly used to prevent water loss from stored tubers. Losses are greatest in storages maintained between 42 and 55°F. Potato pathogens on the surface of tubers could potentially be controlled by addition disinfectants to humidification water. Purogene (Bio-Cide International, Norman, OK) and OxiDate (OxiDate, BioSafe Systems, Glastonbury, CT) have been recommended for this use, but the efficacy of this method of treatment needs to be demonstrated. Testing is currently being conducted at Michigan State University to evaluate this approach. In a temperature controlled storage chamber, three racks (2 ft. x 6 ft. x 6 ft.) were equipped with individual humidification and monitoring systems and sealed with plastic tarps. The racks were humidified with deionized water (control), 50 PPM total available chlorine dioxide as per the Purogene label, and 100:1 dilution as per the Oxidate label. Four replicates of 30 potato (cv Pike) tubers were inoculated with dry rot (Fusarium sambucinum), soft rot (Erwinia carotovora var carotovora) or late blight (Phytophthora infestans) and placed in plastic baskets in October 2000. The baskets were then loaded into the racks and sealed. Humidity and temperature were monitored and maintained at 95% relative humidity and 49°F. The test solutions were applied daily to maintain the target humidity. Samples were taken from the racks at 1-month, 3-month and 6-month intervals for evaluation. Preliminary results from the testing will be presented. 

Peters, RD, AV Sturz, BG Matheson, WJ Arsenault & A Malone. "Characterization of Isolates of Phytophthora erythroseptica from Prince Edward Island According to Metalaxyl Sensitivity and Allozyme Genotype."  [Vol. 78, 475]  

Pink rot of potato, caused by Phytophthora erythroseptica, has become a concern for potato growers in North America, particularly when wet conditions prevail at harvest time. The recovery of metalaxyl-resistant strains of P. erythroseptica in the U.S. in the 1990s, prompted an assessment of pathogen populations on Prince Edward Island. Tuber samples with symptoms of pink rot were collected from 14 fields in 1999. Fifty-eight field isolates recovered from infected tubers were used to generate 97 single zoospore isolates. All isolates were plated onto a clarified V8 agar medium amended with selected concentrations of metalaxyl (mefenoxan) to determine sensitivity. All field and single zoospore isolates of P. erythroseptica from Prince Edward Island were highly sensitive to metalaxyl (EC50 < 0.5 µg/ml) while reference isolates from Maine were either moderately resistant (EC50 = 10 µg/ml) or highly-resistant (EC50 = 500 µg/ml). Inoculation of tubers from field plots receiving foliar applications of metalaxyl indicated that the chemical could inhibit disease development caused by metalaxyl-sensitive strains of P. erythroseptica, even after 4 months in storage. In contrast, metalaxyl-resistant strains of the pathogen were able to infect and colonize these tubers. Allozyme banding patterns at the glucose-6-phosphate isomerase (Gpi) locus were identical (Gpi 91/91) for all isolates of P. erythroseptica in the collection and were useful for distinguishing these isolates from genotypes of P. infestans recovered from potato tubers infected with both pathogens. 

Platt, HW & F Daayf. "Potato Late Blight: Pathogen Population Dynamics across Canada in 2000."  [Vol. 78, 476]  

Late blight of potatoes is caused by the fungus Phytophthora infestans. While the disease is mainly found on potato foliage and tubers, causing extensive plant damage and crop loss, the fungus can attack other solanaceous plants such as tomato. Recently, with the introduction of new strains, the fungus has become more aggressive and the air and water-borne sporangia are surviving and causing more severe disease under conditions that previously reduced disease progress and the survival of these shortlived spores. Furthermore, almost all commercially cultivated potato varieties are susceptible to the disease and the fungicide, metalaxyl, has become less effective due to the occurrence of metalaxyl-resistant strains of the fungus. The fungus exists as two different mating types (A1 and A2) which when in contact with each other in plant tissue can result in the formation of sexually produced oospores. Each of these spores are new or unique strains and are able to survive long periods of time ‘outside’ of living plant tissues (e.g. in soils over-winter) and can then cause disease. This is a major problem for producers as almost all of the disease prevention and management methods currently used against late blight deal with the short-lived sporangia and not the long-lived oospores. In addition, the number of new strains of the fungus found in the pathogen populations have been increasing and late blight outbreaks have been increasing in home garden and commercial production of both tomato and potato. Results of recent investigations on pathogen populations in Canada will be presented.

Rodriguez, G Dorian. "Sensitivity to Metalaxyl, Sexual Compatibility, and Aggressiveness of Phytophthora infestans in Venezuela."  [Vol. 78, 478]

Venezuela grows ca. 20,000 ha of potato and most of the seed used is imported from Canada, Germany and Holland. Late blight is the major disease of the crop and no information about characteristics of the pathogen, except that related to physiological races, is known. To initiate this characterization, 27 isolates from potato and one from tomato were collected in five states and analyzed for sensitivity to metalaxyl, sexual compatibility, and aggressiveness. The first test was performed on Frozen Vegetable-Agar or V8 Juice-Agar media, and the LD50 was used to differentiate the isolates. The compatibility test was run using two known A1 isolates. The aggressiveness test was done in a greenhouse with potato plants and with a selection of six isolates using a suspension of 2.5x104 sporangia/ml. Analysis of variance, area under disease progress curve (AUDPC), and infection rate (r), were used to evaluate the aggressiveness. Variability in the reaction to metalaxyl was found: 57% of the isolates were sensitive (< or = 5 µg/ml) to the fungicide, 25% were moderately sensitive (>5-7µg/ml), and 8% were insensitive (> or = 8 µg/ml). All the isolates were of the A1 compatibility type. On the other hand, there were significant differences (P <0.001) in the aggressiveness among the isolates. The isolate Pi016 was sensitive to metalaxyl and less aggressive (r=0.177; AUDPC=648,7 percent-day), while the isolates Pi004 and Pi006 were more insensitive and also more aggressive (r=0.183; AUDPC=1,053 percent-day and r=0.326; AUDPC=956 percent-day, respectively). Insensitivity and aggressiveness were associates with the locality. The A2 compatibility type has not been found. 

Secor, Gary A, Viviana V Rivera & Fernando Riveros. "Partial Characterization of Phytophthora infestans Isolates from Chile."  [Vol. 78, 481]  

Chile has a thriving potato industry that exports both seed and commercial potatoes throughout South America and other continents. The success of their industry is partly due to natural geographic boundaries that provide a biological isolation. Chile is bordered by the Andes Mountains, the Pacific Ocean, the Atacama Desert, and the Antarctic. The seed potato industry is primarily concentrated in the South, where temperatures are cool and there are few diseases. The commercial industry is primarily concentrated in the northern desert region. In this region, late blight is a constant threat because of the continuous cropping of potatoes, irrigation and morning fog from the ocean. The primary fungicide used for the past ten years has been metalaxyl, which is typically used season long. Over 200 naturally occurring isolates were collected from grower fields in 1998 and 1999. The isolates were tested for mating type, genotype, and metalaxyl sensitivity. All isolates tested were the A1 mating type, US-1 genotype. None of the isolates were sensitive to metalaxyl, and EC50 values ranged from 200 to over 400 ppm. Additional tests are being conducted to determine R-gene composition and DNA homology among the isolates.

Shepherd, CP, RM Geddens & MD Stidham.  "Effects of Temperature and Fungicide Applications on Stem Lesions of Phytophthora infestans on Potato."  [Vol. 78, 482]

The label for Curzateâ 60DF has been amended for 2001 to allow early postemergence applications, in combination with an appropriate contact fungicide, to control early-season infection of potato late blight, caused by Phytophthora infestans. An aspect of interest in the early-season epidemiology of this disease is the appearance of stem lesions, often in the absence of foliar disease symptoms. The symptomatology, development and sporulation of stem lesions were evaluated by artificial inoculations of potato plants, maintained at different temperatures, with a US-8 isolate of Phytophthora infestans. Compared to foliar lesions at the same temperature, stem lesions were more difficult to detect, tended to expand more slowly (especially at lower temperatures), persisted longer and sporulated over a longer period of time. The impact of Curzateâ 60DF on stem lesion growth and sporulation at various temperatures was also evaluated. Two sequential post-infection applications (4 to 5- leaf stage and again 7 days later) of Curzateâ 60DF combined with Manzate â 75DF reduced both stem lesion growth and sporulation . We conclude that stem lesions are an important feature of early-season late blight biology, their characteristics differ from those of foliar lesions and disease control programs must be designed to effectively control early-season stem lesions. 

Shock, Clinton C, Eric P Eldredge, Lamont D Saunders, & Erik GB Feibert. "Optimum Soil Water Potential and Drip Tape Position for Potato (Solanum tuberosum L.) Drip Irrigation."  [Vol. 78, 482]   

The optimum soil water potential to start irrigation for potato on silt loam in Malheur County is -50 to -60 kPa for sprinkler or furrow systems. Optimum soil moisture and drip tape position for drip irrigation are not known. Two drip tape positions and a range of soil water potential were tested on ’Umatilla Russet’ potato in 1999 and 2000. Factorial designs used randomized complete blocks with five replicates. On a two-row flat-topped bed, either two drip tapes were positioned one on each potato row, or one tape was positioned halfway between the two potato rows. In 1999, irrigation levels of -30 and -60 kPa soil water potential were compared, and in 2000, -15, -30, -45, and -60 kPa were compared. Watermark sensors measured the soil water potential, and a CR10 datalogger recorded the sensor data and controlled the irrigation valves every 6 hours. Soil water potential stayed nearly constant in the wetter treatments. Less water was applied than the AgriMet potato Et estimate, possibly because of reduced evaporation from the soil. With irrigation at -45 or -60 kPa, applied water was much less than Et. Tuber yield, grade, and processing quality were better with irrigation at -15 or -30 kPa than at -45 or -60 kPa. One drip tape for two rows of plants was less productive than a drip tape for every row in 1999. The optimum potato irrigation criterion for drip systems may be wetter than for sprinkler or furrow systems. 

Sterrett, SB, MR Henninger, GC Yencho & KG Haynes. "S. phureja-s. stenotomum Contributes High Specific Gravity and Internal Tuber Quality under High Temperature Growing Environments to 4X-2X Hybrids."  [Vol. 78, 485] 

’Atlantic’ is the number one chipping variety grown in the mid-Atlantic states despite its susceptibility to internal heat necrosis. A lack of tetraploid germplasm genetically unrelated to ’Atlantic’ with high specific gravity has hindered the breeding effort in developing new chipping varieties for this area. The purpose of this study was to determine if the high specific gravity diploid Solanum phureja-S. stenotomum population under development in the USDA potato breeding program can contribute to this breeding effort. Twenty-six 4x-2x hybrids, ’Atlantic’ and one breeding selection were evaluated in NC, VA and NJ in 1999 for specific gravity and incidence and severity of internal heat necrosis. ’Atlantic’ was not a parent in any of these hybrids. Eleven of the 26 4x-2x hybrids were significantly higher in specific gravity and had significantly less internal heat necrosis than ’Atlantic’. Of these, 10 chipped acceptably out of 50ºF storage in December in Maine. Two of the 4x-2x hybrids had significantly more internal heat necrosis than 'Atlantic'. Broad-sense heritability and a 95% confidence interval for specific gravity and incidence and severity of internal heat necrosis was estimated as 0.88 (0.78, 0.94) , 0.91 (0.82, 0.95) and 0.89 (0.79, 0.94), respectively. These results indicate that S. phureja-S. stenotomum has the potential to expand the genetic base for new varieties for the mid-Atlantic region that are high in specific gravity and free from internal heat necrosis. 

Tsror (Lahkim), LO, Erlich, M Aharon, M Lavy & I Peretz-Alon. "Control of Black and Silver Scurf on Potato Seed Tubers."  [Vol. 78, 487] 

Black and silver scurf on potato caused by Rhizoctonia solani and Helminthosporium solani, respectively, are considered blemish diseases that reduce tuber quality. Although they usually do not cause yield losses, silver scurf causes weight loss in stored potatoes. Field experiments were conducted in southern Israel to determine the efficacy of fungicides in controlling black and silver scurf. Pencycuron, tolclofos-methyl, flutolanil and fludioxonil, sprayed either in furrow at planting or on seed tubers (in low volume), significantly reduced black scurf incidence on daughter tubers. A lesser reduction in disease incidence resulted from dusting seed tubers with mancozeb and propineb, or low volume spraying with iprodione and carboxin, or furrow treatments. A correlation between levels of infection on seed tubers and disease levels on daughter tubers was observed. In field experiments where control of silver scurf was evaluated, all tested fungicides were significantly more effective when applied as seed tuber treatments than by spraying in furrow. Low volume seed spraying with fludioxonil, prochloraz and azoxystobin, or dusting with mancozeb and propineb, significantly reduced silver scurf incidence on daughter tubers. Treatments of low volume sprayed agents combined with low dosages of mancozeb dusting were also effective. Imazalil formulations were moderately effective. Fluazinam did not reduce disease incidence. In a separate experiment in which imazalil was sprayed (low volume) onto seed tubers at different timings, both prior to and poststorage, or only after storage, disease incidence was significantly reduced. In previous experiments pre-storage treatments had been more effective.