Pink Rot Research Articles

First Report of Phytophthora cryptogea on Potato Tubers in Turkey.

Potato (Solanum tuberosum L.) is an important agricultural crop in Turkey, with 150,000 ha and a production of about 4 million tons per year. There are numerous pathogens that limit potato production. In 2011, a new disease was observed on the potato cultivar Ramos in Erzincan Province in Turkey. Disease symptoms were similar to pink rot. Infected tubers had a rubbery texture and when cut, infected areas were cream colored. When the infected area was exposed to air for 10 min, the color turned to salmon pink and after 15 to 20 min it turned black. A funguslike organism was isolated from diseased tubers on carrot agar. The colonies were uniform and there were no petaloid patterns. Soil extract solution was prepared using 1,000 ml of distilled water and 15 g of field soil according to Jeffers and Aldwinckle (2) and used for sporangia production. Agar discs from 5-day-old colonies were placed in soil extract solution and incubated under continuous fluorescent light at room temperature. Sporangia began forming after 24 h and were abundant after 48 h. Oogonia were not observed on corn meal agar plates supplemented by beta-cytosterol. Sporangia were nonpapillate and noncaducous, mostly ovoid, but some were obpyriform. The mean size of the sporangia was 43 ± 4 × 30 ± 2 μm. The Oomycete was identified as Phytophthora cryptogea Pethybr. & Laff., according to its morphological characters (1). Isolate identity was confirmed by sequence analysis of the ribosomal DNA internal transcribed spacer using primers ITS1 and ITS4. The ITS sequence was a 99% match to P. cryptogea strains (GenBank Accession Nos. AF087475.1, AF228101.1, GU111626.1, AY995400.1, GU111624.1, AY995400.1, and GU111624.1). The isolate from Turkey was deposited in GenBank as Accession No. JQ071495. Pathogenicity tests were conducted on potato tubers (cv. Ramos). Tubers were surface disinfected with 0.5% NaOCl for 5 min., then washed twice with sterile water. When dried, 20 tubers were wounded with a shallow cut made parallel to the surface by a sterile knife. An agar disc from a 1-week-old colony was placed on the artificial wound on each of 10 potatoes. For controls, agar discs without fungal mycelia were placed on the wounds of the other 10 potatoes. Each inoculated and uninoculated potato was incubated for 5 days at 24°C in the dark and in separate plastic cups containing moistened filter paper at the bottom. Tubers were then cut open and examined for disease. Cream colored lesions were first observed; after 10 min lesions turned salmon pink and after 20 min they turned black. Cream colored lesions were not observed inside uninoculated potatoes. To the best of our knowledge, this is the first report of P. cryptogea causing pink rot of potato in Turkey. Pink rot disease of potato is commonly caused by P. erytroseptica, but P. cryptogea can cause similar symptoms (3) and severe tuber rot. This pathogen could cause important losses of potato in Turkey, especially during storage of tubers.

Palisade Russet: A Late Blight Resistant Potato Cultivar Having a Low Incidence of Sugar Ends and High Specific Gravity

Palisade Russet is a medium-late maturing, lightly russeted potato cultivar notable for its resistance to late blight (Phytophthora infestans) infection of foliage and tuber. Palisade Russet is suitable for processing with low tuber glucose concentrations observed following long-term storage at a temperature as low as 5.6°C with consistently acceptable fry color scores (USDA value ≤2.0) following storage at temperatures of 5.6 to 8.9°C. Reducing sugars are also maintained uniformly throughout the tuber, resulting in a low incidence of sugar ends in French fries relative to standard processing cultivars such as Russet Burbank and Ranger Russet. Palisade Russet has shown high specific gravities in western production regions of the U.S. which may limit its acceptance by the western processing industry. However, in potato production regions with inherently low specific gravities, Palisade Russet could have potential as a processing cultivar. In full-season trials conducted in Idaho, Oregon, and Washington over a 5 year period, the average total yield of Palisade Russet across all three states was very similar to yields observed for Ranger Russet and Russet Burbank. However, the U.S. No. 1 yield of Palisade Russet was 3% and 31% higher relative to Ranger Russet and Russet Burbank, respectively. In addition to late blight, Palisade Russet is also resistant to Verticillium wilt, black dot, and pink rot, and has a moderate level of resistance to net necrosis, PVY, and early blight of both the foliage and tuber. The disease resistances of Palisade Russet make it a good candidate for organic production, or for use by growers seeking reduced pesticide inputs. Palisade Russet displays a low incidence of second growth and growth cracks, especially relative to Russet Burbank, and is intermediate between Ranger Russet and Russet Burbank for incidence of hollow heart/brown center. Blackspot bruise expression for Palisade Russet is less pronounced than for either Ranger Russet or Russet Burbank, however it is slightly more susceptible to shatter bruise. Palisade Russet was released in 2011 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.

Effects of postharvest sodium silicate treatment on pink rot disease and oxidative stress-antioxidative system in muskmelon fruit

Sodium silicate (Si) at 100 mM was used as a postharvest treatment agent of induction resistance on muskmelon (Cucumis melon L. cv. Yindi) to investigate the mechanism of controlling pink rot disease, which caused by Trichothecium roseum. Si treatment significantly reduced (P < 0.05) the lesion diameter of melons inoculated with T. roseum during storage. Si treatment increased the content of superoxide (O2•−) and could be further raised by challenged with T. roseum inoculation. The content of hydroxyl radical (·OH) in inoculated fruit was also increased. Both malondialdehyde (MDA) and hydrogen peroxide (H2O2) were also accumulated with Si treatment and challenged inoculation. Si treatment maintained membrane integrity in non-inoculated fruit, as compared to untreated control. Si treatment and challenge inoculation significantly (P < 0.05) increased the activity of superoxide dismutase (SOD), glutathione reductase (GR), peroxidase (POD), and polyphenoloxidase (PPO), while markedly decreased the activity of catalase (CAT) and ascorbic peroxidase (APX). Si treatment and challenge inoculation also enhanced the content of ascorbic acid (ASA) and glutathione (GSH). These findings suggested that the effects of sodium silicate on postharvest disease in muskmelon fruit may be associated with the elicitation of antioxidant defense system in fruit.

Effect of Application Method and Rate on Residual Efficacy of Mefenoxam and Phosphorous Acid Fungicides in the Control of Pink Rot of Potato.

Experiments were conducted to examine the effectiveness of rate and method of phosphorous acid application for controlling pink rot of potato (Solanum tuberosum) caused by Phytophthora erythroseptica. Replicated small-plot and replicated split commercial field trials were established in commercial production fields in Minnesota from 2006 to 2009. Fungicides were applied in-furrow at planting, or as one, two, or three foliar applications via ground sprayer, irrigation system (chemigation), or fixed-wing aircraft. Phosphorous acid efficacy was compared to mefenoxam, the fungicide commonly utilized to manage pink rot, either by determining natural infections in the field or by inoculating eyes of harvested tubers using a mefenoxam-sensitive and -resistant isolate of P. erythroseptica via postharvest challenge inoculation. In replicated small plot trials, both in-furrow and two foliar applications of mefenoxam controlled tuber rot in the field, and significantly controlled tuber rot in storage. Phosphorous acid also reduced tuber rot in the field when applied two or three times to the foliage. Although phosphorous acid was ineffective when applied in-furrow, one, two, and three foliar applications and a postharvest application of phosphorous acid controlled mefenoxam-sensitive and -resistant isolates of P. erythroseptica during storage for 187 days, while mefenoxam failed to control the resistant isolate. In replicated split commercial field trials, two aerial applications of phosphorous acid were as effective as three applications in reducing pink rot incidence in tubers inoculated postharvest. Three aerial applications were as effective as three chemigation applications in replicated split commercial field trials in 2008, but provided significantly greater protection than chemigation in 2009.

Competitive Parasitic Fitness of Mefenoxam-Sensitive and -Resistant Isolates of Phytophthora erythroseptica under Fungicide Selection Pressure.

A 2-year field and laboratory experiment was initiated to study the competitive parasitic fitness of mefenoxam-resistant (50% effective concentration [EC50] > 100 μg ml-1) and mefenoxam-sensitive (EC50 = 0.07 μg ml-1) isolates of Phytophthora erythroseptica with equal aggressiveness. The competitive ability of the mefenoxam-resistant and -sensitive isolates was tested under no selection pressure (nonfungicide treated) as well as under the influence of mefenoxam and non-mefenoxam (phosphorous acid) fungicides. P. erythroseptica isolates were combined in four ratios of mefenoxam-resistant (R) to mefenoxam-susceptible (S) (0R:0S, 1R:1S, 3R:1S, and 1R:3S) and subsequently infested into the soil at the time of planting. In-furrow mefenoxam applications were applied to the soil immediately following infestation with P. erythroseptica. Phosphorous acid was applied at tuber initiation and 14 days after tuber initiation. Noninfested, nonfungicide-treated plots served as controls. P. erythroseptica isolates recovered from field-infected pink rot tubers at harvest and 3 to 4 weeks after harvest were tested for mefenoxam sensitivity in vitro. In vivo studies were performed by challenge inoculating a zoospore suspension in the four ratios described above onto potato tubers harvested from nontreated, phosphorous acid-treated, or mefenoxam-treated field plots. These field plots were not infested with P. erythroseptica at planting. Results from both field and in vivo studies demonstrate that mefenoxam-resistant isolates of P. erythroseptica are as fit as sensitive isolates in the absence of selection pressure or in the presence of a phosphorous acid fungicide treatment. Under mefenoxam selection pressure, mefenoxam-resistant P. erythroseptica isolates were more parasitically fit than -sensitive isolates. These studies suggest the lack of an apparent fitness penalty in mefenoxam-resistant P. erythroseptica populations under field conditions and that these isolates could be stable in most agroecological systems. Based on these results, mefenoxam-based fungicides are no longer recommended for the management of pink rot once mefenoxam-resistant P. erythroseptica populations are detected in a specific field.

Selection of Biocontrol Agents of Pink Rot Based on Efficacy and Growth Kinetics Index Rankings.

The microbiota of 84 different agricultural soils were transferred to separate samples of a γ irradiation-sterilized field soil enriched with potato periderm, and the resulting soils were assayed for biological suppressiveness to Phytophthora erythroseptica and their effect on zoospore production. The 13 most suppressive soil samples, which reduced zoospore production by 14 to 93% and disease severity on tubers by 6 to 21%, were used to isolate 279 organisms. Fourteen strains that reduce pink rot infections in preliminary tests were selected for further study. Six bacterial strains that reduced the severity of disease (P ≤ 0.05, Fischer's protected least significant difference) in subsequent tests were identified as Bacillus simplex (three strains), Pantoea agglomerans, Pseudomonas koreensis, and P. lini. Relative performance indices (RPIs) for biocontrol efficacy and for each of four kinetic parameters, including total colony-forming units (CFUmax), biomass production values (DWmax), cell production after 8 h (OD8), and time of recovery from oxygen depletion (DT) were calculated for each strain. Overall RPIEff,Kin values for each strain then were calculated using strain RPI values for both efficacy (RPIEff) and kinetics (RPIKin). Strains with the highest RPIEff,Kin possess the best biocontrol efficacy of the strains tested and liquid culture growth characteristics that suggest commercial development potential.

ANTIFUNGAL ACTIVITY OF SODIUM SILICATE ON TRICHOTHECIUM ROSEUM IN VITRO

Pink rot caused by Trichotethium roseum is one of the most important postharvest pathogens of muskmelon in China. In this paper, the effect of Si on growth and histolology of T. roseum was studied in vitro. The results indicated that Si significantly inhibited mycelial growth and spores germination, increased cell membrane permeability of hyphal. The inhibiting effect was enhanced with the concentration of Si increasing. Some morphological changes were observed by scanning electron microscopy (SEM) including intertwisting hyphal, distortion and swelling. Ultrastructural alterations of hyphae were also observed using transmission electron microscopy (TEM). The changes involved increasing of vacuoles in the cell, cell organelle dissolved, cell membrane crimple, considerable thickening of the hyphal cell walls and cell wall disruption. It is suggested that Si directly inhibits growth of T. roseum by changing the morphology of mycelium.

Prevalence of Mefenoxam Resistance Among Phytophthora erythroseptica Pethybridge Isolates in Minnesota and North Dakota

In an 8 year survey of Minnesota potato fields, a total of 1,772 isolates of Phytophthora erythroseptica were collected from potato tubers showing symptoms of pink rot. All isolates were evaluated for sensitivity to the systemic fungicide mefenoxam and categorized as mefenoxam-sensitive, -intermediate or -resistant. A significant yearly increase was observed in the frequency of mefenoxam-resistant P. erythroseptica isolates recovered and in the frequency of fields from which mefenoxam-resistant isolates originated. Additionally, isolates with intermediate levels of mefenoxam resistance were recovered in each year of the survey. In a similar survey, greater than 80% of P. erythroseptica isolates recovered were mefenoxam-sensitive among 293 total isolates collected over 3 years in North Dakota, and no P. erythroseptica isolates with intermediate resistance to mefenoxam were recovered. Results reported here confirm the presence of mefenoxam resistance among isolates of P. erythroseptica in Minnesota and North Dakota but at varying levels among years of the survey in both states. The presence of P. erythroseptica isolates with intermediate levels of resistance to mefenoxam collected in Minnesota support earlier studies which indicate that isolates displaying intermediate responses to mefenoxam are indicative of a transitional flux from a mefenoxam-sensitive to a mefenoxam-resistant population.

Erratum to: Freedom Russet—A Dual Purpose Russet Potato Cultivar with Resistance to Common Scab and Good Fry Quality

Freedom Russet was developed from a cross between ND14-1, a parent with scab resistance, and W1005rus, a parent with good processing quality. It is a mid-season cultivar and can be used for dual purposes for both fresh market and processing. The tubers of Freedom Russet are oblong-long with medium-dark russet skin, and have an attractive appearance. Freedom Russet tubers have better external and internal qualities than Russet Burbank tubers. The total and US No. 1 yield of Freedom Russet is equal to or higher than Russet Burbank in most environments. The specific gravity of Freedom Russet is similar or 1–3 unit less than Russet Burbank. Freedom Russet produced better fry color than Russet Burbank when processed after storage at 10, 8.9, and 7.2°C. It showed similar susceptibility to both early blight and late blight compared to Russet Burbank. Freedom Russet is resistant to common scab and moderately resistant to powdery scab. It is similarly susceptible to soft rot and pink rot as Russet Burbank, and clearly expresses bacterial ring rot symptoms. Freedom Russet is tolerant to Verticillium wilt and showed better yield potential than Russet Burbank under early dying pressure.

Phylogenetic relationship of Phytophthora cryptogea Pethybr. & Laff and P. drechsleri Tucker

The phylogeny and taxonomy of Phytophthora cryptogea and Phytophthora drechsleri has long been a matter of controversy. To re-evaluate this, a worldwide collection of 117 isolates assigned to either P. cryptogea, P. drechsleri or their sister taxon, Phytophthora erythroseptica were assessed for morphological, physiological (pathological, cultural, temperature relations, mating) and molecular traits. Multiple gene phylogenetic analysis was performed on DNA sequences of nuclear (internal transcribed spacers (ITS), ß-tubulin, translation elongation factor 1α, elicitin) and mitochondrial (cytochrome c oxidase subunit I) genes. Congruence was observed between the different phylogenetic data sets and established that P. drechsleri and P. cryptogea are distinct species. Isolates of P. drechsleri form a monophyletic grouping with low levels of intraspecific diversity whereas P. cryptogea is more variable. Three distinct phylogenetic groups were noted within P. cryptogea with an intermediate group providing strong evidence for introgression of previously isolated lineages. This evidence suggests that P. cryptogea is an operational taxonomic unit and should remain a single species. Of all the morphological and physiological traits only growth rate at higher temperatures reliably discriminated isolates of P. drechsleri and P. cryptogea. As a homothallic taxon, P. erythroseptica, considered the cause of potato pink rot, is clearly different in mating behaviour from the other two species. Pathogenicity, however, was not a reliable characteristic as all isolates of the three species formed pink rot in potato tubers. The phylogenetic evidence suggests P. erythroseptica has evolved from P. cryptogea more recently than the split from the most recent common ancestor of all three species. However, more data and more isolates of authentic P. erythroseptica are needed to fully evaluate the taxonomic position of this species.

Multi-strain co-cultures surpass blends for broad spectrum biological control of maladies of potatoes in storage

Pseudomonas fluorescens strains S11:P:12, P22:Y:05, and S22:T:04 and Enterobacter cloacae strain S11:T:07 have been documented to suppress four important storage potato maladies – dry rot, late blight, pink rot, and sprouting. This research investigates the efficacy and consistency of strain mixtures produced by co-culturing strains together in one vessel or by blending them together after separate cultivations in pure cultures. Pure and co-cultures were produced in flask or fermentor cultures, viable cell concentrations were assessed using a nutrient-based selective plating method to identify and enumerate strains, and the efficacy of treatments was assessed with respect to dry rot, pink rot, late blight or sprout suppression. Experiments were designed to analyze dry rot suppression versus all strain combinations and the combination method (co-culture or blend). Results of a two-way analysis of variance of disease with strain composition and combination method showed that significantly better dry rot suppression was obtained by co-cultures (30.3±2.4% relative disease) than by similar strain blends of pure cultures (41.3±2.4%) (P<0.001). During a 3-year study, both biocontrol efficacy and consistency were assessed in 16 laboratory and small pilot trials simulating commercial storages. Three-strain co-culture had a lower mean disease rating than the blend in 9 of 16 experiments examining control of the three diseases and sprouting. The co-culture led other treatments in incidences of significant malady reduction relative to the control: 14 of 16 attempts for co-culture, 11 of 16 attempts for blend, 10 of 13 attempts for pure S11:P:12, 8 of 13 attempts for S22:T:04, and 9 of 13 attempts for P22:Y:05. Using relative performance indices to rank treatment performance across all experiments, the co-culture treatment ranked significantly higher than the blend. A synergy analysis suggested that co-culturing strains stimulated inter-strain activities to boost biocontrol efficacy and consistency, a feature not developed in strains grown separately and mixed just prior to addition to potatoes.

Polysaccharide production benefits dry storage survival of the biocontrol agent Pseudomonas fluorescens S11:P:12 effective against several maladies of stored potatoes

Pseudomonas fluorescens S11:P:12 (NRRL B-21133) is a biological control agent able to suppress several potato diseases and sprouting. Notably, it produces a polysaccharide during liquid cultivation, and the objective of this work was to determine the role of this material in the bio-control process. First, the polysaccharide was isolated, purified and identified as marginalan, which accumulated to ~3.3 g/L in cultures. The bioactivity of isolated marginalan applied alone or in combination with washed cells of strain S11:P:12 was tested in potato bioassays of dry rot and pink rot suppressiveness and sprout inhibition. Since the formulation and storage of a dried biocontrol product is preferred for commercial use, the impact of marginalan on cell survival during drying and storage was also studied. Washed bacteria formulated with 0–6.6 g/L polysaccharide were either applied to Hyflo granules, then slowly dried for 24 h with airflow at 50–60% relative humidity, or in 1-µL droplets placed in replicate wells of a micro-plate, then quickly dried for 1 h in a biohazard hood. Both Hyflo and micro-plate dry storage results indicated that marginalan significantly reduced cell death after drying, such that the final stable viable cell density was 2.5–5 orders of magnitude greater, respectively, than if no marginalan were included with cells. Marginalan had no significant impact on disease or sprout suppression by strain S11:P:12, and its main benefit to biocontrol was viable cell preservation during drying and storage. When marginalan was formulated with other selected P. fluorescens strains, its benefits to drying and storage survival were again evident (especially after 4°C instead of 25°C storage), but its effects were more subtle than for strain S11:P:12, and dry rot suppression was not impacted.

Phytophthora erythroseptica (Pink Rot) Development in Russet Norkotah Potato Grown in Buffered Hydroponic Solutions II. pH Effects

Pink rot caused by the pathogen Phytophthora erythroseptica Pethyb. causes severe pre- and post-harvest losses in potato. Severe losses of potato from pink rot infection suggest the need for better information on cultural factors associated with disease development. Soil pH has been regarded as a strong influence on disease development as observed by previous studies and by commercial potato growers. A hydroponic growth system was established to study the effects of pH on P. erythroseptica infection and colonization in Russet Norkotah potato roots. Russet Norkotah plantlets were grown in hydroponic nutrient solutions buffered at pH 5, 6, 7, and 8 and evaluated for infection by means of quantitative Real Time PCR. Acidic pH solutions produced a higher proportion of pathogen to host DNA in root tissue, indicating increased infection and colonization at low pH. Thus, pH has a unique and significant influence on the levels of infection from P. erythroseptica and that commercially grown potatoes would likely develop reduced tuber rot if grown in soils with pH at or above 7.

Phytophthora erythroseptica (Pink Rot) Development in Russet Norkotah Potato Grown in Buffered Hydroponic Solutions I. Calcium Nutrition Effects

Phytophthora erythroseptica Pethyb. causes a disease known as pink rot in potatoes, which is responsible for substantial pre and post harvest tuber loss. Disease outbreaks are associated with excessive soil moisture, moderate temperature, late season development, and a lack of potato cultivar resistance. Because disease resistance is becoming less effective, understanding other potential solutions is critical. Mineral nutrition of plants is known to be associated with disease development and severity of many diseases, but is not generally considered in relation to outbreaks of pink rot. Calcium (Ca) is essential and considered one of the most important nutrients associated with plant defense, but it has not been studied or consequently linked to the severity of pink rot in potato. A hydroponic growth system was established to study the effects of calcium on P. erythroseptica infection and colonization in Russet Norkotah potato roots. Russet Norkotah potatoes were grown with 3, 86, 172, and 343 mg L−1 Ca in association with the pathogen. The degree of disease severity was assessed by means of quantitative real time polymerase chain reaction (RT PCR). The suppression of infection and disease severity by increased available Ca was statistically significant, decreasing with each increment of Ca between 3 and 343 mg L−1. These data provide strong evidence that Ca nutrition is important in disease suppression and that the amount of available soil Ca can affect plant health and the ability of P. erythroseptica to infect the host.

Highland Russet: A Full Season, Processing Variety with High Yields of Uniform U.S. No. 1 Tubers

Highland Russet is a late-season potato variety with light russet skin notable for its high yield of uniform U.S. No. 1 tubers, and good processing and culinary qualities. It resulted from a 1990 cross between Ranger Russet and Russet Legend and has been evaluated for over 15 years in public and industry trials throughout the western U.S. Highland Russet was released in 2006 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon and Washington and is a product of the Northwest Potato Variety (Tri-State) Development Program. It is suitable for processing into French fries and other frozen potato products and due to its large blocky shape, recovers a high proportion of fries per unit weight of tubers. Fry color and processing ratings for Highland Russet were similar to Ranger Russet and Russet Burbank but fry color uniformity was higher than either of the standard varieties. In full-season trials conducted over a three-year period in the states of Idaho, Oregon, Washington, Colorado, and California; Highland Russet averaged 7% and 9% higher total yields and 21% and 52% higher U.S. No. 1 yields than Ranger Russet and Russet Burbank, respectively. It has moderately high specific gravity, with values similar to Ranger Russet and higher than Russet Burbank. Highland Russet is moderately resistant to Verticillium wilt and powdery scab root galling, as well as to tuber infections of late blight. It is also moderately resistant to common strains of potato virus Y (PVYO) but is susceptible to PVYNTN. It is moderately susceptible to pink rot, common scab, powdery scab of the tuber and early blight of the tuber, as well as to Pectobacterium soft rot and Fusarium dry rot. Highland Russet is susceptible to foliar late blight, PLRV infection, Root-knot nematode and corky ringspot but is moderately resistant to PLRV net necrosis. The incidence of hollow heart in Highland Russet is low, similar to that of Ranger Russet and lower than Russet Burbank, Blackspot bruise reaction of Highland Russet is similar to Russet Burbank but it is less susceptible to shatter bruise.

Bacterial Antagonists, Zoospore Inoculum Retention Time and Potato Cultivar Influence Pink Rot Disease Development

Zoospores or germinating encysted zoospores of the pathogen Phytophthora erythroseptica can cause new infections via tuber eyes, lenticels and cracks and cuts that result from tuber harvesting operations; infection courts that theoretically could be protected using microbial antagonists. Ten microbial antagonists that reduce Fusarium dry rot, late blight and/or sprouting in storage were assayed for efficacy against pink rot on tubers of cultivars Russet Burbank and Russet Norkotah. Antagonist strains were grown in a semidefined liquid medium at 25°C for 48 h, diluted to a concentration of approximately 3 × 108 cfu/ml, individually combined with zoospores of P. erythroseptica, and the mixed microbial suspension was used to inoculate shallow puncture wounds on tubers. Data from full factorial experimental designs with ten levels of antagonist, two levels of cultivar, and two levels of inoculum age after inducing zoospore liberation from sporangia indicated that all factors influenced the size of pink rot lesions that developed internally around wound sites (P ≤ 0.05). In two different sets of experiments, Enterobacter cloacae strain S11:T:07 reduced lesion size more than the other antagonists (19% and 32% reduction versus the control) though Pseudomonas fluorescens bv. V S11:P:14, Pseudomonas sp. S22:T:04, and Enterobacter sp S11:P:08 also significantly reduced disease. Lesion size was greater on Russet Norkotah than Russet Burbank tubers (42.3 and 26.5 mm, respectively), but cultivar did not influence antagonist performance. Significantly, zoospore inoculum of the pathogen incited smaller lesions in the early stages of individual bioassays than occurred later in bioassays when most zoospores had encysted. The implications of inoculum potential changing over the course of conducting bioassay experiments on pink rot are discussed.

Dakota Diamond: An Exceptionally High Yielding, Cold Chipping Potato Cultivar with Long-Term Storage Potential

‘Dakota Diamond’, evaluated as ND5822C-7, is a medium to late-maturing cultivar with uniformly sized tubers and very high yield potential. It resulted from the cross of ND4103-2 and ‘Dakota Pearl’. Dakota Diamond is comprised of approximately 23.3% wild potato species germplasm. It combines the characteristics of several species, including Solanum tuberosum L. subsp. andigena Juz. and Bukasov, S. demissum Lindl., S. phureja Juz. and Bukasov, and purportedly, S. chacoense Bitter. Haulms are vigorous and large. Tubers are smooth and round, with bright white skin and white flesh. Dakota Diamond is suitable for the cold chip and fresh tablestock markets, both directly from the field and following storage at 7.2°C. Yield potential under both non-irrigated and irrigated conditions in North Dakota and Minnesota is very high, with total yield, US no. 1 yield, and percent US no. 1 tubers of Dakota Diamond superior to those of ‘Atlantic’ and Dakota Pearl, commercially acceptable chip cultivars. Mean yields for Dakota Diamond across these sites is 40.8 t ha−1. It is widely adapted based upon performance in the North Central Regional Potato Variety Trials and Snack Food Association/US Potato Board Trials. Dakota Diamond sets tubers slightly later than other commercially acceptable chip cultivars, but tubers size quickly. Dakota Diamond demonstrates resistance to common scab (Streptomyces scabies Thaxter) and to pink rot (Phytophthora erythroseptica Pethyb.), and preferential avoidance by Colorado potato beetle (Leptinotarsa decemlineata Say) in pest resistance screening evaluations. Dakota Diamond demonstrates resistance to most internal and external defects. It is susceptible to hollow heart, however, particularly in tubers over 283 g. Dakota Diamond expresses typical symptoms of PVYo. However, infection by PVYn and PVYn:o recombinant genotypes is difficult to detect visually. The specific gravity of Dakota Diamond is high, averaging 1.095 across irrigated and non-irrigated sites in North Dakota and Minnesota. Chip color reaches its optimal, and sugar levels reach their minimum in late January to early February when produced in northern locales, maintaining chip quality parameters throughout the late storage market window. Dakota Diamond is aptly named for its excellent attributes, including beautiful appearance, excellent chip quality particularly from late season storage, resistance to common scab, and exceptionally high yield potential, and in honor of the Diamond Jubilee, the 75th anniversary of the North Dakota State University potato breeding program as part of the North Dakota Agricultural Experiment Station. Dakota Diamond was released by the North Dakota Agricultural Experiment Station on 1 December 2005.

A Foliar Blight and Tuber Rot of Potato Caused by Phytophthora nicotianae: New Occurrences and Characterization of Isolates.

Phytophthora spp. are pathogenic to many plant species worldwide, and late blight, caused by Phytophthora infestans, and pink rot, caused by P. erythroseptica, are two important diseases of potato. Another Phytophthora sp., P. nicotianae, was recovered from pink-rot-symptomatic tubers collected from commercial fields in Nebraska, Florida, and Missouri in 2005, 2006, and 2007, respectively. P. nicotianae also was recovered from foliage obtained from commercial potato fields in Nebraska and Texas exhibiting symptoms very similar to those of late blight. Isolates of P. cactorum also were recovered from foliar infections in a commercial potato field in Minnesota in 2005. Natural infection of potato foliage by P. cactorum and infection of wounded potato tuber tissue via inoculation with zoospores of P. capsici are reported here for the first time. Isolates of P. nicotianae, regardless of origin, were primarily of the A1 mating type. All isolates of P. nicotianae and P. cactorum were sensitive to the fungicide mefenoxam. Optimum growth of P. nicotianae, P. erythroseptica, and P. cactorum in vitro occurred at 25°C; however, only P. nicotianae sustained growth at 35°C. Regardless of the tissue of origin, all isolates of P. nicotianae and P. cactorum were capable of infecting potato tubers and leaves. However, isolates of P. nicotianae were less aggressive than P. erythroseptica isolates only when tubers were not wounded prior to inoculation. Pink rot incidence varied significantly among potato cultivars following inoculation of nonwounded tubers with zoospores of P. nicotianae, ranging from 51% in Red Norland to 19% in Atlantic. Phytophthora spp. also differed significantly in their ability to infect potato leaves. Highest infection frequencies were obtained with P. infestans and levels of infection varied significantly among P. nicotianae isolates. The rate of foliar lesion expansion was similar among isolates of P. nicotianae and P. infestans. Whereas P. infestans infections yielded profuse sporulation, no sporulation was observed with foliar infections of P. nicotianae.

Susceptibility of eight potato cultivars to tuber infection by Phytophthora erythroseptica and Pythium ultimum and its relationship to mefenoxam‐mediated control of pink rot and leak

AbstractIn addition to cultural practices, the application of the fungicide mefenoxam is an important disease management tactic used to control both pink rot and leak on potato tubers grown in the USA. Mefenoxam resistance has been identified in many of the potato growing regions, and therefore resistance management strategies are very important for retaining this fungicide as a tool to manage these storage rot diseases. The relationship between mefenoxam efficacy and cultivar susceptibility to pink rot and leak was assessed in post‐harvest inoculation studies. Mefenoxam was applied to potato (Solanum tuberosum) cultivars known to express varying levels of susceptibility to pink rot and leak caused by Phytophthora erythroseptica and Pythium ultimum, respectfully. Tubers harvested from plants treated with in‐furrow and foliar applications of mefenoxam were inoculated with isolates sensitive to the fungicide. Incidence and severity of both diseases ranged widely among cultivars. Russet Norkotah was the most susceptible to infection by P. erythroseptica, while cvs Pike and Atlantic were the most resistant. Cultivars Dark Red Norland, Russet Norkotah, Goldrush and Russet Burbank were most susceptible to infection by P. ultimum whereas Snowden was most resistant. Control of pink rot differed significantly among cultivars following mefenoxam treatment, ranging from 28% (cv. Goldrush) to 67% (cv. Snowden) and generally provided the greatest level of disease control on susceptible and moderately susceptible cultivars such as Russet Norkotah and Snowden, respectively. In contrast, the impact of mefenoxam on leak development was minimal and disease control did not differ significantly among the cultivars. The fungicide failed to control leak in the susceptible cvs Atlantic and Pike and control ranged from 1.7% to 5.2% in cvs Goldrush, Russet Norkotah, Dark Red Norland, Russet Burbank and Kennebec. The greatest level of leak control was achieved with the moderately resistant cv., Snowden, at 12.7%. Cultivars most likely to benefit from mefenoxam treatments should be targeted as part of a pink rot management programme. Judicious use of the fungicide, when matched with the level of cultivar susceptibility, may prove to be an efficient and effective approach to reduce infection rates and possibly manage mefenoxam resistance thereby maintaining longevity of the compound.

Blazer russet: An early to Mid-Season potato cultivar with high U.S. no. 1 yields and good processing and culinary qualities

‘Blazer Russet’ is an early to mid-season cultivar notable for its high U.S. No. 1 yield of medium-russeted tubers and its good processing and culinary qualities. It was derived from the cross A7816-14 x ‘NorKing Russet’ and was released in 2005 by the USDA-ARS and the Agricultural Experiment Stations of Idaho, Oregon and Washington. Blazer Russet is very suitable for processing into French fries and other frozen potato products directly from the field or from extended storage, with higher merit scores than ‘Russet Burbank’ and ‘Ranger Russet’ in processing and post-harvest evaluations. Blazer Russet also has high merit for use in the fresh market, with sensory evaluations comparable to those of Russet Burbank. Total yields for Blazer Russet at five early harvest trial locations in the western United States were 12% greater than either ‘Russet Norkotah’ or ‘Shepody’, while U.S. No. 1 yields were 12% greater than Russet Norkotah and 35% greater than Shepody. Specific gravities of Blazer Russet tubers were comparable to tubers of Shepody, and higher than those of Russet Norkotah in early harvest trials. In full-season trials in the western United States, total yields for Blazer Rus set were slightly lower than Ranger Russet and slightly higher than Russet Burbank, but U.S. No. 1 yields were 8% greater than Ranger Russet and 38% greater than Russet Burbank. In these full-season trials, tuber specific gravity of Blazer Russet was similar to Russet Burbank, but lower than Ranger Russet. Blazer Russet is resistant to sugar ends, tuber malformations and most internal and external defects, the exception being its moderate susceptibility to hollow heart. Blazer Russet is resistant to common scab, tuber powdery scab and PVX, and has moderate resistance to blackspot bruise and tuber late blight infections. It is moderately susceptible to powdery scab root galling, PVY0, early blight infection of the tuber, Erwinia soft rot and Fusarium dry rot. Blazer Russet is susceptible to Verticillium wilt, pink rot, PLRV net necrosis, corky ringspot, and foliar early blight and late blight.