Russet Norkotah Research Articles

Gibberellic Acid and Ethephon Alter Potato Minituber Bud Dormancy and Improve Seed Tuber Yield

While greenhouse production of minitubers has markedly improved production of disease free seed, minituber dormancy can be an issue. This study tested application of abscisic acid (ABA), ethylene (E), gibberellic acid (GA) and the combination of E+GA on release of dormancy in potato minitubers, sprout development, and subsequent effects on field plant growth and yield of seed tubers. Cultivars were categorized on the basis of known dormancy responses as follows: (1) one short dormancy cultivar, Silverton Russet, (2) three intermediate dormancy cultivars, Russet Norkotah (RNK), Sangre S-14 and Desiree, and (3) two long dormancy cultivars, Nooksack and Russet Norkotah Selection 3 (RNK-S3). Eighty eight to 93% of E+GA treated minitubers from cultivars in the long dormancy group developed sprouts signaling the end of dormancy within 5 weeks, while the control and ABA treated minitubers were totally dormant with 0% bud break. With the intermediate cultivars E+GA treated minitubers had 100% bud break compared to 37 to 55% bud break in the control minitubers. Treated long dormant minitubers also had 2.1 to 2.5 more sprouts per minituber and 1.6 to 2.4 cm longer sprouts. E+GA treated minitubers planted in field plot trials produced mature plants that were 19 to 36 cm per plant taller, with up to 3.9 to 8.8 more seed tubers per plant, and 1.9 to 4.2 kg per plot higher yields. The laboratory protocol developed to predict dormancy breaking attributes provided a reasonable estimate of cultivar dormancy under field conditions.

Potato virus Y: An Evolving Concern for Potato Crops in the United States and Canada.

North American potato production differs from other geographical regions such as Europe in that it is essentially a closed system, i.e., seed potatoes are not imported and production is dominated by only a few cultivars. The lack of significant seed imports provides a mechanism for seed certification to be extremely effective at minimizing virus levels in seed lots, especially if the changes in seed laws, postharvest testing, and tolerance limits discussed above are adopted. This is an opportunity to effectively manage PVY at levels that are at or below detection and well below economic significance. Aiding the seed certification programs in the adoption of the Canada/US-Management Plan for Potato Viruses that Cause Tuber Necrosis has and continues to build consensus and cooperation within the industry to reform and modernize seed certification practices and, as importantly, modernize best management practices that growers can implement so that their production meets or exceeds virus tolerances set within the seed certification standards. Seed inspectors could also benefit from continually updated information from the research community to help them better recognize the spectrum of symptoms caused by the various strains and variants of PVY in all the different cultivars now being grown in their states and provinces. They could also benefit from improved field diagnostics that will assist them and the growers in identifying problem plants that should be rogued. If PVY levels in seed can be minimized and on-farm management strategies can be optimized, then PVY incidence in the potato crop will be marginalized. The restricted distribution of the tuber necrotic strains also offers an opportunity to prevent these strains from becoming economically significant if appropriate testing of seed lots in those areas could prevent them from being planted. Shipping point inspections of tubers will also help in identifying and eliminating tuber necrotic viruses. The dominance of a few cultivars has been eroding in recent years. Russet Burbank, a cultivar introduced over 100 years ago, still accounts for 40 to 50% of the U.S. acreage, but acreage in the Northwestern United States has been declining steadily as other russet cultivars come on the market and gain acceptance. Potato cultivar has had a significant impact on the PVY problem, as with the release and widespread acceptance of Shepody, Russet Norkotah, and other asymptomatic carriers of PVY (http://oregonstate. edu/potatoes/latenttoPVYlist.htm), which in 2008 comprised more than 15 and 12% of the total U.S. and Canadian seed acreage, respectively. These cultivars have certainly contributed to the overall increase in PVY in the seed potato crop and by extension the commercial potato crop. The increased diversity of potato cultivars grown in both countries has also introduced a wider spectrum of PVY symptoms, most notably the milder symptoms that are characteristic of the PVYN/NTN and PVYN-Wi strains on many cultivars. Since the success of seed certification is dependent upon visual assessment of the crop, mild or absent symptoms means that many more infected plants go unnoticed. The more symptomatic PVYO strains are observed and removed, but the other strains remain in the crop and are passed along in the seed, contributing to an overall increase in PVY incidence and more importantly to a shift in PVY strain composition. The U.S. and Canadian potato industry stakeholders are increasingly aware of the PVY-associated challenges and have been moving rapidly to work with researchers and all aspects of the industry to implement plans to suppress PVY incidence. Continued education of growers, seed certification officials, and researchers alike, coupled with the development and adoption of new or revised best management practices and diagnostic tools, and the renewed inter est of breeders to develop virus resistant cultivars, will be the keys to success in bringing PVY incidence under control and in minimizing tuber necrotic strains.

Planting System Effect on Yield Response of Russet Norkotah to Irrigation and Nitrogen under High Intensity Sprinkler Irrigation

Conversion of potato ridged-row planting systems to wide bed planting systems may increase water and nitrogen use efficiency in commercial irrigated potato production systems by reducing the amount of irrigation water and water applied nitrogen fertilizer bypassing the potato root zone. Wide bed planting systems consist of planting multiple rows on a wide bed with 20 to 35% higher plant population than found in conventional ridged-row planting systems. The objective of this study was to evaluate the effect planting system has on yield response of ‘Russet Norkotah’ potato to irrigation and nitrogen. Planting systems evaluated were (1) conventional ridged-row with dammer-diking; (2) 3.7 m wide bed with five potato rows spaced 66 cm between adjacent rows centered on the bed and; (3) 3.7 m wide bed with seven potato rows spaced 46 cm between adjacent rows. Six irrigation amounts, 50, 70, 85, 100, 115, and 130%, of estimated evapotranspiration after tuber initiation and four nitrogen rates, <20, 50, 100, and 150%, of conventional recommendations were applied to the three planting systems. Interactions between irrigation amounts and nitrogen rate were significant for total and U.S. No. 1 yield, irrigation water use efficiency, and gross return in one or both study years. Interactions between nitrogen rate and planting system were significant for total and U.S. No. 1 yield, irrigation water use efficiency and gross return in the first year of the study. Interactions between irrigation amount and planting system were not significant. In the first study year, total and U.S. No. 1 yields were significantly increased 12 and 19 percent, respectively, under the 7-row bed planting system compared to ridged-row planting system. Comparison of ridged-row planting system and 5-row bed planting system on 31 commercial potato fields in eastern Idaho representing a combined area of 2,800 ha over 5 years resulted in significantly higher total yield and irrigation water use efficiency with the bed planting system. The 5-row bed planting system averaged 6% higher total yield, 5% less water application and an 11% increase in irrigation water use efficiency. The results of this study demonstrate that under high intensity rate sprinkler irrigation in the soil and climatic conditions prevalent in eastern Idaho, bed planting systems provide viable production alternatives for irrigated potato production that may increase total yield, gross return, and irrigation water use efficiency.

Reducing Tuber Damage by Potato Tuberworm (Lepidoptera: Gelechiidae) With Cultural Practices and Insecticides

Cultural practices and insecticide treatments and combinations were evaluated for effect on tuber damage by potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) in the Columbia basin of eastern Oregon and Washington. A range of intervals between initial application of several insecticides and vine-kill were tested to determine how early to implement a program to control potato tuberworm tuber damage. Esfenvalerate, methamidophos, and methomyl were applied at recommended intervals, with programs beginning from 28 to 5 d before vine-kill. All insecticide treatments significantly reduced tuber damage compared with the untreated control, but there was no apparent advantage to beginning control efforts earlier than later in the season. Esfenvalerate and indoxacarb at two rates and a combination of the two insecticides were applied weekly beginning 4 wk before and at vine-kill, and indoxacarb was applied at and 1 wk postvine-kill as chemigation treatments. Application of insecticides at and after vine-kill also reduced tuberworm infestation. 'Russet Norkotah' and 'Russet Burbank' plants were allowed to naturally senesce or were chemically defoliated. They received either no irrigation or were irrigated by center-pivot with 0.25 cm water daily from vine-kill until harvest 2 wk later. Daily irrigation after vine-kill reduced tuber damage, and chemical vine-kill tended to reduce tuber damage compared with natural senescence. Covering hills with soil provides good protection but must be done by vine-kill. Data from these trials indicate that the most critical time for initiation of control methods is immediately before and at vine-kill.

Evaluation of Verticillium Wilt Resistance in Russet Norkotah and Six Strain Selections

Strain selections of Russet Norkotah have been selected for enhanced vigor and high yield. In addition, they exhibit less severe expression of disease symptoms in the presence of Verticillium dahliae, a soil-borne fungal pathogen that causes Verticillium wilt. However, this apparent resistance may be due to later maturity in the strain selections. This study was designed to compare the levels of Verticillium wilt resistance in Russet Norkotah with that of six popular strain selections. In two years, trials were carried out on a V. dahliae-infested field and an adjacent fumigated field. Comparisons were made between Russet Norkotah and its strains for maturity, symptom expression, stem colonization, and tuber yield. Compared to Russet Norkotah, the strains were later in maturity, exhibited fewer Verticillium wilt symptoms, and were higher yielding in the absence of V. dahliae. However, they were similar to Russet Norkotah in stem colonization and yield in the presence of the pathogen. Apparent resistance in the strain selections appears to be due to immature plant physiology rather than their ability to limit fungal growth and reproduction in stem tissues.

Sprout Suppressing Residue Levels of 1,4dimethylnaphthalene (1,4DMN) in Potato Cultivars

Research on new sprout control methods led to the discovery of 1,4dimethylnaphthalene (1,4DMN) in the late 1970s. This compound has been registered in the USA since 1996 as a reduced risk chemical for use on stored potatoes for the purpose of sprout suppression. Relatively little is known about the levels of tuber residues required to maintain sprout suppression. The objective of this study was to identify the minimum 1,4DMN tuber residue levels above which sprout growth was inhibited. Using modified steel drums to store and treat potatoes, rates of 0 µL kg−1 to 56 µL kg−1 1,4DMN were applied to non-dormant, slightly “peeping” seed tubers of four different cultivars (Russet Burbank, Russet Norkotah, Shepody and FL1879) stored at 15 C ± 2C. Tubers were treated by dribbling 1,4DMN onto a gauze that was placed on top of a return air pipe that re-circulated forced air inside the drum. Higher application rates resulted in higher 1,4DMN residues and longer suppression of sprout growth. Sprout growth was controlled for more than 50 days for all cultivars in both years for tubers treated at the highest rate. The duration of sprout inhibition corresponded with the time it took for tuber residues to drop below an estimated residue level of 1.4–2.1 ppm, for R. Burbank, Shepody and FL1879, and 2.7 ppm for Russet Norkotah. Below these levels, sprouting was no longer suppressed and resumed for all cultivars.

Effect of Potato Virus Y on Yield of a Clonal Selection of Russet Norkotah

Successful selections of Russet Norkotah lines have produced larger, more vigorous vines and higher yields than the standard Russet Norkotah (RN). Potato Virus Y (PVY), while producing mild or “latent” symptoms in this cultivar, has been shown to significantly reduce yields. To determine PVY’s effect on yield of a RN selection, PVY infected RN and Russet Norkotah selection 3 (RN3) yields were compared after planting in Hermiston, Oregon in 2001, 2003, and 2006. After emergence, individual plants were ELISA tested for PVY multiple times during the growing season to confirm infection. Plants were categorized when infected; 1) current season, 2) seed borne or 3) “no PVY”. At harvest, total and marketable yield data were collected. RN3 produced higher total yields than RN, regardless of infection categories. Highest yield reductions of RN and RN3 due to PVY were in the following order; seed borne PVY >>current season PVY >>no PVY.

Detection of Nitrogen Sufficiency in Potato Plants Using Gene Expression Markers

In-season chemical or optical measures of crop N status can be effective tools in optimizing potato fertilizer N management. The feasibility of using a gene expression as an alternative approach for early detection of potato nitrate deficiency was examined using three potato cultivars (Shepody, Russet Norkotah, and Red Pontiac) with abundant (7.5 mM NO3), limited (0.75 mM NO3) or deficient (0 mM NO3) nitrate supply in nutrient culture over a 7 d period. RNA was extracted from the last fully expanded leaf and quantified using realtime RT-qPCR. Reduced nitrate supply had no measurable effect on shoot dry weight or leaf chlorophyll concentration, but decreased petiole nitrate concentration. Under deficit nitrate supply, down-regulation of nitrate reductase and nitrite reductase was measured within 3 days for all cultivars, and down-regulation of asparagine synthetase was measured in two cultivars. Nitrate supply had no effect on expression of ammonium transporter. In this experimental system, plant gene expression markers detected a reduction of nitrate supply prior to measureable reductions in plant growth or in N status measured using common chemical or optical methods.

Potato Cultivars Differ in Current Season Potato Virus Y (PVY) Infection

Research plots were established in 2004, 2005, and 2006 at Hermiston, Oregon and in 2005 and 2006 in Othello, Washington to determine if potato cultivars differ in current season PVY infection. Eight potato cultivars were used; Gem Russet, GemStar Russet, Russet Norkotah, Shepody, Alturas, Ranger Russet, Umatilla Russet and Russet Burbank. The first four listed produce mild symptoms due to current season infection with PVY. Cultivars were planted in a randomized complete block design with four replications where each block contained a single 50-hill row for each cultivar. Leaf samples were evaluated monthly via ELISA to follow naturally occurring PVY infection. Cultivars that produce mild symptoms had higher current season infection levels. Over the 3 years at Hermiston, Shepody (93.8%), Gem (92.8%), Gemstar (89.8%) and Russet Norkotah (82.7%) had the highest infection levels, while Russet Burbank (68.8%), Umatilla Russet (58.0%), Ranger Russet (49.6%) and Alturas (48.1%) had the least infection. At Othello, infection levels were much lower and cultivar differences were minimal though Gem Russet had the highest current season infection (30.4%), Ranger Russet had the lowest (4.9%) and was significantly lower than Gem Russet and Shepody. Higher levels of infection occurred in 2006 at Hermiston and Othello (77.1% and 18.2%, respectively) compared to 2005 (66.7% and 10.2%, respectively). This is the first report where different cultivars of potatoes, growing side by side, had different levels of PVY infection. Possible explanations for differing current season infection levels between cultivars are discussed.

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.

Ability of Potato Cultivars to Tolerate and Suppress Weeds

Potato producers rely heavily on herbicides for the majority of weed control. However, recent occurrences of herbicide-resistant weed populations and the lack of new herbicide registrations have stimulated interest in alternative strategies. The choice of potato cultivars that can suppress or tolerate weed competition could be a component of an integrated weed management system to reduce reliance on herbicides. The competitive ability of 10 potato cultivars—‘Atlantic’, ‘Bannock Russet’, ‘Dark Red Norland’, ‘Goldrush’, ‘Rodeo’, ‘Russet Burbank’, ‘Russet Norkotah’, ‘Snowden’, ‘Superior’, and ‘Villetta Rose’—was evaluated in 2006 and 2007 in Hancock, WI. Weed competition treatments included (1) weedy throughout the season, (2) weed-free from emergence to 4 wk after emergence (WAE) by hand-weeding, and (3) weed-free by hand-weeding for the entire season. Potato cultivars did not differ in ability to reduce weed biomass. Early-season time of potato emergence and canopy closure, as well as weed competition treatments, were strongly related to potato tuber yield. In general, Bannock Russet yield relative to weed-free controls of the same cultivar was less than that of most other cultivars. Overall, Atlantic, Russet Burbank, Snowden, and Superior yields (relative to weed-free control yields) usually were greater than the yields of other cultivars under weedy conditions. Although the ability to suppress weeds was similar among cultivars, differences in yield among cultivars grown in the presence of weeds suggest differential tolerances of weed competition.

Evidence that the Zebra Chip Disease and the Putative Causal Agent Can be Maintained in Potatoes by Grafting and In Vitro

In the last several years, a disorder of chipping potatoes that causes internal browning of raw tubers and very dark chip color when the tubers are fried has been described from the southwestern United States. The discoloration often shows as rays or stripes and the common name “zebra chip” (ZC) has been used to describe the disorder. Foliar symptoms include chlorosis, purpling of shoot tips, and leaf scorch. Aerial tubers are sometimes produced on diseased plants. The disease has been associated with the potato psyllid, Bactericera cockerelli, but a suspected pathogen that may be associated with the ZC disorder has only very recently been described. In our efforts to identify the causal agent we have been maintaining the disease in the greenhouse by tip grafting symptomatic potato shoots onto healthy plants of several commercially important cultivars of potatoes, including Atlantic, Russet Burbank, and Russet Norkotah. Most of the grafted plants subsequently developed ZC symptoms. Many of the grafted plants produced tubers with symptoms typical of the disease. In cultivar Atlantic, 104 of 138 grafted plants developed foliar symptoms of ZC and 72 of the grafted plants produced ZC-symptomatic daughter tubers. Grafted plants without foliar symptoms did not produce symptomatic tubers. Herein we report the results of these grafting experiments and describe the symptoms produced in grafted plants and daughter tubers. We have also maintained the disease by placing surface-sterilized symptomatic shoots onto growth medium in vitro. In addition, the putative ZC pathogen, a new Candidatus Liberibacter spp., has been detected in symptomatic grafted plants, symptomatic in vitro plants, and potato psyllids by PCR.

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.

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.

Colonization Dynamics and Spatial Progression of Verticillium dahliae in Individual Stems of Two Potato Cultivars with Differing Responses to Potato Early Dying.

Potato early dying (PED), caused by Verticillium dahliae, is a chronic yield-limiting disease of potato (Solanum tuberosum). In this study, we describe the colonization dynamics of V. dahliae in two potato cultivars with varying responses to PED. We utilized a quantitative real-time polymerase chain reaction (Q-PCR) assay to assess the colonization and spatial progression of V. dahliae in cvs. Ranger Russet (moderately resistant) and Russet Norkotah (highly susceptible). Ninety plants per cultivar were inoculated with a conidial suspension in the greenhouse. Every 2 weeks until week 10, we collected basal samples from 15 plants, and repeatedly sampled the growing apices of another 15 plants. The mean infection coefficient (IC) values in the basal and apical samples were significantly lower in cv. Ranger Russet at all five sampling dates. The pathogen was detected in basal samples of both cultivars by week 2, and in apical samples of cv. Russet Norkotah at week 4 and of cv. Ranger Russet at week 6. Colonization of cv. Russet Norkotah consistently increased in apical and basal samples during the 10 weeks, while it plateaued after week 6 in cv. Ranger Russet. Differences in response to PED appear associated with the speed of colonization and the establishment of a higher population density by V. dahliae in the plant.

Resistance to green peach aphid,Myzus persicae (Sulzer), and potato aphid,Macrosiphum euphorbiae (Thomas), in potato cultivars

Previous research suggests that extant potato cultivars offer little promise as sources of useful aphid resistance. However, few prior studies have critically measured the effects of host cultivar on aphid age-dependent life table statistics or related these measures to field performance. Therefore, a comprehensive field and greenhouse study was undertaken to assess 49 commercial potato cultivars, primarily of North American origin, for resistance to green peach aphid,Myzus persicae (Sulzer), and potato aphid,Macrosiphum euphorbiae (Thomas). Cultivars were found to show considerable differences in resistances to each aphid species, but these resistances were not significantly correlated (R2=0.032). In greenhouse life table studies, the intrinsic rate of increase (rm) of green peach aphid was lowest (0.167) on cv Russet Norkotah and highest (0.350) on cv Red La Soda. Potato aphidrm was lowest (0.122) on cv Aracy and highest (0.229) on cv Irish Cobbler. Among cultivars, year of release, maturity class and yield potential did not significantly influence number of progeny per female per day for either green peach aphid or potato aphid (P=0.987 and 0.954, respectively). In field trials (2004 and 2005), yield potential was significantly correlated with green peach aphid counts, (P=0.006 and <0.0001, respectively). Aphid/predator population models using aK value of 15.2 predicted that following colonization green peach aphid populations would remain stable for 20 days on Russet Norkotah (resistant), whereas on Red La Soda (susceptible) populations would reach over 54,000. With non-persistent foliar insecticides as the only control, population models indicated that three applications would be necessary to maintain green peach aphid below the Minnesota recommended action threshold on Red La Soda for 21 days, while just one application would be needed for green peach aphid on Russet Norkotah. In combination with biological control or insecticide use, this resistance could provide substantial control while reducing the reliance on pesticides.

Suppression of volunteer potatoes with maleic hydrazide applications

Volunteer potato plants are difficult weeds to control in a wide variety of rotation crops and are not effectively controlled by tillage and herbicides because buried tubers can vigorously resprout. Maleic hydrazide (MH) may provide some of the needed control. This study investigated the efficacy of MH applications for volunteer plant suppression. ‘Russet Burbank’, ‘Ranger Russet’, ‘Russet Norkotah’ and ‘Shepody’ plants were treated with 3.4 kg ai ha-1 Royal MH-30 Xtra® (MH) each of three years. Tuber samples (<57, 57 to 113, 113 to 284 g) were assayed for MH residue and planted the following spring to measure plant emergence.

Resistance to phytophthora erythroseptica and pythium ultimum in a potato clone derived from s. berthaultii and s. etuberosum

Tubers of several potato clones and cultivars were screened for susceptibility to infection by zoospores of Phytophthora erythroseptica (causal agent of pink rot) and mycelia of Pythium ultimum (causal agent of leak) over a three-year period, from 2003-2005. Incidence of infected tubers (%) and penetration of rot (mm) were the parameters used to determine the susceptibility of each potato clone. Responses of each potato clone were compared to cultivars with known resistance or susceptibility to these pathogens. Tubers of cultivars Atlantic and Snowden have moderate resistance to infection and colonization by P. erythroseptica and P. ultimum, respectively, and were used as the resistant checks. Cultivars Russet Norkotah and Red Norland are susceptible to infection by both pathogens. A number of potato clones demonstrated resistance to pink rot equal to or greater than the control cultivar Atlantic, including Etb 6-5-2, ND5822C-7, ND6956b-13, ND7443Ab-44, ND7443Ab-181, ND7818-1Y and J101K6A22. In addition to demonstrating the highest resistance to pink rot, Etb 6-5-2 was the only clone that demonstrated resistance to leak greater than or equivalent to the resistant cultivar Snowden. Etb 6-5-2 is a backcross derivative from a somatic hybrid of Solanum etuberosum and Solanum berthaultii and will be investigated further as a potential source of resistance to these two storage rot diseases.