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The potato psyllid, Bactericera cockerelli (Šulc), is a major pest of potato (Solanum tuberosum L.; Solanales: Solanaceae) as a vector of ' Candidatus Liberibacter solanacearum', the pathogen that causes zebra chip. Management of zebra chip is challenging in part because the noncrop sources of Liberibacter-infected psyllids arriving in potato remain unknown. Adding to this challenge is the occurrence of distinct genetic haplotypes of both potato psyllid and Liberibacter that differ in host range. Longleaf groundcherry (Physalis longifolia Nutt.) has been substantially overlooked in prior research as a potential noncrop source of Liberibacter-infected B. cockerelli colonizing fields of potato. The objective of this study was to assess the suitability of P. longifolia to the three common haplotypes of B. cockerelli (central, western, and northwestern haplotypes), and to two haplotypes of ' Ca. L. solanacearum' (Liberibacter A and B haplotypes). Greenhouse bioassays indicated that B. cockerelli of all three haplotypes produced more offspring on P. longifolia than on potato and preferred P. longifolia over potato during settling and egg-laying activities. Greenhouse and field trials showed that P. longifolia was also highly susceptible to Liberibacter. Additionally, we discovered that infected rhizomes survived winter and produced infected plants in late spring that could then be available for psyllid colonization and pathogen acquisition. Results show that P. longifolia is susceptible to both B. cockerelli and ' Ca. L. solanacearum' and must be considered as a potentially important source of infective B. cockerelli colonizing potato fields in the western United States. [ABSTRACT FROM AUTHOR]

Potato psyllid (Bactericera cockerelli Sulc)-transmitted "Candidatus Liberibacter solanacearum" (Lso) has been negatively impacting the potato industry in the United States as well as other potato-producing countries. Lso has been linked to a condition known as zebra chip (ZC) that affects yield and quality of potato tubers. Efforts to find sources of resistance to ZC have primarily focused on greenhouse evaluations based on a single inoculation time prior to harvest. Plant response to infection, however, could be influenced by the developmental stage of the host plant, and ZC may continue to develop after harvest. The objectives of this study were to quantify Lso inoculation success, Lso titer, ZC severity and Lso development during storage in eight potato genotypes. These evaluations were conducted on plants infested with Lso-positive psyllids at 77, 12, and 4 days before vine removal (DBVR). The evaluated genotypes were categorized according to their relative resistance to Lso and tolerance to ZC symptoms. Lso inoculation success in the genotype family A07781, derived from Solanum chacoense, was lower than that of the susceptible control ('Russet Burbank'). A07781-4LB and A07781-3LB genotypes were characterized relatively resistant to the pathogen and highly tolerant to ZC symptoms, while A07781-10LB was categorized as susceptible to Lso but relatively tolerant to symptom expression. In stored potatoes, increase in Lso concentrations was observed for all infestation times. However, significantly higher Lso titer was detected in tubers infested 12 DBVR and the effect was similar across genotypes. Overall, the A07781 family can be considered as a promising source of resistance or tolerance to ZC. [ABSTRACT FROM AUTHOR]

Common scab of potato is a superficial tuber disease caused by Streptomyces species that produce the phytotoxin thaxtomin. Because common scab development is highly dependent on the effects of this single toxin, the current operating paradigm in common scab pathology is that a potato cultivar resistant to one strain of the common scab pathogen is resistant to all strains. However, cultivar resistance to common scab disease identified in one breeding program is often not durable when tested in other potato breeding programs across the United States. We infected 55 potato cultivar populations with three distinct species of the common scab pathogen and identified cultivars that were resistant or susceptible to all three species and cultivars that had widely varying resistance dependent on the pathogen species. Overall lower virulence was associated with the strain that produces the least thaxtomin. This result showcases several cultivars of potato that are expected to be resistant to the majority of common scab populations but also highlights that many potato cultivars are resistant to only specific species of the pathogen. These results demonstrate that extension specialists and growers must consider their local population of the common scab pathogen when selecting which cultivars to plant for common scab resistance. [ABSTRACT FROM AUTHOR]

Potato has about 100 wild species relatives that are multiplied in the form of botanical seed populations by genebanks and distributed for use in research and breeding, so understanding factors that affect seed germination is valuable. This is especially true for problematic seedlots that have slow and low (“trickle”) germination even when subjected to germination techniques that give optimal results in most other seedlots in the genebank. Twelve seedlots with trickle germination even after at least 2 years of storage and 2 robustly-germinating positive control seedlots encompassing 9 species were germinated in petri plates, and subjected to day/night = 10 h/14 h = 20C/6C alternating temperature (AT) trials along with constant room temperature (RT) controls, in the spring of 2015 and 2016. When Relative Area Under the Germination Progress Curve (RAUGPC) was calculated, normal germinating seedlots’ germination in AT was not significantly different from RT control. Some species’ seedlots’ RAUGPC germination in AT was nearly zero, some were about 50% of RT control, and some in AT germination had RAUGPC double or even triple that of RT control. In a separate trial in 2017, four seedlots most responsive to AT were shown to germinate significantly better in constant cold than their RT controls, but not as well as seeds germinated under AT. Also in 2017, two seedlots known to be very dependent on gibberellin pretreatment were tested. RT germination without gibberellin had RAUGPC of only 13% of RT control, but AT without gibberellin pretreatment increased this to 65%, showing AT substantially substitutes for gibberellin pretreatment in these seedlots. AT could be a useful application to all seed germination assays in the genebank if it facilitated a better assessment of the potential viability of trickle-germinating seedlots. But one would need to identify and exclude those seedlots for which alternating temperature greatly depresses germination. [ABSTRACT FROM AUTHOR]

Zebra Chip disease vectored by the potato psyllid Bactericera cockerelli (Šulc) was first reported in Idaho and the Columbia Basin of Oregon and Washington in 2011. Since then growers have incurred significant costs for managing the disease. Thus, we conducted an expert opinion survey to estimate expenditure on insecticides dedicated to controlling potato psyllids in the largest potato producing regions of Idaho, Oregon, and Washington. Results highlight a total of about 9 million US dollars spent on active ingredients targeted at psyllid control. When application costs are added to the cost of insecticides, expenditures total about 11 million US dollars. [ABSTRACT FROM AUTHOR]

Black dot disease of potato, caused by Colletotrichum coccodes (Wallr.) Hughes, is widely distributed in the United States. However, little is known regarding the population biology of this fungus. A total of 370 single-spore isolates of C. coccodes were collected from naturally infected potato plants in nine states and analyzed using amplified fragment length polymorphism (AFLP) markers and three primer pairs, yielding 190 polymorphic bands with 90.7 % polymorphism. The isolates were assigned to four vegetative compatibility groups (AFLP/VCG): AFLP/VCG1, AFLP/VCG2, AFLP/VCG4/5, and AFLP/VCG6/7. No isolates tested belonged to AFLP/VCG3. The United States C. coccodes population structure was confirmed with a high differentiation value ( G = 0.30) among VCGs. AFLP/VCG2 was the dominant group in the population ( n = 262) and was the most frequent AFLP/VCG among states, fields, farms, and plants. However, in several instances, more than one AFLP/VCG was isolated from the same plant, field, farm, and state, indicating variability within the C. coccodes population in the United States. A geographic pattern was found for isolates originating from Texas, Montana, North Dakota, and Wisconsin. Diversity within states accounted for 73 % of the total genetic diversity, and among populations accounted for 27 %. These results suggest that several AFLP/VCGs are widely distributed in the United States and that they form a single large population of C. coccodes. [ABSTRACT FROM AUTHOR]

A number of Alternaria spp. have been isolated from potato worldwide but only Alternaria solani and A. alternata have been described as pathogenic to this host in the United States. These taxa are easily differentiated based on conidial morphology but species delimitation among the small-spored Alternaria spp. associated with potato are much more challenging. Accurate identification methods for small-spored Alternaria spp. are necessary so that a more thorough understanding of Alternaria epidemiology can be obtained. Isolations of Alternaria fungi from lesions on potato leaves collected in the U.S. Northwest were made between 2008 and 2011. Large-spored taxa (putatively A. solani), were isolated less frequently than small-spored taxa (putatively A. alternata sensu lato), except in 2010. Colletotrichum coccodes was isolated from necrotic lesions in 2008 to 2010 but not in 2011. Frequency of isolation ranged from 0.05 (5%) to 0.11 (11%) during the 3 years the fungus was detected. Anonymous genomic region OPA1-3, previously used for Alternaria systematics, allowed for the discrimination of phylogenetic lineages among 210 small-spored isolates. When OPA1-3 was restricted using enzyme ApaI, 65 isolates (31%) displayed a restriction banding pattern consistent with previously characterized morphospecies A. alternata and A. tenuissima and 145 (69%) displayed a restriction banding pattern consistent with the previously characterized morphospecies A. arborescens. Morphological characterization of a subsample of 59 small-spored Alternaria isolates randomly selected with each restriction pattern was compared with phylogenetic lineage. In all, 54 (92%) isolates were consistently assigned to the same group by both methods. Three isolates exhibited conidial morphologies that were inconsistent with any described morphospecies. A small number of isolates were identified as A. arbusti (infectoria group) via sequencing of the glyceraldehyde-3-phosphate-dehydrogenase locus and BLAST searches. [ABSTRACT FROM AUTHOR]

Tecia solanivora (Lepidoptera: Gelechiidae) (Povolny 1973), is the most important insect pest of potato (Solanum tuberosum L.) in Central and South America, and Spain. The species was recently reported in Mexico, demonstrating the power of invasion by this insect. In Peru, the insect is quarantined, and could become a damaging pest in America. Larvae attack potato tubers, causing economic loss of 50 to 100%. We used eight microsatellites in 152 individuals from Antioquia (North), Boyacá (Center), Nariño (South), and Norte de Santander (East), Colombia, and found T. solanivora genetically different based on an AMOVA test (FST = 0.094, P < 0.01, RST = 0.175, P < 0.01). The differentiation was supported by Bayesian analysis where we estimated K = 2. The outcome suggests populations from Antioquia and Boyacá are genetically similar whereas populations from Nariño and Norte de Santander differ because of geographical separation from other regions. We found T. solanivora had not undergone a recent bottleneck effect suggested by other authors. On the contrary we found that this species has undergone recent population expansion in the country. We suggest that movement of potatoes caused genetic homogenization. Movement occurs from Boyacá where most potatoes are produced, to the rest of Colombia. [ABSTRACT FROM AUTHOR]

Verticillium wilt, caused by Verticillium dahliae Kleb., is a primary component of the early dying complex of potato ( Solanum tuberosum L.) in the United States. Although genetic resistance to V. dahliae exists and has been incorporated into several potato cultivars, the commercial potato industry is still dominated by cultivars susceptible to the pathogen. As a result, soil fumigation with metam sodium remains an important means by which Verticillium wilt is controlled, despite its expense and potentially negative environmental impact. Recent restrictions on metam sodium use by the Environmental Protection Agency directed at reducing exposure to vapor emissions have increased the need to improve shank injection of the soil fumigant. In studies reported here, the application of metam sodium reduced the severity of Verticillium wilt, however, soil temperature at the time of injection, metam sodium injection depth, and application rate had little overall effect. In 2011, temperature at the time of metam sodium injection did not result in significant differences in any parameter evaluated. However, in 2012, soil populations of V. dahliae, wilt severity and host colonization were significantly reduced when metam sodium was applied at 4 °C compared to 13 or 15 °C. No significant differences were observed between a single or two metam sodium injection depths in any parameter evaluated across the 2 years the study was conducted. While all rates of metam sodium significantly reduced soil populations of V. dahliae compared to the non-treated control, significant differences across rates were rarely observed. Improved control of Verticillium wilt and increased yield can be achieved as a result of these studies. The effective control of Verticillium wilt can be obtained by using metam sodium at a comparatively low rate of 373 l/ha, particularly when applied at a relatively cold soil temperature of 4 °C using a single injection depth of 25 cm. The potential impact of these application modifications of metam sodium in reducing emissions and non-target exposure is discussed. [ABSTRACT FROM AUTHOR]

Potato virus F(PVY) is one of the oldest known plant viruses, and yet in the past 20 years it emerged in the United States as a relatively new and very serious problem in potato. The virus exists as a complex of strains that induce a wide variety of foliar and tuber symptoms in potato, lead-ing to yield reduction and loss of tuber quality. PVY has displayed a distinct ability to evolve through accumulation of mutations and more rapidly through recombination between different strains, adapting to new potato cultivare across different environments. Factors behind PVY emergence as a serious potato threat are not clear at the moment, and here an attempt is made to analyze various properties of the virus and its interactions with potato resistance genes and with aphid vectors to explain this recent PVY spread in potato production areas. Recent ad-vances in PVY resistance identification and mapping of correspond-ing genes are described. An updated classification is proposed for PVY strains that takes into account the most current information on virus molecular genetics, serology, and host reactivity. [ABSTRACT FROM AUTHOR]

Early blight, caused by Alternaria solani, is an important chronic foliar disease of potato (Solanum tuberosum) present every growing season in the Midwestern United States. Most currently grown potato cultivars lack resistance to early blight; therefore, foliar fungicides are relied upon for disease management. Foliar fungicides with high efficacy against the pathogen, such as boscalid, frequently are used under high disease pressure situations, such as potatoes grown under overhead irrigation. Boscalid is a member of the succinate dehydrogenase in-hibiting (SDHI) fungicide group and was registered for use on potato in 2005. Baseline sensitivity of A. solani to the SDHI fungicides bos-calid, penthiopyrad, and fluopyram using a spore germination assay demonstrated similar intrinsic activity against A. solani with mean EC50 values of 0.33, 0.38, and 0.31 pg/ml, respectively. However, iso-lates varied in their sensitivity to each of these fungicides, resulting in very low correlations (r) among isolate sensitivity to each fungicide. Resistance to boscalid in A. solani was detected in the states of North Dakota, Minnesota, Nebraska, Texas, Idaho, Wisconsin, and Florida from early blight samples collected in 2010 and 2011. Two phenotypes of boscalid resistance were detected. Approximately 80% of all A. solani assayed were found to have some level of resistance to boscalid with about 5 and 75% of the population moderately resistant (5 to 20 pg/ml) and highly resistant (>20 pg/ml), respectively, to the fungicide. Nearly 99% of all boscalid resistant isolates possessed the F129L mutation in the cytrochrome b gene, indicating that an A. solani population with dual fungicide resistance predominates in the states surveyed. However, A. solani isolates resistant to boscalid remained sensitive to fluopyram, and a large proportion of moderately resistant and resistant isolates were sensitive to penthiopyrad. Disease control data from in vivo trials demonstrated a significant loss of fungicide efficacy when boscalid and fluxapyroxad were used to control moder-ately and highly resistant isolates of A. solani relative to the control these fungicides provided wild-type isolates. Fluopyram, however, controlled boscalid resistant isolates as well as it controlled wild-type isolates of A. solani. These data will assist potato growers in regions where boscalid resistance is prevalent by assisting them in avoiding fungicides that do not effectively control early blight and in selecting SDHI fungicide molecules that remain efficacious. [ABSTRACT FROM AUTHOR]

Zebra chip, or zebra complex (ZC) has become an important invasive disease of potato in the United States and New Zealand and is caused by a phloem-limited bacterium, ' Candidatus Liberibacter solanacearum' (Lso). A PCR assay using a single pair of simple sequence repeat (SSR) primers was developed for simultaneous detection and genotype differentiation of Lso haplotypes associated with zebra chip disease of potato. The sensitivity of the SSR PCR was similar to a 16S PCR assay, with detection limit of 100 copies of the Lso genome in haplotype A infected potato and psyllid samples and 10 copies of Lso genome in haplotype B potato and psyllid samples. The Lso detection frequency of the SSR PCR assay was 79.1 % in potato and 26.4 % in psyllid samples, respectively; whereas the detection frequency of the 16S PCR assay 59.0 % in potato and 25.9 % in psyllid samples, respectively. Samples of Lso positive potato plants and psyllids from multiple states in the US were demonstrated to have either haplotype A or haplotype B Lso and occasionally both haplotypes were found in individual samples. This is the first report that co-infection of the two haplotypes of Lso exists in potato and potato-psyllid samples. Only haplotype A Lso was detected in North Dakota psyllid samples collected in 2010, in Idaho and Washington ZC potato samples sampled from storage in 2011, and in Idaho ZC potato samples in 2012. Haplotype A Lso was also detected in New Zealand ZC affected potato samples and psyllid samples collected in 2010 and 2011. The PCR assay developed is as sensitive as previously developed assays and has the advantage of simultaneously detecting and differentiating Lso haplotypes of the ZC bacterium, thus making it extremely useful for epidemiological studies. [ABSTRACT FROM AUTHOR]

Zebra chip disease (ZCD) of potato (Solanum tuberosumL.) has caused significant economic losses to the potato industry in the USA. ‘CandidatusLiberibacter solanacearum’ Lieftinget al. has been associated with ZCD. This non-culturable bacterium dwells within the phloem of plants where other endophytic bacteria may also live. Knowledge concerning phloem colonization by ‘Ca. L. solanacearum’ and other endophytic bacteria may provide a better understanding about disease biology and could facilitate the development of novel disease management strategies. In this study, endophytic bacteria in potato tubers afflicted with ZCD were evaluated by scanning electron microscopy (SEM),in vitrocultivation, and PCR analyses. Bacillus, coccus, and filamentous bacterial cells were observed by SEM in phloem tissue of ZCD-diseased tubers, but were absent in healthy potato tubers. Fifty-one bacterial isolates were obtainedin vitrofrom ZCD-affected tubers and 34 isolates were from non-ZCD tubers. Comparison of 16S rDNA sequences identified bacteria belonging to 16 genera. Seven (Brachybacterium,Enterobacter,Microbacterium,Paenibacillus,Staphylococcus,StenotrophomonasandVariovorax) were only isolated from ZCD-affected potato tubers, whereas four (Bosea,Nocardia,SphingomonasandSphingopyxis) were only isolated from non-ZCD potato tubers. However, a more sensitive PCR analysis diminished the specific association of the bacteria to either ZCD or non-ZCD tubers, suggesting that infection by ‘Ca.L. solanacearum’ influenced the titres of other endophytic bacteria in potato tubers. [ABSTRACT FROM AUTHOR]

Potato chips are the most popular snack food in the United States with annual retail sales of over US$6 billion. Stem-end chip defect, which is characterized by dark color of the vasculature and surrounding tissues at the tuber stem end portion of fried chips, is an important tuber quality concern for U.S. chip production. The cause of stem-end chip defect is not known. Verticillium wilt, caused by a vascular fungal pathogen Verticillium dahliae Kleb., is a persistent disease of potato (Solanum tuberosum L.) and other vegetables that causes early plant senescence and yield reductions. A 2-yr field trial was conducted to investigate the effects of V. dahliae on stem-end chip defect development and the activity of acid invertase at the apical (bud) and basal (stem) ends of tubers. Our results show that potato plants that were more infected with V. dahliae had a higher incidence of severe stem-end chip defects than plants with less V. dahliae infection. Verticillium dahliae infection of plants was correlated with an upregulation of acid invertase activity and an accumulation of reducing sugars on the stem end of tubers. Reducing sugars give rise to dark-colored defects as a result of pigments produced by the Maillard reaction during frying. [ABSTRACT FROM AUTHOR]

Abstract: Guatemalan potato moth, Tecia solanivora, lay eggs in the soil nearby potato Solanum spp. and larvae feed on the tubers. We investigated the oviposition behaviour of T. solanivora females and the survival of larval offspring on healthy vs. stressed, i.e. light exposed and/or damaged potato tubers. In choice tests, females laid significantly more eggs in response to potato odour of healthy tubers and female oviposition preference correlated with higher larval survival. Survival of larvae was negatively correlated with the tuber content of the steroid glycoalkaloids α-solanine and α-chaconine: healthy potatoes contained lower amounts than stressed tubers, ranging from 25 to 500μgg−1 and from 30 to 600μgg−1, respectively. Analysis of volatile compounds emitted by potato tubers revealed that stressed tubers could clearly be distinguished from healthy tubers by the composition of their volatile profiles. Compounds that contributed to this difference were e.g. decanal, nonanal, isopropyl myristate, phenylacetaldehyde, benzothiazole, heptadecane, octadecane, myristicin, E,E-α-farnesene and verbenone. Oviposition assays, when female moths were not in contact with the tubers, clearly demonstrated that volatiles guide the females to lay fewer eggs on stressed tubers that are of inferior quality for the larvae. We propose that volatiles, such as sesquiterpenes and aldehydes, mediate oviposition behaviour and are correlated with biosynthetically related, non-volatile compounds, such as steroidal glycoalkaloids, which influence larval survival. We conclude that the oviposition response and larval survival of T. solanivora on healthy vs. stressed tubers supports the preference performance hypothesis for insect herbivores. [Copyright &y& Elsevier]

Zebra chip (ZC), a new and economically important disease of potato ( Solanum tuberosum L.), has been documented to occur in commercial potato fields in the United States, Mexico, Central America, and New Zealand. This disease has caused millions of dollars in losses to the potato industry. Whole crops might be rejected because of ZC, often leading to abandonment of entire fields. Plant growth and yield are severely affected by the disease. Additionally, chips or fries processed from ZC-infected tubers exhibit dark stripes that become markedly more visible with frying, and hence are commercially unacceptable. The disease causes serious losses to the fresh market, tablestock and export potato industry as well. ZC-infected tubers usually do not sprout and if they do, produce hair sprouts or weak plants. Finally, there are indications that ZC symptoms might develop in tubers during storage. ZC has been associated with a previously undescribed species of liberibacter, tentatively named ' Candidatus Liberibacter solanacearum', also known as ' Ca. L. psyllaurous'. The bacterium is transmitted to potato by the potato psyllid, Bactericera cockerelli (Šulc). All commercial potato cultivars appear to be susceptible to ZC, and management tactics targeted against the potato psyllid are currently the only means to effectively manage the disease. Furthermore, there are concerns about quarantine and trade issues in psyllid-affected regions because some countries may require that shipments of potatoes from certain growing regions be tested for the disease before the shipments are allowed entry. ZC history, geographic distribution, biology, epidemiology, and management are discussed herein. [ABSTRACT FROM AUTHOR]

The potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae), is a vector of the bacterium "Candidatus Liberibaeter solanacearum," the putative causal agent of potato zebra chip disease that has seriously affected the potato industry in the Central and Southwestern United States for the past decade. The 2011 potato growing season saw the first report of zebra chip disease in Washington, Oregon, and Idaho; however, B. cockerelli has been recorded in this region every season at least for the past 7 yr. Studies were conducted to determine the relationship between psyllids collected from the Pacific Northwest potatoes in 2011 and those from the Southwestern and Central United States. High resolution melting analysis of the B. cockerelli mitochondrial Cytochrome C Oxidase subunit l-like gene was conducted on over 450 psyllids collected from numerous locations across the Central and Western United States. Results suggest that at least three potato psyllid haplotypes exist in the United States, correlating to the Central, Western, and Northwestern United States geographical regions. The high resolution melting analysis results were subsequently supported by DNA sequencing data. [ABSTRACT FROM AUTHOR]

Beet leafhoppers (Circulifer tenellus Baker) have been identified as the vector for a plant-pathenogenic phytoplasma known as beet leafhopper-transmitted virescence agent. Beet leafhopper- transmitted virescence agent causes purple top disease in potatoes, which can reduce yields and tuber quality. A trapping network, composed of ∼100 sites, monitors leafhoppers in the Columbia Basin of Oregon and Washington through a collaborative effort of regional researchers and stakeholders. Yellow sticky cards were used to determine the timing and spatial distribution of beet leafhoppers in the Columbia Basin; insects were counted weekly from early April through late October in 2006, 2007, and 2008. Weather data collected from a network of weather stations in Oregon and Washington were used in a nonparametric multiplicative regression analysis to determine which abiotic environmental variables might influence beet leafhopper populations. Weather conditions (mean temperature, dew point, precipitation, and wind speed) for 2006-2008 were also characterized using CIs established based on weather data from 1998 to 2004 for each weather variable. Several abiotic environmental factors significantly correlated with beet leafhopper populations, including temperatures the preceding fall and winter, elevation, and precipitation. Beet leafhopper populations appear to be highly variable across the region, with low numbers at a majority of the sites and only a limited number of high populations in localized areas [ABSTRACT FROM AUTHOR]

BACKGROUND: Neonicotinoid insecticides were first used commercially for Colorado potato beetle [ Leptinotarsa decemlineata (Say), Coleoptera: Chrysomelidae] control in the United States in 1995, and since then have been critical for management of this pest. Field populations from the northeastern and midwestern United States were tested from 1998 to 2010 for susceptibility to imidacloprid and thiamethoxam using standard topical dose assays with adults. RESULTS: From 1998 to 2001, imidacloprid resistance was present in only a few locations in the eastern United States. By 2003, imidacloprid resistance was common in the northeastern Unites States. In 2004, imidacloprid resistance in Colorado potato beetle was detected for the first time in the midwestern United States. In 2003, the first case of resistance to thiamethoxam was found in a population from Massachusetts. Neonicotinoid resistance in summer-generation adults was higher than in overwintered adults from the same locations. By 2009, 95% of the populations tested from the northeastern and midwestern United States had significantly higher LD50 values for imidacloprid than the susceptible population. CONCLUSIONS: The increasing resistance to neonicotinoid insecticides raises concerns for the continued effective management of Colorado potato beetles in potatoes and highlights the need for more rigorous practice of integrated pest management methods. Copyright © 2011 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Zebra chip (ZC), an emerging and serious disease of potato has caused millions of dollars in losses to the potato industry in the United States, Mexico, Central America, and New Zealand. The disease has recently been associated with a previously undescribed species of liberibacter tentatively named ' Candidatus Liberibacter solanacearum' transmitted to potato by the potato psyllid, Bactericera cockerelli (Šulc). At present, applications of insecticides targeted against the potato psyllid are the only means to manage ZC. Given the low psyllid density and short inoculation access period required to induce the disease, insecticides may not act fast enough to prevent transmission of liberibacter to potato by the psyllid and development of ZC. Identification and development of ZC-resistant or tolerant varieties may offer the most efficient and sustainable way to manage this potato disease. Susceptibility of selected potato varieties to ZC was evaluated under controlled field cage conditions in 2009 and 2010 in WA by inoculating potato plants with ' Ca. L. solanacearum' using infective potato psyllids and monitoring them for ZC symptom development. All potato varieties evaluated in both years of the study were determined to be very susceptible to the disease, with almost 100% of the inoculated plants developing severe ZC foliar and tuber symptoms. Potato yield in all tested varieties was significantly affected by ZC, with yield losses ranging from 49.9% to 87. 2%. Information from this research suggests that there is an urgent need to develop new potato varieties that are resistant or tolerant to this damaging potato disease. [ABSTRACT FROM AUTHOR]

Pectobacteriu,n species cause disease worldwide in many crop and ornamental plants, including potato. A new Pectobacteriu,n subspecies, P carotovorum subsp. brasiliensis was recently described in Brazil and later found in the United States, Israel, and South Africa. Its virulence traits and host range remain unknown. A comparison of three taxa commonly found on potato showed that both P carotovorum subsp. carotovorum and subsp. brasiliensis are more aggressive in causing tuber and stem soft rot than P atrosepticum. Also, despite bacterial growth inhibition in vitro of P carotovorum subsp. carotovorum and P atrosepticum strains by P carotovorum subsp. brasiliensis, this new subspecies and P carorovorum subsp. carotovorurn are able to co-colonize in the same infected tissue. Both subspecies were motile in lesions. Pathogenesis assays showed that host ranges of all three overlap, but are not identical. The host ranges of individual strains of P carobvorum subsp. carotovorum and subsp. brasiliensis are limited, whereas P atrosepticum can macerate many plant species in addition to potato. There was high variability in virulence assays with potato tuber; thus physiological factors were investigated. Tuber size, maturity, and field location had significant effects on susceptibility to soft rot, with larger, more mature tubers being more susceptible. [ABSTRACT FROM AUTHOR]

The article discusses a study that determines the effect of potato virus Y (PVY) on the quality of solanaceous crops in the U.S. and Canada. The researchers investigate the prevalence of PVY across the two countries and its harmful effects on the Solanaceae including tomato, eggplant and tobacco. Study reveals that the reproduction of PVY can be minimized by restricting the distribution of the tuber necrotic strains.

Colonization of potato (Solanum tuberosum) tissue, including roots, stolons, and above and below ground stems, by Colletotrichum coccodes, the causal agent of black dot, was evaluated following soil infestation, inoculation of seed tubers and foliage, and every combination thereof, in field trials over two growing seasons in North Dakota and Minnesota. A total of 107,520 isolations for C. coccodes performed across four site-years allowed for an extensive comparison of fungal colonization of the host plant and disease severity. The black dot pathogen was detected in potato stems at the first sampling date in all four site-years, as early as 14 days prior to emergence. Colonization of above and below ground stems occurred at a higher frequency than in roots and stolons in all four site-years, resulting in significantly higher relative area under the colonization progress curves (RAUCPCs) (α = 0.05). Although fungal colonization and disease incidence were higher in inoculated and/or infested treatments, sufficient natural inoculum was present to result in substantial levels of disease in noninoculated and noninfested plots. However, noninoculated and noninfested plots displayed the lowest RAUCPC values across three of four site-years and those treatments with multiple inoculation events tended to have higher RAUCPC values. Isolates belonging to vegetative compatibility group (VCG)2 and -5 were recovered from plants sampled in 2004 more frequently than isolates belonging to VCG1 and -3. A significant difference in disease incidence on stems was observed only in North Dakota in 2004 and Minnesota in 2003 (α = 0.05). Noninoculated and noninfested plots displayed the lowest disease incidence, whereas those treatments with more than one inoculation and/or infestation event tended to have higher disease incidence. Results of this study, including the disease severity and yield data, provide a better understanding of colonization of potato plants by C. coccodes and its impact. [ABSTRACT FROM AUTHOR]

An emerging disease of potato in the United States, known as "Zebra Chip" or "Zebra Complex" (ZC), is increasing in scope and threatens to spread further. Here, we report on studies performed to understand the role of tuberborne ZC in the epidemiology of this disease. Depending on variety, up to 44% of ZC-affected seed tubers (ZCST) were viable, producing hair sprouts and weak plants. Chip discoloration in progeny tubers of ZCST was more severe than those from ZC-asymptomatic seed tubers but varied depending on whether progeny tubers or foliage were positive or negative for 'Candidatus Liberibacter solanacearum'. A low percentage of greenhouse-grown plants produced by ZCST tested positive for 'Ca. Liberibacter'. No adult potato psyllids became infective after feeding upon these plants but they did acquire 'Ca. Liberibacter' from field-grown plants produced by ZCST. Plants with new ZC infections near plants produced by ZCST were not significantly different from healthy plants, whereas plants affected with ZC from infectious potato psyllids had significantly more ZC infections near either plants produced by ZCST or healthy plants. We conclude that, in areas where ZC is currently established, plants produced by ZCST do not significantly contribute to ZC incidence and spread within potato fields. [ABSTRACT FROM AUTHOR]

The potato tuberworm, Phthorimaea operculella Zeller, is one of the most damaging pests of potatoes worldwide. Although tuberworm was recorded in California as early as 1856, it was first reported in damaging numbers in Oregon and Washington in the early 2000s. The objective of this study was to provide baseline information on the population structure of potato tuberworm in the United States. Potato tuberworm adults were collected from potato fields in the major production regions in the United States. Amplified fragment length polymorphisms (AFLP) were used to determine the genetic population structure of potato tuberworm. We used 219 individuals and 335 polymorphic AFLP bands to infer the geographic population structure of potato tuberworm. Posterior probabilities calculated using the model-based clustering method implemented in STRUCTURE, and Fst values calculated using AFLP-SURV confirmed the existence of two distinct populations in the United States (one mostly associated to the western United States and the other one mostly associated to the eastern United States). This study provides baseline data for the molecular characterization of potato tuberworm populations, which will aid in tracking the origin of future invasions within the United States. [ABSTRACT FROM AUTHOR]

A new disease of potatoes, tentatively named zebra chip (ZC) because of the intermittent dark and light symptom pattern in affected tubers which is enhanced by frying, was first found in Mexico in 1994 and in the southwestern United States in 2000. The disease can cause severe economic losses in all market classes of potatoes. The cause of ZC has been elusive, and only recently has been associated with `Candidatus Liberibacter' sp. Field samples of potato plants were collected from several locations in the United States, Mexico, and Guatemala to determine transmission to potato and tomato by grafting of ZC-infected scions and psyllid feeding. The disease was successfully transmitted, through up to three generations, by sequential top- and side-grafting ZC-infection scions to several potato cultivars and to tomato. The disease was also successfully transmitted to potato and tomato plants in greenhouse experiments by potato psyllids collected from potato plants naturally affected with ZC. Transmission electron microscopic observation of ZC-affected tissues revealed the presence of bacteria-like organisms (BLOs) in the phloem of potato and tomato plants inoculated by grafting and psyllid feeding. The BLOs were morphologically similar in appearance to BLOs associated with other plant diseases. Po- lymerase chain reaction (PCR) amplified 16S rDNA sequences from samples representing different geographic areas, including the United States, Mexico, and Guatemala, were almost identical to the 16S rDNA of `Ca. L. solanacearum' previously reported from solanaceous plants in New Zealand and the United States. Two subclades were identified that differed in two single base-pair substitutions. New specific primers along with an innovative rapid PCR were developed. This test allows the detection of the bacteria in less than 90 mm. These data confirm the association of 'Ca. L. solanacearum' with potatoes affected by ZC in the United States, Mexico, and Guatemala. [ABSTRACT FROM AUTHOR]

Common scab is a serious disease of potatoes (Solanum tuberosum) and other root and tuber crops, affecting the quality and market value of these crops. The disease is caused by gram-positive soil bacteria in the genus Streptomyces. A new common scab-causing streptomycete was isolated from scabby potatoes originating in southeastern Idaho. Research has supported a model of horizontal transfer of pathogenicity determinants among streptomycetes, and the new strain has hallmarks of the recently characterized Streptomyces pathogenicity island (PAI); it has genes encoding the synthetase for the pathogenicity determinant thaxtomin and for a second pathogenicity factor, tomatinase, although it lacks a third gene characteristic of the Streptomyces PAT, the nec1 gene. The new strain has a unique 16s rDNA gene sequence closely related to those of other pathogenic Streptomyces species. This 16s rDNA sequence was also found in isolates lacking a PAT, suggesting that the new pathogenic strain arose by horizontal transfer of a PAT into a saprophytic streptomycete. Isolates of the new strain are pathogenic on radish and potato, and are more virulent than the S. scabies type strain. In addition to scab lesions on potato tubers, lesions were also seen on underground stems and stolons. This new strain represents additional complexity in the pathogenic strains causing plant disease in the United States. [ABSTRACT FROM AUTHOR]

A large number of soilborne diseases that affect potato are important in the United States. In the Midwestern USA, early dying, involving Verticillium dahliae and Colletotrichum coccodes and the storage rots, pink rot and leak tuber rot, caused by Phytophthora erythroseptica and Pythium ultimum are among the most serious. Various aspects of the biology and aetiology of these pathogens have been investigated to improve our understanding of the factors involved in disease development. These studies have addressed knowledge gaps and have assisted in the development of management strategies and tactics for each disease. Disease management integrates cultural practices, use of agrochemicals and to some degree, host resistance. Unfortunately, cultural management practices alone are currently inadequate to control these diseases, causing the potato industry to become over-reliant on the use of agrochemicals for effective management. Current research efforts are directed at the identification and incorporation of genetic resistance into cultivars with acceptable horticultural characteristics to provide more effective disease management. [ABSTRACT FROM AUTHOR]

The vegetative compatibility of 123 isolates of Colletotrichum coccodes from North America (United States and Canada) originating from potato, tomato, pepper, and mint was tested using nitrate-nonutilizing (nit) mutants. The North American isolates did not anastomose with previously selected European/Israeli vegetative compatibility group (VCG) testers; therefore, eight isolates were selected as VCG testers for the North American population. The 123 isolates distributed to seven VCGs at 1.6, 1.6, 4.0, 8.1, 13.8, 19.5, and 36.6%, with 14.6% of the isolates not assigned to any of the seven VCGs. Among the North American (NA)-VCGs, the average frequency of the nit1/nit3 nit mutants was lower (P < 0.05) for isolates belonging to NA-VCG I than for isolates belonging to the NA-VCGs 2, 3, and 5. In contrast, the frequency of NitM nit mutants did not vary (P > 0.05) among the NA-VCGs and was collectively 5.14%. The results also indicated significant (P < 0.05) differences among NA-VCGs and European/Israeli (EU/I)-VCGs regarding the frequency of nit mutants. The aggressiveness trials of the North American isolates to potato indicated that plants infected with isolates belonging to NA-VCG2 and NA-VCG5 had more (P < 0.05) sclerotia on the roots and crowns than plants infected with isolates belonging to NA-VCGs 1 and 3. The plants infected with isolates belonging to NA-VCG2 had sclerotia formed higher (P < 0.05) up the stem than the plants infected with isolates belonging to NA-VCGs 1, 3, or 5. The plants infected with isolates assigned to NA-VCG2 had more (P < 0.05) infected progeny tubers than the plants infected with isolates belonging to NA-VCGs 1, 3, or 5; and the plants infected with isolates belonging to NA-VCGs 1, 2, and 5 yielded fewer (P < 0.05) potato tubers than the noninoculated control plants. A naming system for the population of C. coccodes based on the continent source of the population, the VCG number, and the isolate's code was suggested. [ABSTRACT FROM AUTHOR]

Experiments were conducted to determine whether the beet leafhopper, Circulifer tenellus (Baker) (Hemiptera: Cicadellidae), transmits the purple top phytoplasma to potato, Solanum tuberosum L.; beets, Beta vulgaris L.; and selected weed hosts. The beet leafhopper-transmitted virescence agent (BLTVA) phytoplasma was identified as the causal agent of the potato purple top disease outbreaks that recently occurred in the Columbia Basin of Washington and Oregon. The phytoplasma previously was found to be associated almost exclusively with the beet leafhopper, suggesting that this insect is the probable vector of BLTVA in this important potato-growing region. Eight potato cultivars, including ‘Russet Burbank’, ‘Ranger Russet’, ‘Shepody’, ‘Umatilla Russet’, ‘Atlantic’, ‘FL-1879’, ‘FL-1867’, and ‘FL-1833’, were exposed for a week to BLTVA-infected beet leafhoppers. After exposure, the plants were maintained outdoors in large cages and then tested for BLTVA by using polymerase chain reaction after 6 to 7 wk. The leafhoppers transmitted BLTVA to seven of the eight exposed potato cultivars. Sixty-four percent of the exposed plants tested positive for the phytoplasma. In addition, 81% of the BLTVA-infected potato plants developed distinct potato purple top disease symptoms. Beet leafhoppers also transmitted BLTVA to beets and several weeds, including groundsel, Senecio vulgaris L.; shepherd's purse, Capsella bursa-pastoris (L.) Medik); kochia, Kochia scoparia (L.) Schrad; and Russian thistle, Salsola kali L. This is the first report of transmission of BLTVA to potatoes, beets, and the above-mentioned four weed species. Results of the current study prove that the beet leafhopper is a vector of the potato purple top disease. [ABSTRACT FROM AUTHOR]

Late blight, caused by Phytophthora infestans (Mont.) de Bary, is the most destructive disease of potato worldwide. As this pathogen can rapidly overcome major race-specific resistance genes, identifying the basis for enhanced quantitative resistance has become a crucial element for implementing advanced breeding strategies. A population of 230 full-sib progeny derived from a cross between two diploid hybrid Solanum phureja × S. stenotomum clones was evaluated for foliage resistance against late blight in replicated trials at multiple locations in Pennsylvania between 1999 and 2002. In field experiments, plants were evaluated visually for per cent defoliation, and area under the disease progress curve (AUDPC) was determined. The two parents and three control cultivars (‘Atlantic’, ‘Kennebec’ and ‘Katahdin’) were included in all trials. In all three experiments, the presence of a significant number of clones exhibiting transgressive segregation were observed. There were significant differences among environments as well as among clones, and the clone × environment interaction was also significant. Stability analysis revealed that 37 clones made a significant contribution to the overall environment × clone interaction. Broad-sense heritability for resistance, measured as AUDPC, was estimated as 0.67. The overall results indicate the presence in this potato family of a high level of field resistance against late blight. This segregating diploid family appears to be a good candidate for quantitative trait loci mapping to identify and characterize the genetic components of partial late blight resistance. [ABSTRACT FROM AUTHOR]

Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is a recurrent disease on potato in the Columbia Basin of Washington. The role of ascospores in association with disease onset and stem rot incidence in commercial fields and the role of flower blossoms on plant infection were investigated in 10 fields over 2 years. Ascospores of S. sclerotiorum were detected on a semiselective medium over several weeks, with a peak in number of ascospores near initial full bloom. A high proportion of blossoms at initial full bloom were contaminated with S. sclerotiorum prior to blossom fall in most fields. Stem lesions occurred after row closure and blossom drop, and were associated with mycelial mats growing from contaminated blossoms that had dropped on plant stems in the plant canopy or blossoms that dropped on the ground and stems contacting the ground. Incidence of Sclerotinia stem rot was reduced significantly when blossoms were removed from plants before blossom drop. Flower blossoms were shown to be a paramount bridge between airborne ascospores of S. sclerotiorum and stem infection in the potato canopy. [ABSTRACT FROM AUTHOR]

Isolates of Alternaria solani, cause of potato early blight, collected in 1998 through 2001 from various potato growing areas across the midwestern United States, were tested for sensitivity to azoxystrobin. Isolates collected in 1998, prior to the introduction of azoxystrobin, were tested to establish the baseline sensitivity of the fungus to this fungicide. Isolates collected in subsequent years, not necessarily from the same sites as baseline isolates, were tested to determine if populations of A. solani had become less sensitive to azoxystrobin. Azoxystrobin sensitivity was determined utilizing an in vitro spore germination assay. The effective fungicide concentration that inhibited spore germination by 50% (EC[sub 50]) was determined for each isolate. There was no significant difference in mean EC[sub 50] values between baseline isolates and all other isolates collected through 1999. Mean azoxystrobin EC[sub 50] values of A. solani isolates collected in 2000 and 2001 were significantly higher compared with means from previous years, and mean azoxystrobin EC[sub 50] values from 2001 were significantly higher than means from isolates collected in 2000. A subset of 54 A. solani isolates was evaluated in vitro for cross-sensitivity to pyraclostrobin and trifloxystrobin. A highly significant and strong correlation among the isolates tested for fungicide cross-sensitivity was detected between azoxystrobin and pyraclostrobin; however, the correlation between azoxystrobin and trifloxystrobin, and between trifloxystrobin and pyraclostrobin, was significant but weak. A second subset of five isolates was chosen for in vivo assessment of azoxystrobin, pyraclostrobin, and trifloxystrobin sensitivity. Disease severity on plants treated with azoxystrobin and pyraclostrobin was significantly greater with reducedsensitive A. solani isolates compared with sensitive isolates. Disease severity was not statistically different between azoxystrobin reduced-sensitive and sensitive A. solani isolates on plants treated with trifloxystrobin. This is the first report of a shift in sensitivity to Q[sub o]I fungicides in a fungus possessing only an anamorphic stage. [ABSTRACT FROM AUTHOR]

This article examines suspected potato spindle tuber virus in England. Spindle tuber virus is widely distributed in the U.S. and Canada, where it has been recognized since 1922. It was generally considered an unimportant virus until about 1950 when it reached serious proportions in certain areas and certain varieties. American literature indicates that spindle tuber virus may spread very readily by leaf contact and farm implements in the same way as potato virus X. and can also be transmitted by a variety of insects including aphids, flea beetles, leaf hoppers and grasshoppers. A disease resembling potato spindle tuber has been detected in several crops of Redskin grown in England. Affected crops contained a large proportion of plants with many stems, resembling wildings.

In the last decade several insect genomes have been sequenced, but for most the chromosomal mapping of the identified scaffolds/annotated genes is not available. The lack of this information makes it difficult to analyse various genetic aspects, including the presence of genome rearrangements and the extent of synteny within and across species. We mapped five multigenic DNA families (major and minor rDNAs, histone gene cluster, esterases and carotenoid desaturases) and seven scaffolds corresponding to 9 Mb of the soybean aphid, Aphis glycines, genome and identified loci spanning the four soybean aphid chromosomes. A comparative analysis of the localization of the annotated A. glycines genes with respect to the peach potato aphid, Myzus persicae, and the fly, Drosophila melanogaster, evidenced a lower degree of synteny between the two aphid species than in the aphid-fly comparison. Only 1.4 genes per syntenic block were observed in aphids in contrast to 2.3 genes per block in flies. This higher chromosomal rearrangement rate in aphids could be explained considering that they possess holocentric chromosomes that can favour the stabilization and inheritance of chromosomal rearrangements. Lastly, our experiments did not detect the presence of chimeric assemblies in the newly available A. glycines biotype 1 genome, differently from what reported in assembled genome of other aphid species, suggesting that chromosomal mapping can be used to ascertain the quality of assembled genomes. Image 1 • Aphis glycines is a significant insect pest of soybean in United States, where it causes damages for more than 2 billion dollars annually. • Chromosomal mapping of the A. glycines scaffolds avoided chimeras and/or artefacts in the genome assembly. • The identification of chromosomal markers makes possible the comparison of biotypes. • Comparative studies of A. glycines evidenced a higher rate of genome recombination in aphids than in other insects. [ABSTRACT FROM AUTHOR]

The article reveals the continuous problem posed by nematode viruses to potato crops in the U.S. Two decades ago, existing regulations and scientific breakthroughs had seemingly brought the threats posed by the virus under control. But two events jeopardized that, according to plant pathologist Stewart Gray of the Plant Protection Research Unit (PPRU) of the U.S. Agricultural Research Service (ARS). First, a new race, or population, of this nematode has emerged and second, widespread acceptance and planting of potato varieties that turned out to be symptomless carriers of potato virus Y (PVY) has allowed the disease to reemerge.

The article discusses the green peach aphid or Myzus persicae. The green peach aphid attacks potatoes by siphoning their juices and infecting them with viruses such as the potato leafroll virus which can cause up to $100 million in damage to U.S. potatoes. Entomologist Thomas R. Unruh with the Agricultural Research Service's Yakima Agricultural Research Laboratory developed a tracking and capture method for the aphid which uses egg proteins, mesh screens, and an antibody based test. This will help researchers find out where and when the aphid transmits virus pathogens.

The article reports that the well-tested and superior potato Defender is the only commercial variety in the U.S. whose leaves and tubers are resistant to Phytophthora infestans. Defender's natural resistance allows growers to reduce or eliminate pesticide applications, making it ideal for either conventional or organic production. Scientists scrutinized Defender's performance in test fields from Maine to Washington and from Idaho to Texas. Processors also evaluated its suitability for french fry production and found its starch/sugar proportions suitable for making into frozen potato products.

Provides information on a research conducted by U.S. Agricultural Research Service scientists in Albany, California in 2004 on the development of potato plants which fight Phytophthora infestans, a fungus-like microbe that causes late blight. Discovery of the gene Solanum bulbocastenum (Sbul), a late-blight-resistant species of wild potato that grows in Mexico; Creation of unique hybrids from the fusion of Sbul with the domesticated potato; Performance of Sbul1-equipped potatoes when exposed to the microbe.

Discusses the abstract of the article "Black and Hairy Nightshade, the First Weedy Hosts of Potato virus A in the United States," by P.E. Thomas.

Focuses on the United States Agricultural Research Service's (ARS) Schultz Potato Virus Collection located at the Aroostook Farm in Maine and at the ARS Vegetable Laboratory in Maryland. Basis of the names given to the infectious potato diseases; Cause of potato spindle tube disease; Maintenance of the viruses.

Reports on the testing of bacteria strains that attack fungus on potatoes by the Agricultural Research Service.

Presents news briefs relating to biology. Report that researchers in the U.S. and Italy have analyzed surname distribution in telephone books to estimate human migration rates in Italy; Use of cell fusion to create a potato plant containing high levels of leptine and makes the plants resistant to the Colorado potato beetle, a major pest in the potato industry; Efforts of Jared M. Diamond to explain divorce in nonhuman monogamous animals in darwinian terms; Efforts of marine biologists to understand the massive bleaching of reef-building corals which occurred throughout the Caribbean during the summer and fall of 1987.