Commercial Potato Cultivars Research Articles

In Search of Better Management of Potato Common Scab

Common scab (CS) is an important disease and quality problem in potato crops worldwide. CS degrades the appearance of the potato tubers, thereby diminishing market value. Knowledge of CS has expanded considerably over recent years, enabling improved detection of the causal pathogens and increased understanding of mechanisms of pathogenicity, and providing potential methods of modulating pathogen response for disease resistance. However, effective control of this disease remains elusive, and will require increased understanding of both the host and the pathogen. Traditional control strategies such as irrigation and reduced soil pH are not sufficient and often fail. Optimizing environmental conditions for reduction of CS can also lead to favorable conditions for other diseases. The most desirable control method would be disease-resistant potato cultivars. However, no currently available commercial potato cultivar has been shown to be completely resistant to CS. In this review, we provide an overview of potato CS caused by plant pathogenic Streptomyces species, recent research on mechanisms and management of the disease, and knowledge gaps that limit successful control of this ubiquitous and troublesome disease.

Persistence of Metalaxyl and Mancozeb on Potato Leaves and Their Residues in Tubers

The persistence of fungicides on two commercial cultivars of potato was determined under field conditions at Punjab Agricultural University, Ludhiana, Punjab. Initial deposits of mancozeb on potato leaves were found to be 26.9 and 38.7 mg kg(-1), following application of ready mixture of fungicide metalaxyl 8% + mancozeb 64% (Ridomil MZ) at the rate of 1260 and 2520 g a.i. ha(-1), whereas metalaxyl residues were found to be 35.1 and 49.5 mg kg(-1), respectively. The residue level of mancozeb in potato leaves 15 days after application at single and double doze were 19.0 and 27.0 mg kg(-1) showing a loss of 29.6 and 30.3%, whereas the values for metalaxyl at single and double doze were 0.40 and 0.80 mg kg(-1) showing a loss of 98.9 and 98.4%, respectively. Residues of mancozeb and metalaxyl were not detected at 0.04 and 0.02 mg kg(-1) level in potato tubers at harvest (PHI = 53 days) at both the dosages, respectively. The persistence and dissipation of mancozeb with the application of Ridomil MZ followed similar trend as in Indofil M-45. The rate of fungicide dissipation increased with time after application in both the potato cultivars 'Kufri Chandramukhi' and 'Chipsona'. No significant difference was observed on initial deposit, persistence and dissipation of the two molecules between the two potato cultivars.

Occurrence of potato wart disease (Synchytrium endobioticum) in Bulgaria: identification of pathotype(s) present

Potato wart disease caused by Synchytrium endobioticum was detected for the first time in Bulgaria in 2004. Laboratory tests, pot tests and field tests were carried out to determine which pathotype is present, specifically in Prodanovtsi near the town of Samokov. In addition, potato cultivars were tested for levels of resistance, in order to be used in buffer zones surrounding infested fields. Based on the results obtained in this study, it was found that most probably pathotype 8(F1) is present in Bulgaria. Most of the commercial potato cultivars tested were found to be susceptible to this pathotype. The local cultivars Koral and Bor were resistant, but these are not very important cultivars commercially. The potato cultivars Panda, Désirée and Amorosa were recommended for cultivation in the fields adjacent to infested plots.

Single nucleotide polymorphism discovery in elite north american potato germplasm

BackgroundCurrent breeding approaches in potato rely almost entirely on phenotypic evaluations; molecular markers, with the exception of a few linked to disease resistance traits, are not widely used. Large-scale sequence datasets generated primarily through Sanger Expressed Sequence Tag projects are available from a limited number of potato cultivars and access to next generation sequencing technologies permits rapid generation of sequence data for additional cultivars. When coupled with the advent of high throughput genotyping methods, an opportunity now exists for potato breeders to incorporate considerably more genotypic data into their decision-making.ResultsTo identify a large number of Single Nucleotide Polymorphisms (SNPs) in elite potato germplasm, we sequenced normalized cDNA prepared from three commercial potato cultivars: 'Atlantic', 'Premier Russet' and 'Snowden'. For each cultivar, we generated 2 Gb of sequence which was assembled into a representative transcriptome of ~28-29 Mb for each cultivar. Using the Maq SNP filter that filters read depth, density, and quality, 575,340 SNPs were identified within these three cultivars. In parallel, 2,358 SNPs were identified within existing Sanger sequences for three additional cultivars, 'Bintje', 'Kennebec', and 'Shepody'. Using a stringent set of filters in conjunction with the potato reference genome, we identified 69,011 high confidence SNPs from these six cultivars for use in genotyping with the Infinium platform. Ninety-six of these SNPs were used with a BeadXpress assay to assess allelic diversity in a germplasm panel of 248 lines; 82 of the SNPs proved sufficiently informative for subsequent analyses. Within diverse North American germplasm, the chip processing market class was most distinct, clearly separated from all other market classes. The round white and russet market classes both include fresh market and processing cultivars. Nevertheless, the russet and round white market classes are more distant from each other than processing are from fresh market types within these two groups.ConclusionsThe genotype data generated in this study, albeit limited in number, has revealed distinct relationships among the market classes of potato. The SNPs identified in this study will enable high-throughput genotyping of germplasm and populations, which in turn will enable more efficient marker-assisted breeding efforts in potato.

Population density and life-history parameters of the psyllid Bactericera nigricornis (Forster) on four commercial cultivars of potato

The psyllid Bactericera nigricornis (Forster) (Hemiptera: Triozidae) is one of the most important pests of potato, Solanum tuberosum L., in the Ardabil region, Iran. The use of host plant resistance is an essential component of the integrated management of B. nigricornis. In this study, we investigated the population density of B. nigricornis on four commercial cultivars of potato under field conditions and its life-history parameters under laboratory conditions. In field experiments, the lowest and highest densities of B. nigricornis were observed on cvs. Agria and Marfona, respectively. Population densities did not differ significantly between cvs. Kaiserkrone and Satina. In experiments on life-history parameters, the longest and shortest developmental times of nymphs were observed on cv. Agria (22.3 days) and cv. Marfona (18.2 days). The developmental time of nymphs on Kaiserkrone did not differ significantly from that on Satina. The lowest number of eggs laid per female (47.2) and the lowest survival rate (50%) were observed on Agria. The survival rate on Agria did not differ significantly from that on Kaiserkrone and Satina. The intrinsic rate of natural increase ( r m ) and population growth rate ( λ) were lowest on Agria and highest on Marfona. The generation time on Agria and Kaiserkrone was significantly longer than on Satina and Marfona. The doubling time ( DT) was longest on Agria (15.9 days) and shortest on Marfona (11.8 days). Amongst the cultivars investigated, host plant resistance acted by decreasing the numbers of eggs laid per female, increasing the development time and reducing the survival rate of B. nigricornis, so decreasing population growth. Of the cultivars tested, Agria is the most resistant host and has potential for use in the integrated management of B. nigricornis on potato.

The Golden Potato Cyst Nematode Globodera rostochiensis Pathotype Ro1 in the Saint-Amable Regulated Area in Quebec, Canada.

The golden potato cyst nematode, Globodera rostochiensis (Wollenweber, 1923) Behren, is an economically important parasite of potato (Solanum tuberosum L. subsp. tuberosum) and is recognized as a quarantine pest internationally (2). This pest attacks potato plants and causes stunting of the haulm and the root system, leaf yellowing, and tuber yield losses (2). The pathotype scheme proposed by Kort et al. distinguishes five pathotypes (Ro1, Ro2, Ro3, Ro4, and Ro5) of G. rostochiensis using differential Solanum clones (1). Several resistance genes and quantitative trait loci (QTL) that have been identified in wild Solanum species confer resistance to different G. rostochiensis pathotypes and have been introgressed into commercial potato cultivars (2). Determining G. rostochiensis pathotype(s) is essential to implement efficient management strategies, which include using resistant potato varieties. G. rostochiensis was discovered in the municipality of Saint-Amable, Quebec (QC), Canada in 2006 (3) and was subsequently characterized (4). In this study, cysts were collected from 11 representative infested fields and confirmed to be G. rostochiensis (3). The pathotypes of these nematodes were assessed on seven differential clones (S. tuberosum subsp. tuberosum cv. Desiree, S. tuberosum × S. andigena cv. Maris Piper, S. kurtzianum hybrid 60.21.19, S. vernei hybrid 62.33.3, S. vernei hybrid 58.1642/4, S. vernei hybrid 65.346/19, and S. multidissectum hybrid P55/7) in 2007 and 2009. Briefly, in each 1-liter plastic pot containing 907 g (2 lbs) of soil (3:1 loam/grit v v-1), a single differential Solanum clone was planted and 15 cysts from 1 of 11 fields were inoculated. Five replicates were set up for each Solanum-nematode combination and the pots were arranged in a completely randomized design in a greenhouse at 22°C with a 16-h light period per day. Nine weeks after inoculation, cysts were extracted from each pot and counted. Reproduction factor (Rf) for each replicate was calculated (Rf = Pf/Pi; Pf is the final cyst number and Pi is the initial cyst number added to each pot). Rf values were used to categorize the differential clones into two groups, "susceptible" leading to increase in nematode numbers (Rf > 1) and "resistant" resulting in decrease in nematode numbers (Rf ≤ 1) (1). Our results in 2007 and 2009 were consistent and the pathotype of the nematodes collected from all the fields were identified as Ro1. To our knowledge, this is the first time that the pathotype of G. rostochiensis in the Saint-Amable regulated area was identified. Accordingly, potato cultivars carrying genes or QTL resistant to G. rostochiensis pathotype Ro1 can be used to reduce the nematode numbers in infested fields in the Saint-Amable area, QC.

Resistência de cultivares de batata a Myzus persicae (Sulz.)(Hemiptera: Aphididae)

Aphids are the most important vectors of viruses infecting potato (Solanum tuberosum). We focused on the response of the aphid vector Myzus persicae (Sulzer) to five commercial potatocultivars: Ágata, Jaette Bintje, Mondial, Monalisa and Santè, by traditional antibiosis and antixenosis tests and by the EPG (Electrical Penetration Graph) technique, as a step forward to the design of effective management practices. Our aim was to identify plant factors involved in resistance of these cultivars against M. persicae, both at the surface and in deeper plant tissues. Results from the antixenosis test confirmed a strong preference of M. persicae for the Mondial cultivar. The antibiosis study indicated a lower population development of the aphid in 'Monalisa' when compared to 'Ágata' and 'Jaette Bintje'. EPG assays indicated that 'Santè' inhibited the initial feeding process of M. persicae, whereas 'Monalisa' showed a physical-type of resistance as demonstrated by a very high number of short probes. The cultivar Mondial showed average values for all EPG variables analyzed. The behavior in 'Jaette Bintje' indicated this cultivar was an ideal host for aphid feeding and reproduction. Together, the EPG data revealed the existence of pre and post-phloematics factors in the cultivars under study, which have important implications on the efficiency of transmission and spread of virus in potato by M. persicae.

APPLICATION OF A FUNCTIONAL MATHEMATICAL QUALITY INDEX TO ASPARAGINE, FREE SUGAR AND PHENOLIC ACID CONTENT OF 20 COMMERCIAL POTATO VARIETIES

ABSTRACTIn this article, we apply a functional mathematical index (FMI), introduced in a previous publication, to 20 commercial potato varieties. The index allows evaluation of nutritional, safety and processing “quality parameters” of different potato cultivars. The main goal of the index is to link the quality of the chemical composition with factors that may affect the growth, production, distribution and processing of potatoes and potato products for commercial use. The index has been used to assess FMI values of 20 commercial potato cultivars in terms of their content of asparagine and reducing sugars, which form heat‐induced potentially toxic acrylamide and of antioxidative phenolic compounds, which participate in nonenzymatic browning reactions and may exert beneficial effects after consumption.PRACTICAL APPLICATIONSThe index could be useful to a wide set of users, including consumers of potatoes as well as to potato producers and breeders, because it makes it possible to relate the index to the potato price and operate a more accurate choice for selection of so‐called “optimal potatoes.” Potato producers may find the index useful because it can help them detect the critical points throughout the whole food production chain in order to facilitate selection of high‐quality potatoes for sale to consumers. Potato breeders could apply the index to the development and selection of improved cultivars for commercial use.

Molecular characterization and genetic diversity of potato cultivars using SSR and RAPD markers

This study aimed to evaluate the genetic diversity and identify potato cultivars by RAPD and SSR markers. The genomic DNA of 16 potato cultivars was amplified with 25 RAPD primers that generated 92 polymorphic bands and 20 SSR primer pairs that produced 136 polymorphic bands. The dendrograms generated by cluster analysis distinguished the cultivars genetically although the dendrograms were not correlated in the comparison of the two markers used. The PIC values demonstrated the high information content of the primers used and 16 potato varieties were identified based on six RAPD primers and three SSR primer pairs. Thus, by means of RAPD and SSR markers the genetic diversity was assessed and the 16 commercial potato cultivars analyzed in this study were identified.

Characterization of the multiple resistance traits of somatic hybrids between Solanum cardiophyllum Lindl. and two commercial potato cultivars

Interspecific somatic hybrids between commercial cultivars of potato Solanum tuberosum L. Agave and Delikat and the wild diploid species Solanum cardiophyllum Lindl. (cph) were produced by protoplast electrofusion. The hybrid nature of the regenerated plants was confirmed by flow cytometry, simple sequence repeat (SSR), amplified fragment length polymorphism (AFLP), microsatellite-anchored fragment length polymorphism (MFLP) markers and morphological analysis. Somatic hybrids were assessed for their resistance to Colorado potato beetle (CPB) using a laboratory bioassay, to Potato virus Y (PVY) by mechanical inoculation and field trials, and foliage blight in a greenhouse and by field trials. Twenty-four and 26 somatic hybrids of cph+cv. Agave or cph+cv. Delikat, respectively, showed no symptoms of infection with PVY, of which 3 and 12, respectively, were also resistant to foliage blight. One hybrid of cph+Agave performed best in CPB and PVY resistance tests. Of the somatic hybrids that were evaluated for their morphology and tuber yield in the field for 3years, four did not differ significantly in tuber yield from the parental and standard cultivars. Progeny of hybrids was obtained by pollinating them with pollen from a cultivar, selfing or cross-pollination. The results confirm that protoplast electrofusion can be used to transfer the CPB, PVY and late blight resistance of cph into somatic hybrids. These resistant somatic hybrids can be used in pre-breeding studies, molecular characterization and for increasing the genetic diversity available for potato breeding by marker-assisted combinatorial introgression into the potato gene pool.

Genetic Stability in Potato Germplasm for Resistance to Root Galling Caused by the Pathogen Spongospora subterranea

Spongospora subteranea, the causal agent of potato powdery scab is becoming increasingly important worldwide. Little is known about the genetic basis of resistance to this disease. The present study tested the hypothesis that potato genotypes with stable genetic resistance to “Spongospora root galling” were present in potato germplasm. Root galling index values of 24 genotypes screened for resistance in four field trials (environments) in 2004 and 2005 in Washington State and Idaho were analyzed. Genotypes tested included five resistant, four industry standards and advanced selections from the USDA-ARS, Prosser, WA program. Broad-sense heritability was calculated as 0.76 with a 95% confidence interval of 0.55–0.89, indicating a fairly high genetic component of the trait. Of the 24 genotypes that were tested, eight showed no genotype*environment interactions while six of the remainder had significant variance (i.e., they were unstable) after removal of genotype*environment variance. Among the five resistant genotypes, PA95B2-4 was stable, and PA98N5-2, PA98NM38-1, PO94A009-7 and POR00HG5-1 were stable after the removal of environmental heterogeneity. Among the four industry standards, Shepody was unstable, whereas Ranger Russet, Russet Burbank and Umatilla Russet were stable after the removal of genotype*environment variance. Stable resistance to “Spongospora root galling” was identified. A large portion of the variation was genetic, which will enable breeders to use resistant and stable potato genotypes as parents in future breeding to develop superior commercial potato cultivars with resistance to “Spongospora root galling”.

Performance of a North American Field Population and a Laboratory Colony of the Potato Tuberworm,Phthorimaea operculella, on Foliage of Resistant and Susceptible Potato Clones

Foliar resistance of two potato clones was tested against a Columbia Basin field population (CBFP) and a Colorado laboratory colony (COLC) of the potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae). The first clone was a cross of a cultivated potato, Solanum tuberosum L. (Solanales: Solanaceae), and a wild potato, Solanum berthaultii Hawkes (Q 174-2); the second clone was cv. Allegany, S. tuberosum L.. In no-choice assays, defoliation by P. operculella larvae of COLC and CBFP did not differ on Allegany and Q174-2. Larval weight and production of COLC and CBFP colonies were similarly reduced on Q174-2 compared to cv. Allegany, although larval weights and production of the CBFP population were slightly less affected by the host. Larval production by the COLC on Allegany was greater than that on Q174-2, while that of the CBFP on Allegany and Q174-2 did not differ. However, production of P. operculella larvae by the CBFP on Q174-2 during no-choice assays was greater than that in choice tests, indicating reduced host preference. Most of the larvae recovered from either host were fourth instars, followed by third instars. Although the levels of resistance expressed by Q174-2 potato clone to the two P. operculella populations differed in magnitude, nearly all of P. operculella performance criteria measured in this study were adversely affected by Q174-2 foliage compared to the commercial potato cultivar, cv. Allegany.

Identification and Quantification of Steroidal Alkaloids from Wild Tuber-Bearing Solanum Species by HPLC and LC-ESI-MS

Wild Solanum species are characterized by several types of glycoalkaloids (GAs), which are usually not found in commercial potato cultivars. These alkaloids serve as defence compounds against herbivores and microorganisms, especially fungi. In this study, the GA composition of tuber and leaf material of 17 wild Solanum species was analysed qualitatively by liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) and quantitatively by high-performance liquid chromatography. The GAs identified were α-solanine, α-chaconine, β-chaconine, solasonine, solamargine, demissine, dehydrodemissine, α-tomatine, dehydrotomatine, commersonine, dehydrocommersonine, leptine I and leptine II. Most species accumulated the common potato GAs α-solanine and α-chaconine in tubers and solasonine and solamargine additionally in leaves. In some species, such as S. acaule ssp. acaule, S. demissum and S. polyadenium, substantial amounts of unusual alkaloids were detected. By using LC-ESI-MS, we detected several minor alkaloids such as dehydrogenated forms of α-tomatine, demissine and commersonine for the first time. Total GA content, expressed as the sum of the four main alkaloids α-solanine, α-chaconine, solamargine and solasonine differed from species to species. In general, GA contents in leaf tissue were higher and GA patterns were more complex than those of tubers.

Transgenic resistance of Bulgarian potato cultivars to the Colorado potato beetle based on Bt technology

Colorado potato beetle, Leptinotarsa decemlineata Say, is the most destructive insect pest of potatoes. When the population of beetles is high, plants can be completely defoliated and commercial potato production is nearly impossible without control of the beetle. The beetles have shown a tremendous ability to develop resistance against insecticides. Previously, a biotechnology approach to control Colarado potato beetle based on the use of the synthetic Bt gene was developed. In this article, a transformation procedure for three commercial Bulgarian potato cultivars was developed and potentially commercial transgenic lines have been selected based on field resistance to Colorado potato beetles and yield. Plants were transformed with the Bacillus thuringiensis (Bt) cry3A gene using Agrobacterium-mediated transformation. 110 plants from the three cultivars were regenerated and tested by double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). The Cry3A protein accumulation varied across the transgenic lines, rating from very low to 71.5 μg/g fresh weight. 21 transgenic lines expressing the Cry3A protein at levels above 10 μg/g fresh weight were tested in two successive years in filed conditions at two different locations of the country. All transgenic lines compared with the controls, nontransgenic potatoes from the respective cultivar, were consistently protected from foliar damages from all developmental stages of the beetle. The comparison of all properties of the tested transgenic lines, including variety phenotypes and tuber yield, allowed the selection of the most promising 2–3 lines per cultivar. Selected lines produced tuber amounts 80–100% higher compared with the control, non-transgenic plants. Those lines were grown for mass propagation during the third year of field experiments. The presence of the transgene in these lines was confirmed with the use of primers specific to the transgene by polymerase chain reaction (PCR). Additionally, the results from the insect bioassay showed that these lines were highly resistant to insect feeding, leading to 100% of mortality of larval populations. In summary, we generated potentially commercial potato lines highly resistant to Colorado potato beetle using Bt technology that may have a profound impact on development of sustainable agriculture in Bulgaria. This is one of the several agriculture biotechnology products entirely developed and tested in Bulgaria.

Host resistance and influence of tuber surface on larval performance of potato tuberworm (Lepidoptera: Gelechiidae)

Potato tuberworm (PTW), Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae), is one of the most important pests of potatoes in tropic and subtropic regions. Previous studies suggested that tuber periderm may limit larval penetration and establishment of PTW. Short term influence of parental host plant acclimatization, influence of tuber dormancy and influence of tuber periderm (the outer cork layer of tubers) on aspects of PTW biology were investigated on tubers of a susceptible commercial potato cultivar, cv. Allegany (Solanum tuberosum L.), and a resistant hybrid potato clone, Q174-2 (S. tuberosum × S. berthaultii Hawkes). Short-term parental host plant acclimatization did not affect numbers of PTW larvae on resistant and susceptible tubers. Numbers of larvae produced on tubers of Q174-2, and Allegany, were similar although larval weight was less on Q174-2 than on Allegany. Larval production increased with tuber age on both susceptible and resistant potato clones, suggesting that bud sprouts may enhance fitness by providing food and shelter for first instars prior to tuber entry. Removal of tuber periderm led to a significant increase in larval survival on Allegany and Q174-2, although proportional survival on Allegany and Q174-2 was similar to that on intact tubers, suggesting the involvement of internal rather than external periderm factors in tuber resistance of Q174-2. Weights of larvae reared on Q174-2 were consistently less than those of larvae reared on susceptible potato tubers in both intact and peeled tuber assays. Although the expression of periderm-mediated tuber resistance declines with tuber age, such resistance could significantly reduce preharvest field infestations by PTW and constitute an important component of sustainable PTW management, particularly for fresh market crops and for those potato crops stored for several months or less in the absence of refrigeration.

Estimating Maximum Tuber Length of Potato Based on the Number of Fully Expanded Leaves

Defining growth stages of the potato plant (Solanum tuberosum L.) based on aboveground morphological characteristics could be more practical than using underground characteristics such as tuber size. The applicability of this approach was tested in Cyprus for a spring‐harvested crop sown in a Tera Rosa soil with three different within‐row spacings (15, 25, and 35 cm). The development of various tuber characteristics of three commercial potato cultivars (cvs. “Cara”, “Nicola”, and “Spunta”) was monitored for two growing seasons. The three cultivars represent late, medium, and early maturity classes. Various tuber sizes obtained from each cultivar were related with the number of fully expanded leaves (NFEL) based on linear equations. For individual cultivars, the NFEL appeared to be a reliable aboveground parameter for estimating the size of the largest tuber during the early stages of growth. Defining growth stages based on NFEL could also be a practical approach for the farmers to perform activities, which must be done at a specific developmental stage.

Adaptation of potato to high temperatures and salinity-a review

Because most commercial potato cultivars were developed in temperate regions, they are adapted, therefore producing the greatest yield under long photoperiods and moderate temperatures. Both heat and salinity stress reduce yield markedly. As potato production moves to areas of the globe where either or both heat and salinity stress are likely to be factors that affect production, our need increases for potato germplasm that can tolerate these adverse conditions. Genetic studies on germplasm variability have revealed species or even cultivars of potato that can resist abiotic stress. The inheritance of abiotic stress resistance is likely to be multigenic, a factor that may limit the utility of transgenic approaches to stress tolerance. However, the development of new methodology, such as association genetics in conjunction with marker-assisted selection, offers promise that stress-tolerant germplasm can be developed as our need increases.

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.

Occurrence of the R1 allele conferring resistance to late blight in potato R‐gene differentials and commercial cultivars

A total of 23 Scottish and 14 Dutch potato R‐gene differentials as well as five Austrian, two Dutch and two German commercial potato cultivars were screened for the R1 allele conferring resistance to Phytophthora infestans carrying Avr1, via PCR amplification and sequencing. A single 1400 bp fragment with complete sequence identity to the corresponding part of the R1 allele, was obtained from genomic DNA of all potato R‐gene differential clones whose denomination indicates R1 or a combination of R1 and other major resistance factors. The R1 allele was detected, as expected, in all these clones. This fragment also occurred in one Austrian and one German cultivar. Unexpectedly, the same R1 allele also was detected within all R5, R6 and R9 differentials.

Improving the nutritive value of tubers: Elevation of cysteine and glutathione contents in the potato cultivar White Lady by marker-free transformation

The amino acids that limit the nutritive value of potato are the sulfur containing amino acids methionine and cysteine. Manipulation of the targeted amino acid biosynthesis is a way to circumvent this problem. Cysteine is synthesised from O-acetyl-l-serine formed by serine acetyltransferase (SAT). To increase the cysteine content of the commercial potato cultivar White Lady the chimeric SAT-coding cysE gene from Escherichia coli under the control of the constitutive CaMV 35S promoter and fused to the chloroplast targeting rbcS 5'-transit peptide sequence was introduced into the White Lady genome. Novelty of the approach was the application of marker-free transformation. Two transgenic lines were obtained that accumulated the cysE mRNA in high amounts. Crude leaf extracts of these plants exhibited up to 80- and 20-fold higher SAT activity in leaves and tubers, respectively, than those prepared from non-transformed plants. Levels of cysteine and glutathione both in leaves and tubers were 1.5-fold higher in average than in control plants. The alterations observed had no effect on tuber yield and sprouting behaviour. Gas chromatography coupled to mass spectrometry showed that all other amino acids than cysteine were unaffected. Here we demonstrate for the first time that the cysteine content of tubers can be enhanced by metabolic engineering.