Tuber Tissue Research Articles

Cultivated and wild Solanum species as potential sources for health-promoting quality traits

In this study, several genotypes of cultivated (Solanum tuberosum subsp. andigena, S. phureja) and wild, tuber-bearing Solanum species (S. chacoense, S. pinnatisectum) were examined for concentrations of antioxidants, soluble phenols and proteins in their tuber tissue. The potato genotypes differed considerably in all these traits. Amounts of antioxidants ranged from 0.06 to 4.22 μg/mg fresh weight (fw) when the ascorbic acid equivalent was measured and from 0.08 to 3.98 μg/mg fw for the trolox equivalent. The wild species S. pinnatisectum exhibited on average higher levels of both types of antioxidants than the other Solanum species, and it also had the highest quantities of soluble phenols and proteins in its tuber tissue. Among the species, S. phureja ranked on the lowest level of antioxidant potential.

EFFECT OF IRRIGATION WATER QUANTITY AND FARMYARD MANURE ON POTATO PLANT GROWN IN SANDY SOIL

This experiment was carried out during the two successive summer seasons of 2009 and 2010 at a Private Farm in EL-Salhaia El-Gadida region, Sharkia Governorate on potato plant (Solanum tuberosum L.) cultivar Diamantgrown under sandy soil conditions using drip irrigation system to study the effect of quantity of irrigation water (750, 1250 and 1750 m3/ fed.) and farmyard manure (10, 20 and 30 m3/ fed.) as well as their interactions on growth, yield and its quality as well as water use efficiency. Plant height, number of leaves/ plant, shoot dry weight, free and total water in leaf tissues, N, P and K percentages and their uptake by shoot significantly increased with increasing irrigation water quantity up to the highest level (1750 m3/ fed). Irrigation water quantity of 1250 or 1750 m3/ fed. recorded the maximum values of average tuber weight, tuber yield/ plant and total yield/ fed, N, P, carbohydrates, starch and DM percentages in tuber tissues. Bound water, cell sap, osmotic pressure and proline amino acid in leaf tissues as well as water use efficiency (WUE) by potato plants were significantly increased with decreasing irrigation water quantity up to the lowest level (750 m3/ fed). Farmyard manure (FYM) at 20 m3/ fed. significantly increased plant height, number of leaves/ plant, shoot dry weight, free and total water percentages, P % and its uptake by shoot, N, P, total carbohydrates, starch and dry matter % in tubers, on the other hand, N and K contents and their uptake by shoot, average tuber weight, yield/ plant and total yield/ fed. as well as water use efficiency were significantly increased with increasing FYM up to 30 m3/ feddan. Interaction treatment between water quantity at 1250 m3/ fed. and FYM at 30 m3/ fed. was the superior treatment for enhancing shoot dry weight/ plant, N % and its uptake by shoot, N, K and total carbohydrates in tubers. While, the interaction treatment between 1750 m3/ fed. water quantity and 30 m3/ fed. FYM gave the highest values of P and K percentages and their uptake by shoot, tuber yield/ plant and total yield/ feddan.

Study on the Relationship Between the Toxin of Phytophthora infestans (Mont.) de Bary and Resistance of Potato

Plant pathogenic fungi produce mycotoxins which may lead host plants to produce disease symptoms and may have a significant positive role in the course of disease development. The putative Phytophthora infestans toxins were prepared by culturing in liquid medium (60 g rye and 10% tomato juice L- 1) for 1 mon at 17°C, filtering through four layers of cheesecloth and being precipitated by ammonium sulfate. The resulted putative toxin solutions were used to study the effects on 3 potato varieties (both leaf and tuber tissues). The results show that potato leaves and tubers exhibit symptoms similar to the late blight resulted from P. infestans infection. Potato varieties reacting differentially to both the toxin dilutions and toxins produced by different P. infestans isolates suggested the presence of toxin-mediated specificities between potato and P. infestans. Potato leaf and tuber tissues have different and contrary reactions to the toxin. Toxin-mediated specificities are likely present between potato and P. infestans.

Coordinate expression of AOS genes and JA accumulation: JA is not required for initiation of closing layer in wound healing tubers

Wounding induces a series of coordinated physiological responses essential for protection and healing of the damaged tissue. Wound-induced formation of jasmonic acid (JA) is important in defense responses in leaves, but comparatively little is known about the induction of JA biosynthesis and its role(s) in tuber wound-healing. In this study, the effects of wounding on JA content, expression of JA biosynthetic genes, and the involvement of JA in the initiation of closing layer formation in potato tubers were determined. In addition, the role of abscisic acid (ABA) in wound-induced JA accumulation was examined. The basal JA content in non-wounded tuber tissues was low (<3 ng g −1 FW). Two hours after wounding, the JA content increased by >5-fold, reached a maximum between 4 and 6 h after wounding, and declined to near-basal levels thereafter. Tuber age (storage duration) had little effect on the pattern of JA accumulation. The expressions of the JA biosynthetic genes ( StAOS2, StAOC, and StOPR3) were greatly increased by wounding reaching a maximum 2–4 h after wounding and declining thereafter. A 1-h aqueous wash of tuber discs immediately after wounding resulted in a 94% inhibition of wound-induced JA accumulation. Neither JA treatment nor inhibition of JA accumulation affected suberin polyphenolic accumulation during closing layer development indicating that JA was not essential for the initiation of primary suberization. ABA treatment did not restore JA accumulation in washed tuber tissues suggesting that leaching of endogenous ABA was either not involved or not solely involved in this loss of JA accumulation by washing. Collectively, these results indicate that JA is not required for the induction of processes essential to the initiation of suberization during closing layer development, but do not exclude the possibility that JA may be involved in other wound related responses.

Association genetics in Solanum tuberosum provides new insights into potato tuber bruising and enzymatic tissue discoloration

BackgroundMost agronomic plant traits result from complex molecular networks involving multiple genes and from environmental factors. One such trait is the enzymatic discoloration of fruit and tuber tissues initiated by mechanical impact (bruising). Tuber susceptibility to bruising is a complex trait of the cultivated potato (Solanum tuberosum) that is crucial for crop quality. As phenotypic evaluation of bruising is cumbersome, the application of diagnostic molecular markers would empower the selection of low bruising potato varieties. The genetic factors and molecular networks underlying enzymatic tissue discoloration are sparsely known. Hitherto there is no association study dealing with tuber bruising and diagnostic markers for enzymatic discoloration are rare.ResultsThe natural genetic diversity for bruising susceptibility was evaluated in elite middle European potato germplasm in order to elucidate its molecular basis. Association genetics using a candidate gene approach identified allelic variants in genes that function in tuber bruising and enzymatic browning. Two hundred and five tetraploid potato varieties and breeding clones related by descent were evaluated for two years in six environments for tuber bruising susceptibility, specific gravity, yield, shape and plant maturity. Correlations were found between different traits. In total 362 polymorphic DNA fragments, derived from 33 candidate genes and 29 SSR loci, were scored in the population and tested for association with the traits using a mixed model approach, which takes into account population structure and kinship. Twenty one highly significant (p < 0.001) and robust marker-trait associations were identified.ConclusionsThe observed trait correlations and associated marker fragments provide new insight in the molecular basis of bruising susceptibility and its natural variation. The markers diagnostic for increased or decreased bruising susceptibility will facilitate the combination of superior alleles in breeding programs. In addition, this study presents novel candidates that might control enzymatic tissue discoloration and tuber bruising. Their validation and characterization will increase the knowledge about the underlying biological processes.

Pathogenicity and potential capacity for producing mycotoxins by Fusarium sambucinum and Fusarium solani isolates derived from potato tubers

Studies of potential abilities of F. sambucinum to produce trichothecenes was conducted on isolates previously confirmed as belonging to this species by PCR. In all cases, A positive result for the presence of Tri5 gene, coding the ability to synthesize these mycotoxins. There was no potential to synthesize trichothecenes by F. solani. Further analysis concerned the potential ability of F. sambucinum to produce group B trichothecenes (DON and NIV). No isolate gave the expected amplification product (282 bp for deoxynivalenol and 312 bp for nivalenol), which would indicate the potential for producing these mycotoxins. Studies have shown the ability to produce trichothecenes of group A. Analysis of the potential ability for the synthesis of enniatins by F. sambucinum showed that 91% of isolates gave of 332 bp amplification product, which proves them as potencial producers of these mycotoxins. There were significant differences in the pathogenicity of F. sambucinum and F. solani represented by the size of decay caused by these species. The rotten tissue area caused by F. sambucinum was about 10 times bigger than after inoculation by F. solani. Furthermore, isolates within the same species (F. sambucinum) showed diverse pathogenicity. It should be noted, however, that the concentration of mycotoxins does not depend on the size of rotten tissue of potato tubers. Isolate, which caused the most severe disease symptoms, produced low concentrations of mycotoxins.

Expression of the Viral Antigen VP60 in Transgenic Potatoes and its Effect on the Nutritional Composition of Tubers

Recombinant plant-derived pharmaceuticals have been investigated for the last two decades and some products will soon be brought to market. Since veterinary pharmaceuticals seem to be the front-runners of plant-derived vaccines, we selected one model subunit vaccine, the structural capsid protein VP60 against rabbit haemorrhagic disease, and analyzed the expression of three different sequences representing the VP60 open reading frame in potato plants. The generation of antigenic VP60 molecules in the leaf and tuber tissue of potato was tremendously enhanced by replacing virus-derived sequences with plant-optimized codons. In order to identify potentially undesirable alterations in the composition of these genetically modified food components, we studied their nutrient composition and nutritional value in comparison to two parental conventional breeding varieties (Albatros and Desiree). The largest differences in nutrient composition were found between the two conventional breeds and between conventional Desiree and its near-isogenic genetically modified potato plant, indicating that genetic modification as well as conventional breeding can influence nutrient composition. Nevertheless, most parameters of nutritional value seemed to be more affected by conventional breeding than by genetic modification.

First Report of Potato mop-top virus in North Dakota.

Potato mop-top virus (PMTV) is the type member of the genus Pomovirus. PMTV is an important pathogen of potato, causing significant economic losses in Northern Europe, North and South America, and Asia (3). PMTV in the United States was first reported in Maine (2). PMTV is vectored by the plasmodiophoromycete Spongospora subterranea cv. subterranea, which causes powdery scab of potato (1). S. subterranea and PMTV are usually associated with cool and humid environments. In the spring of 2010, six potato tubers of cv. Russet Burbank were received from a commercial potato farm in Grand Forks County in North Dakota. The tubers had multiple, internal, concentric, necrotic arcs and circles. The presence of PMTV in the necrotic lesions was verified by a positive double-antibody sandwich-ELISA (Agden Ltd., Ayr, Scotland). The tuber lesions had an absorbance value (405 nm) at least two times greater than that of the negative control sample, which consisted of a healthy tuber. Total RNA was extracted from lesions of six different tubers that tested positive by ELISA using a Total RNA Isolation kit (Promega Corp. Madison, WI). These extracts were tested for PMTV by reverse transcription (RT)-PCR using two different sets of primers. The primer set H360/C819 targeted the coat protein (CP) of PMTV and yielded an amplicon of 460 bp (4). The amplicons generated from the necrotic lesions were cloned (TOPO Cloning; Invitrogen, Carlsbad, CA) and sequenced. Another set of primers, pmtF4/pmtR4, designed to bind to a region in RNA 2 of PMTV, yielded a 417-bp amplicon that also was cloned and sequenced (3). The sequences from all six tuber lesions were identical for the respective primer sets. A consensus sequence for each primer pair was submitted to GenBank (Accession No. HM776171 for primers pmtF4/pmtR4 and No. HM776172 for primers H360/C819). The sequences obtained from the H360/C819 and pmtF4/pmtR4 amplicons were 99% identical to the corresponding regions of PMTV isolates from Northern Europe (GenBank Accession Nos. AM503629 and AJ277556, respectively). Freeze-dried, necrotic tuber tissue from all six tubers was also tested at a USDA Laboratory in Prosser, WA by RT-PCR with the H360/C819 primer pair (4), confirming the results above. Cloning and sequencing of one of the amplicons revealed 100% similarity to the sequence described above for these primers (GenBank Accession No. HM776172), confirming the presence of PMTV in the symptomatic tubers. None of the symptomatic tubers tested positive for Tobacco rattle virus, Tomato spotted wilt virus, Alfalfa mosaic virus, Potato leafroll virus, or the necrotic strains of Potato virus Y by RT-PCR. To our knowledge this is the first report of PMTV in North Dakota.

Mechanical Properties of Plant Cell Walls Probed by Relaxation Spectra

Transformants and mutants with altered cell wall composition are expected to display a biomechanical phenotype due to the structural role of the cell wall. It is often quite difficult, however, to distinguish the mechanical behavior of a mutant's or transformant's cell walls from that of the wild type. This may be due to the plant's ability to compensate for the wall modification or because the biophysical method that is often employed, determination of simple elastic modulus and breakstrength, lacks the resolving power necessary for detecting subtle mechanical phenotypes. Here, we apply a method, determination of relaxation spectra, which probes, and can separate, the viscoelastic properties of different cell wall components (i.e. those properties that depend on the elastic behavior of load-bearing wall polymers combined with viscous interactions between them). A computer program, BayesRelax, that deduces relaxation spectra from appropriate rheological measurements is presented and made accessible through a Web interface. BayesRelax models the cell wall as a continuum of relaxing elements, and the ability of the method to resolve small differences in cell wall mechanical properties is demonstrated using tuber tissue from wild-type and transgenic potatoes (Solanum tuberosum) that differ in rhamnogalacturonan I side chain structure.

Relative quantitative proteomic analysis reveals wound response proteins correlated with after‐cooking darkening

Many common potato tuber defects are difficult to elucidate because of the degree of genetic complexity involved, making systems biology approaches necessary. Interaction between chlorogenic acid and iron is responsible for the darkening of potato tuber tissues upon heating--termed after-cooking darkening (ACD). To explore mechanisms of darkening severity in tuber tissues, we have employed relative quantitative proteomics to discover differentially expressed proteins involved in ACD. Tuber tissue samples were collected from a family of diploid clones which possess a highly segregated degree of the darkening. Exploiting this segregation, as well as the observation that darkening is more prevalent in the stem end of the tuber than the apical end, three sample groups were formed: (i) stem ends of three high-ACD clones, (ii) stem ends of three low-ACD clones, and (iii) apical ends of three low-ACD clones. Protein samples were digested and differentially labeled using isotopic reductive methylation, allowing for an orthogonal two-way comparison of protein profiles of the sample groups using 2-D-LC-MS/MS. Using a cutoff fold change of 2 between the high- and the low-ACD sample groups, 30 proteins showed a correlation with tissue darkening. Overall, we observed changes in relative protein abundance that showed an enhanced wound-response program in high-ACD tissues. Among these proteins, five proteins were further validated at the transcript level using qRT-PCR. These proteins may be incorporated into design strategies to create potato cultivars with low levels of ACD.

POSTHARVEST SODIUM SILICATE TREATMENT INDUCES RESISTANCE IN POTATO AGAINST FUSARIUM SULPHUREUM

Dry rot, caused by Fusarium spp. is reported as the most important postharvest disease of potato in China. Farsarium sulphureum is one of the principal pathogens. Potato ('Atlantic') tuber and slices treated by sodium silicate at 100 mM were investigated to reduce dry rot and to induce defense responses. The results showed that sodium silicate significantly decreased lesion expansion on tuber challenged inoculation 3 days after treatment and infection ability of F. sulphureum inoculated on slices 48 hours after treatment. The activity of peroxides (POD), polyphenoloxidase (PPO), phenylalanine ammonialyase (PAL) and β-1, 3-glucanase (GLU) and the production of total phenolic, flavanoid in tuber tissue after treatment with 100 mM of sodium silicate were not higher than that of control, even lower during early treatment period, although the value of them gradually increased with treatment time prolonging. However, the activity of POD, PPO, PAL and GLU and the production of total phenolic, flavanoid dramatically increased after challenging with F. sulphureum. The results suggested that sodium silicate could enhance defense responses in potato tubers against pathogen infection.

Thermoelectric effect on potato tuber (Solanum tuberosum L.) - short communication

For scaning rheological properties of tuber tissue during heating, different physical techniques are used. The experiments done on low solids tubers of cv. Magda have shown that maximum thermoelectric effect was obtained at about 60&amp;deg;C in the temperature region where the gelatinisation process of intra-cellular starch starts and some few cell disruptions occur.

Histochemical analysis of the root tuber of Polygonum multiflorum Thunb. (Fam. Polygonaceae)

Authentication is the first priority in quality evaluation of Chinese herbal medicines (CHMs). The most commonly used authentication methods are morphological identification and microscopic identification. Unfortunately, these two methods cannot provide the chemical information needed to assess the quality of CHMs. In this study, a combination of fluorescence microscopy and high performance liquid chromatography-mass spectrometry (HPLC-MS) was used to analyze the chemical profiles of the tissues of the raw root tubers of Polygonum multiflorum Thunb. The results showed that the cork cells, cortex, and vessels in transverse sections of the raw root tuber of P. multiflorum fluoresced differently. Further analysis by HPLC-MS revealed that anthraquinones are mainly distributed in the cortex, and 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucopyranoside could be found in all tissues of the raw root tubers of P. multiflorum with its relative content as cork > cortex > xylem of allotype vascular bundles > xylem of central vascular bundles. Moreover, the fluorescence characteristics of the tissues from the steamed root tuber of P. multiflorum were compared and showed different fluorescence from those of raw material. From these results, it can be deduced that the root tuber of P. multiflorum with a broader cortex and fewer vascular bundles visible in a transverse section should be of better quality. The different fluorescence characteristics can be used to differentiate raw root tubers of P. multiflorum from those that have been steamed.

A quantitative real-time PCR method for in planta monitoring of Phytophthora infestans growth

To establish a reliable and rapid protocol to simultaneously obtain high quality DNA from an infected host plant and the infecting pathogen. To develop an accurate and sensitive low-cost assay for the quantification and in planta monitoring of Phytophthora infestans growth. In this study, we describe a SYBR Green-based quantitative real-time PCR (qPCR) method for the quantification of P. infestans. The method is based on a simultaneous plant-pathogen DNA purification followed by a qPCR in which the relative quantification of pathogen and plant DNA is performed. Besides assuring an accurate quantification, the use of a plant gene provides a reliable indicator of sample quality, allowing the exclusion of inappropriate samples. By applying this methodology, we were able to detect P. infestans in potato leaf and tuber tissue before the first symptoms of the disease were observed and to monitor the in planta growth of the pathogen for 6 days. This is a reliable low-cost assay that provides rapid, accurate and sensitive quantification of the late blight pathogen, allowing the in planta monitoring of P. infestans growth. The quantitative nature of the assay described in this study may be useful in plant breeding programmes and basic research. The method is appropriate for the comparison of cultivars with different, and even subtle, degrees of pathogen resistance and in the screening of new anti-oomycete compounds. The method can be easily adapted to tomato and the model plant Nicotiana benthamiana.

First Report of Soft Rot of Potatoes Caused by Dickeya dadantii in Zimbabwe

A survey was carried out in the potato- (Solanum tuberosum L.) growing regions of Zimbabwe in April 2009 to assess the prevalence of bacterial soft rot. A total of 125 tubers with soft rot symptoms were collected. The disease caused severe economic losses ranging from 20 to 60% on tubers in the field and in storage. Affected tubers had symptoms that ranged from light vascular discoloration to complete seed piece decay. Infected tuber tissue was often cream colored and soft to the touch. In the field, plants showed severe wilting, often accompanied by a slimy, brown necrosis of the lower stems. Seventy-five of 125 isolations from diseased tubers yielded pectolytic bacteria on crystal violet pectate (CVP) medium and colonies were characterized after purification on King's B medium. All 75 isolates were gram-negative rods, oxidase negative, facultatively anaerobic, able to degrade pectate, and rot potato slices. They grew at 37°C, were sensitive to erythromycin, positive for phosphatase, indole production, cis-aconitate, lactose, d-arabinose, meso-tartrate, casein, d-melibiose, myo-inositol, and malonate utilization, while negative for acid production from trehalose, inuline, and α-methyl glucose. Dickeya dadantii (Erwinia chrysanthemi 3937 from the Scottish Research Institute) was included in all biochemical and pathogenicity tests. These characteristics are typical for two species, D. zeae and D. dadantii (2). Thus, the 75 isolates were further identified by PCR amplification with BOX and REP primers (3) and five isolates by gyrB sequence analysis (1). These analyses give support for the isolates being D. dadantii. Partial gyrB sequence analysis showed that the analyzed isolates had 96% sequence identity with the D. dadantii type strain Ech 586T (GenBank Accession No. CP001836.1). One-microliter suspensions (108 CFU per ml) of 20 samples were injected into the stolon end of potato tubers (S. tuberosum L.) cv. BP1. Each isolate was inoculated into three tubers, which were maintained at 25°C. Three control tubers were inoculated with sterile distilled water. Soft rot symptoms identical to those observed in the field and in storage appeared on all inoculated tubers 1 to 2 days after inoculation but not on the control tubers. A bacterium with identical characteristics to those described above was consistently reisolated from the rotted tissue of inoculated tubers. To our knowledge, this is the first report of soft rot on potato in Zimbabwe caused by D. dadantii, formerly referred to as E. chrysanthemi. This finding has implications for import and export of potato material into and out of Zimbabwe. Zimbabwe imports seed from various countries because of the current seed shortage and exports table potatoes to other African states.

Magnetic Resonance Imaging Characteristics of Nonthermal Irreversible Electroporation in Vegetable Tissue

We introduce and characterize the use of MRI for studying nonthermal irreversible electroporation (NTIRE) in a vegetative tissue model. NTIRE is a new minimally invasive surgical technique for tissue ablation in which microsecond, high electric-field pulses form nanoscale defects in the cell membrane that lead to cell death. Clinical NTIRE sequences were applied to a potato tuber tissue model. The potato is used for NTIRE studies because cell damage is readily visible with optical means through a natural oxidation process of released intracellular enzymes (polyphenol oxidase) and the formation of brown-black melanins. MRI sequences of the treated area were taken at various times before and after NTIRE and compared with photographic images. A comparison was made between T1W, T2W, FLAIR and STIR MRIs of NTIRE and photographic images. Some MRI sequences show changes in areas treated by irreversible electroporation. T1W and FLAIR produce brighter images of the treated areas. In contrast, the signal was lost from the treated area when a suppression technique, STIR, was used. There was similarity between optical photographic images of the treated tissue and MRIs of the same areas. This is the first study to characterize MRI of NTIRE in vegetative tissue. We find that NTIRE produces changes in vegetative tissue that can be imaged by certain MRI sequences. This could make MRI an effective tool to study the fundamentals of NTIRE in nonanimal tissue.

Gene transfer into Solanum tuberosum via Rhizobium spp.

Agrobacterium tumefaciens-mediated transformation (ATMT) is the preferred technique for gene transfer into crops. A major disadvantage of the technology remains the complexity of the patent landscape that surrounds ATMT which restricts its use for commercial applications. An alternative system has been described (Broothaerts et al. in Nature 433:629-633, 2005) detailing the propensity of three rhizobia to transform the model crop Arabidopsis thaliana, the non-food crop Nicotiana tabacum and, at a very low frequency, the monocotyledonous crop Oryza sativa. In this report we describe for the first time the genetic transformation of Solanum tuberosum using the non-Agrobacterium species Sinorhizobium meliloti, Rhizobium sp. NGR234 and Mesorhizobium loti. This was achieved by combining an optimal bacterium and host co-cultivation period with a low antibiotic regime during the callus and shoot induction stages. Using this optimized protocol the transformation frequency (calculated as % of shoots equipped with root systems with the ability to grow in rooting media supplemented with 25 μg/ml hygromycin) of the rhizobia strains was calculated at 4.72, 5.85 and 1.86% for S. meliloti, R. sp. NGR234 and M. loti respectively, compared to 47.6% for the A. tumefaciens control. Stable transgene integration and expression was confirmed via southern hybridisation, quantitative PCR analysis and histochemical screening of both leaf and/or tuber tissue. In light of the rapid advances in potato genomics, combined with the sequencing of the potato genome, the ability of alternative bacteria species to genetically transform this major food crop will provide a novel resource to the Solanaceae community as it continues to develop potato as both a food and non-food crop.

Evidence that Cell Death is Associated with Zebra Chip Disease in Potato Tubers

Zebra chip (ZC) is an established and highly destructive disease of potato (Solanum tuberosum L.) that occurs in several southwestern states of the United States, Mexico, Central America, and New Zealand. The causal agent for this disease has not been identified. However, the bacterium “Candidatus Liberibacter solanacearum” and the potato psyllid, Bactericera cockerelli (Sulc), its insect vector, are associated with the disease. Tubers from ZC-affected potato plants exhibit dramatic browning of vascular tissue concomitant with “necrotic flecking” both of which can affect the entire tuber. Upon frying, these tubers develop a characteristic striped pattern of discoloration rendering them unmarketable. These characteristic ZC symptoms in the tubers have been suggested to be associated with general cell death, though no evidence to confirm this hypothesis has been shown. In order to determine if cell death is associated with ZC disease, a series of experiments were undertaken. Cell death was initially quantified by comparing cellular ion leakage from ZC-affected and ZC-free tubers. Levels of ion leakage were found to be significantly higher in ZC-affected tubers compared to ZC-free tubers. To examine further the association of cell death with ZC disease, ZC-affected and ZC-free tubers were compared using classical histochemical staining methods in conjunction with optical microscopy, which revealed layers of dead cells surrounding numerous, small, irregularly-shaped lesions throughout the parenchymatic medullary region, vascular ring and cortex of ZC-affected tubers. This cell death was confirmed using high-resolution, field-emission scanning electron microscopy (FE-SEM) of fresh-cut tuber tissue.

Expression of multiple expansin genes is associated with cell expansion in potato organs

Expansin proteins can induce the extension of isolated cell walls and are proposed to mediate the cell wall loosening that leads to cell expansion. Nine α-expansin cDNAs were isolated from potato ( Solanum tuberosum), and their expression was examined in developing tubers and in rapidly growing etiolated stems. EXPA1 mRNA accumulated to high abundance in young expanding tubers, and in etiolated stems high EXPA1 mRNA accumulation in growing apical regions and low accumulation in basal non-growing regions was correlated with growth rate. The mRNAs of EXPA7 and EXPA8 also accumulated at relatively high levels in young expanding tubers, but not in elongating stems. Auxin treatment of excised stem segments rapidly increased cell elongation, and the mRNAs of EXPA1, EXPA3, EXPA4 and EXPA5 increased within 1 h. Growth rate under auxin treatment remained high for at least 7 h, and the mRNA abundance of EXPA1, EXPA4 and EXPA5 remained above that of the control during this time. The data show that multiple α-expansin genes are expressed in expanding cells of potato tuber and stem tissues, and expression of at least some of these genes is hormonally regulated during growth.

Boron Fertilization and Evaluation of Four Soil Extractants: Russet Burbank Potato

Yield‐response correlations with old and improved soil extraction methods for boron (B) are needed. Russet Burbank potato (Solanum tuberosum L.) was grown with two, four, and six B treatments applied in 2004, 2005, and 2006, respectively. Zero and 1.1, 2.2, or 3.4 kg B ha−1 soil and 0.22 or 0.28 kg B ha−1 foliar treatments were applied. Boron fertilization did not significantly increase tuber yield or quality despite initially low hot‐water‐extractable B (0.34–0.50 mg kg−1), although postseason B for unfertilized treatments increased (0.51–0.57 mg kg−1). Soil‐applied B generally reflected B application relative to the untreated control and the low foliar rates in all three years for the four soil extractions utilized [hot water, pressurized hot water, diethylenetriaminepentaacetic acid (DTPA)–sorbitol, and Mehlich III]. Boron content of potato petiole did reflect application of B in 2 years, but tuber and peel tissues did not consistently reflect application of B.