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PubMed1998

Phylogenetic characterization of the bacterium-like organism associated with marginal chlorosis of strawberry and proposition of a Candidatus taxon for the organism, 'Candidatus phlomobacter fragariae'.

Marginal chlorosis is a new disease of strawberry which was first seen in France in 1988. A phloem-restricted bacterium-like organism was found associated with the disease. Even though the organism could not be cultured and resembles in this way most other phloem-restricted pathogens, characterization was achieved from the sequence of its PCR-generated 16S rDNA, and comparison with other organisms. From these studies, the strawberry agent was found to be a new bacterium within group 3 of the gamma subclass of Proteobacteria, a group of Gram-negative bacteria including, in particular, insect symbionts or parasites as well as enterobacteria. Its closest relative, Arsenophonus nasoniae, is the causal agent of the son-killer trait in wasps. The two bacteria share 92% 16S rDNA sequence identity. We propose a Candidatus taxon for the marginal-chlorosis-associated bacterium, 'Candidatus Phlomobacter fragariae'.

Fruit↗

PubMed1979

Ontogeny of Photosynthetic Performance in Fragaria virginiana under Changing Light Regimes.

Apparent photosynthesis and dark respiration were followed during development in four light environments of leaves of Fragaria virginiana Duchesne. Leaf expansion was completed more rapidly the higher the growth photon flux density and leaves senesced more quickly in high light. Maximum photosynthetic capacity coincided with the completion of blade expansion and declined quickly thereafter. Leaves were transferred from high to low and low to high photon flux densities at several stages during expansion. Leaf photosynthetic performance and anatomy were subsequently analyzed. Leaf anatomy and apparent photosynthesis per unit dry weight can be modified during expansion to reflect the predominant light conditions. Adaptive potential is greatest early in blade expansion and decreases as expansion is completed.

Journal Article↗

PubMed1981

Temperature and Aging Effects on Leaf Membranes of a Cold Hardy Perennial, Fragaria virginiana.

The lipid composition of leaves of wild strawberry (Fragaria virginiana Duchesne) was analyzed throughout an annual growth cycle in the field. Cellular hardiness to temperature stress was assessed concomitantly by a solute leakage technique. Leaves were shown to be very sensitive to an applied temperature of -5 degrees C during the summer months but insensitive to a 35 degrees C treatment. This general pattern was also seen in young overwintering leaves but was reversed after a period of low-temperature hardening of these same leaves. Associated with cold hardening of the overwintering leaves was a twofold increase in the phospholipid content of the leaf membranes with a proportionately smaller increase in free sterols. The large increase in phospholipids presumably is due primarily to the proliferation of a sterol-poor membrane fraction, probably the endoplasmic reticulum. These quantitative changes in membrane material may be important in increasing freezing tolerance in the overwintering leaf cells by enhancing the overall capacity of the cell for plasma membrane and tonoplast extension through vesicle fusion using components from this endomembrane pool. Analysis of electron micrographs of hardened leaf cells showed an increase in vesiculated smooth endoplasmic reticulum and tonoplast membrane over nonhardened leaf cells, the latter resulting in an enhanced tonoplast surface area to vacuolar volume ratio. During this same period, no changes in the fatty acid or free sterol composition were detectable, suggesting that regulation of membrane fluidity via these components is not required for cold acclimation in this species. During aging and senescence of both the overwintering and the summer leaves, the cellular membranes remained functionally intact but became progressively more vulnerable to temperature stress. Free sterol content increased during this time. This feature may be related to the inability of the older leaves to withstand environmental stress. Increasing sensitivity of the cellular membranes to stress may, in turn, be causally related to the actual onset of senescence in these leaves, thus explaining why only the older leaves senesce when the plant is challenged by periodic environmental stress.

Journal Article↗

PubMed1982

Effects of Light and Nutrients on Leaf Size, CO(2) Exchange, and Anatomy in Wild Strawberry (Fragaria virginiana).

Plants of a single genotype of wild strawberry, Fragaria virginiana Duchesne, were grown with or without fertilizer in high (406 microeinsteins per square meter per second) and low (80 microeinsteins per square meter per second) light. High-light leaves were thicker than low-light leaves and had greater development of the mesophyll. Within a light level, high-nutrient leaves were thicker, but the proportions of leaf tissues did not change with nutrient level. Maximum net CO(2) exchange rate and leaf size were greatest in high-light, high-nutrient leaves and lowest in high-light, low-nutrient leaves. Changes in mesophyll cell volume largely accounted for differences in CO(2) exchange rate in low-light leaves, but not in high-light leaves.Leaf size in these experiments was apparently determined by nutrient and carbon supply. This may explain the observation that the largest leaves produced by wild strawberries in the field occur in high-light, mesic habitats, rather than in shady habitats.

Journal Article↗

PubMed1983

Role of Osmotic Potential Gradients during Water Stress and Leaf Senescence in Fragaria virginiana.

The physiological basis underlying differences in sensitivity of different aged leaves to water stress was investigated in Fragaria virginiana Duchesne. Differential susceptibility of only older leaves to water stress in the field during summer months appeared related to gradients in leaf osmotic potential within the plant and by an age dependency in the ability of leaves to adjust osmotically when challenged by periodic water deficits. Under greenhouse conditions, older leaves senesced invariably during an imposed water stress while control leaves of comparable age and stressed younger leaves remained green. Osmotic potentials of intermediate aged and younger leaves became approximately 1 to 2 bars lower after a single cycle of imposed stress and up to 10 bars lower after two cycles of stress. Pronounced gradients in leaf osmotic potential within individual whole plants were observed following two cycles of water stress that were significantly different from control values. Osmotic adjustment was dependent on leaf age with the greatest capacity for adjustment in the intermediate aged leaves. Loss of osmotic adjustment was rapid upon rewatering with a half-life of 4 days. An irreversible component of adjustment was observed, amounting to about 10% (or 2 bars) of the maximally adjusted state. This irreversible component could be accounted for in part by significant changes in cell size and other anatomical alterations in the leaf that affect cellular osmotic volume, and, hence, cellular water relations.

Journal Article↗

PubMed1983

Osmotic Adjustment and the Development of Freezing Resistance in Fragaria virginiana.

Cold temperature acclimation in strawberry (Fragaria virginiana) leaves apparently involves the alteration of cellular osmotic properties. Alterations in leaf osmotic potential were closely correlated with alterations in soluble carbohydrate content of the leaf tissue and changing temperatures. Leaf starch content was inversely related to soluble carbohydrate levels, suggesting that starch is a partial source of osmoticum during osmotic adjustment associated with cold temperature stress. Free amino acid changes were more closely linked to senescence and growth processes while changes in ion content suggested a rapid mobilization of solutes at the onset of freezing temperatures. This was supported by changes in whole plant gradients in leaf osmotic potential before and after exposure to freezing temperatures. In terms of freezing resistance and the role of osmotic adjustment in the development of resistance, it was found that of all leaves undergoing osmotic adjustment only the younger leaves survived, suggesting an age-dependent component to freezing resistance in leaves. Freezing resistance appears to involve alterations in several cellular properties that act in concert to confer a hardy state of the tissue. Although osmotic adjustment may be an important component of the final combination of cellular properties, this study indicates that solute accumulation does not function alone to confer freezing resistance.

Journal Article↗

PubMed2004

Identification, cloning and expression analysis of strawberry (Fragaria x ananassa) mitochondrial citrate synthase and mitochondrial malate dehydrogenase.

Salt-extractable proteins from the cell walls of immature and ripe strawberry (Fragaria x ananassa Duch. cv. Elsanta) fruit were separated using two-dimensional polyacrylamide gel electrophoresis. Seven polypeptides (enzymes) were characterized from their N-terminal sequences: (1) glyceraldhyde-3-phosphate dehydrogenase (EC 1.2.1.12); (2) triose phosphate isomerase (TPI; EC 5.3.1.1); (3) mitochondrial malate dehydrogenase (mMDH; EC 1.1.1.37); (4) NADH glutamate dehydrogenase (EC 1.4.1.3); (5) chalcone synthase (ChS; EC 2.3.1.74); (6) mitochondrial citrate synthase (mCS; EC 4.1.3.7); and (7) UDP glucose:flavonoid 3-O-glucosyltransferase (UDPG:FGT; EC 2.4.1.91). The sequenced polypeptides identified only cytosolic proteins, two of which (ChS and UDPG:FGT) had already been identified as being up-regulated in ripening (strawberry) fruit and important contributors to ripe fruit character. Our focus was therefore diverted to the enzymes mMDH and mCS for further molecular characterization as potentially important determinants of fruit flavour via regulation of the sugar : acid balance. Citrate synthase (CS) and malate dehydrogenase (MDH) enzyme activities increased substantially during ripening, as did citrate and malate contents. The increase in CS activity is supported by western blot analysis. One strawberry mCS (Fa-mCS-I) and two mMDH (Fa-mMDH-I and -II) cDNAs were cloned that were 77, 82 and 53% identical (respectively) to sequences from other plant sources. Northern analysis showed that CS and MDH expression did not correlate with enzyme activities and these findings are discussed.

Journal Article↗

PubMed1998

Isolation of genomic DNA containing a cytosolic ascorbate peroxidase gene (ApxSC) from the strawberry (Fragaria x ananassa).

We isolated a genomic DNA harboring a cytosolic ascorbate peroxidase gene (ApxSC) from a genomic library of the strawberry (Fragaria x ananassa). Restriction mapping and sequence analyses showed that the DNA is composed of 2.5 kb of the full-length ApxSC gene, 3.7 kb of the 5'-upstream region, and 0.5 kb of the 3'-downstream region. The ApxSC genomic DNA contains 10 exons and 9 introns, which is similar to the structure of pea ApxI. A primer extension analysis suggested that the transcription of ApxSC gene was started at three start sites with different degrees. The promoter region of ApxSC gene contains a sequence or structure distinct from other reported plant ascorbate peroxidase genes, though with several known functional elements such as a TATA box.

Amino Acid Sequence↗

PubMed2000

Dissecting the causes of variation in intra-inflorescence allocation in a sexually polymorphic species, Fragaria virginiana (Rosaceae).

In this study we dissect the causes of variation in intra-inflorescence allocation in a sexually polymorphic species, Fragaria virginiana. We separated out the effects of resource competition during flowering from those of inflorescence architecture, as well as identified the effects of sex morph and genotype. We found position-based variation in petal length, ovule, pollen, and flower number to be influenced more by architecture than by our resource manipulations during flowering. We also found both genotype- and sex-specific intra-inflorescence patterns. Furthermore, our data indicate that the sex morph-specific intra-inflorescence patterns result from architectural modifications of the basic pattern. In fact, sex-differential intra-inflorescence patterns suggest that fitness through male and female function may be maximized by different resource distribution patterns within the inflorescence and may have been modified by past selection. Specifically, females invested heavily in ovules at positions where fruit set was most likely (primary and secondary), at the expense of flower number and allocation per flower at more distal positions. Whereas functional males invested minimally in ovules at all flower positions and produced the most abundantly flowered inflorescences, hermaphrodites, on the other hand, showed intermediate patterns, implying a compromise between sex functions. We suggest that consideration of intra-inflorescence allocation and inflorescence architecture may reveal the mechanism underlying sexual dimorphism in flower allocation and number.

Journal Article↗

PubMedDate not supplied

Endopolygalacturonase, an extracellular pectic enzyme of Rhizoctonia fragariae.

A pectolytic enzyme from culture filtrates of Rhizoctonia fragariae was purified approx. 29-fold. The enzyme exhibited maximal depolymerizing activity on Na-polypectate rather than pectin at pH 5.0 and was inhibited at different extent by divalent cations Mg++, Mn++, Ca++. The analysis by paper chromatography of the products of enzyme hydrolysis suggested that the enzyme attacks the substrate by a random mechanism. The absorption spectrum of the chromogen formed by the hydrolysis products and thiobarbituric acid suggested that the enzyme is a hydrolytic enzyme. On the basis of these results the enzyme is classifiable as endo-polygalacturonase (poly alpha-1,4-galacturonide glycanohydrolase E.C. 3.2.1.15).

Calcium↗

PubMed2005

Genetic variance and breeding values for resistance to a wind-borne disease [Sphaerotheca macularis (Wallr. ex Fr.)] in strawberry (Fragaria x ananassa Duch.) estimated by exploring mixed and spatial models and pedigree information.

A mixed model approach was used to estimate variance components and heritabilities for resistance to powdery mildew, a wind-borne disease in strawberry. In order to improve precision in the statistical computations, spatial error control effects were included to account for systematic environmental variations in the large field trials. Pedigree information was included where feasible. Seedling families obtained from an incomplete 63-by-63 diallel cross were grown at six locations and scored subjectively for mildew attack three times during the growing season. The 63 parents included both European and American cultivars as well as advanced selections from various breeding programmes. A total of 298 full-sib families were realized, including 26 reciprocal families. No reciprocal differences were found. On a plot-mean basis, the broad-sense heritability was found to be intermediate, H(2) = 0.44-0.50, depending on whether the pedigree information was included in the model or not. The increase was mainly due to a substantial increase in the additive variance component. Likewise, the narrow-sense heritability increased from h(2) = 0.39 to h(2) = 0.45 when the pedigree information was included, while the ratio of the specific combining ability variance to the general combining ability variance fell from 13% to 10%. The predicted breeding values of the 63 parents demonstrate that important cultivars such as Elsanta and Korona are unlikely to produce progenies with a high degree of resistance. On the other hand, the Norwegian cultivar Solprins, the Canadian cultivar Kent and the Italian cultivar Patty appeared to give highly resistant progeny. At the full-sib level, the estimated disease scores ranged from 1.15 (Kent x Induka) to 4.19 (Cavendish x Avanta), revealing a huge range of variation for powdery mildew resistance available for selection.

Analysis of Variance↗

PubMed2002

Adventitious shoot regeneration from seven commercial strawberry cultivars (Fragaria x ananassa Duch.) using a range of explant types.

The parameters for optimal regeneration of seven commercial strawberry cultivars were tested using a range of explants and culture conditions. Efficient levels of regeneration--those needed to carry out transformation experiments--with the cultivars Calypso, Pegasus, Bolero, Tango and Emily were achieved with leaf discs, petioles, roots and stipules. Regeneration from cv. Elsanta proved to be difficult from all explant material, although unpollinated ovaries proved to be a promising explant source, with 12% of the explants regenerating shoots. In cv. Eros, regeneration occurred only from root tissue. A comparison of the genetic background suggests that there is a strong genetic component amongst the different cultivars determining their regeneration capacity. The development of these regeneration systems provides a means to use almost the whole stock plant for the efficient genetic transformation of commercial strawberry varieties.

Culture Techniques↗

PubMed2005

Epiphytic microorganisms on strawberry plants (Fragaria ananassa cv. Elsanta): identification of bacterial isolates and analysis of their interaction with leaf surfaces.

Epiphytic bacteria were isolated from strawberry plants cultivated in the field or in the greenhouse in order to investigate their interaction with leaf-surface transport properties. Colonization of lower leaf sides was higher on field-grown plants, whereas upper leaf sides were more densely colonized on plants cultivated in the greenhouse. Fungal isolates significantly contributed to total microbial biomass on leaf surfaces of greenhouse-grown strawberry plants, whereas these organisms were rarely abundant on field-grown plants. Microscopic investigations of bacteria in the phyllosphere revealed that the highest densities of bacteria were observed on living trichomes, which obviously provide a source of nutrients. Isolated strains were characterized by colony morphology, microscopy and histochemistry. About 324 isolated bacterial strains were grouped into 38 morphotypes. Of the morphotypes, 12 were identified by 16S rRNA gene sequencing. Dominating bacteria belonged to the genus Pseudomonas, Stenotrophomonas, Bacillus and Arthrobacter. Cuticular water permeability of isolated cuticular membranes and intact leaf disks was measured before and after treatment with one of the most prominent epiphytic bacteria, Pseudomonas rhizosphaerae. Results showed that cuticular transpiration was significantly increased by P. rhizosphaerae. This shows that leaf-surface properties, such as cuticular water permeability, can be influenced by bacteria, leading to improved habitable conditions in the phyllosphere.

Bacteria↗

PubMed2003

Folate content in strawberries (Fragaria x ananassa): effects of cultivar, ripeness, year of harvest, storage, and commercial processing.

Folate concentrations in strawberries and folate retention during storage and commercial processing of strawberries were investigated. No previous study has focused on the effects of cultivar, ripeness, and year of harvest of strawberries with respect to the folate content. This study showed the folate concentration in strawberries to significantly depend on all of these different factors. Total folate was quantified using a modified and validated radioprotein-binding assay with external calibration (5-CH(3)-H(4)folate). Folate content in 13 different strawberry cultivars varied from 335 microg/100 g of dry matter (DM) for cv. Senga Sengana to 644 microg/100 g of DM for cv. Elsanta. Swedish harvests from 1999 and 2001 yielded higher folate concentrations than did the harvest from 2000, and the grade of ripeness affected the folate content in strawberries. This study indicated high folate retention in intact berries during storage until 3 or 9 days at 4 degrees C (71-99%) and also in most tested commercial products (79-103%). On the basis of these data fresh strawberries as well as processed strawberry products are recommended to be good folate sources. For instance, 250 g (fresh weight) of strawberries ( approximately 125 microg of folate) supplies approximately 50% of the recommended daily folate intake in various European countries (200-300 microg/day) or 30% of the U.S. recommendation (400 microg/day).

Folic Acid↗

PubMed2004

Antioxidants, low molecular weight carbohydrates, and total antioxidant capacity in strawberries (Fragaria x ananassa): effects of cultivar, ripening, and storage.

Four cultivars of strawberries (Senga Sengana, BFr77111, Elsanta, and Honeoye) were studied for their content of antioxidants, total antioxidant capacity, and low molecular weight carbohydrates in relation to harvest year, ripening stage, and cold storage. For ascorbic acid, chlorogenic acid, ellagic acid, and total antioxidative capacity, measured in both water-soluble and water-insoluble extracts, there was a 2-5-fold variation among cultivars. Unripe berries contained lower concentrations of chlorogenic acid and p-coumaric acid and also quercetin and kaempferol compared with riper berries. During cold storage for up to 3 days, relatively few changes in the concentration of the different antioxidants occurred. The concentrations of several investigated parameters were interrelated, for example, for ascorbic acid and water-soluble antioxidant capacity and for ellagic acid and water-insoluble antioxidant capacity. The dominating sugars in strawberries were fructose and glucose, but considerable amounts of sucrose were also present, and their contents varied among cultivars, giving a predicted glycemic index of approximately 81. Verbascose, raffinose, and stachyose were found in only minor amounts. The study shows that the concentration of a number of bioactive compounds in strawberries varied according to cultivar, ripening stage, and storage. This information should make it possible to select strawberries with an optimal content of bioactive compounds.

Antioxidants↗

PubMed2003

Effects of yam starch films on storability and quality of fresh strawberries (Fragaria ananassa).

Yam starch films, formulated with yam starch (4.00 g/100 g of solution) and glycerol (1.30 and 2.00 g/100 g of solution) in filmogenic solution, were employed as packaging to extend storage life of strawberries stored at 4 degrees C and 85% RH. The effects of yam starch films on fruits were compared to the effect of PVC (poly(vinyl chloride)) packaging. Starch and PVC films significantly reduced decay of the fruits compared to control. Compared to starch films, PVC presented the better behavior on weight and firmness retention of fruits, especially in the last 7 days of storage. Considering microbiological counts, the shelf life of control fruits was 14 days, and of all packaged samples, stored at same conditions, was 21 days. Two different formulations of yam starch film were tested and had different mechanical properties as a function of glycerol content (1.30 and 2.00 g/100 g of solution) but showed no difference when employed as strawberries packaging.

Dioscorea↗

PubMed2005

Phenolic composition and antioxidant activities in flesh and achenes of strawberries (Fragaria ananassa).

High performance liquid chromatography coupled with diode array and coulometric array detectors were used to characterize and quantify phenolic compounds in achenes and flesh of ripe strawberries (cv Totem and Puget Reliance). Total phenolics and total monomeric anthocyanins were measured and antioxidant activities were evaluated by the FRAP and the ORAC assays. Strawberries contained 1% achenes on a fresh weight basis; however, they contributed to about 11% of total phenolics and 14% of antioxidant activities in strawberries. Ellagic acid, ellagic acid glycosides, and ellagitannins were the main contributors to the antioxidant activities of achenes. The major anthocyanin in flesh was pelargonidin-3-glucoside, whereas achenes consisted of nearly equal amounts of cyanidin-3-glucoside and pelargonidin-3-glucoside. Phenolic content and antioxidant activity of strawberry achenes were reduced by industrial processing. However, the levels were still high and strawberry waste byproduct could thus be a possible source of nutraceuticals or natural antioxidants.

Anthocyanins↗

PubMed2004

Identification and quantification of phenolic compounds in berries of Fragaria and Rubus species (family Rosaceae).

High-performance liquid chromatography combined with diode array and electrospray ionization mass spectrometric detection was used to study soluble and insoluble forms of phenolic compounds in strawberries, raspberries (red and yellow cultivated and red wild), arctic bramble, and cloudberries. Hydroxycinnamic acids were present as free forms in cloudberries and mainly as sugar esters in the other berries. Quercetin 3-glucuronide was the typical flavonol glycoside in all of the berries studied. The composition of the predominant anthocyanins can be used to distinguish the studied red Rubus species from each other since cyanidin was glycosylated typically with 3-sophorose (56%) in cultivated red raspberry, with 3-sophorose (30%) and 3-glucose (27%) in wild red raspberry, and with 3-rutinose (80%) in arctic bramble. Ellagic acid was present as free and glycosylated forms and as ellagitannins of varying degrees of polymerization. Comparable levels of ellagitannins were obtained by the analysis of soluble ellagitannins as gallic acid equivalents and by the analysis of ellagic acid equivalents released by acid hydrolysis of the extracts.

Anthocyanins↗