Effect of phosphite fertilization on growth,yield and fruit composition of strawberries

Traditionally, phosphates (Pi, salts of phosphoric acid, H₃PO₄) have been used for plant fertilization, and phosphites (Phi, salts of phosphorous acid, H₃PO₃) have been used as fungicides. Nowadays several Phi fertilizers are available in the EU market despite the fact that in research trials Phi has often had a negative influence on plant growth. The objective of this study was to elucidate the effect of a Phi fertilizer on plant growth, yield and fruit composition of strawberries (Fragaria × ananassa Duch.). Experiments were carried out with ‘Polka’ frigo plants in South Estonia in 2005 and 2006. The number of leaves per plant, total and marketable yields, fruit size, fruit ascorbic acid content (AAC), soluble solids content (SSC), titratable acidity (TA), anthocyanins (ACY) and total antioxidant activity (TAA) were recorded.     

Water relations and yield of lysimeter-grown strawberries under limited irrigation

The effects of partial root-zone drying (PRD), as compared to deficit irrigation (DI) and full irrigation (FI), on strawberry (cv. Honeoye) berry yield, yield components and irrigation water use efficiency (WUE_I) were investigated in a field lysimeter under an automatic rain-out shelter. The irrigation treatments were imposed from the beginning of flowering to the end of fruit maturity. In FI the whole root zone was irrigated every second day to field capacity viz. volumetric soil water content (θ) of 20%; while in DI and PRD 60% water of FI was irrigated to either the whole or one-half of the root system, respectively, at each irrigation event. In PRD, irrigation was shifted from one side to the other side of the plants when θ of the drying side had decreased to 8–11%. Compared to FI plants, leaf water potential was significantly lower in DI and PRD plants in 3 out of 10 measurement occasions, while stomatal conductance was similar among the three treatments. Leaf area, fresh berry yield (FY), individual berry fresh weight, berry water content, and berry dry weight (DW) were significantly lower in DI and PRD plants than those of FI plants; whereas the total number of berry per plant was similar among treatments. Compared with FI, the DI and PRD treatments saved 40% of irrigation water, and this led to a 28 and 50% increase of WUE_I based on berry FY and DW, respectively, for both DI and PRD. Conclusively, under the conditions of this study PRD had no advantage compared to DI in terms of berry yield and WUE_I. DI and PRD similarly decreased berry yield and yield components and thus cannot be recommended under similar conditions.     

Effects of plant growth promoting bacteria (PGPB) on yield,growth and nutrient contents of organically grown strawberry

The effects of plant growth promoting bacteria (PGPB) on the fruit yield, growth and nutrient element content of strawberry cv. Fern were investigated under organic growing conditions between 2006 and 2008. The experimental plot was a completely randomized design with 3 replicates. Three PGPB strains (Pseudomonas BA-8, Bacillus OSU-142 and Bacillus M-3) were used alone or in combination as bio-fertilizer agent in the experiment. Data through 3 years showed that the use of PGPB significantly increased fruit yield, plant growth and leaf P and Zn contents. Root inoculation of M3 and floral and foliar spraying of OSU-142 and BA-8 bacteria stimulated plant growth resulting in significant yield increases. M3 + BA-8, BA-8 + OSU-142, M3, M3 + OSU-142 and BA-8 applications increased cumulative yield by 33.2%, 18.4%, 18.2%, 15.3% and 10.5%, respectively. Number of fruits per plant significantly increased by the applications of M3 + BA-8 (91.73) and M3 (81.58) compared with the control (68.66). In addition, P and Zn contents of strawberry leaves with bacterial inoculation significantly increased under organic growing conditions. Available P contents in soil were increased from 0.35 kg P₂O₅/da at the beginning of the study to 2.00, 1.97 and 1.82 kg P₂O₅/da by M3 + OSU-142, M3 + BA-8 and M3 + BA-8 + OSU-142 applications, respectively. Overall, the results of this study suggest that root inoculation of Bacillus M3 alone or in combination with spraying Bacillus OSU-142 or Pseudomonas BA-8 have the potential to increase the yield, growth and nutrition content of strawberry plant under organic growing conditions.     

Chromosome observation method at metaphase and pro-metaphase stages in diploid and octoploid strawberries

Chromosome observation is necessary to elucidate the structure, function, organization, and evolution of octoploid strawberry plants’ genes and genomes. However, distinguishing strawberries’ chromosomes from one another using light microscopy is extremely difficult, not only because of their small size and large number, but also because current chromosome observation methods are insufficient. Chromosome preparation and staining using maceration enzymes, acetic acid, and DAPI (4′,6-diamidino-2-phenylindole) were improved for this study to obtain clear images of somatic chromosomes in Fragaria vesca (2n = 14) and Fragaria×ananassa (2n = 56). Collected root tips of octoploid plants were placed in 0.002 M 8-hydroxyquinoline solution for 1 h and stored at 4 °C for 16 h. Subsequently, they were fixed using 3:1 absolute alcohol:glacial acetic acid for 40 min, hydrolyzed in the 1N HCl solution at room temperature for 2 h, macerated using an enzyme solution for 25 min at 42 °C, and stained in 1.5% lacto-propionic orcein solution. On the other hand, in case of DAPI staining, the macerated root tips of octoploid plants were soaked in 60% acetic acid for 5 min before staining. Clear digital images of F. vesca and F.×ananassa were obtained using light and fluorescent microscopy. Their respective 14 and 56 chromosomes were counted. Fluorescent microscopy yielded clear chromosome images at the pro-metaphase in F. vesca and F.×ananassa. This chromosome observation method alleviates the difficulties that have heretofore hindered chromosome analyses of strawberry plants.     

Fruit yield and quality of strawberry plants transformed with a fruit specific strawberry pectate lyase gene

Two transgenic strawberry lines (Pel 1 and Pel 3) containing the open reading frame of a fruit specific strawberry pectate lyase gene (FaplC) under the control of the CaMV35S promoter have been obtained to evaluate the role of this gene on fruit softening. Ripen fruits from both lines showed a significant down-regulation of FaplC, being the percentage of silencing of 84 and 71% on Pel 1 and Pel 3, respectively. The agronomic behaviour of transgenic plants was evaluated during two consecutive years. Fruit set increased in the two transgenic lines when compared with control plants, although Pel 1 showed a significant reduction on fruit weight. Firmness of full ripen fruits from Pel lines was significantly higher than control fruits, while color and soluble solids were not affected. The increase of firmness in Pel lines was maintained when ripe fruits were stored for 3 days at 25 °C. Histological analysis of ripe fruits showed lower intercellular spaces and a higher degree of cell to cell contact area in transgenic fruits when compared with controls. Altogether, these results suggest a direct relationship between pectate lyase gene expression and strawberry fruit softening.     

Effect of plant growth temperature on membrane lipids in strawberry (Fragaria × ananassa Duch.)

Changes in membrane lipid composition are important in the acclimation of plants. The influence of four day/night growing temperature combinations (18/12, 25/12, 25/22, and 30/22 °C) on membrane lipids of ‘Earliglow’ and ‘Kent’ strawberry (Fragaria × ananassa Duch.) were studied. The monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) were the major galactolipids in the strawberry leaves. ‘Earliglow’ contained a higher amount of galactolipids in the leaves than ‘Kent’. The major phospholipids in the strawberry leaves, roots, and fruit were phosphatidylcholine (PC), phosphatidylinositol (PI), phosphatidylglycerol (PG), and phosphatidylethanolamine (PE). PC and PE were the two predominant phospholipids in the strawberry. The leaves and fruit of ‘Earliglow’ contained higher amounts of phospholipids compared to those of ‘Kent’, whereas ‘Kent’ strawberry roots had higher phospholipids. Palmitic (C16:0), stearic (C18:0), oleic (C18:1), linoleic (C18:2), and α-linolenic (C18:3) acids were major fatty acids in galacto- and phospholipids of the ‘Earliglow’ and ‘Kent’ strawberry. PC is very rich in linolenic acid in leaves compared to the fruit and root tissues. PC had the highest ratio of unsaturated to saturated fatty acids among all phospholipids. There was a significant increase in the content of galactolipids (MGDG, DGDG) and phospholipids (PC, PI, PG and PE) and unsaturation of their fatty acids in the cool day/night growth temperature. Increasing day/night growth temperatures decreased MGDG/DGDG ratios. The shifts in saturation and composition of fatty acids observed with strawberry may be an adaptation response of plants to the temperature changes.     

Fruit nutrient content and lipoxygenase activity in relation to the production of malformed and button berries in strawberry (Fragaria × ananassa Duch.)

Fruit nutrient content and lipoxygenase (LOX) activity were determined in strawberry fruit to establish a relationship, if it exists, between nutrients, and LOX activity with the fruit malformation and nubbins or button berry disorders. Nearly 17% fruit were affected by malformation and 10% by nubbins in open-field-grown strawberries. ‘Etna’ produced higher proportion of malformed (22.7%) as well as button berries (16.9%) and ‘Sweet Charlie’ the lowest (8.9% and 3.3%, respectively). Dry matter content (%) was lower in malformed (5.2%) and button berries (3.23%) than normal berries (7.41%). The concentration of P and Mg did not differ significantly, but that of N and K was notably higher and of Ca and B was lower in malformed and button berries than normal berries. Consequently, the N/Ca and K/Ca ratios were higher in malformed and button berries. LOX activity was significantly higher in malformed as well as button berries than normal berries, with significant differences among cultivars. The correlations between N, K and malformed and button berries were positive and between Ca and B, and malformed and button berries were negative. Similarly, the correlation between LOX activity and malformed, and button berries were also positive, indicating that excess of N and K, and deficiency of Ca and B are related to the production of malformed and buttons or nubbins in strawberry.     

Improvement of staining method for observation of mitotic chromosomes in octoploid strawberry plants

An important strategy to conduct intentional breeding of octoploid strawberry plants is to recognize the functions of every chromosome. To do so, a methodology must be developed to distinguish chromosomes one by one. We reported the possibility of distinguishing chromosomes using light microscopy when somatic cells of octoploid strawberry plants were stained using ordinary methods with lacto-propionic orcein (LPO). However, karyotype analysis of octoploid strawberry plants required clearer chromosome images. This study obtained clearer chromosome images of octoploid Fragaria × ananassa and F. chiloensis plants. Three staining methods were examined: 60% acetic acid (AA) alone, 1.5% LPO alone, and two-step treatments with 60% AA and 1.5% LPO. Collected root tips of the plants were placed in 2 mM 8-hydroxyquinoline solution for 1 h and were subsequently stored at 4 °C for 15 h. The samples were then fixed in a 3:1 absolute alcohol: glacial acetic acid solution for 40 min, followed by mixture with 1N HCl solutions at room temperature for 2 h and then at 60 °C for 10 min. For separate staining using 60% AA and 1.5% LPO, the root tip was expelled on the glass slide with a drop of each solution for a few minutes to stain the chromosomes. For the two-step staining method, the samples stained with 60% AA were frozen at −80 °C for at least 5 min. The cover slip was removed using a razor blade. Subsequently, the specimens were air-dried and stained with the 1.5% LPO for 3 min. Digital images of chromosomes were obtained using light microscopy. Samples of the two-step staining method produced the clearest chromosome images in both F. × ananassa and F. chiloensis. Furthermore, the greatest color difference between the chromosomes and the cytoplasm was obtained from images of the two-step staining method among the three staining methods. These results demonstrate that the two-step staining method is useful for chromosome counting and karyotype analysis in strawberry plants.     

Effect of high temperature stress on the reproductive growth of strawberry cvs. ‘Nyoho’ and ‘Toyonoka’

High temperatures are known to reduce fruit size and fruit weight in strawberry, but cultivar differences in the response to high temperature stress during the reproductive stage up to the second inflorescence have not been sufficiently reported. We examined the effect of two day/night temperature regimes on fruit set and fruit growth in two cultivars, ‘Nyoho’ and ‘Toyonoka’. A high day/night temperature of 30/25 °C reduced the number of inflorescences, flowers, and fruits in both cultivars compared with plants grown at 23/18 °C. The percentage of fruit set in ‘Nyoho’ was not significantly different between the two temperature treatments, while that in ‘Toyonoka’ was much lower at 30/25 °C than at 23/18 °C. Days to ripening was shorter at 30/25 °C than at 23/18 °C, and no cultivar differences were observed. Fresh weight of primary, secondary, and tertiary fruits was greater at 23/18 °C than at 30/25 °C in both cultivars, and no cultivar differences were observed, except in tertiary fruits. The diameter of fruits from all positions was also reduced at 30/25 °C in both cultivars. Relative growth rates of fruits showed two peaks in both cultivars and in both temperature treatments. Both peaks appeared earlier at 30/25 °C than at 23/18 °C. Percentage of fruit set at 30/25 °C in the second inflorescence was also significantly lower in ‘Toyonoka’ than in ‘Nyoho’. These results indicate that high temperature stress negatively affects the reproductive process in strawberry and that plant response to high temperature stress is cultivar-related in such responses.     

Aneuploid strawberry (2n = 8x + 2 = 58) was developed from homozygous unreduced gamete (8x) produced by second division restitution in pollen

Unreduced gamete formation is significant in the evolutionary development of complex polyploidy series found in wild strawberry, genus Fragaria (Rosaceae). Also, it is important for genetics and breeding in strawberry plants to elucidate the mechanism of unreduced gamete formation. The objective of this study was to search for ploidy anomalies resulting from artificial diploid × octoploid crosses, and examine the mechanism through which these unreduced gametes were produced. Five everbearing cultivars of Fragaria vesca L. diploid (2n = 2x = 14) were crossed with pollen from six June-bearing cultivars of Fragaria × ananassa Duch., octoploid (2n = 8x = 56). A total of 3000 mature seeds, 100 from each of the 30 parental combinations were sown at 23 °C/20 °C (day/night) under artificial lighting with a 16 h day. The seedlings were transplanted to pots and grown in a greenhouse. Reproductive and morphological observations, flow cytometry analyses, chromosome counts and DNA analyses using CAPS markers were performed to identify the genetic background of the offspring. Most of the seed (79%) did not germinate or died soon after germination. Of the seedlings produced, 7% seemed to be pure F. vesca based on morphological characteristics, flow cytometry analyses and chromosome counts; 14% were pentaploids (2n = 5x = 35), 0.1% were hexaploids (2n = 6x = 42), and 0.03% (one individual) was aneuploid (2n = 8x + 2 = 58). Electrophoresis banding patterns obtained by CAPS marker analysis were heterozygotic in the 8x pollen parent but homozygotic in the aneuploid progeny. Judging from the chromosome counts and the CAPS marker analysis, the aneuploid was the result of a homozygous unreduced pollen grain (8x) crossed with an incomplete chromosome compliment from the egg. Because of the homozygosity, the unreduced male gamete must have been derived from second division restitution (SDR) in the octoploid pollen parent.     

Long-term effects of managed grass competition and two pruning methods on growth and yield of peach trees

Ground cover competition and tree training strongly affect development of newly planted peach trees and eventual productivity of peach orchards. This experiment characterized the long-term interactive effects of three levels of competition and two pruning criteria on yield, fruit size, and marketable yield efficiency. Trees of two cultivars (’Jersey Dawn’, JD, and ‘Redskin’, RS, on Lovell) of peach (Prunuspersica (L.) Batsch) were planted in an orchard in 1993 and grown for 14 years in a vegetation free area (VFA) width of 0.6 or 2.4 m. A separate group of trees that were in the 2.4 m VFA had grass seeded beneath them in 1998 to obtain 0 m VFA. All trees were pruned to maintain canopy size with wide-angled scaffold limbs and intense pruning (IP) or upright branch form with reduced pruning (RP). In general, RS had greater yield than JD and yield was greatest in the 2.4 m VFA with RP and least in the 0.6 m VFA with IP. Cumulative marketable (≥6.35 cm) and average annual total yield of both cultivars was similar for RP trees in 0 m VFA and IP trees in 2.4 m VFA's although more of the fruit were in the largest size class (>6.98 cm) in the IP trees. Reduced pruning increased crop load. Fruit weight decreased with increased crop load more in RS than JD and this response was similar for all VFA's within each cultivar. Grass competition tended to reduce both the number and weight of fruit per tree but the average weight of individual marketable fruit was reduced only in the 0.6 m VFA of RS. Tree size was reduced by grass competition and pruning times measured from 1995 to 2000 were less in RP than IP. Consequently, marketable yield efficiency of marketable fruit (grams fruit ≥6.35 cm/cm² trunk cross-sectional area, TCSA) measured from 2004 to 2007 was generally greater in trees with RP than IP and in the 0.6 than the 0 and 2.4 m VFA. The results indicate that persistent competition will reduce total annual yield per tree but with reduced pruning the concomitant increased crop load can help maintain marketable yield.     

Strawberry fruit quality attributes after application of plant growth stimulating compounds

Strawberry plants cv. Camarosa were treated with different plant growth stimulators, in order to examine their effect on both yield and product quality. The treatments comprised an untreated control and a mixture of a seaweed extract plus a commercial mixture of nitrophenolates and a commercial mixture of an auxin (phenothiol) plus gibberellic acid at two dose rates. The plant growth stimulators increased marketable yield and fruit size, while they had no significant impact on fruit juice pH, titratable acidity and total soluble solids concentration. Furthermore, they had no significant effect on fruit organic acid and carbohydrate concentration and on fruit color, although they enhanced total anthocyanin concentration. The antioxidant activity of the fruit juice was slightly higher in the fruits of control treatment, which could be the result of their higher total phenol, o-diphenol, flavonoid and flavanol concentration. When a taste panel took place, the panelists gave the best score to those fruits deriving from plants treated with the mixture of auxin plus gibberellic acid.     

Interactions of photoperiod,temperature, duration of short-day treatment and plant age on flowering of Fragaria x ananassa Duch. cv. Korona

The effects of photoperiod (10, 12, 16, 20 or 24 h), day-temperature (12, 15, 18, 24 or 30 °C), the number of short days (14, 21 or 28 days), plant age (4, 8 or 12 weeks) and their interactions on flower and inflorescence emergence were investigated in strawberry cv. Korona. No flowers emerged in plants exposed to photoperiods of 16, 20 or 24 h or to a short-day treatment for 14 days. All plants exposed to short days at daily photoperiods of 10 or 12 h for 21 days or longer, emerged flowers at temperatures between 12 and 18 °C. A further increase in temperature led to a drastic decrease in the total number of flowers per plant. A short-day treatment (10 or 12 h photoperiod) of 28 days resulted in highest numbers of inflorescences and flowers per plant, while a short-day treatment of 21 days resulted in the highest numbers of flowers per inflorescence. Complete flower induction was observed in only 4-week-old runner plants. The number of inflorescences and the number of flowers per inflorescence increased with plant age. However, the start of flowering was delayed with increasing plant age.     

Effects of simple and double grafting melon plants on mineral absorption,photosynthesis, biomass and yield

The Spanish type cultivar ‘Piel de Sapo’ (Cucumis melo L. var. saccharinus), has a limited compatibility with the Cucurbita maxima × Cucurbita moschata hybrids currently used as rootstocks. Double grafting can be used to improve compatibility between rootstock and scion by means of an intermediate rootstock compatible with both. Non-grafted, single, and double grafted melon plants of the cultivar Piel de Sapo were evaluated for water, nutrient absorption, photosynthesis activity, biomass production in early phases, as well as for yields and fruit quality in a long term trial. The hybrid ‘Shintoza’ (C. maxima × C. moschata) was used as rootstock, and the cantaloupe type melon cultivar ‘Sienne’ as an intermediate scion. Grafting did not affect net photosynthetic values, yet increased water use efficiency (35%). Double grafted plants increased aerial dry weights (66% and 31% with respect to non-grafted and simple graft plants, respectively), and also increased capacity for uptaking beneficial minerals (between 61% and 13% and particularly for NO₃⁻, P, K, Ca, Mn, and Zn) with respect to non-grafted and single grafted plants. The quantum efficiency PSII photochemistry values increased in double grafted plants (12%) with respect to the control plants. Consequently, double grafting on a vigorous rootstock such as ‘Shintoza’, with an intermediate scion, results in improved mineral and water absorption and achieves an increase in ion influx to the scion – so enabling an increase in light photosynthetic reaction and biomass. Double grafted plants increased fruit yield when compared to simple grafted and non-grafted plants (12% and 56%, respectively) and did not affect fruit quality in terms of °Brix and colour. In conclusion, double grafting presents several beneficial aspects that are counter-balanced by the extra cost of the technique. The difference in yields reflects compatibility problems.     

Inoculation of growing media with the rhizobacterium Variovorax paradoxus 5C-2 reduces unwanted stress responses in hardy ornamental species

Inoculation of growing media with plant growth promoting rhizobacteria (PGPR) has a number of potential benefits for the production of ornamental plants. Certain rhizobacteria synthesise the enzyme ACC deaminase, which cleaves ACC, the precursor of the plant hormone ethylene. Bacterial metabolism is now known to lead to a reduction in [ACC] in the plant transpiration stream and bacteria are hypothesised to act on ACC exuded from roots. This in turn reduces the ethylene generated in plants growing in growing media inoculated with these bacteria. Here we tested if applications of the ACC deaminase containing rhizobacteria Variovorax paradoxus⁵C–²could be of benefit to ornamental growers by reducing ethylene generation in stressed plants. Ethylene is produced at levels that are inhibitory to growth and development under a number of abiotic stresses. The propagation and production of hardy ornamentals is deleteriously affected by abiotic stresses that involve ethylene signalling, including drought and physical wounding. Inoculation of growing media with V. paradoxus 5C-2 lowered ethylene emission from mature leaves of Cytisus × praecox experiencing drought stress. In addition, bacterial inoculation of the growing media resulted in significantly reduced abscission of the mature leaves under drought treatment. Beneficial effects of inoculation where also found in the wounding response of Fargesia murielae following divisional propagation and late season senescence in Aquilegia × hybrida in response to drought stress. Together these results demonstrate that V. paradoxus⁵C–²has real potential for use on ornamental nurseries in situations where plant stresses are unavoidable.     

Temperature responses,flowering and fruit yield of the June-bearing strawberry cultivars Florence,Frida and Korona

The effect of night temperature on short day (SD) floral induction has been studied in three June-bearing strawberry cultivars of different geographic origin and compared with yield performance in the cool Nordic environment. At the optimum day temperature of 18 °C, the SD flowering response of the cultivars ‘Florence’ and ‘Korona’ increased significantly with increasing night temperature from 9 to 18 °C, while an optimum was reached at 15 °C in the cultivar ‘Frida’ that is selected under cool-environment conditions in Norway. Also, while saturated flowering response was obtained with 3 weeks of SD treatment at all temperatures in ‘Frida’, several plants of ‘Florence’ and ‘Korona’ failed to initiate flowers at 9 °C night temperature even with 5 weeks of SD. The effect of extended SD period was particularly pronounced in ‘Florence’. The slow SD floral induction response of ‘Florence’ was associated with a 2 week delay of anthesis in subsequent long day (LD) conditions at 21 °C. Yield performance of the same cultivars during 2 years under field conditions at Nes Hedmark and in North Norway also demonstrated that the yield potential of ‘Florence’ was not realized under the climatic conditions prevailing at these locations. In both years the yields varied significantly among the cultivars, ‘Frida’ having the highest yields followed by ‘Korona’, with ‘Florence’ far below. It is concluded that, in the Nordic environment, autumn (September) night temperatures are obviously sub-optimal for yield performance of some June-bearing strawberry cultivars, and that this effect is mediated by autumn temperature effects on flower initiation responses.     

Modeling plant morphology and development of petunia in response to temperature and photosynthetic daily light integral

The effects of mean daily temperature (MDT) and mean photosynthetic daily light integral (MDLI) on flowering during the finish stage of two petunia (Petunia × hybrida) cultivars were quantified. Petunia ‘Easy Wave Coral Reef’ and ‘Wave Purple’ were grown in glass-glazed greenhouses at 14–23 °C or 14–26 °C and under 4–19 mol m⁻² d⁻¹ with a 16-h photoperiod. The flower developmental rate was predicted using a model that included a linear MDT function with a base temperature multiplied by an exponential MDLI saturation function. The flower developmental rate increased and time to flower decreased as MDT increased within the temperature range studied. For example, under a MDLI of 12 mol m⁻² d⁻¹, as MDT increased from 14 to 23 °C, time to flower of ‘Easy Wave Coral Reef’ and ‘Wave Purple’ decreased from 51 to 22 d and 62 to 30 d, respectively. Flower developmental rate increased as MDLI increased until saturation at 14.1–14.4 mol m⁻² d⁻¹. Nonlinear models were generated for effects of MDT and MDLI on flower bud number and plant height at flowering. The number of flower buds at flowering increased as MDT decreased and MDLI increased. For example, at an MDT of 14 °C with 18 mol m⁻² d⁻¹, plants had 2.5–2.9 times more flower buds than those grown at 23 °C and 4 mol m⁻² d⁻¹. Models were validated with an independent data set, and the predicted time to flower, flower bud number, and plant height were within ±7 d, ±20 flowers, and ±4 cm, respectively, for 96–100%, 62–87%, and 93–100% of the observations, respectively. The models could be used during greenhouse crop production to improve scheduling and predict plant quality of these petunia cultivars.     

Random sample estimates of tree mean for fruit size and colour in apple

Data obtained in 2005 from thinning experiments with ‘Ariane’ and ‘Pitchounette’ apples (Malus × domestica L. Borkh.) were used to estimate tree mean fruit diameter (MD), weight (MW) and proportion of red overcolour (MC) using random samples. Twenty fruit per tree were taken from the boxes containing the fruit harvested at each picking. To avoid taking only fruit in the upper layers of the boxes, fruit from each tree were spread out on a table beforehand. The estimated values were compared with the true MD, MW or MC calculated from each picking and from the entire crop. Statistical techniques were used to assess agreement between the values obtained with estimation methods and the true values. Estimates obtained from a sample averaging ∼15–20% of total crop may range from 2 to 3% of the true mean diameter, and from 6.0 to 8.5% of the true mean weight. Estimates for MC obtained from the same samples may range from 10 to 25% of the true mean overcolour. The error margin associated with estimating fruit diameter and weight from the sampling method employed in this study seems to be small enough to consider it reasonably adequate to detect treatment differences that would be considered biologically or economically significant. Blind sampling and colour determination through image analysis are suggested as a means to obtain unbiased and objective data for fruit colour determinations.     

Genetic assessment of local apple cultivars from La Palma,Spain, using simple sequence repeats (SSRs)

Apple cultivars from Canary Islands can possibly be valuable genetic resources for subtropical areas. We localised 31 accessions considered by growers to be local, and confirmed by historical references that apple crop was introduced in XV century. These accessions were compared with 77 Spanish and 26 commercial cultivars in order to detect synonyms. A set of 10 SSRs were studied, and 2 of them presented 2 loci. Cultivars from La Palma (Canary Islands) presented five specific alleles not found in other Spanish regions. Those polymorphisms allowed detecting one introgressant in La Palma from non-native cultivars, and the other 30 accessions were classified into 14 genotypes. Some accessions derived from non-native cultivars such as Golden Delicious. A main cultivar could be detected, Del País, with 14 accessions. Secondary ones were Camuesa and Pero. Genetic differentiation was small between regions (Fst = 0.057) but significant, confirmed by analysis of molecular variance (AMOVA). Major genetic differentiation was found between non-native cultivars and cultivars from Asturias and Basque Country. Bayesian method and admixture analysis reconstructed three ancestral groups (RPP), Asturian and Basque cultivars grouped in RPPI (mainly those used for cider production), a mixture of cultivars from Galicia and La Palma in RPPII and non-native cultivars were in RPPIII. This genetic differentiation was also confirmed by factorial correspondence analyses (FCA). AMOVA over RPPs increased the genetic differentiation. Allelic variation found in this study showed that Spanish local cultivars represent a differentiated genetic pool that will provide original genotypes to diversify the reduced number of cultivars used in commercial production. In addition, differentiated genotypes localised in La Palma will be preserved in the local Germplasm Bank.     

Fruit calcium content and lipoxygenase activity in relation to albinism disorder in strawberry

Nutrient elements and lipoxygenase (LOX) activity were determined in strawberry fruit to establish a relationship, if it exists, between nutrient ratios (N/Ca and K/Ca), and lipoxygenase activity with albinism disorder. About 33% strawberry fruit were affected by albinism. Etna had highest incidence of albinism (48.6%) and Sweet Charlie the lowest (16.2%). Dry matter content (%) was lower in albino fruit (5.23%) than normal fruit (7.36%). The concentration of N, P, and Mg did not differ significantly, but that of K (1.87 mg g⁻¹ fresh weight) was notably higher and of Ca (0.105 mg g⁻¹ fresh weight) was lower in albino fruit than normal fruit. Consequently, the nutrient ratios, N/Ca (9.78) and K/Ca (16.96) were higher in albino fruit than normal fruit. Cultivars differed widely in respect to dry matter (%), mineral content and nutrient ratios. LOX activity determined on dry weight or fresh weight basis was significantly higher in albino fruit than normal fruit, with significant differences among cultivars. Positive correlations existed between nutrient ratios and albinism incidence (r = +0.338), LOX activity and albinism incidence (r = +0.412), and LOX and nutrient ratios (r = +0.448). Thus, it appears from the study that calcium and LOX activity may not the basic cause of albinism in strawberry, but these may be involved in senescence or fruit ripening process, as LOX activity was lower in albino than in normal fruit.