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BACKGROUND: Bud dormancy is a quantitative condition that is gradually acquired and lost. Better and more convenient methods for assessment of the time of dormancy entrance of woody plants are highly needed. OBJECTIVE: To demonstrate a simple and convenient method for determination of dormancy in woody plants. METHODS: We employed a seasonal series of soft tipping of vigorously growing annual shoots and used the loss of ability of subtending lateral buds to break and grow as a measure of entrance into dormancy. RESULTS: There was a gradual decline in the ability of the buds to burst and grow during the month of July and early August, culminating with a complete loss of this ability. This coincided with the known time of growth cessation and dormancy induction in shoots of intact plants and occurred in the berry shrubs raspberry and black currant and the forest tree silver birch. CONCLUSIONS: The decline and loss of ability of the buds to grow during late summer is a direct expression of the entrance of buds into the state of endodormancy, rendering the tipping method a simple and convenient method for precise determination of the time of entrance into dormancy in woody plants.

BACKGROUND: The predicted and ongoing climate warming can have far-reaching effects on plant growth and life cycle. Therefore, there is need for simple and convenient methods for analysis and monitoring of consequences of the ongoing warming. OBJECTIVE: To demonstrate the usefulness of so-called climate-photothermographs for studying the consequences of the ongoing warming for production of berry crops. METHODS: Local photothermal climates can be expressed by so-called climate-photothermographs, which show the relationship between temperature and daylength for each month of the year in a rectangular coordinate diagram. When superimposing critical response curves for plant development processes on top of such a diagram, the limitations of the given climate for fulfilment of the processes can be readily assessed. RESULTS: Consequences of 2°C warming for critical development processes such as transition to flowering and breaking of winter dormancy in the berry crops raspberry, black currant and strawberry were clearly exposed by the technique. The locations Geisenheim, Germany and Ås, Norway were used as examples. Inadequate winter chill was identified as the most limiting factor for these crops. CONCLUSIONS: We conclude that the technique is an efficient and convenient tool for monitoring the consequences of climate warming for berry crops.

It is not known to what degree growth and fruit yield are source-limited in everbearing strawberry plants. The growth and yield performance effect of bi-weekly removal of all runners and/or one or two leaves during the cropping season of tunnel-grown ‘Favori’ everbearing strawberry plants was determined. Plants were grown on a table-top system in an open plastic tunnel under natural light conditions in Norway from May to October. Removal of runners and leaves was bi-weekly from 5 June until 25 September. Fruits were harvested from 5 July to 7 October. Bi-weekly runner removal increased total and marketable yield and number and size of fruits, while increasing leaf thinning had the opposite effects. However, none of the treatments affected the fruit number and yield of the first fruiting flush. The treatments did not affect realization of the yield potential of the plants at planting, whereas the continued floral initiation and fruit growth were enhanced by runner removal. Increasing leaf thinning had the opposite effects. Both floral initiation and fruit growth in heavily flowering and fruiting everbearing strawberry are source-limited owing to the high fruit/leaf ratio of such plants.

We studied short-day induction of the strawberry (Fragaria x ananassa Duch.) cultivar ‘Malwina’ under both phytotron and field conditions. Flowering was assessed by crown dissection of treated plants and subsequent flowering performance. Serial dissections revealed no visible changes in crown apices during the first 4 weeks of short day (SD) at 18°C in the phytotron, while after 6 weeks, all plants had formed rudimentary flower primordia with visible sepals. At 9°C, the same stages were reached after 8 and 10 weeks of SD, respectively. When subsequently forced in long day (LD) at 20°C, no substantial flowering took place after less than 6-week SD treatment at 18°C, while full flowering required 10 weeks of SD induction. At 9°C, full flowering was not obtained even after 10 weeks of SD treatment. Under field conditions, the ‘Malwina’ plants did not reach floral development stage 2 before 22 October, approximately a month after ‘Frida’ and ‘Sonata’ which reached this stage on 21 September, and 3 weeks after ‘Florence’. SD exposure resulted in repeated crown branching in ‘Malwina’ and we suggest that early spontaneous abortion of the emerging floral primordium takes place under unsaturated SD induction conditions, thus causing crown branching and hence, delayed floral initiation and development.

Flowering performance and phenology of six new pear cultivars of Nordic origin were examined during a 12 year period. The seasonal timing of shoot growth and flower initiation were monitored in thr...

Effects of annual versus biennial cropping with varying shoot densities on plant structure, berry yield and quality were studied in ‘Glen Ample’ raspberry over a period of four seasons (two croppin...

Juvenility and maturation in plants are briefly reviewed with emphasis on the regulation of phase change and rejuvenation. The invariable rejuvenation of offspring by the process of sexual reproduc...

The environmental control of dormancy and its relation to flowering and runner formation is poorly understood in everbearing (EB) strawberry cultivars. We studied the topic by growing plants of the seed-propagated F1-hybrid ‘Delizzimo’ and the runner-propagated ‘Favori’ cultivar in daylight phytotron compartments under short day (SD) and long day (LD) conditions at temperatures of 6, 16 or 26 °C for 5 and 10 weeks. This was followed by forcing at 20 °C and 20-h photoperiod for 10 weeks with and without preceding chilling at 2 °C for 6 weeks. The results showed that dormancy in EB strawberry is regulated by a complex interaction of temperature, photoperiod and chilling in much the same way as known for seasonal flowering (SF) cultivars. Surprisingly, the EB cultivars exhibited the same SD dormancy induction response as SF cultivars, despite their opposite photoperiodic flowering requirements. However, at 26 °C the EB cultivars developed partial dormancy also under LD conditions. As known for SF cultivars, none of the EB cultivars became dormant at 6 °C regardless of daylength conditions, whereas they were increasingly sensitive to SD dormancy induction at intermediate and high temperatures. Similar to SF cultivars, the EB cultivars needed exposure to SD and relatively high temperatures for at least 10 weeks for attainment of the semi-dormant state that is typical for strawberry in general. As reported for SF cultivars, there was a close interrelation between the control of flowering, runner formation and dormancy also in the EB cultivars. ‘Favori’ had an obligatory LD requirement for flowering at 26 °C and was almost day neutral at 16 °C, while ‘Delizzimo’ behaved as a quantitative LD plant at both temperatures, and both cultivars were completely day neutral at 6 °C. Except for the stricter LD control of flowering in ‘Favori’, the overall environmental responses were quite similar in the two genetically distant cultivars. Chilling for six weeks at 2 °C was adequate for complete reversal of the constrained elongation of leaf petioles and flower trusses in dormant plants, but had little or no effect on the degree of flowering and runner formation.

Field fertilization experiments with black currants have given inconsistent and often nonsignificant results. Therefore, we used an experimental system with single-stemmed plants grown in pots and fertilized by controlled trickle fertigation during both the period of flower formation in autumn and during berry development to study fertilization effects in black currants. Continuation of nutrient supply until mid-September, or a one-week pulse of generous supply in early September delayed growth cessation and floral initiation, and increased total flowering and berry yield in the following season. Such autumn fertilization did not adversely affect plant winter survival and growth vigour in the spring. Berry yield and fruit size also increased with increasing nutrient supply during fruit development in cultivars ‘Ben Tron’ and ‘Narve Viking’, while they were unaffected in ‘Hedda’ and decreased with increasing supply in the high-arctic ‘Imandra’. However, berry dry matter and the concentration of soluble solids and a range of health-related chemical constituents decreased with increasing nutrient supply in all cultivars. This was mainly a dilution effect related to increases in berry size. Yield potential and berry concentrations of nutritionally related chemical constituents varied significantly between the cultivars, being generally highest in ‘Ben Tron’ and ‘Narve Viking’, and lowest in ‘Hedda’. Leaf macro-mineral content at harvest time increased with increasing nutrient supply, but varied markedly between the cultivars. While ‘Imandra’ had higher leaf concentration of N than the other cultivars, ‘Ben Tron’ had remarkably low concentrations of K, as also reported in other investigations. The recommended range of leaf K content is therefore imprecise as a basis for fertilization of this cultivar. The results are discussed and we conclude that the present experimental system has clear advantages over traditional, long-term field experiments. We further conclude that black currants should preferentially be fertilized in early autumn, immediately after berry harvest, as this will enhance flower formation and subsequent berry yield without adversely affecting berry concentrations of important fruit quality constituents.

Introduction Blackcurrant (Ribes nigrum L.) is an excellent example of a “super fruit” with potential health benefits. Both genotype and cultivation environment are known to affect the chemical composition of blackcurrant, especially ascorbic acid and various phenolic compounds. Environmental conditions, like temperature, solar radiation and precipitation can also have significant impact on fruit chemical composition. The relevance of the study is further accentuated by the predicted and ongoing changes in global climate. Objectives The aim of the present study was to provide new knowledge and a deeper understanding of the effects of post flowering environmental conditions, namely temperature and day length, on fruit quality and chemical composition of blackcurrant using an untargeted high performance liquid chromatography–photo diode array–mass spectrometry (HPLC–PDA–MS) metabolomics approach. Methods A phytotron experiment with cultivation of single-stemmed potted plants of blackcurrant cv. Narve Viking was conducted using constant temperatures of 12, 18 or 24 °C and three different photoperiods (short day, short day with night interruption, and natural summer daylight conditions). Plants were also grown under ambient outdoor conditions. Ripe berries were analysed using an untargeted HPLC–PDA–MS metabolomics approach to detect the presence and concentration of molecules as affected by controlled climatic factors. Results The untargeted metabolomics dataset contained a total of 7274 deconvolved retention time-m/z pairs across both electrospray ionisation (ESI) positive and negative polarities, from which 549 metabolites were identified or minimally annotated based upon accurate mass MS. Conventional principal component analysis (PCA) in combination with the Friedman significance test were applied to first identify which metabolites responded to temperature in a linear fashion. Multi-block hierarchical PCA in combination with the Friedman significance test was secondly applied to identify metabolites that were responsive to different day length conditions. Temperature had significant effect on a total of 365 metabolites representing a diverse range of chemical classes. It was observed that ripening of the blackcurrant berries under ambient conditions, compared to controlled conditions, resulted in an increased accumulation of 34 annotated metabolites, mainly anthocyanins and flavonoids. 18 metabolites were found to be regulated differentially under the different daylength conditions. Moreover, based upon the most abundant anthocyanins, a comparison between targeted and untargeted analyses, revealed a close convergence of the two analytical methods. Therefore, the study not just illustrates the value of non-targeted metabolomics approaches with respect to the huge diversity and numbers of significantly changed metabolites detected (and which would be missed by conventional targeted analyses), but also shows the validity of the non-targeted approach with respect to its precision compared to targeted analyses. Conclusions Blackcurrant maturation under controlled ambient conditions revealed a number of insightful relationships between environment and chemical composition of the fruit. A prominent reduction of the most abundant anthocyanins under the highest temperature treatments indicated that blackcurrant berries in general may accumulate lower total anthocyanins in years with extreme hot summer conditions. HPLC–PDA–MS metabolomics is an excellent method for broad analysis of chemical composition of berries rich in phenolic compounds. Moreover, the experiment in controlled phytotron conditions provided additional knowledge concerning plant interactions with the environment. Electronic supplementary material The online version of this article (10.1007/s11306-018-1462-5) contains supplementary material, which is available to authorized users.

The predicted and ongoing climate warming is expected to affect many aspects of plant development. We analysed data from a 31-year series of observations (1985–2016) on spring phenology and flowering and fruiting performance of three plum cultivars in an experimental orchard at Ås in southeast Norway (59° 40′N; 10° 50′E). Regression analyses revealed a trend of increasing March and April temperature during the study period that was highly significantly (P

In order to assess to what degree the ongoing global warming has affected flowering time of apple trees in the Nordic climate, we studied flowering phenology of trees in an orchard in Southern Norway. Correlation analysis of a 70-year (1946–2016) data series for flowering time of the cultivar ‘Gravenstein’ revealed a close relationship of the flowering phenophase with April–May heat accumulation (r = −0.98). Over the last 50-year period, flowering was advanced by 16 days in response to the temperature rises. Similarly, on average for 12 cultivars of varying earliness, flowering was advanced by 9 days over the latest 30-year period (1986–2016). Furthermore, the interrelationship between various phenological stages and floral morphogenesis of the same cultivars in the years 2013 and 2014 was studied, and related to flower-bud formation. The different stages of floral morphogenesis were identified, presented and used as a basis for assessment of flower-bud development in serial dissections. Floral in...

The effect of fertility status and temperature conditions during floral induction on flowering, berry yield, and weight and drupelet numbers of individual berries were studied in ‘Glen Ample’ raspberries grown under controlled conditions. Withdrawal of normal fertilization prior to and at various stages during floral induction did not affect yield and berry size, but marginally advanced flowering and fruit ripening. The successive stages of floral initiation and differentiation were studied and identified by scanning electron microscopy of the uppermost lateral buds of plants grown for six weeks under naturally decreasing autumn photoperiods at temperatures of 9, 15 and 21 °C. Low temperature advanced floral initiation, and advanced and enhanced flowering and berry yield in the following season. However, at variance from earlier studies, the plants eventually initiated flower primordia even at 21 °C. Marginal low temperature and short day conditions during the last days before the temperature treatments were started on 17 September might possibly have reduced the subsequent induction requirements enough to explain this unexpected result. Correlation analyses revealed an over-all positive correlation between fruit weight and drupelet numbers (r = 0.568, P = 0.01). In berries from the early harvests, the number of drupelets per berry increased with decreasing temperature, while the numbers converged to the same level regardless of temperature in the later harvests. Based on the progress of the floral initiation process at the various temperatures, we interpret this to mean that only the early initiated flowers, that gave rise to the early maturing berries, were differentiated during the actual period of controlled temperature exposure, whereas the remaining flowers were differentiated afterwards when all plants were exposed to identical low temperature conditions. Increased femaleness under optimal floral induction conditions is in agreement with results in both monoecious and dioecious plants and circumstantial evidence suggest that, in the raspberry, this might be mediated by changes in gibberellin activity which acts as a male sexual hormone in plants and is known to inhibit growth cessation and floral initiation in raspberry.

BACKGROUND Marked effects of the climatic environment on fruit chemical composition have often been demonstrated in field experiments. However, complex covariations of several climatic factors in the natural environment complicate the interpretation of such experiments and the identification of the causal factors. This can be better achieved in a phytotron where the various climatic factors can be varied systematically. Therefore, we grew four black currant cultivars of contrasting origin in a phytotron under controlled post-flowering temperature and photoperiod conditions and analysed the berries for their ascorbic acid, sugar and organic acid contents. RESULTS The analyses revealed significant effects of genotype on all investigated compounds. Particularly large cultivar differences were observed in the concentrations of l-ascorbic acid (AA) and sucrose. The concentrations of both AA and dehydroascorbic acid (DHAA), as well as the concentrations of all major sugars, decreased consistently with an increasing temperature over the temperature range 12–24 °C. Fructose and glucose were the predominant sugars with concentrations several fold higher than that for sucrose. AA was the main contributor to the total ascorbate pool in black currant berries. The AA/DHAA ratio varied from 5.6 to 10.3 among the studied cultivars. The concentration of citric acid, which was the predominant organic acid in black currant berries, increased with an increasing temperature, whereas the opposite trend was observed for malic and shikimic acid. Quninic acid was always present at relatively low concentrations. By contrast, photoperiod had no significant effect on berry content of any of the investigated compounds. CONCLUSION It is concluded that the post-flowering temperature has marked effects on the concentration of important chemical compounds responsible for taste and nutritional value of black currant berries, whereas photoperiod has no such effect in the studied cultivars. © 2016 Society of Chemical Industry

The effects of postflowering temperature and daylength on the concentration of individual phenolic compounds were studied in black currant (Ribes nigrum L.) berries under controlled phytotron conditions. The four cultivars studied varied greatly in their concentrations of individual phenolic compounds and temperature stability for accumulation. The concentrations of a wide range of identified phenolic compounds were strongly influenced by temperature over the 12-24 °C range, often with opposite temperature gradient patterns for compounds within the same subclass. Accumulation of anthocyanins and flavonols increased under natural long day conditions, which provided an increased daily light integral, while under identical light energy conditions, photoperiod had little or no effect on the concentration of phenolic compounds. Furthermore, with the exception of members of the hydroxycinnamic acid subclass, the concentration of most phenolic compounds was higher in berries ripened outdoors than in the phytotron, apparently due to screening of UV-B radiation by the glass cover.

The effects of post-flowering temperature and daylength on chemical composition of four black currant cultivars originating from distinct geographical locations have been studied under controlled environment conditions. Special emphasis was placed on establishing photoperiodic conditions that are not biased by simultaneous changes in daily light integral. Unexpectedly, berry ripening in terms of colour change was delayed by high temperature, apparently due to high temperature suppression of anthocyanin biosynthesis. The concentration of l -Ascorbic acid decreased with increasing temperature (12–24 °C), while the concentrations of total anthocyanins and total phenolics were at an optimum at 18 °C. Under identical daily light energy conditions (night interruption), photoperiod had no specific effect on the analysed fruit quality components, while natural long day conditions (with 9% additional daily light energy) lowered the pH and increased the concentration of total monomeric anthocyanins, and to a lesser extent, the concentration of soluble solids. The cultivars varied significantly in fruit chemical composition. The high-boreal cultivar ‘Imandra’ was the one least affected by environmental conditions. This study provides evidence that accumulation of ascorbic acid and total anthocyanins in black currant fruits is favoured by low post-flowering temperatures, while high daily light integrals also seem favourable for anthocyanin biosynthesis.

In order to identify the optimal harvest time and monitor changes in raspberry ( Rubus idaeus L. cv. Glen Ample) fruit quality during ripening and storage, quality was assessed and compared by physical, chemical and sensory fruit quality criteria. Visual classification of fruit colour according to the Natural Colour System (NCS) chart and by physical measurement of fruit adherence to the receptacle or fruit compression resistance yielded parallel and highly significant results. The light red colour stage corresponding to NCS S code 3060-Y90R was identified as the optimal harvest stage for commercial fresh marketing of the ‘Glen Ample’ cultivar. Fruit harvested at this stage developed the same chemical and sensory qualities as in situ matured fruits and maintained high sensory quality after 8 days of storage in the dark at 2–3 °C. As the fruits mature, the concentration of titratable acids decreases, whereas the concentrations of anthocyanins and the sugar:acid ratio increase in parallel with colour development. While correlation analysis revealed a correlation between sensory traits like sweetness and acidity with sucrose and the sugar:acid ratio, respectively, the overall fruit tastefulness was not strongly correlated with any specific phytochemical component, thus illustrating the complex nature of this sensory trait. Due to its ease of performance, picking raspberry fruits related to a standardised colour chart is recommended for picking raspberry fruits with optimal quality.

The aim of this study was to examine the genetic and climatic impact on yield parameters and fruit chemical composition of black currant cultivars (Ribes nigrum L.). Correlation analysis between fr...

Blackcurrant is a short day plant that ceases growing and initiates flowers at photoperiods shorter than a critical length. Surprisingly, however, the flowering response was found to be several-fold stronger in the near-critical photoperiod of 15 h than in shorter photoperiods down to 10 h ( Heide and Sonsteby, 2011 ). This unusual response of a short day plant was confirmed by the present experiments where plants were exposed to 15 and 10 h photoperiods for 5 weeks at 18 °C. Also, plants exposed to naturally decreasing day-length from July, produced significantly more flowers than plants exposed to the shorter day-lengths in August. Furthermore, plants exposed to controlled photoperiods decreasing from 15 h to 10 h responded in much the same way as those in constant 15 h, while the reverse changes from 10 h to 15 h mimicked the response to constant 10 h photoperiod. Superior flower induction was always associated with a gradual reduction in growth rate followed by a delayed cessation of growth, while the sparse-flowering plants underwent an early and abrupt cessation of growth. We therefore conclude that the prompt growth cessation induced by an abrupt change to SD well below the critical length also interferes with flowering by arresting floral initiation at an early stage. Accordingly, the optimum photoperiod for flowering in black currant must be short enough to allow flower initiation and still long enough to prevent premature dormancy.

In many perennial woody plants growing in the temperate and cold regions, regulation of seasonal growth cessation and floral initiation are closely integrated, both taking place in photoperiods shorter than a critical length. In the temperate shrub black currant (Ribes nigrum L.), the two processes proceed harmoniously in parallel under naturally decreasing autumn photoperiods, whereas an abrupt shift to photoperiods well below the critical length results in an immediate growth cessation and premature dormancy. As a result, floral initiation is suppressed and arrested. Other perennial plants such as hop (Humulus lupulus), which have the same dual short day responses, behave in the same way. In such plants, optimal flowering takes place at near-critical photoperiods, which are short enough to induce flowering and still long enough to prevent premature dormancy. These responses deviate from the situation in annual plants, which have predominated in studies on photoperiodic control of flowering. Another example of linkage between flowering and dormancy responses is the well-known dual effects of chilling temperature on vernalization and its relation to dormancy. Elucidation and disentangling of these networks of integrated processes are now awaiting joint research efforts in the areas of molecular genetics and experimental plant physiology.

a b s t r a c t Chilling requirements for bud dormancy release and subsequent flower development in contrasting black currant (Ribes nigrum L.) cultivars were assayed at temperatures ranging from +10 to −10 ◦ C using single node cuttings, entire detached shoots, and intact plants. While single node cuttings underestimated the chilling requirements of intact plants, severed shoots and intact plants produced similar results. Chilling at −5 ◦ C for 14 weeks or more were optimal for breaking of bud dormancy and promotion of flower development in most cultivars, flower development usually having greater chilling needs than bud break itself. Within certain limits, extension of the chilling period compensated for non-optimal chilling temperature. However, while exposure to −10 ◦C for 8 weeks caused bud dormancy release, continued chilling for another 8 weeks inhibited bud break completely. We propose that excessive chilling induces secondary bud dormancy, a principle that is well established in seeds, but has to our knowledge, not been recognized for bud dormancy before. Marked genotypic differences were found and discussed. The observed severe chilling requirements of black currants concur with the reported vulnerability of this crop to declining winter chill in the wake of the ongoing global warming. Furthermore, elevated autumn temperature was found to induce a particularly deep dormancy state that further increases the chilling need.

The effect of photoperiod on nutritional quality and chemical composition of ‘Glen Ample’ red raspberry has been studied under controlled environment conditions. Long day (LD) conditions during fruit growth and maturation significantly increased fruit concentrations of ascorbic acid, total phenolics, organic acids such as malic, quinic and ellagic acids, as well as the ferric reducing activity power, while reducing the concentrations of soluble solids, sucrose and the sugar/acid ratio. The levels of total anthocyanin and oxalic acid were not significantly affected by photoperiod whereas semi-quantitative analysis indicated a significant increase in the levels of some ellagitannins. The same responses were found whether LD was established by day-length extension with low-intensity light or by night interruption, thus demonstrating that the observed changes in nutritional quality of raspberry fruit was mediated through specific photoperiodic mechanism(s) independently of the daily light energy supply.

SummaryCold hardiness and the chilling requirements for breaking bud dormancy in red raspberry (Rubus idaeus L.) were studied by exposing dormant plants and severed shoots of the cultivars ‘Glen Ample’ and ‘Asker’ to temperatures ranging from +10oC to –20oC for periods of 7 – 21 weeks. Temperatures in the +5oC to –5oC range were optimal for breaking bud dormancy and the promotion of flower development across all chilling periods, while +10oC and –10oC were outside the optimum chilling temperature range. The effect of the various temperatures varied with the duration of the chilling period. However, even at optimal chilling temperatures, both bud burst and flowering were promoted and advanced in both cultivars by sustained chilling for up to 21 weeks. Experiments with intact potted plants and severed canes of ‘Glen Ample’ produced almost identical dormancy-breaking results. Neither plants nor severed canes of ‘Glen Ample’ survived storage at –10oC or –20oC, whereas canes of ‘Asker’ survived at –10oC.We the...

We grew young sweet cherry (Prunus avium L.) trees under controlled temperature and natural summer daylight conditions in order to study the control of flowering of the species. Two experiments with the cultivars ‘Lapins’ and ‘Van’, were conducted and compared with field results with the same cultivars at As in southeast Norway (59° 40′N, 10° 50′E, 90 m a.s.l.). Shoot growth increased with increasing temperature in the 12–21 °C range, but ceased in late summer (August) regardless of temperature conditions. A marked drop in temperature always induced an immediate cessation of growth. Under field conditions at As, both growth cessation and floral initiation took place by about 1 August. Low temperature (12–15 °C) significantly enhanced flowering of both cultivars compared with 21 °C, which tended to depress flower bud formation during the summer but stimulated the subsequent flower differentiation process. These results concur with earlier regression analyses, which revealed a close positive correlation between historical records of sweet cherry yields over a 40-year period in farmer’s fields in the fjord districts of western Norway and previous year August-September temperature, and a negative correlation with previous year July temperature. Practical implications of the results are discussed and it is suggested that inadequate temperature control in rain-protected cultivation in plastic tunnels might have negative consequences for next year’s flowering and yield.

The production of ready-to-flower strawberry forcing plants with high yield potential has been studied by manipulation of temperature and fertilization during the natural transition to inductive SD conditions at a South Norwegian locality (60°40′ N; 10°52′ E, 250 m altitude). The cultivars ‘Korona’, Polka’ and ‘Sonata’ were used. It was demonstrated that, in this environment, sub-optimal temperature is a limiting factor for adequate floral induction in these strawberry cultivars under natural out-door conditions, while the prevailing natural photoperiod is not a limiting factor. Elevated temperature (>15 °C) during the month of September increased flowering and fruit yield, and this effect was significantly enhanced when elevated temperature was combined with a pulse of extra fertilization. The highest flowering and yield potential was obtained when fertilization was applied for a three-week period starting shortly after the photoperiod had declined to the inductive length. It is concluded that, in the cool Nordic environment, strawberry forcing plants with high yield potential can only be produced on a regular basis by greenhouse cultivation at elevated temperature (>15 °C). Under these conditions flowering and yield potentials of the plants are further significantly enhanced by timely application of a pulse of autumn fertilization. While excessive flowering with reduced fruit size was often experienced with ‘Korona’, this did not occur in the large-fruited ‘Sonata’.

SummaryTwo main categories of flowering and fruiting habits exist in strawberry: 1) seasonal flowering (SF) genotypes which produce only one flush of flowering and fruiting in the Spring; and 2) recurrent flowering or everbearing (EB) genotypes which, in addition to a spring flush, produce more or less continuous flowering and fruiting throughout the growing season. Both types are represented in the octoploid cultivated strawberry, Fragaria × ananassa Duch., as well as in the diploid wood strawberry, F. vesca L. Independent of ploidy level, SF genotypes have proved to be basically short-day (SD) plants, while EB genotypes are basically long-day (LD) plants. However, flower induction is controlled in both groups, by a pronounced interaction of photoperiod and temperature, which has complicated resolution of the underlying response mechanisms. At low temperatures (< 10oC), both SF and EB genotypes are essentially day-neutral, while, at higher temperatures, they exhibit contrasting photoperiodic responses. S...

SummarySeasonal time-courses of flower bud initiation and differentiation were monitored during two growing seasons (2011 and 2012) in 19 black currant cultivars of distant geographic origin, grown in the field at a South Norwegian locality (60°40’N, 10°52’E; 250 m asl). For comparison, the time-courses of shoot elongation growth in 15 of the same cultivars were also monitored during the 2012 growing season. The results revealed widely different seasonal timings of growth cessation and floral initiation in cultivars of different latitudinal origin. High latitude cultivars originating from crosses and selections of local, wild black currant populations from the Kola peninsula and Swedish Lapland were particularly early and had ceased growing and had initiated floral primordia by mid-June. This was approx. 5 – 6 weeks earlier than any of the other cultivars from lower latitudes. However, these also varied in their earliness of growth cessation and flower initiation in relation to their latitudinal origin. M...

SummaryExperiments were conducted on-Station and in growers’ nurseries with the aim of developing cheap techniques for the production of pot-grown raspberry long canes with high yield potential. In an earlier paper, we reported the feasibility of producing raspberry long canes with a yield potential of > 3 kg fruit per cane.The experiments presented here confirm that such high yields can be achieved on a regular basis, even when applying intensified and cheaper production techniques.Thus, the pot size could be reduced from the previous 3.5 l, to 2.5 l and the plant spacing could be decreased from 200 cm20 cm, to 100 cm×20 cm without loss of cane yield potential. Even at a plant spacing of 55 cm×20 cm, canes with a yield potential close to 3 kg per cane were produced. It was also shown that, during the cropping year, an additional one or two new canes with the same high yield potential could be raised concurrently with flowering and fruiting of the old cane, without a significant loss of yield on the old f...

This is the peer reviewed version of the following article: Koskela, E.A., Kurokura, T., Toivainen, T., Sønsteby, A., Heide, O.M., Sargent, D.J., ... Hytönen, T. (2017). Altered regulation of TERMINAL FLOWER 1 causes the unique vernalisation response in an arctic woodland strawberry accession. New Phytologist, 216(3), 841-853. https://doi.org/10.1111/nph.14734, which has been published in final form at https://doi.org/10.1111/nph.14734. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. Vernalisation requirement is an agriculturally important trait that postpones the development of cold‐sensitive floral organs until the spring. The family Rosaceae includes many agriculturally important fruit and berry crops that suffer from crop losses caused by frost injury to overwintering flower buds. Recently, a vernalisation‐requiring accession of the Rosaceae model woodland strawberry (Fragaria vesca) has been identified in northern Norway. Understanding the molecular basis of the vernalisation requirement in this accession would advance the development of strawberry cultivars better adapted to temperate climate. We use gene silencing, gene expression analysis, genetic mapping and population genomics to study the genetic basis of the vernalisation requirement in woodland strawberry. Our results indicate that the woodland strawberry vernalisation requirement is endemic to northern Norwegian population, and mapping data suggest the orthologue of TERMINAL FLOWER1 (FvTFL1) as the causal floral repressor. We demonstrate that exceptionally low temperatures are needed to downregulate FvTFL1 and to make these plants competent to induce flowering at low postvernalisation temperatures in the spring. We show that altered regulation of FvTFL1 in the northern Norwegian woodland strawberry accession postpones flower induction until the spring, allowing plants to avoid winter injuries of flower buds that commonly occur in temperate regions.

The effects of daylength and temperature on flowering of the cultivated octoploid strawberry (Fragaria x ananassa Duch.) have been studied extensively at the physiological level, but information on the molecular pathways controlling flowering in the species is scarce. The flowering pathway has been studied at the molecular level in the diploid short-day woodland strawberry (F. vesca L.), in which the FLOWERING LOCUS T1 (FvFT1) SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (FvSOC1)-TERMINAL FLOWER1 (FvTFL1) pathway is essential for the correct timing of flowering. In this work, we show by transgenic approach that the silencing of the floral repressor FaTFL1 in the octoploid short-day cultivar 'Elsanta' is sufficient to induce perpetual flowering under long days without direct changes in vegetative reproduction. We also demonstrate that although the genes FaFT1 and FaSOC1 show similar expression patterns in different cultivars, the regulation of FaTFL1 varies widely from cultivar to cultivar and is correlated with floral induction, indicating that the transcription of FaTFL1 occurs at least partially independently of the FaFT1-FaSOC1 module. Our results indicate that changing the expression patterns of FaTFL1 through biotechnological or conventional breeding approaches could result in strawberries with specific flowering and runnering characteristics including new types of everbearing cultivars.

In order to investigate the relationship between environmental conditions and vegetative growth and reproductive development in the strawberry, freshly rooted runner plants of the cultivar ‘Sonata’ were grown in a phytotron at temperatures of 12, 18 and 24 °C and photoperiods of 10 h short day (SD) and 20 h long day (LD) for 31 d and harvested at 10 d intervals. Plant dry weight and leaf area increases were exponential versus time, giving a linear regression with the natural log (ln). This rendered the relative growth rate (RGR) constant over time at each environmental condition. Over the entire 31 d growth period, the RGR increased linearly with increasing temperature across the range of temperatures with a further 10–13% enhancement by LD. A maximum RGR value of 0.077 g/g/d was determined in LD at 24 °C. Increases in the RGR was driven by a combined increase in net assimilation rate (NAR) and leaf area ratio (LAR) and was associated with an increased allocation of dry matter production into leaves and less into crowns and roots. Because of this, the shoot/root ratio increased consistently with increasing temperature and photoperiod, which was also associated with a significant increase in the tissue C/N concentration ratio. Low temperature promoted starch accumulation markedly in all parts of the plants, with a further enhancement by LD conditions, while the concentrations of soluble sugars were less affected by the climatic environment. Forcing of plants exposed to the various growth conditions for 31 d showed that all plants at 12 and 18 °C and 80% of those at 24 °C had initiated flowers in SD, whereas none had initiated flowers in LD regardless of temperature conditions. All these results demonstrate an opposite environmental relationship between vegetative growth and reproductive development in the strawberry.

a b s t r a c t Effects of plant size, photoperiod, temperature and duration of short day (SD) exposure on flowering and dormancy induction in black currant cultivars (Ribes nigrum L.) were studied under controlled environ- ment conditions. In concurrence with our earlier findings (Heide and Sonsteby, 2011), it was confirmed that flowering increased several-fold when plants were exposed to the near-critical photoperiod of 15 h compared with the presumed optimal photoperiod of 10 h. It is suggested that this unusual response of a SD plant in some way may be associated with the strong dormancy inducing effect of the shorter photope- riod, resulting in termination of the floral initiation process at an early stage. Clearly, a gradual change to shorter photoperiods, as takes place under natural seasonal changes, is optimal for the sustained floral initiation that is required for abundant flowering in the black currant. In agreement with earlier studies with other cultivars, approx. 14 d of SD exposure (10 h) were needed for 100% floral initiation in the culti- vars 'Ben Tron' and 'Narve Viking' at temperatures of 15-21 ◦ C, while 21 SDs were required for flowering of cv. Ben Hope at the same temperatures. In this cultivar the induction requirement exceeded 21 SDs at 9 ◦ C. However, in the high latitude cultivar 'Imandra' full flowering was triggered by as little as 7 SDs even at 9 ◦C. High temperature during SD dormancy induction resulted in a deep dormancy state that

SummaryGrowth and flowering were studied in six black currant cultivars grown under natural photoperiodic conditions at As, Norway (59°40'N) at constant temperatures of 9°C, 15°C, or 21°C during an entire growing season (May to late-September). Growth cessation and floral initiation were advanced and promoted by increasing temperature in the cultivars ‘Ojebyn’, ‘Ben Tron’, ‘Kristin’, ‘Ben Hope’, and ‘Narve Viking’, while early cessation of growth was advanced by low temperatures in ‘Murmanschanka’, a cultivar originating from the Kola Peninsula. In all cultivars, flowering was significantly increased by warm temperatures during the preceding growing season. A decline in growth preceded floral initiation by 2 – 3 weeks, indicating critical photoperiods of approx. 17 h and 16 h at 21°C for the two processes, respectively, for all cultivars except ‘Murmanschanka’, which initiated floral primordia shortly after mid-Summer. Warm summer temperatures also affected flowering indirectly by the promotion of growth ...

It was previously shown that nitrogen fertilization immediately after commencement of SD exposure enhanced the floral induction effect of SD in June-bearing strawberries ( Sonsteby et al., 2009 ). In order to optimize the timing of such fertilization under field conditions, seasonal timing of floral initiation in the strawberry cultivars ‘Frida’, ‘Polka’, ‘Korona’ and Florence’ was studied in the field at five contrasting latitudinal and altitudinal geographic locations in Norway and, for comparison, under controlled environment conditions with 12 h photoperiod and temperatures ranging from 9 to 18 °C. Serial collections and dissections of crowns from the various locations revealed that floral initiation was successively delayed with increasing latitude and altitude of the location, and with decreasing temperature under controlled environment conditions. Both in the field and in the phytotron, floral initiation was earliest in ‘Frida’ closely followed by ‘Polka’ and in due course by ‘Korona’ and finally ‘Florence’ which was particularly slow to respond. Floral initiation in the phytotron was progressively advanced with increasing temperature and was optimal at 15–18 °C. Flowering time in the field was mainly determined by thermal relations in the spring and early summer, and accordingly, it was strongly delayed with increasing latitude and altitude of the location. In addition, late floral initiation in autumn also delayed flowering in the spring. Based on these observations, optimal timing of autumn fertilization for the various locations and cultivars are suggested.

SummaryRecent research on how the structure and physiological development of red raspberry (Rubus idaeus L.) plants are controlled by genotype and the climatic environment is reviewed. Some older work, especially on plant structure relations, is also included. Physiological differences between annual- and biennial-fruiting plant types are highlighted. One major difference is the different requirements for flower formation. While biennial-fruiting cultivars have an absolute low temperature (≤ approx. 15°C) requirement for floral initiation, annual-fruiting cultivars readily initiate floral primordia at temperatures as high as a constant 30°C. Also, while biennial-fruiting cultivars are facultative short-day plants with a critical photoperiod of 15 h at intermediate temperatures, flowering is promoted by long photoperiods in at least some annual-fruiting cultivars. However, the essential difference that determines whether the shoot life-cycle becomes annual or biennial is that, in biennial-fruiting genotype...

SUMMARY Actively-growing, single-stemmed plants of five Scandinavian and British cultivars of black currant (Ribes nigrum L.) were exposed to autumn temperatures of 9o, 12o, 18o, and 24oC in daylight phytotron compartments with natural daylength conditions at As, Norway (59o 40' N) in order to evaluate the effects of elevated autumn temperature on growth cessation and floral initiation in this species. The treatments were started on 11 August and lasted until 13 October (9 weeks) when the plants were moved outdoors for cold-hardening for 7 weeks, then cold-stored at ‐2oC over the Winter. The following Spring, the plants were moved into a heated greenhouse at 15oC with natural daylength conditions and monitored for bud burst and flowering and fruiting performance. Unexpectedly, the cessation of growth in the Autumn was promoted by increasing temperature, and was earliest at 24oC. The high-latitude cultivar, ‘Ojebyn’, and the Norwegian-bred ‘Kristin’ were the most temperature-responsive cultivars, while the Norwegian cultivar, ‘Narve Viking’ was least influenced by Autumn temperature. Leaf senescence and abscission, which followed in due course, were also promoted by high Autumn temperature in ‘Ojebyn’, but by low Autumn temperature in all other cultivars. Bud burst in the following Spring was consistently delayed by a few days by high Autumn temperature, while flowering was earliest in plants from intermediate temperatures. Furthermore, the magnitude of flowering was increased several-fold by elevated Autumn temperature, usually reaching an optimum at 18oC. Again, this enhancement effect was least in ‘Narve Viking’, in which the extent of flowering was also significantly reduced when autumn temperatures increase from 18oC to 24oC. It is concluded that elevated Autumn temperature, as a consequence of global warming, does not represent a threat to the normal cessation of growth or floral initiation in black currant.

SUMMARY Actively growing, single-stemmed plants of three black currant cultivars, each with 15 ‐ 16 nodes, were exposed to photoperiods of 10, 14, 15, 16, 17, 18, 20, and 24 h at 18°C for 8 weeks for determination of the critical photoperiods for growth cessation and floral initiation. In all three cultivars, growth cessation was induced by short day (SD) conditions, with a critical photoperiod of 16 h, and the response was advanced by decreasing the photoperiod. The critical photoperiod for 50% flowering was 16 h in the cultivars ‘Ojebyn’ and ‘Ben Tron’, and 17 h in ‘Kristin’. Unexpectedly, however, not all plants flowered after exposure to a 10 h photoperiod, and the number of flowers per plant increased several-fold as the photoperiod was increased from 10 h to 15 h in all cultivars. Apparently, this unexpected result was due to the fact that all plants had only 15 ‐ 16 nodes at the start of the experiments, which is marginal for “ripeness to flower” in black currant. While growth cessation was almost immediate in a 10 h photoperiod, causing only a few additional leaves to be formed during the experiment, the slower response to longer photoperiods apparently enabled the plants to reach the critical size at an earlier stage of the treatment period. However, although plants with 15 ‐ 16 nodes were only marginally responsive to SD induction, buds situated as far down the shoot as the fifth or sixth node were competent to flower. It is therefore suggested that the inability of small black currant plants to flower resides in limitations of the leaves to respond to SD and to produce a florigenic signal, while their buds are fully competent to respond to such a signal.

SummaryEarliness, fruit yield and quality of six annual-fruiting raspberry (Rubus idaeus L.) cultivars were tested under protected cultivation in a cool Nordic environment. After raising plants for 5 weeks in greenhouses with average mean temperatures of 20°C, 22°C, or 26°C, the plants were cropped in an open plastic tunnel at latitude 61°N. The highest yielding cultivars were ‘Autumn Bliss’ and ‘Polka’, with 640 g plant–1. Overall, the most promising cultivar was ‘Polka’ which combined high yield with large fruit of good flavour and firmness. In earliness, ‘Polka’ was surpassed only by ‘Autumn Bliss’, which confirmed its position as the earliest commercial annual-fruiting cultivar. However, ‘Autumn Bliss’ had soft fruits with little flavour and a short shelf-life, which greatly reduced the potential of the cultivar for the fresh fruit market. The later ripening cultivar ‘Erika’ did not complete its crop under these conditions, but its large unrealised yield potential and good fruit quality rendered it ex...

The effects of timing of nitrogen (N) fertilization relative to the beginning of a 4-week floral-inducing short-day (SD) period have been studied in ‘Korona’ strawberry plants under controlled environment conditions. Groups of low fertility plants were fertilized with 100 ml of calcium nitrate solution for 3 days a week for a period of 3 weeks starting at various times before and at the beginning of the SD period, as well as at different times during the SD period. All plants, including SD and long day (LD) control plants, received a weekly fertilization with a low concentration complete fertilizer solution throughout the experiment. Leaf area, fresh and dry matter increments of leaves, crowns and roots, as well as leaf chlorophyll concentration (SPAD values) were monitored during the experimental period. A general enhancement of growth took place at all times of N fertilization. This was paralleled by an increase in leaf chlorophyll concentration, indicating that the control plants were in a mild state of N deficiency. When N fertilization was started 2 weeks before beginning of the SD period, flowering was delayed by 7 days, and this was gradually changed to an advancement of 8 days when the same treatment was started 3 weeks after the first SD. The amount of flowering was generally increased by N fertilization although the effect varied greatly with the time of N application. The greatest flowering enhancement occurred when N fertilization started 1 week after the first SD when the number of flowering crowns and the number of inflorescences per plant were more than doubled compared with the SD control, while fertilization 2 weeks before SD had no significant effect on these parameters. Importantly, the total number of crowns per plant was not affected by N fertilization at any time, indicating that enhancement of flowering was not due to an increase in potential inflorescence sites. No flowering took place in the control plants in LD. Possible physiological mechanisms involved and practical applications of the findings are discussed.

Techniques for the production of raspberry long canes with high yield potential were studied on a research station and in two commercial nurseries in South Norway. Potted ‘Glen Ample’ plants were grown in the open and in polyethylene greenhouses during two seasons in order to optimize cultural practices. Dates of propagation and transfer to the production sites were varied. Following cold storage from December to early June, the canes were tipped (cut) at 160 cm height and grown in open plastic tunnels in the fruiting season for the evaluation of growth and yield performance. Remarkable berry yields of 1.5–3.8 kg per plant (cane) were regularly achieved. When grown in the open, later starts than June 1 (June 15 and July 1) successively reduced yields. On the other hand, an earlier start involves risks of growth cessation due to low spring temperature. When grown in greenhouses, high yields were still possible when plants were transferred from propagation conditions as late as July 1, although optimal yields of nearly 4 kg per plant were obtained with transfer on June 15. In a year with unusually high summer temperatures, the yields of canes produced in the open and in greenhouses did not vary significantly, whereas in the second year with normal summer temperatures, canes produced in greenhouses consistently out-yielded those produced in the open by about 1 kg per cane. Regression analyses revealed that high yields were associated with fruiting cane architecture traits such as cane height, number and length of laterals, and a low proportion of dormant buds. The single most important component was lateral length which alone accounted for 82% of the yield variation. Since lateral lengths increased from the shoot tip towards the base, cane heights in excess of 2 m are required for the attainment of top yields as the uppermost nodes with short and low-yielding laterals then can be eliminated by tipping.