Inger Martinussen

Head of Department/Head of Research

(+47) 976 78 488
inger.martinussen@nibio.no

Place
Holt

Visiting address
Holtveien 66, 9269 Tromsø

Abstract

Rhodiola rosea is a perennial flowering plant with a long history as a medicine plant. The plant contain a range of bioactive compounds including salidroside, rosavin, rosarian and rosin. Some of the compounds are characterized as adaptogens, meaning they can increase the body’s resistance to various stressors. An increased demand for better pharmaceuticals has stimulated the development of new methods for agricultural as well as in vitro cultivation of medicinal plants. A new technology, called rhizosecretion of biologically active chemicals, can provide a continuous supply of biologically active compounds over the lifetime of plants. The plants will then be grown under controlled conditions. In order to increase the production of bioactive compounds in Rhodiola rosea under these conditions it is therefore hypothesized that the biosynthesis can be upregulated by growing it under specific temperature and light quality treatments. An experiment with different light and temperature regimes was established for optimal accumulation of biologically active compounds. Four different clones of Rhodiola rosea were grown under three different light conditions (red, blue and white) combined with two different temperatures (9 and 18 °C) for three weeks. The gene expression of Tyrosine decarboxylase (TyrDC), found to have a key role in the biosynthesis of salidroside, were investigated. In addition, the content of various bioactive compounds were quantified before and after treatment. The results indicate that use if high producing clones is most important for high production and that there is a short-term upregulation during blue light treatment. During the three-week treatment, there was no significant effect of the temperature treatments.

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Abstract

The population structure of cloudberry (Rubus chamaemorus L.), collected from Krkonose Mountains (the Czech Republic), continental Norway and Spitsbergen, was examinedusing microsatellite analyses (SSR). Among 184 individuals, 162 different genotypeswere identified. The overall unbiased gene diversity was high (̂h=0.463). A high level of genetic differentiation among populations (FST = 0.45; p < .01) indicated restricted gene flow between populations. Using a Bayesian approach, six clusters were found which represented the genetic structure of the studied cloudberry populations. The value of correlation index between genetic and geographical distances (r = .44) indicates that gene flow, even over a long distance, could exist. An exact test of population differentiation showed that Rubus chamaemorus populations from regions (Krkonose Mountains,continental Norway and Spitsbergen) are differentiated although some individuals within populations share common alleles even among regions. These results were confirmed by AMOVA, where the highest level of diversity was found within populations(70.8%). There was no difference between 87 pairs of populations (18.7%) mostly within cloudberry populations from continental Norway and from Spitsbergen. Based on obtained results, it is possible to conclude that Czech and Norwegian cloudberry popula-tions are undergoing differentiation, which preserves unique allele compositions most likely from original populations during the last glaciation period. This knowledge will be important for the creation and continuation of in situ and ex situ conservation of cloud-berry populations within these areas.

Abstract

Rhodiola rosea is a well-known herbal medicinal plant, valued for highly active secondary metabolites. It is growing wild in most parts of Norway and mountainous areas in a number of countries. Some of the most important metabolites are believed to be salidroside, cinnamyl alcohol, glycosides (rosine, rosavine, rosarine), flavonoids (rhodionin, rhodiosin,rhodiolin) and terpenes (Galambosi 1999). In Norway, germplasm collections of R. rosea are maintained by NIBIO; at Apelsvoll in southern Norway, consisting of 97 different clones. The ranges in content of secondary metabolites in the collection are for rosavin 2.90-85.95 mg g-1, salidroside 0.03-12.85 mg g-1, rosin 0.08-4.75 mg g-1, tyrosol 0.04-2.15 mg g-1 and cinnamyl alcohol 0.02-1.18 mg g-1. Clones selected from the collection has throughout been studied for different aspects affecting plant growth and production of secondary metabolites. We have looked into cultivation requirements of the plant like water requirement, effects of nutrient levels (N and K) and soil types. Postharvest treatment from washing, cutting,drying and differences in the plant parts. Finally we will in this presentation also present results on requirements for dormancy release and the clonal differences and also how use of primers may affect production of secondary metabolites.

Abstract

Cloudberry (Rubus chamaemorus L.) is a wild perennial shrub growing on peatland with a circumpolar distribution. The combined berries have a high polyphenol content comprised primarily of ellagitannins. A few commercial cultivars are available, and pre-breeding trials on clonal material from different geographical origins are in progress. The objective of this study was to investigate how the content of polyphenols of four different cloudberry cultivars were affected by harvesting time and climatic variations during a 3-year-period. Plants were grown outside in plots and berries were harvested when mature. Berries were analyzed for total polyphenols and total anthocyanins by spectrophotometer. Total ellagic acid was identified and quantified using HPLC-MS after hydrolysis of the extracts. Results showed that all measured parameters; total anthocyanins, total polyphenols and ellagic acid are strongly influenced by the genetic background. Although low anthocyanin contents were present in all genotypes, they were highly affected by climatic conditions, being highest at low temperatures. However, the content of ellagic acid was less affected by environmental conditions and showed little response to changing temperatures. In conclusion, ellagitannin content was the most dominating polyphenol group observed in this study and was affected by genetics and is therefore a good breeding criterion for increased health benefit of cloudberry.

Abstract

Two field trials with five strawberry cultivars planted on a woven black polyfibre ground cover sheet with or without translucent sheet plant coverage during winter and the growing season as combined treatments were started in 2004 and 2005. In total, nine different cultivars were included in the two fields. One early cv. ‘Polka’ and one late cv. ‘Korona’ acted as standard cultivars, while the other cultivars were new, named or labelled selections from Norwegian, Finnish and Swedish breeding programs. Winter survival, spring vigour, earliness, saleable and total berry yield, berry size and berry quality were registered for three years. The cultivars differed in earliness, berry size, yield (gram per plant) and total production (sum of all years). A combination of fibre sheet winter and spring coverage and more open net sheet harvest season coverage showed favourable results for overwintering, earliness and berry yield, and enhanced the ripening process in all cultivars.

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Abstract

Anthocyanins are the main pigments in the Vaccinium berries. Besides contributing to the characteristic bluish to reddish colors of the berries, anthocyanins are also recognized as potential health beneficial compounds. The biosynthesis of anthocyanins is well understood and the key regulators have been characterized in many plant species. The final anthocyanin composition in ripe berries is regulated by developmental and environmental factors, determined by the genetic background. We have studied the role of different light and temperature conditions on the accumulation of anthocyanins in wild bilberry (V. myrtillus L.) and cultivated highbush blueberry (V. corymbosum L.), in controlled and in field experiments. These experiments include specific growth conditions with clones from northern and southern latitudes as well as from different altitudes. The results show speciesspecific interactions in quantitative and qualitative composition of anthocyanins as a response to light and temperature conditions. For instance, lower temperature and specific light wavelengths induced accumulation of delphinidin glycosides in bilberry.

Abstract

The paper is a mini review on the climatic effects on berry production and berry quality in the Arctic north. Plants in the north are facing short growing seasons with low temperatures and long days with a unique light quality. The winter time is cold but with fluctuating temperatures, especially along the coast. Fluctuating winter temperatures and unstable snow cover is a challenge for the perennials that need to be dormant during winter time. Dormancy is induced in the autumn by a combination of day length and temperature. The wild berries domestic to the Nordic countries are adapted to these growth conditions while many of the commercially important berry species originate from more southern areas. Pre-breeding studies on interactions between genotype and environment are essential in order to develop climatically adapted berry cultivars for northern growth conditions.

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Abstract

Glucosinolates are plant secondary metabolites with important roles in plant defence against pathogens and pests and are also known for their health benefits. Understanding how environmental factors affect the level and composition of glucosinolates is therefore of importance in the perspective of climate change. In this study we analysed glucosinolates in Arabidopsis thaliana accessions when grown at constant standard (21 °C), moderate (15 °C) and low (9 °C) temperatures during three generations. In most of the tested accessions moderate and pronounced chilling temperatures led to higher levels of glucosinolates, especially aliphatic glucosinolates. Which temperature yielded the highest glucosinolate levels was accession-dependent. Transcriptional profiling revealed also accession-specific gene responses, but only a limited correlation between changes in glucosinolate-related gene expression and glucosinolate levels. Different growth temperatures in one generation did not consistently affect glucosinolate composition in subsequent generations, hence a clear transgenerational effect of temperature on glucosinolates was not observed.

Abstract

Important losses in strawberry production are often caused by the oomycete Phytophthora cactorum, the causal agent of crown rot. However, very limited studies at molecular levels exist of the mechanisms related to strawberry resistance against this pathogen. To begin to rectify this situation, a PCR-based approach (NBS profiling) was used to isolate strawberry resistance gene analogs (RGAs) with altered expression in response to P. cactorum during a time course (2, 4, 6, 24, 48, 96 and 192 h post-infection). Twenty-three distinct RGA fragments of the NB-LRR type were identified from a resistance genotype (Bukammen) of the wild species Fragaria vesca. The gene transcriptional profiles after infection showed that the response of most RGAs was quicker and stronger in the resistance genotype (Bukammen) than in the susceptible one (FDP821) during the early infection stage. The transcriptional patterns of one RGA (RGA109) were further monitored and compared during the P. cactorum infection of two pairs of resistant and susceptible genotype combinations (Bukammen/FDP821 and FDR1218/1603). The 5′ end sequence was cloned, and its putative protein was characteristic of NBS-LRR R protein. Our results yielded a first insight into the strawberry RGAs responding to P. cactorum infection at molecular level.

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Abstract

Effects of different environmental factors (origin, climate, fertilization and soil properties) on berry nutritional quality were studied in eight forest fields of bilberry (Vaccinium myrtillus) in Northern-, Mid- and Southern Norway. No clear trend between locations could be found, however untargeted multivariate analysis of metabolite profiles revealed clear segregation patterns between locations. Anthocyanin, and phenolics content, and titratable acidity were significantly affected by mineral fertilization (Mid-Norway), while organic fertilization did not show any significant effects (Northern Norway). Bilberry chemical composition was affected by harvest time point, as indicated by a potentially higher nutritional quality regarding the content of phytochemicals when harvesting at mid or towards the end of the production season (Southern Norway). Regional and annual climate had strongest impact on the nutritious content of bilberries. Significant differences were found between locations, however previous findings on increasing anthocyanin content with latitude were not confirmed due to environmental impacts confounding the population effects.

Abstract

An investigation of the wild European blueberry (E. blueberry; Vaccinium myrtillus L.) was financed for four years starting in 2008. One part of the project was to examine natural development of E.blueberry in five Norwegian fields, effect of fertilization and cutting of plants. Examinations were undertaken in two fields in Bardu municipality in Troms county and of three fields in Snåsa and Lierne municipalities in Nord-Trøndelag county. The basic idea was to examine the possibility of half cultivation on situ in the forest, a similar system as developed in north America with Vaccinium angustifolium. The five fields were arranged in block designs, and in the Bardu fields Organic Matter (OM) were added (compost and wood chips) and in the Snåsa/Lierne fields mineral fertilizers (N-P in kg haa-1: 0-0, 3-2, 3-4, 6-4). Treatments were compared with natural development. In addition to fertilization and OM the Snåsa field had two more treatments, cutting of the plants to the ground in autumn 2008 and site (placed on two moraine ridges). From our research and investigations we can conclude that the soil O-layer is very important. The fields that performed best had thick O-layers. It could be suggested that layers close to 7 cm or thicker would be optimal. The C/N ratios indicate that N was not easily available in any field. This may explain why long shoot growth increased and more nodes were developed, when mineral fertilizer, and especially N, was added. However, number of short shoots per long shoot was not clearly influenced by fertilizer, except last year when the effect was positive- maybe a long term effect. This was not followed by higher yields throughout the years, rather the contrary, but it should be added that weather conditions the last two years were rainy; and the high yield in 2009 could have initiated alternate bearing, and more browsing because of more attractive shoots and leaves; factors that would reduce the yield in subsequent years. Adding OM had some positive influence on tiller growth in the Bardu birch-field (F1), but not in the pine-field (F2). However, annual shoot growth increased in the pine-field in the first of two years. Yields, however, were clearly reduced by adding OM in average of two years. The importance of a thick O-layer was confirmed in the examination of growth conditions on two moraine ridges. The ridge with lowest yield had less loss of ignition in the O- and B-layers, a shallower O-layer and lower levels of P, Mg and Ca in both O- and B- layers. Cutting of shoots to the ground was not beneficial and full yield potential was not recovered before the third year after cutting. Fruit quality was influenced by latitude, soil factors and fertilization treatments. However, variations between years were the most important single factor.

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Abstract

After pollination outdoors individual bilberry plants from two Northern and two Southern clones were studied for climatic effects on berry yield and quality in a controlled phytotrone experiment at 12 °C and 18 °C. At each temperature the following light treatments were tested; 1) 12 h natural light; 2) 24 h natural light and 3) 24 h natural light plus red light. The first experimental year there was no difference in yield between temperatures, however, the second experimental year the berry yields was significantly higher at 18 °C. Berry ripening was faster in the Northern than in the Southern clones at 12 °C. Northern clones also showed significantly higher contents of total anthocyanins, all measured anthocyanin derivatives, total phenolics, malic acid and sucrose. Metabolic profiling revealed higher levels of flavanols, hydroxycinnamic acids, quinic acid and carbohydrates at 12 °C.

Abstract

Bilberry (Vaccinium myrtillus L.), also called European blueberry, is native to Norway and strongly preferred by the Norwegian food industry due to its genuine flavour and high content of phytochemicals. However, Norwegian natural resources are underexploited, and only few investigation have focused on quality aspects of bilberries from wild populations with regard to potential cultivation and industrial utilization. Important goals of the 4-years study were to investigate (a) Berry quality parameters, (b) Fertilization effects, and (c) Geographic and seasonal variation in trial locations at regions in Southern, Mid and Northern Norway. Berry quality assessment included parameters such as total anthocyanins (ACY) and phenols (TPH), antioxidant capacity (AOX), pH, titratable acidity (TAC) and soluble solids (SS). Based on multivariate statistics (PCA), regional segregation patterns could be observed which were strongly overlapped by year-to-year variation. Within-seasonal variation of parameters were recorded for berries harvested at different time points throughout the season (Southern location/ Hedmark), but between-seasonal effects were generally stronger. Similar year-to-year effects were also found in bilberries from Northern Norway (Bardu), but not in berries harvested from the field in Mid Norway/Langvatnet. The field in Northern Norway was treated with organic fertilizer (compost and wood chippings), while the field in Mid Norway was fertilized with mineral fertilizer combinations (N+P). Application of organic fertilizer did not have any clear effect on berry quality, while mineral fertilizer resulted in clear segregation patterns of berry samples after three years of treatment, thus minimizing year-to year variation. Mean values of quality parameters ACY, TPH and AOX, measured at the different locations (all years and treatments) varied between 330-427 mg/100 g f.w., 531-640 mg/100 g f.w., and 5-8 mmol/100 g f.w., respectively, thus underscoring the phytochemical value of bilberries from Norwegian populations.

Abstract

Individual bilberry plants from two Northern and two Southern clones were studied for climatic effects on production and quality in a controlled phytotrone experiment at 12 °C and 18 °C in a 2-year trial. At each temperature the following light conditions were tested: 1) 12 h natural light (short day); 2) 24 h natural light (long day) and 3) 24 h natural light (long day) plus red light. In order to ensure sufficient and comparable fruit set between treatments, flower pollination was executed outdoors. Berry yield, quality parameters such as total anthocyanins, total phenols and antioxidant capacity, and chemical composition (GC/MS-based metabolite profiling) were recorded in both years, while HPLC-based anthocyanin analysis was only carried out in the second year. All analyzed compounds showed significant year-to-year variation with the exception of antioxidant activity. The experiment was conducted under natural light conditions, and therefore light intensity and quality varied between the two growing seasons. The first experimental year there was no difference in yield between temperatures, however, the second experimental year the berry yield was significantly higher at 18 °C. Temperature treatments led to faster berry ripening in the Northern than in the Southern clones at 12 °C. Metabolite profiling also revealed higher levels of flavanols, hydroxycinnamic acids, quinic acid and carbohydrates at 12 °C. Clonal effects showed that the content of all anthocyanin derivatives, as well as levels of antioxidants, total phenolics, malic acid and sucrose were highest in the Northern clones, while Southern clones had higher levels of hydroxycinamic acids, epicatechin, quinic acid and myo-inositol. Northern clones were also more responsive to additional red light with highest levels of anthocyanins under long-day treatment.

Abstract

The effects of climate on production and the quality of bilberries have been studied in a controlled phytotrone experiment using clonal material originating from Northern and Southern parts of Finland. In the experiment individual plants from two Northern clones and two Southern clones have been grown at 12° and 18°C. At each temperature 3 different light treatments have been tested; 1) 24 h natural light (long day), 2) 12 h natural light (short day) and 3) 24 h natural light with an addition of extra red light. All berries produced by each plant have been harvested at maturity and have been analyzed for several important quality parameters. The metabolic profiling results show that levels of flavonols (epicatechin and catechin), hydroxyl acids (chlorogenic acid, hydroxyl cinnamic acid), quinic acid and all analyzed carbohydrates (myo-inositol, fructose, glucose and sucrose) are highest at 12°C. On the contrary, total anthocyanins levels were highest at 18°C and this was also reflected in the results on analysis of several anthocyanins derivates with the exception of Del 3‑Ara that was significantly higher at 12°C than 18°C. Northern clones had significantly higher levels of total anthocyanins, all measured anthocyanin derivates, total phenols, malic acid and sucrose than Southern clones.

Abstract

Blueberries belong to the genus Vaccinium, a widespread genus with more than 200 species of woody plants. In Northern Europe, the European blueberry (EB), also called bilberry, is one of the most important wild berries. EB (Vaccinium myrtillus) is very demanded by the processing industry, due to its delicious taste and high dietary value. However, to our knowledge there has been made no efforts of domestication of the species, and it is still harvested in forest fields without any cultivation. The successful management of the sweet lowbush blueberry (V. angustifolium), which in many ways is similar to the EB, suggests that there are opportunities to increase yield and decrease the significant yearly variation in EB yield, by practices including fertilization, irrigation, cutting trees, and weed control. The fruit yield in wild stands of EB is very variable, but the potential is probably close to 2 tons per hectare. Results from literature on growth of the EB, development and ecology are discussed in relation to possibilities for domestication.

Abstract

The fruit quality of European blueberry (EB) is mainly determined by taste compounds (sugars, acids, flavour) and health-beneficial structures generally denoted as antioxidants (vitamin C, phenolic acids, flavonols, anthocyanins, proanthocyanidins). Content and compound composition is strongly affected by the growth environment regarding light, temperature, water and edaphic factors. In order to assess genotypic relationships (northern and southern clones of EB) and environmental impact (temperature, day length) on berry quality parameters, a high-throughput system for blueberry metabolite profiling of nutritional compounds was established based on gas chromatography coupled with mass spectrometry (GC/MS). Dried methanol/H2O extracts from fresh-frozen berry tissue were derivatized, and subjected to GC/MS in order to detect polar compounds such as organic acids from Krebs-cycle, amino acids, sugars, polyols, and partly secondary metabolites (phenols, flavonoids). In addition, general quality parameters such as total phenols, total anthocyanins and antioxidant capacity (FRAP) were measured. Fructose (5 g), glucose (5 g), and sucrose (0.5 g/ 100 g f.w. at average) were the most abundant carbohydrates, together with high levels of organic acids such as citric acid (1.3 g), quinic acid (1.6 g), and malic acid (0.3 g/ 100 g f.w. at average). More than 50 metabolites per sample (identified compounds and not-annotated mass spectral tags) could be detected, and established the basis for multivariate statistics using principal component analysis, hierarchical clustering, and metabolite network analysis. Genotypic differences, modulation of metabolite pools and biosynthetic relationships are being discussed in-depth.

Abstract

Two female and two male cultivars have previously been released as a result of clone evaluation at Bioforsk Nord Holt. Selection criteria have been number of pistils or stamens per flower, number of flowers and number of shoots per m2. Currently a new group of clones are evaluated with the aim of finding new cultivars for release. The clones are collected from different parts of Norway, as well as from England and Spitsbergen. Preliminary results from harvesting 2005, 2006, 2007 and 2008 indicate good production potential for a couple of the tested clones. In addition to prior selection criteria based on berry yield, the levels of total anthocyanins and total phenols have been analyzed. This includes studies on the role of female clone, male pollinator and temperature on berry quality.

Abstract

Two female and two male cultivars have previously been released as a result of clone evaluation at Bioforsk Nord Holt. The selection criteria were the number of pistils or stamens per flower, the number of flowers and the number of shoots per m2. Currently a new group of clones are being evaluated with the aim of finding new cultivars for release. The preliminary results on flowering and berry production show a strong variance in these traits. Over three years of registration, the number of produced flowers varied from under 100 for the weakest clone to more than 1000 for the best clone. The number of produced berries varied from 9 for the weakest clone to 242 for the best clone. The three clones that produced the most flowers all had very low berry production and deviated from the rest of the clones by having high numbers of flowers per harvested berry. New selection criteria will be considered before selection of new cultivars for release. In addition to the production traits, new selection criteria will most likely include berry contents, such as the levels of antioxidants.

Abstract

Wild berries are a characteristic part of Northern nature and a particular speciality of Nordic countries. Wild berries are also a rich and valuable resource that has not yet been exploited in a satisfactory level. Approximately 90 – 95 % of the whole wild berry crop yield is left unpicked in the Nordic forests every year. The challenges of wild berry utilization are similar in Nordic countries - the logistics of berry picking including traceability, fragmented sector structure as well as the high share of unprocessed raw material in export. The Nordic project focusing on bilberry (Vaccinium myrtillus) “Bilberry: Towards functional food markets” (2007 – 2009) is a part of the New Nordic Food programme funded by the Nordic Innovation Centre. The programme aims to enhance cooperation and innovation among companies that utilize the natural resources of the Nordic countries. The aim of the project is to improve wild berry production and utilization in the Nordic and global market. To achieve this goal a network between the Nordic experts presenting the different fields of the wild berry sector has been established. The project has focused on marketing research, quality issues, biodiversity and the traceability of wild berries; especially the bilberry. The results of the marketing survey were published in November 2008. The aim of the survey was to generate an overall picture of the companies working with wild berries in Nordic countries and to gather information on the existence and willingness of the berry companies to cooperate in wild berry supply, logistics, marketing and research and development. According to the results, a general agreement for the need of increased cooperation at the Nordic level was highlighted.

Abstract

Plant polyphenolics continue to be the focus of attention with regard to their putative impact on human health. An increasing and ageing human population means that the focus on nutrition and nutritional enhancement or optimisation of our foodstuffs is paramount. Using the raspberry as a model, we have shown how modern metabolic profiling approaches can be used to identify the changes in the level of beneficial polyphenolics in fruit breeding segregating populations and how the level of these components is determined by genetic and/or environmental control. Interestingly, the vitamin C content appeared to be significantly influenced by environment (growth conditions) whilst the content of the polyphenols such as cyanidin, pelargonidin and quercetin glycosides appeared much more tightly regulated, suggesting a rigorous genetic control. Preliminary metabolic profiling showed that the fruit polyphenolic profiles divided into two gross groups segregating on the basis of relative levels of cyanidin-3-sophoroside and cyanidin-3-rutinoside, compounds implicated as conferring human health benefits.

Abstract

In a preliminary experiment terminal stem cuttings (4 – 5 cm) were collected in the spring (May) from a wild population of lingonberry near Holt Research Center, Tromsø, Norway. The cuttings were rooted in peat mixed with 30% perlite with and without auxin treatment (Seradix 1 or Seradix 2: 3-indol-butyric-acid). The effect of dipping in a fungicide (Rovral) was also tested. With the best treatment, control without auxin and fungicide, as much as 66% of the cuttings rooted. Both dipping in Seradix and in the fungicide reduced rooting of the cuttings. To test the seasonal variations in rooting of lingonberry cuttings, terminal cuttings were harvested regularly every month in more than one year. The results indicate that a relatively short cold period is needed to induce bud break and shoot growth. Cuttings harvested during spring and summer rooted poorly compared to cuttings harvested in late autumn and during winter. The best rooting was obtained using cuttings harvested in September and November.

Abstract

Photoperiodic effects on woody plants were reported already by Gardner and Allard in 1923 and comprehensive studies during the ’50s confirmed the role of photoperiod as an important environmental regulator of growth and growth cessation in many northern tree species (Nitsch, 1957; Wareing, 1956). In woody plants cessation of apical growth is a prerequisite for cold acclimation (Weiser, 1970) and photoperiod, as a factor controlling growth cessation, is therefore an important environmental signal for initiation of cold acclimation. In many cases a proper timing of acclimation and deacclimation, in respect to annual variation of temperature conditions, is more critical for winter survival than the maximum level of frost hardiness. Also in such coniferous species where cessation of apical growth is not controlled by photoperiod, short photoperiod is necessary for good cold acclimation, low temperature causes no or only a limited level of hardiness if combined with long day conditions (Schwarz, 1970; Aronsson, 1975; Christersson, 1978; Jonsson et al., 1981). Thus, photoperiod may have both an indirect, through induction of growth cessation, and a more direct influence on cold acclimation in woody plants.