Wild Strawberry Fragaria Vesca Research Articles

Identification and analysis of imprinted genes in wild strawberry uncover a regulatory pathway in endosperm development.

Fertilization is a fundamental process that triggers seed and fruit development, but the molecular mechanisms underlying fertilization-induced seed development are poorly understood. Previous research has established AGamous-Like62 (AGL62) activation and auxin biosynthesis in the endosperm as key events following fertilization in Arabidopsis (Arabidopsis thaliana) and wild strawberry (Fragaria vesca). To test the hypothesis that epigenetic mechanisms are critical in mediating the effect of fertilization on the activation of AGL62 and auxin biosynthesis in the endosperm, we first identified and analyzed imprinted genes from the endosperm of wild strawberry. We isolated endosperm tissues from F1 seeds of two wild strawberry Fragaria vesca subspecies, generated endosperm-enriched transcriptomes, and identified candidate Maternally-Expressed and Paternally-Expressed Genes (MEGs and PEGs). Through bioinformatic analyses, we identified four imprinted genes that may be involved in regulating the expression of FveAGL62 and auxin biosynthesis genes. We conducted functional analysis of a maternally expressed gene FveMYB98 through CRISPR-knockout and overexpression in transgenic strawberry as well as analysis in heterologous systems. FveMYB98 directly repressed FveAGL62 at stage 3 endosperm, which likely serves to limit auxin synthesis and endosperm proliferation. These results provide an inroad into the regulation of early stage seed development by imprinted genes in strawberry, suggest potential function of imprinted genes in parental conflict, and identify FveMYB98 as a regulator of a key transition point in endosperm development.

Genome-Wide Identification and Characterization of the OFP Gene Family in the Wild Strawberry Fragaria vesca

OVATE family proteins (OFPs) are a kind of plant-specific transcription factor, which play important roles in the growth and development of plants. Here, we performed a genome-wide investigation of the OFP gene family members in the wild diploid strawberry (Fragaria vesca, 2n = 14), and analyzed their physical and chemical properties, gene structure, phylogeny, expression patterns, and the subcellular localizations of these genes. Fourteen OFP genes from F.vesca were identified. Collinearity analysis showed ten pairs of collinearity between F. vesca and Arabidopsis. Phylogenetic analysis divided FvOFP genes into five different clades. The expression patterns of the FvOFP genes assayed in different tissues of F. vesca by Reverse Transcription Quantitative Polymerase Chain Reaction (RT-qPCR) showed that FvOFP1, FvOFP11, FvOFP12, and FvOFP14 were highly expressed in achene and their expression was further verified in the fruits at different developmental stages. Additionally, the subcellular localizations of FvOFP1, FvOFP11, FvOFP12, and FvOFP14 were preliminarily analyzed in tobacco leaves. The results showed clear fluorescent signals in the nucleus. Our results provided a comprehensive understanding of the potential function of FvOFP genes in strawberries.

Wild strawberry Fragaria vesca as potential source for phytonematode resistance

AbstractPhytonematode infections are a major constraint to agriculture and can cause pre-harvest losses of up to one-third of the crop in affected fields. With increasing restrictions on the use of chemical pesticides due to environmental and human hazards, and increasing nematode pressure due to climate change, soil degradation and agricultural intensification, more sustainable ways to manage such plant pests are needed to meet the growing demand for food. Therefore, the reproduction of thermophilic Meloidogyne spp. was evaluated in comparison with that of the northern root-knot nematode Meloidogyne hapla on the wild strawberry Fragaria vesca vs. semperflorens cv. Alexandria, a potential source of resistance to nematode infection. M. hapla showed a high reproductive rate in F. vesca, while the thermophilic Meloidogyne species tested showed significant lower reproductive rates. This suggests that F. vesca vs. semperflorens cv. Alexandria, although not resistant to the nematode species tested, could be used in a management system to down-regulate nematode pressure. In addition, this study helps to reinforce the importance of crop wild relatives in the search for resistance traits to support a more sustainable agriculture.

Two MYB activators of anthocyanin biosynthesis exhibit specialized activities in petiole and fruit of diploid strawberry.

The R2R3-MYB transcription factor FveMYB10 is a major regulator of anthocyanin pigmentation in the red fruits of strawberry. fvemyb10 loss-of-function mutants form yellow fruits but still accumulate purple-colored anthocyanins in the petioles, suggesting that anthocyanin biosynthesis is under distinct regulation in fruits and petioles. From chemical mutagenesis in the diploid wild strawberry Fragaria vesca, we identified a green petioles (gp)-1 mutant that lacks anthocyanins in petioles. Using mapping-by-sequencing and transient functional assays, we confirmed that the causative mutation resides in a FveMYB10-Like (FveMYB10L) gene and that FveMYB10 and FveMYB10L function independently in the fruit and petiole, respectively. In addition to their tissue-specific regulation, FveMYB10 and FveMYB10L respond differently to changes in light quality, produce distinct anthocyanin compositions, and preferentially activate different downstream anthocyanin biosynthesis genes in their respective tissues. This work identifies a new regulator of anthocyanin synthesis and demonstrates that two paralogous MYB genes with specialized functions enable tissue-specific regulation of anthocyanin biosynthesis in fruit and petiole tissues.

Wild Strawberry Fragaria vesca L.: Kinetics of Fruit Drying and Quality Characteristics of the Dried Fruits

The aim of this study was to determine the effect of the temperature of convection and freeze–drying of wild strawberry Fragaria vesca L. fruits on the drying kinetics and on selected quality features of the dried fruits. The process of convection drying was carried out at the temperatures of 25 °C, 40 °C, and 60 °C, whereas freeze–drying was carried out at the temperatures of 20 °C, 40 °C, and 60 °C of the heating shelves and at the pressure of 63 Pa in the lyophilizer chamber. The drying kinetics were best described by the Midilli model for both drying methods. An increase of the drying temperature to 60 °C, for both convection drying and freeze–drying, resulted in a decrease of the total content of phenolic compounds and of the antioxidant activity of the dried fruits. An increase in the temperature of convection drying reduced the lightness of the dried fruits. However, during freeze–drying, these features changed little despite the increase in the drying temperature. The dried fruits with the highest brightness were obtained at a freeze–drying temperature of 60 °C. The method of freeze–drying is proposed as the best because of the resulting color, L-ascorbic acid retention, and antioxidant properties of the dried fruits.

Whole-genome duplication decreases clonal stolon production and genet size in the wild strawberry Fragaria vesca.

Clonal reproduction is often associated with polyploidy and is expected to influence polyploid establishment success, but the immediate effects of whole-genome duplication (WGD) on clonal reproduction in autopolyploids are unknown. We used synthesized neopolyploids to assess the direct effects of WGD on stolon and plantlet production in the wild strawberry Fragaria vesca by (1) comparing absolute clonal investment between diploids and neotetraploids under high and low resource conditions in the greenhouse and (2) determining realized clonal plantlet establishment and genet spatial structure using artificial field populations comprising both cytotypes. Neotetraploids produced fewer stolons and plantlets than diploids at slower weekly rates in the greenhouse when resources were high, resulting in lower total investment in clonal reproduction. Low resources led to smaller reductions in clonal biomass for neotetraploids and less pronounced differences between cytotypes. Comparisons between neotetraploids representing 13 independent WGD events and close diploid relatives revealed considerable variation in the response to polyploidization for some clonal traits. Field populations corroborated greenhouse results; neotetraploid genets were smaller than diploid genets, containing 28% fewer stolons and 46% fewer rooted plantlets. WGD significantly decreases the clonal output of neotetraploid F. vesca, which is likely attributable to slower whole-plant growth of the neotetraploids than the diploids. In natural populations, smaller neotetraploid genets could decrease the probability of polyploid establishment in this species. However, variation between separate neopolyploid lines emphasizes that the response of clonal investment to WGD may not be uniform across polyploid origins.

Efficient genome editing of wild strawberry genes, vector development and validation.

SummaryThe clustered regularly interspaced short palindromic repeats (CRISPR)–Cas9 system is an effective genome editing tool for plant and animal genomes. However, there are still few reports on the successful application of CRISPR–Cas9 to horticultural plants, especially with regard to germ‐line transmission of targeted mutations. Here, we report high‐efficiency genome editing in the wild strawberry Fragaria vesca and its successful application to mutate the auxin biosynthesis gene TAA1 and auxin response factor 8 (ARF8). In our CRISPR system, the Arabidopsis U6 promoter AtU6‐26 and the wild strawberry U6 promoter FveU6‐2 were each used to drive the expression of sgRNA, and both promoters were shown to lead to high‐efficiency genome editing in strawberry. To test germ‐line transmission of the edited mutations and new mutations induced in the next generation, the progeny of the primary (T0) transgenic plants carrying the CRISPR construct was analysed. New mutations were detected in the progeny plants at a high efficiency, including large deletions between the two PAM sites. Further, T1 plants harbouring arf8 homozygous knockout mutations grew considerably faster than wild‐type plants. The results indicate that our CRISPR vectors can be used to edit the wild strawberry genome at a high efficiency and that both sgRNA design and appropriate U6 promoters contribute to the success of genomic editing. Our results open up exciting opportunities for engineering strawberry and related horticultural crops to improve traits of economic importance.

Reduced Anthocyanins in Petioles codes for a GST anthocyanin transporter that is essential for the foliage and fruit coloration in strawberry.

The red color of the foliage and fruit in strawberry comes from anthocyanins stored in the vacuole; however, how this anthocyanin accumulation is regulated remains unclear. A reduced anthocyanin in petioles (rap) mutant was identified in an N-ethyl-N-nitrosourea (ENU) mutagenized population of YW5AF7, a white-fruited variety of the wild strawberry Fragaria vesca. The causative mutation was identified to be a premature stop codon in a glutathione S-transferase (GST) gene. In addition to the foliage coloration, RAP also mediates fruit pigmentation and acts downstream of the fruit-specific transcription factor FvMYB10. Among all eight GST genes in the same subfamily, RAP is most abundantly expressed in the ripening fruit. Expression analysis and transient expression assays demonstrated that RAP is the principal transporter of anthocyanins among the paralogs. Moreover, domain-swap experiments showed that both the N- and C-terminals of RAP are essential for the binding capability of anthocyanins. In addition, transient knock-down of RAP resulted in reduced fruit coloration in cultivated strawberry. Collectively, our results demonstrate that RAP encodes the principal GST transporter of anthocyanins in the strawberry foliage and fruit, and it could be modified to alter the fruit color in strawberry.

Soilless systems as an alternative to wild strawberry (Fragaria vesca L.) traditional open-field cultivation in marginal lands of the Tuscan Apennines to enhance crop yield and producers’ income

ABSTRACTYield and quality of wild strawberry (Fragaria vesca L.) cultivars ‘Regina delle Valli’ and ‘Alpine’ cultivated in soil, as the traditional production system, and in soilless (both in open air and protected environments), as an innovative and sustainable production system, were investigated in a marginal and inner area of the Pistoiese Apennine Mountains during two production seasons. An earlier marketable production was obtained in soilless culture, but total marketable yield was higher from plants grown in a traditional open-field environment. Fruits obtained from the protected soilless system were larger, but developed some mildew, had some visual defects, and revealed a reduced skin chroma index, flesh firmness, and total soluble solids content compared to fruits harvested from plants grown under direct sunlight, while no significant differences were observed in total titratable acidity and pH between growing systems. ‘Alpine’ was more suited to soilless protected cultivation, with a much higher yield compared to ‘Regina delle Valli’. Physicochemical properties of berries were not affected by the cultivar, but fruit quality changed with plant age and seasonal crop cycle. ‘Alpine’ fruits gained a greater sensorial preference, both in traditional soil and soilless culture.

An eFP browser for visualizing strawberry fruit and flower transcriptomes

Wild strawberry Fragaria vesca is emerging as an important model system for the cultivated strawberry due to its diploid genome and availability of extensive transcriptome data and a range of molecular genetic tools. Being able to better utilize these tools, especially the transcriptome data, will greatly facilitate research progress in strawberry and other Rosaceae fruit crops. The electronic fluorescent pictograph (eFP) software is a useful and popular tool to display transcriptome data visually, and is widely used in other model organisms including Arabidopsis and mouse. Here we applied eFP to display wild strawberry RNA sequencing (RNA-seq) data from 42 different tissues and stages, including various flower and fruit developmental stages. In addition, we generated eight additional RNA-seq data sets to represent tissues from ripening-stage receptacle fruit from yellow-colored and red-colored wild strawberry varieties. Differential gene expression analysis between these eight data sets provides additional information for understanding fruit-quality traits. Together, this work greatly facilitates the utility of the extensive transcriptome data for investigating strawberry flower and fruit development as well as fruit-quality traits.

Global identification of alternative splicing via comparative analysis of SMRT- and Illumina-based RNA-seq in strawberry.

Alternative splicing (AS) is a key post-transcriptional regulatory mechanism, yet little information is known about its roles in fruit crops. Here, AS was globally analyzed in the wild strawberry Fragaria vesca genome with RNA-seq data derived from different stages of fruit development. The AS landscape was characterized and compared between the single-molecule, real-time (SMRT) and Illumina RNA-seq platform. While SMRT has a lower sequencing depth, it identifies more genes undergoing AS (57.67% of detected multiexon genes) when it is compared with Illumina (33.48%), illustrating the efficacy of SMRT in AS identification. We investigated different modes of AS in the context of fruit development; the percentage of intron retention (IR) is markedly reduced whereas that of alternative acceptor sites (AA) is significantly increased post-fertilization when compared with pre-fertilization. When all the identified transcripts were combined, a total of 66.43% detected multiexon genes in strawberry undergo AS, some of which lead to a gain or loss of conserved domains in the gene products. The work demonstrates that SMRT sequencing is highly powerful in AS discovery and provides a rich data resource for later functional studies of different isoforms. Further, shifting AS modes may contribute to rapid changes of gene expression during fruit set.

Reprogramming of Strawberry (Fragaria vesca) Root Transcriptome in Response to Phytophthora cactorum.

Crown rot (Phytophthora cactorum) causes significant economic losses in strawberry production. The best control strategy would be to use resistant cultivars, but polygenically inherited resistance makes the breeding of the garden strawberry (Fragaria × ananassa) challenging. The diploid wild strawberry Fragaria vesca Hawaii 4 genotype was shown previously to have resistance against crown rot. To explore the resistance mechanisms, we inoculated the roots of Hawaii 4 with P. cactorum in a novel in vitro hydroponic system to minimize interference caused by other microbes. Major reprogramming of the root transcriptome occurred, involving 30% of the genes. The surveillance system of the plant shifted from the development mode to the defense mode. Furthermore, the immune responses as well as many genes involved in the biosynthesis of the defense hormones jasmonic acid, ethylene and salicylic acid were up-regulated. Several major allergen-like genes encoding PR-10 proteins were highly expressed in the inoculated plants, suggesting that they also have a crucial role in the defense responses against P. cactorum. Additionally, flavonoids and terpenoids may be of vital importance, as several genes involved in their biosynthesis were up-regulated. The cell wall biosynthesis and developmental processes were down-regulated, possibly as a result of the down-regulation of the key genes involved in the biosynthesis of growth-promoting hormones brassinosteroids and auxin. Of particular interest was the expression of potential resistance genes in the recently identified P. cactorum resistance locus RPc-1. These new findings help to target the breeding efforts aiming at more resistant strawberry cultivars.

Sublethal effects of imidacloprid on interactions in a tritrophic system of non-target species

Imidacloprid is one of the most used insecticides worldwide, but is highly toxic to non-target arthropods. Effects of sublethal imidacloprid intoxication can potentially propagate in food webs, yet little is known about the impact on non-target populations and communities. We investigated short-term sublethal toxicity of imidacloprid in a tritrophic model system of wild strawberry Fragaria vesca, wood cricket Nemobius sylvestris and nursery web spider Pisaura mirabilis. Strawberries were treated two times with 0mg (control), 1mg (low rate) and 10mg (high rate) of Confidor® WG 70 and crickets were allowed to feed on them. In four lab experiments, we quantified the impact of imidacloprid on leaf damage, growth, behaviour and survival of crickets. The high imidacloprid rate reduced feeding, mass gain, thorax growth and mobility in crickets compared to the control, while mortality was similarly low in all treatments. The low rate reduced mass gain only. Cricket survival of spider predation was higher in the low rate treatment than in the control.Overall, herbivory and predation were reduced at sublethal imidacloprid rates in a non-target organism, three-level food chain, which demonstrates possible propagation of sublethal effects through trophic interactions.

Molecular cloning and expression analyses of FaFT, FaTFL, and FaAP1 genes in cultivated strawberry: their correlation to flower bud formation

In this study, we cloned flowering-related genes FLOWERING LOCUS T (FT) and TERMINAL FLOWER1 (TFL1) from domesticated octaploid strawberries (Fragaria × ananassa) and analyzed their expression patterns in cultivars Tochiotome and Akihime. The floral meristem generation was induced under the short day and low temperature (SDLT), but not under the long day and high temperature (LDHT). We found that FaFT1, which is an orthologue of the Arabidopsis floral activator FT, was highly expressed in leaves under LDHT but not expressed in leaves under SDLT. On the other hand, the expression of FaTFL2, which belongs to the TFL1 family of flowering repressing genes, decreased in crowns (stem tissue including meristem) under SDLT. These results suggest that FaTFL2, as opposed to FvTFL1 in wild diploid strawberry Fragaria vesca, is related to flowering of the cultivated strawberry. Moreover, the FaTFL2 expression might be regulated by temperature rather than by photoperiod. We demonstrated that a reduction of the FaTFL2 expression is a key signal for flowering in domesticated strawberries.

Ecological consequences of plant clonality.

Clonal plants are those that reproduce asexually by means of vegetative offspring that remain attached to the parent, at least until they establish. Clonal plant species are widespread, dominate a variety of habitats and probably play key roles in the maintenance of biodiversity, ecosystem function and biological invasion. For example, many of the most invasive introduced plants in the world are clonal. This makes it important to deepen our understanding of the ecology of clonal plants, including effects of clonality on ecosystem function, species abundance, plant performance in different habitats, capacity for evolution and invasiveness. The six papers in this Highlight explore these effects. The effects of clonality on ecosystem function have been under-studied. In a conceptual review, Cornelissen et al. (2014) discuss likely potential effects based on a response – effect trait framework, and call for research that links clonal traits to traits that affect carbon, nutrient and water cycling. In order to promote understanding of how clonality shapes species abundance, Herben et al. (2014) examine the relationships between plant traits and species abundance in 836 perennial, herbaceous species in Central Europe. Their results show that clonal growth traits explain a substantial proportion of variation in abundance, and that capacity for clonal growth and lateral expansion are positively correlated with abundance at both regional and local scales. Patterns of resource sharing between connected ramets vary between and within clonal species and may reflect selection for performance in different habitats. Using a spatially explicit, dynamic model, Oborny and Hubai (2014) test how the proportion of resource-rich patches in a heterogeneous environment determine the relative foraging efficiencies of clones in which parental ramets do or do not subsidize the growth of offspring in resource-poor patches. Not sharing is more efficient than sharing when more than half of patches are rich, but a mixed strategy is most efficient over a wide range of environments. While clonal integration is well known to increase growth in patchy habitats, the underlying physiological mechanisms remain elusive. Roiloa et al. (2014) test the effects of integration on photochemical efficiency, leaf spectral reflectance, photosynthesis and discrimination between isotopes of carbon and nitrogen in the wild strawberry Fragaria vesca. Their results provide novel evidence that clonal plants may preferentially transport specific forms of nitrogen between connected ramets. Potential for the evolution and local adaptation of clonal plant species might be limited if reproduction is mainly asexual. James and McDougall (2014) use microsatellite analysis and chromosome counts to document genetic diversity in all known populations of the clonal shrub Grevillea renwickiana. They find that triploidy has probably rendered the species exclusively asexual, but somatic mutation has generated diversity within clones. Introduced, invasive, clonal plants often spread both via seed dispersal and vegetative growth. Qi et al. (2014) document inhibition of seedling establishment under existing clones in the clonal, invasive plant Wedelia trilobata. Removal of adult plants fosters seedling establishment: important information for controlling the spread of this species. These six papers illuminate different aspects of the ecology of clonal plants and tackle current questions about the ecological consequences of clonality. We hope that this Highlight will stimulate further ecological research on clonal plants.

Combining 1,4-dimethoxybenzene, the major flower volatile of wild strawberry Fragaria vesca, with the aggregation pheromone of the strawberry blossom weevil Anthonomus rubi improves attraction

The aggregation pheromone of strawberry blossom weevil [Anthonomus rubi Herbst (Col.: Curculionidae)], a 1:4:1 blend of Grandlure I, II and racemic lavadulol, has been available for pest monitoring for several years but shows low attractancy. Attempts to control A. rubi using the pheromone alone were also unsuccessful. This paper reports the finding that addition of the major flower volatile from wild strawberry flowers [Fragaria vesca L. (Rosaceae)], 1,4-dimethoxybenzene (comprising 98% of the volatiles emitted from wild strawberry flowers), to the aggregation pheromone increased trap catches by over two fold compared to the pheromone alone. There was no significant difference between the response of overwintered or summer emerged adults. Field trials in 2007–2008 in central and southern Norway, Denmark and southern England used green funnel traps with white cross vanes for the evaluations. (-)-Germacrene D, previously shown to be emitted by plants in increased amounts in the presence of pheromone producing weevils, did not improve trap catches. Thus, the combined use of the aggregation pheromone and 1,4-dimethoxybenzene is promising for improved monitoring and possibly control of this important pest of strawberry.

Demethylation of oligogalacturonides by FaPE1 in the fruits of the wild strawberry Fragaria vesca triggers metabolic and transcriptional changes associated with defence and development of the fruit

Ectopic expression of the strawberry (Fragaria×ananassa) gene FaPE1 encoding pectin methyl esterase produced in the wild species Fragaria vesca partially demethylated oligogalacturonides (OGAs), which conferred partial resistance of ripe fruits to the fungus Botrytis cinerea. Analyses of metabolic and transcriptional changes in the receptacle of the transgenic fruits revealed channelling of metabolites to aspartate and aromatic amino acids as well as phenolics, flavanones, and sesquiterpenoids, which was in parallel with the increased expression of some genes related to plant defence. The results illustrate the changes associated with resistance to B. cinerea in the transgenic F. vesca. These changes were accompanied by a significant decrease in the auxin content of the receptacle of the ripe fruits of transgenic F. vesca, and enhanced expression of some auxin-repressed genes. The role of these OGAs in fruit development was revealed by the larger size of the ripe fruits in transgenic F. vesca. When taken together these results show that in cultivated F. ananassa FaPE1 participates in the de-esterification of pectins and the generation of partially demethylated OGAs, which might reinforce the plant defence system and play an active role in fruit development.

IDENTIFICATION OF FLOWERING RELATED CANDIDATE GENES FROM FRAGARIA VESCA USING EST SEQUENCING

We are using wild strawberry (Fragaria vesca L.) as a diploid model plant to investigate genetic regulation of flowering. F. vesca is a facultative short-day (SD) plant that initiates flowers only in SD at high temperature, or daylength independently at low temperature. In Europe, everbearing (EB) forms have been identified in F. vesca. Using both daylength response types, our aim is to explore the genetic mechanisms involved in regulation of flowering in order to enhance the potential of strawberry cultivation and breeding. We have identified flowering related candidate genes in a SD genotype and EB F. vesca 'Baron Solemacher' seedlings using EST sequencing. Subtracted cDNA libraries were prepared from long day grown apical bud samples of SD and EB genotypes with the aim to enrich either putative flowering repressing or activating genes, respectively. The preliminary annotation of the sequenced ESTs show that we were able to identify several candidate genes based on homology with the Arabidopsis thaliana flowering pathway genes.

Partial demethylation of oligogalacturonides by pectin methyl esterase 1 is required for eliciting defence responses in wild strawberry (Fragaria vesca)

In addition to the role of the cell wall as a physical barrier against pathogens, some of its constituents, such as pectin-derived oligogalacturonides (OGA), are essential components for elicitation of defence responses. To investigate how modifications of pectin alter defence responses, we expressed the fruit-specific Fragaria x ananassa pectin methyl esterase FaPE1 in the wild strawberry Fragaria vesca. Pectin from transgenic ripe fruits differed from the wild-type with regard to the degree and pattern of methyl esterification, as well as the average size of pectin polymers. Purified oligogalacturonides from the transgenic fruits showed a reduced degree of esterification compared to oligogalacturonides from wild-type fruits. This reduced esterification is necessary to elicit defence responses in strawberry. The transgenic F. vesca lines had constitutively activated pathogen defence responses, resulting in higher resistance to the necrotropic fungus Botrytis cinerea. Further studies in F. vesca and Nicotiana benthamiana leaves showed that the elicitation capacity of the oligogalacturonides is more specific than previously envisaged.

Interactions of temperature and photoperiod in the control of flowering of latitudinal and altitudinal populations of wild strawberry (Fragaria vesca)

Floral induction and development requirements of a range of latitudinal and altitudinal Norwegian populations of the wild strawberry Fragaria vesca L. have been studied in controlled environments. Rooted runner plants were exposed to a range of photoperiods and temperatures for 5 weeks for floral induction and then transferred to long day (LD) at 20°C for flower development. A pronounced interaction of temperature and photoperiod was shown in the control of flowering. At 9°C, flowers were initiated in both short day (SD) and LD conditions, at 15 and 18°C in SD only, whereas no initiation took place at 21°C regardless of daylength conditions. The critical photoperiod for SD floral induction was about 16 h and 14 h at 15 and 18°C, respectively, the induction being incomplete at 18°C. The optimal condition for floral induction was SD at 15°C. A minimum of 4 weeks of exposure to such optimal conditions was required. Although the populations varied significantly in their flowering performance, no clinal relationship was present between latitude of origin and critical photoperiod. Flower development of SD‐induced plants was only marginally advanced by LD conditions, while inflorescence elongation and runnering were strongly enhanced by LD at this stage. The main shift in these responses took place at photoperiods between 16 and 17 h. Unlike all other populations studied, a high‐latitude population from 70°N (‘Alta’) had an obligatory vernalization requirement. Although flowering and fruiting in its native Subarctic environment and after overwintering in the field in south Norway, this population did not flower in the laboratory in the absence of vernalization, even with 10 or 15 weeks of exposure to SD at 9°C. Flowering performance in the field likewise indicated a vernalization requirement of this high‐latitude population.