In order to best conserve, as well as utilize, traditional apple germplasm in Norway, an apple heritage cultivar collection was established in Ullensvang, western Norway, which aims to become the National Clonal Germplasm Repository. The establishment of the apple heritage cultivar collection was preceded by a molecular study that aimed to genotype a large number of apple accessions maintained in various ex situ sites in western and south-eastern Norway, using a rather small set of eight SSR markers. However limited, the marker set managed to identify synonyms, homonyms, and duplicates within and among the investigated collections. In this study, 171 apple accessions from the Ullensvang apple heritage cultivar collection were genotyped using a set of 20 different SSR markers. Approximately half of the accessions have been previously genotyped using eight SSR markers, enabling an assessment of whether the use of a larger marker set would yield a more accurate characterization. Based on the obtained molecular data, the apple heritage cultivar collection was determined to hold a key part of the overall genetic diversity of the Norwegian apple germplasm. Furthermore, the twelve additional SSR markers were able to differentiate several accessions groups originally thought to be synonyms, as well as to provide a more detailed insight into the genetic structure of this germplasm.

European plum cultivars (Prunus domestica L.) are hexaploid and partially self-fertile or self-sterile requiring compatible pollinizers with overlapping bloom times. Therefore, inter-planting of different pollinizer cultivars is recommended. In order to identify successful pollinizers of the plum cultivars ‘Edda’, ‘Opal’ (self-fertile), ‘Jubileum’, ‘Reeves’, ‘Mallard’, ‘Avalon’, ‘Cacanska Lepotica’ (self-fertile), and ‘Valor’, 60 fruits per cultivar were collected from nine orchards in 2017 and 2018, all of which were located in Ullensvang, western Norway. DNA extraction was subsequently conducted from the obtained embryos, followed by genetic characterization using seven microsatellite markers. Tissue samples from all possible pollinizers were collected during the summer of 2017 and the same DNA approach was conducted. Results showed that ‘Opal’ was the most successful pollinizer among the investigated plum cultivars. The main exception was ‘Cacanska Lepotica’, which consistently displayed very high level of self-pollination. The most successful foreign pollinizer of ‘Opal’ was ‘Mallard’. However, in more than two thirds of embryos extracted from ‘Opal’ fruits self-fertilization was determined. ‘Reeves’ was identified as the most successful pollinizer among embryos collected from ‘Valor’. Among the five cultivars (‘Edda’, ‘Jubileum’, ‘Reeves’, ‘Mallard’, and ‘Avalon’) that did not display self-pollination, the pollinizer success rate of ‘Opal’, ranged from 36.5% (‘Mallard’) to 93.5% (‘Edda’) in 2017, while in 2018 this rate ranged from 43.5% (‘Jubileum’ and ‘Reeves’) up to 96.5% (‘Edda’). Overall, genotyping embryos using SSRs (simple sequence repeats) proved an effective method in determining the success rate of individual pollinizers among European plum cultivars.

The diploid Celina/QTee^® (‘Colorée de Juillet’ × ‘Williams’), one of the most promising pear cultivars developed by the Norwegian breeding program Graminor, was launched in 2010. In Norway, the flowering is medium to late, while the fruits ripen in the beginning of September. The fruits are attractive with an intense red blush (50%) on a green background. Although, ‘Celina’ is cultivated in the most climatically suitable regions for fruit cultivation, present in Norway, unfavorable environmental conditions for pear pollination can have a very negative effect on fruit set and consequent yield. The aim of this study was to determine the S-alleles of ‘Celina’, as well as its frequently used pollinizers, and, through paternity testing of ‘Celina’ seeds, give a recommendation regarding the most important pollinizers of this pear cultivar. In order to accomplish this, ‘Celina’ and its potential pollinizers were all S-genotyped. After harvest, seeds collected from ‘Celina’ fruit in 2017 and 2018 were genotyped using eleven microsatellite markers. Genomic DNA was also extracted from leaf material collected from ‘Celina’, as well as from five pear cultivars used as pollinizers in the three examined orchards, and analyzed using the same marker set. Subsequently a simple sequence repeat (SSR) database was constructed and used for gene assignment analyses with the aim of quantifying pollen donor contribution from individual pollinizers. The obtained results indicate that ‘Anna’, the only examined pollinizer that was fully cross-compatible with ‘Celina’, together with ‘Fritjof’, the genotype which had the highest flowering overlap with ‘Celina’, proved to be the most successful pollinizers across all seasons and orchards. Although both cultivars were ubiquitous in the examined orchards, either as planted trees or as branches introduced during the flowering period, they were the most abundant pollinizers in only one orchard each. It is therefore possible to conclude that pollinizer abundance has a secondary significance in pollinizer success within investigated ‘Celina’ orchards.

In order to determine the pollinizer success rates between twelve apple cultivars in 2021 and 2022, 671 apple embryos were collected from 19 different orchards in Ullensvang (southwestern Norway) and Svelvik (southeastern Norway). Genomic DNA was extracted from the collected embryos and, afterward, a genetic characterization with 15 polymorphic microsatellite markers was conducted. An identical set of markers was also used on all twelve mother cultivars, as well as on six crabapple pollinizers, which were found in the investigated orchards. The obtained molecular data enabled paternity analyses to be performed with the objective of assigning a male parent to each embryo. The paternity analyses identified pollen donors for all, except for 3% of the embryos. In most cases, it was possible to identify the most successful pollinizers for each cultivar, with ‘Aroma’ and ‘Discovery’ being the most efficient pollen donors overall. Tree abundance seems to be a major factor in pollinizer success, while semi-cross-compatible characteristics represent a hindrance. Only 7% of the analyzed embryos were determined to have been fertilized by pollinizers outside the orchard, confirming the significance of pollinizer proximity for efficient pollination.

In order to ensure the long-term sustainability of the conservation process of Norwegian plum germplasm, as well as to enhance the possibility of its utilization, a central plum heritage cultivar collection was established in 2020. In this study, 40 plum accessions maintained at the Ullensvang plum heritage cultivar collection were genetically characterized using a set of nine microsatellite markers recently approved by the ECPGR Prunus working group. The obtained molecular data were used to investigate the genetic identity, diversity, and structure among the analyzed accessions. No redundancies were detected among the plum accessions, which is in stark contrast to the previous molecular study on plum samples collected through an on-farm inventory of Southern Norway. Furthermore, the obtained data indicate that the Ullensvang collection contains a significant genetic diversity of Norwegian plum germplasm, previously held in decentralized sites. With that in mind, this collection can certainly be considered for the role of the National Clonal Plum Germplasm Repository. The nine microsatellite markers, recommended by ECPGR, revealed a genetic structure not entirely tied to previously proposed pomological groups, possibly indicating a history of hybridization among members of the various groups.

Commercial production of sweet cherries is possible up to approximately 60° N latitude in Norway and is among the most economically important fruit crops in the country. The harvest is late, but yields are very high, and the fruit is intended solely for the fresh market. The objective of this study was to assess whether sweet cherry can be grown in pots and to determine fruit quality (sugar, acid, polyphenol, and mineral content) of three sweet cherry cultivars (‘Van’, ‘Lapins’, and ‘Regina’) grown in high tunnels with varying levels of fertigation (F) and the application of slow-release (SR) fertilisers. Trees were planted in 35 L plastic bags, trained as spindle trees, with a spacing of 1 × 2.5 m (4000 trees/ha). The tunnel was covered with polythene from flowering until harvest. Fruit produced in pots had low levels of sugars and acids and high levels of phenolic acids and flavonoids, while the mineral content depended on treatment and cultivar. The main sugar components (glucose and fructose), the sweetness index, phenolic acids (chlorogenic acid and ferulic acid), flavanols (catechin, rutin, quercetin, and hyperoside), and minerals (P, K, Mg, Ca, and Na) were much higher in the F treatment. SR treatments were more effective in increasing the content of acids (shikimic, malic, and quinic) and total phenolic content (TPC). Radical scavenging activity (RSA) and total sugars showed no statistically significant differences between the treatments studied. ‘Lapins’ fruit obtained from the fertigation regimes (when Kristalon brown + Calcinit + Magnesium-sulphate were added from mid-April to 1 September and plain water for the rest of the season, up to an electric conductivity (EC) of 0.5 and 1.0) contained the highest levels of minerals (P, K, Mg, Ca). The ‘Van’ cultivar from F treatments, especially VF2 (when Kristalon brown + Calcinit + Magnesium-sulphate were added from mid-April to 1 September and plain water for the rest of the season, with EC 1.0) and VF3 (when Kristalon brown is added in July, Kristalon brown + Calcinit + Magnesium-sulphate in August, and plain water for the rest of the season) had the highest sweetness index, glucose, fructose, chlorogenic acid, ferulic acid, and hyperoside in sweet cherry fruit. ‘Regina’ under the RSR1 (50 g Multicote and 30 g chalk lime per tree) and RSR2 regimes (100 g Multicote and 30 g chalk lime per tree) produced fruit with the highest acid components, RSA and TPC. This suggests that sweet cherry trees can be grown in pots under high tunnels, but nutrition should be adjusted for each cultivar according to its physiological responses to specific microclimate conditions.