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European hazelnut ( Corylus avellana L.) is an economically and nutritionally important nut crop with wild and cultivated populations found throughout Europe and in parts of Asia. This study examined the molecular genetic diversity and population structure of 402 genotypes including 143 wild individuals, 239 landraces, and 20 cultivars from the Turkish national hazelnut collection using simple sequence repeat (SSR) markers. A total of 30 SSR markers yielded 407 polymorphic fragments. Diversity analysis of the Turkish hazelnut genotypes indicated that they fell into three subpopulations according to ad hoc statistics and neighbor-joining algorithm. Although all cultivars clustered together, they overlapped with the wild accessions and landraces. Thus, the dendrogram, principal coordinate, and population structure analyses suggest that they share the same gene pool. A total of 78 accessions were selected as a core set to encompass the molecular genetic and morphological diversity present in the national collection. This core set should have priority in preservation efforts and in trait characterization.

Turkey is a rich source of European hazelnut (Corylus avellana) germplasm with nearly 400 accessions in the national collection. This genetic material encompasses cultivars, landraces and wild genotypes which were characterized for 12 nut and 13 kernel traits over 2 years in the 1990s. Analysis of these attributes revealed both the positive and negative impacts that human selection and breeding have had on hazelnut. Thus, while selection has resulted in larger nuts and kernels, cultivars have fewer nuts per cluster and kernels with larger internal cavities. Breeding has also resulted in a propensity for cultivars to have higher proportions of double kernels and empty nuts, two traits which reduce quality and yield. In addition, it is clear that while selection has successfully increased hazelnut fat content it has not impacted overall flavor, a much more complex trait. The nut and kernel phenotypic data were combined with genotypic data from 406 simple sequence repeat marker alleles for association mapping of the quantitative trait loci (QTL) for the traits. A total of 78 loci were detected in the population with the highest proportions for nut (24%) and kernel (26%) appearance parameters followed by quality (19%), shell thickness (16%) and yield-related (15%) traits. It is hoped that some of the identified QTL will be useful for future breeding of hazelnut for improved nut and kernel yield and quality.

This study investigated the effect of pollen storage on viability and germination in ‘Foşa’, ‘Kara’, ‘Kalınkara’, ‘Mincane’ and ‘Palaz’ hazelnut cultivars (Corylus avellana L.). Pollen was kept at room temperature (22 °C), +4 °C and −18 °C, and on the 7th, 14th, 21st, 30th, 45th, 60th, 75th, 90th, 105th and 120th day, pollen viability was determined according to triphenyl tetrazolium chloride (TTC) and acetocarmine tests. Pollen germination was assessed at 15 and 20% sucrose according to the agar method. The highest viability at +4 °C was determined in ‘Mincane’ (64.67%) on the 7th day of storage, and the lowest was determined in ‘Palaz’ (11.50%) on the 120th day of storage in the TTC test. The highest pollen viability at −18 °C was determined on the 7th day in ‘Foşa’ (71%), and the lowest was determined on the 120th day in ‘Palaz’ (19%). Cultivar × temperature, cultivar × time and temperature × time interactions were found to be significant in the acetocarmine test. The highest germination was detected in ‘Kara’ (55.23%) with 15% sucrose and in ‘Mincane’ (73.8%) with 20% sucrose in pollen stored at −18 °C. Based on the analysis of pollen viability and germination during storage, it was determined that the ‘Foşa’ and ‘Mincane’ were among the most suitable cultivars. As the storage period rose, there were reductions in viability. However, it was found that pollen held at −18 °C had a longer viability compared to pollen stored at +4 °C. Pollen germination was found to be greater when exposed to 20% sucrose compared to 15% sucrose.

Environmental factors significantly impact plant physiological processes, especially during pollination and fertilization. Pollen germination (PG) and pollen tube length (PTL), crucial in plant reproduction, are particularly vulnerable to environmental contaminants that affect fruit sets adversely. This study investigated the impact of varying cadmium (Cd) doses, a significant toxic heavy metal, and the alleviative potential of external 24-epibrassinolide (24-epiBL) applications on cadmium stress, determined through PG and PTL. Quince pollen viability rates, assessed using the TTC (2-3-5-triphenyl tetrazolium chloride) viability test, varied between 38.58% and 55.80%. PG and PTL rates decreased in response to higher Cd doses. The application of epiBL increased PG and PTL, but a notable decline was observed at the 2.00 μM application. A positive relationship between the application dosage of epiBL and its alleviation effect on Cd stress on PG and PTL was observed except for the 2.00 mM. Results revealed variability in PG and PTL rates among quince varieties, and PG and PTL rates decreased with higher Cd doses. This study suggests that epiBL up to 0.50 mM is an efficient tool for alleviating Cd stress in quince pollens.

More than half of European hazelnut (Corylus avellana) production occurs in Turkey. Despite this dominance, the yield of Turkish cultivars has remained stagnant over the past 10 years with Italian yield nearly double that in Turkey. This difference is due to Turkey’s unique cultivation system; hazelnuts are grown in bushy clusters (“ocak” system), not as single trees. Current hazelnut breeding efforts are shifting toward the development of materials for single plant orchards which are much higher yielding; thus, there is a need to explore germplasm for relevant agro-morphological traits and to determine their genetic control. The objectives of this study were to examine data for 44 such traits in 390 hazelnut accessions: 16 cultivars, 232 landraces and 142 wild individuals from nine provinces in Turkey and to map the loci associated with these characteristics using simple sequence repeat markers. Comparison of cultivars, landraces and wild hazelnut accessions revealed the effects of domestication and selection on the crop and indicated that useful alleles for traits such as cropping and reduced alternate bearing may exist in the wild germplasm. A total of 145 quantitative trait loci (QTL) were detected with the largest proportions identified for involucre (26%) and inflorescence (14%) morphology. Several markers co-localized with more than one trait including markers for male catkin abundance which were shared with plant vigor and height. Similarly, markers for female flower abundance co-localized with suckering and alternate bearing. Such markers and their linked QTL should be studied in more detail as they might help breeders select for plant vigor, decreased suckering and increased flower production: traits which will be extremely useful for Turkey’s transition to single plant orchards.

This research was conducted to selecting 'Palaz' clones which carried out select on the highest character clones of 'Palaz' hazelnut cultivar grown in villages of Unye district of Ordu province in 2005-2006 years. In this research, 56 and 46 Palaz hazelnut clones investigated in 2005 and 2006, respectively. The 18 clones from the first year were also investigated at the second year. Totally, 84 clones were investigated. The results of the study were evaluated with the 'Weight Ranked Method'. At the end of the evaluation '52Ü05', '52Ü55', '52Ü17', '52Ü82', '52Ü81', '52Ü43', '52Ü44' and '52Ü61' hazelnut genotypes were selected and determined as nut weight 2.13-2.27 g, kernel weight 1.14-1.21 g, kernel percentage %52.1-54.4, shell thickness 0.98-1.12 mm, nut size 17.3-17.8 mm, marketable kernel %79.6-92.6, pellicle removal %50.3-95. The least fibrously taken from '52Ü43' and '52Ü55' clones.

The study was conducted to determine the effects of different rootstocks (Ma × Ma 14, GiselA 5, GiselA 6 and SL 64) on quality properties and bioactive compounds of ‘0900 Ziraat’ sweet cherry fruit. Fruit weight, thickness and length of Ma × Ma 14 and SL 64 was higher than the GiselA 5 and GiselA 6. Firmness of GiselA 6 was lower than the other rootstocks (Ma × Ma 14, GiselA 5 and SL 64). The chroma value of GiselA 5 was greater than the other rootstocks, whereas the hue angle of SL 64 was lower than the other rootstocks. While the lowest SSC and acidity was obtained in GiselA 5, the highest vitamin C was determined in Ma × Ma 14. Total phenolics and total flavonoids, thus antioxidant activity of GiselA 6 and SL 64 rootstocks was higher than Ma × Ma 14 and GiselA 5 rootstocks. Catechin was the major phenolic acid in ‘0900 Ziraat’ sweet cherry fruit. GiselA 6 had higher catechin and 4‑hydroxybenzoic acid content than the other rootstocks. As a result, it was revealed that sweet cherry rootstocks were effective on bioactive compounds and fruit quality characteristics.