The quantity and quality of seedlings in the nursery has an impact on the success of re-establishment and later growth. High germination rates enable a sufficient number of seedlings, and their quality is assessed using a number of parameters, including seedling height and root collar diameter. These parameters are influenced in some species by seed size, but the correlation between them is species-specific. The model species in this research was sweet chestnut (Castaneasativa Mill.), and seeds from 12 populations from two distinct biogeographical regions of Croatia were collected. We examined the influence of seed size on four parameters: germination rate, seedling height, root collar diameter and sturdiness quotient. Seed size has been shown to have a positive influence on both seedling height and root collar diameter, whereas no such correlation was noted for germination rate and sturdiness quotient. Significant differences in nut size and seedling growth parameters were found between the Mediterranean and continental populations, with higher values observed in the coastal Mediterranean populations. We concluded that seed origin and seed size have a significant impact on seedling growth and are important factors to consider when choosing seed material. Further nursery operations should consider seed origin and local environmental conditions when choosing seedlings for reforestation efforts and general forest operations.

The chemical composition, morphometric and qualitative nut characteristics were studied in four traditional sweet chestnut and hybrid varieties produced on private estates in the Lovran surroundings, on the eastern slopes of Mount Učka, under the specific conditions of the sub-Mediterranean climate. Seven morphological characteristics were measured, and 12 nut and kernel qualitative characteristics were estimated using standardized descriptors. In addition, the samples were analyzed for proximate constituents (moisture, crude fat, crude protein, ash and total carbohydrates) and macro- and micro-nutrients (K, Mg, Ca, Na, Mn, Fe, Zn and Cu). Significant differences between traditional sweet chestnut and hybrid varieties were found in almost all of the studied morphometric and chemical nut characteristics. In general, chestnuts of hybrid varieties were characterized by larger fruits with higher moisture, crude protein, potassium, magnesium, sodium, iron and copper contents than in traditional sweet chestnut varieties. On the other hand, nuts of traditional sweet chestnut varieties were richer in total carbohydrates and crude fat. In addition, the presence of raised stripes, a small hilar scar and transversally ellipsoid nut shape were found to be typical for the traditional sweet chestnut varieties. Overall, our results suggest that the traditional varieties of the sweet chestnut can be easily differentiated from the new modern hybrid varieties by both morphological and chemical characteristics of the nut, and because of these differences, these two groups of chestnut varieties can have different practical uses.

Service tree, Sorbus domestica L., is a rare and neglected wild fruit tree species of southern and central Europe. Being distributed in different eco-geographical regions, with fragmented and low-density populations, S. domestica represents an interesting model case for investigating patterns of within- and between-population diversity at geographical and environmental scales. This study aimed to analyze the proximate composition, antioxidant activity, and morphometric fruit characteristics. We examined the diversity and population divergences of 49 S. domestica individuals originating from seven populations across continental and Mediterranean eco-geographical regions. In addition, tests of isolation by distance and environment were performed to detect the magnitude of divergence explained by geographic and environmental variables. Significant differences between the studied populations were found in almost all of the studied morphometric and chemical fruit characteristics. The studied service tree populations were characterized by high phenotypic variation despite the low number of trees per population. Model-based population structure analysis using morphometric and chemical fruit characteristics revealed three groups of service tree populations. We concluded that non-effective pollen and seed dispersal along with genetic drift and specific environmental factors resulted in a distinct phenotype with a specific chemical composition in the isolated island population. In addition, a pattern of isolation by the environment was revealed. We infer that morphological and chemical differences between the studied populations in the true service tree from different eco-geographical regions were mediated by adaptation to the specific environmental conditions.

Almond-leaved pear (Pyrus spinosa Forssk., Rosaceae) is a scientifically poorly researched and often overlooked Mediterranean species. It is an insect-pollinated and animal-dispersed spiny, deciduous shrub or a small tree, with high-quality wood and edible fruits. The aim of the study was to assess the phenotypic diversity of almond-leaved pear in the eastern Adriatic region. The examination of phenotypic diversity was based on a morphometric analysis of 17 populations using ten phenotypic traits of leaves. Varieties of multivariate statistical analyses were conducted to evaluate the within- and among-population diversity. In addition, the Mantel tests were used to test the correlations between geographic, environmental, and phenotypic differences among populations. High phenotypic variability was determined both among and within the studied populations. Leaf-size-related traits proved to be the most variable ones, in contrast to more uniform leaf shape traits. Furthermore, three groups of populations were detected using multivariate statistical analyses. The first group included trees from northern- and southernmost populations characterized by high annual precipitation. However, the trees from the second and third group were highly overlapped without a clear geographical pattern. In addition, we revealed that both environmental and geographical interactions proved to be responsible for the patterns of phenotypic variation between almond-leaved pear populations, indicating significant isolation by environment (IBE) and isolation by distance (IBD) patterns. Overall, our results provide useful information about phenotypic diversity of almond-leaved pear populations for further conservation, breeding, and afforestation programs.

Almond-leaved willow (Salix triandra L., Salicaceae) is a dioecious shrub, rarely a small tree that grows under various environmental conditions. We examined the population structure of 12 populations of almond-leaved willow using nine leaf morphological traits and specific leaf area. Populations were selected from a range of habitats, from continental to the sub-Mediterranean zone, to examine the influence of environmental conditions (climate and altitude) and geographic distance on leaf variability. Significant differences were confirmed among all populations for all traits, with significant correlations between geographic location of populations and morphological traits, and between environmental conditions and morphological traits. Large-leaved populations were found in continental and sub-Mediterranean climates, while small-leaved populations were found in higher elevations and smaller karstic rivers. In addition, populations from floodplains showed greater variability than populations from the karstic habitats, indicating a positive influence of lowland habitats and possible underlying differences in gene pool size. In conclusion, we found that environmental conditions and geographical distances in addition to genetic drift, are the main influences on the variability in almond-leaved willow, with the species showing a high level of plasticity and adaptation to local environmental conditions.

Invasive species, especially plant pathogens, have a potential to completely eradicate native plant species and remodel landscapes. Tripartite interactions among sweet chestnut (Castanea sativa), chestnut blight-causing invasive fungus Cryphonectria parasitica, and hyperparasitic virus Cryphonectria hypovirus 1 (CHV1) were studied in two populations. The number of different vegetative compatibility (vc) types of C. parasitica more than doubled over the 10 years, while the hypovirulence incidence dropped in one population and slightly increased in the other one. Over the course of our 3-year monitoring experiment, the prevalence of hypovirulent isolates obtained from monitored cankers increased slowly (i.e., more hypovirulent isolates were being obtained from the same cankers over time). Within studied cankers, considerable changes in vc type and CHV1 presence were observed, indicating a highly dynamic system in which virulent and hypovirulent mycelia, sometimes of discordant vc types, often appeared together. The increase in hypovirulence prevalence did not have any observable curative effect on the cankers and, occasionally, reactivation of healed cankers by new, virulent C. parasitica isolates was observed. Both short- and long-term observations and revalidation of the infected plant populations are necessary to accurately estimate disease progress and formulate an adequate disease management strategy.