Characterization of autochtonous Walnut germplasm in Fiuli Venezia Giulia

Juglans regia is mostly distributed in the temperate and subtropical regions of the Northern Hemisphere. During the last ice age, the species survived only in refugial areas. In Europe it survived in the Italian and Balkan peninsulas. Friuli Venezia Giulia is the natural corridor where the two populations met during the re-colonization after the glaciation. In the present study 220 autochtonous accessions were sampled and georeferenced and a genetic analysis with 20 microsatellite loci taken from the literature was carried out. The local population shows a moderate genetic diversity and can be classified in two clusters. The first one shows a great mixture between genotypes coming from different areas, even particularly far away from each other. To this first cluster belongs the vast majority of the samples. The second cluster consist of three genotypes originated from an import of Walnuts from Russia at the beginning of the XX century. On the genotypes that during the investigation produced enough fruits carpometric analysis were performed. The best accessions were included in a ranking list compiled using a multivariate analysis considering all the traits valuable for breeding and selection, such as nut weight, kernel weight, shell thickness, kernel skin colour, ease of kernel extraction and fruit appearance. These best accessions will either be selected as they are for vegetative propagation or employed in breeding programs. For every genotype that produced fruits the oil content and its acidic spectrum were determined. Both turned out not to be influenced by the year of sampling. The studied wild walnut trees shown a significant linear relationship and a positive relationship between the minimum daily temperature and the oleic acid content. Many of the accessions could be used in breeding programs for the selections of cultivars with high oil contents and with differentiated acidic spectra, depending on the purpose of the oil. The last part of the investigation was about the diffusion in Friuli Venezia Giulia of two non-local walnut pests come from America, a leafminer belonging to the genus Coptodisca and the carpophagous Rhagoletis completa. Coptodisca lucifluella has been found in 55 out of the 219 considered sites. This is the first report of the species for the region. The species has been identified not only by typical leaf symptoms but also by means of mitochondrial DNA barcode. The DNA sequences were submitted to Genebank. The level of pest infestation in Friuli Venezia Giulia resulted lower than in other Italian areas and its diffusion was negatively correlated with the altitude. The species was observed in sites above 600 m a.s.l. The low infestation observed could be associated with the activity of native natural enemies, as parasitoids of the genus Chrysocharis (Hymenoptera, Encyrtidae) that were observed into the mines. Rhagoletis completa was found in 89 out of the 185 walnut trees with fruits. In many sites, especially in lowland localities, the infestation level was very high, as to suggest treatments with insecticides. The level of infestation decreased with altitude: at sites above 700 m a.s.l. either there was no infestation or the infestation was very low. No correlation has been found between the average weight of the fruits and the level of infestation.