The olive tree (Olea europaea subsp. europaea var. europaea) represents the cornerstone crop of Apulian agriculture, which is based on the production of oil and table olives. The high genetic variability of the Apulian olive germplasm is at risk of genetic erosion due to social, economic, and climatic changes. Furthermore, since 2013, the spread of the Gram-negative bacterium Xylella fastidiosa subsp. pauca responsible for the olive quick decline syndrome (OQDS) has been threatening olive biodiversity in Apulia, damaging the regional economy and landscape heritage. The aim of this study was to investigate the differential response to X. fastidiosa infection in a collection of 100 autochthonous Apulian olive genotypes, including minor varieties, F1 genotypes, and reference cultivars. They were genotyped using 10 SSR markers and grown for 5 years in an experimental field; then, they were inoculated with the bacterium. Symptom assessments and the quantification of bacterium using a qPCR assay and colony forming units (CFUs) were carried out three and five years after inoculation. The study allowed the identification of nine putatively resistant genotypes that represent a first panel of olive germplasm resources that are useful both for studying the mechanisms of response to the pathogen and as a reserve for replanting in infected areas.

Phytosanitary legislation involves government laws that are essential to minimize the risk of the introduction and diffusion of pests, especially invasive non-native species, as a consequence of the international exchange of plant material, thus allowing us to safeguard agricultural production and biodiversity of a territory. These measures ensure compliance with adequate requirements relating to the absence of pests, especially of harmful quarantine organisms through inspections and diagnosis tests of the consignments to ascertain the presence of the pests concerned. They also regulate the eradication and containment measures that are implemented in the eventuality of an unintentional introduction of these organisms. In the present contribution, the current plant protection legislation for the exchange of plants or propagation material within the European Union or for export to foreign countries, represented by Regulation (EU) 2016/2031, has been reviewed, with a particular focus on the olive tree (Olea europaea L.). Furthermore, a brief summary of the main olive tree pests transmissible with the propagation material is also reported, indicating their current categorization with respect to the relative quarantine status.

Xylella fastidiosa is a xylem-limited phytopathogenic bacterium under regulation in the European Union as a priority pest. Given the potential risk posed by this pathogen to cultivated and ornamental plants, mandatory annual surveys and laboratory testing are required in Member States to early detect outbreaks. In the course of surveys carried out during early spring 2024 in the Apulia region (Southern Italy), X. fastidiosa subsp. multiplex was identified using quantitative real-time Polymerase Chain Reaction (qPCR), in a non-symptomatic sample from an almond tree (Prunus dulcis) in an orchard located in Santeramo in Colle, in Bari province. Multilocus sequence typing (MLST) was used to identify the subspecies and sequence type (ST) of the bacterium using the genomic DNAs extracted from the infected sample. Comparative sequence analysis of the seven MLST allele genes indicated that the obtained nucleotide sequences completely matched allele sequences of X. fastidiosa in PubMLST database corresponding to the allelic profile (Sequence Type) ST26 related to subsp. multiplex. Bacterial colonies consistent in morphology with X. fastidiosa were isolated from asymptomatic host samples and identity was confirmed by real-time PCR analysis. This is the first report of detection of X. fastidiosa subsp. multiplex ST26 in the EU.

The new trends in the consumption of table grapes and the growing interest in the environmental impact of this crop have pushed breeders toward the development of seedless cultivars endowed with resistance, through crossbreeding programs. To obtain seedless grapes, the use of embryo-rescue techniques is fundamental. In this research, a grape embryo-culture protocol was optimized and validated by using 39 cultivars and 41 cross-combinations carried out in the framework of a large private table grape program of the private network Italian Variety Club in the period 2017–2021 evaluating several factors, such as the improvement in embryo formation, germination and growth, and plantlet development. The embryo culture attitude of crosses between different combinations of seedless parents was assessed, and the rates of embryo development from the extracted ovules mostly ranged from 3.5 to 35.5% with 5 out of 43 genotypes outliers. Experiments conducted at different sampling times, in a range of 43–62 days after pollination (DAP), did not show significant differences between the samples analyzed, while the rate of embryos developed with the applied protocol proved its employability on multiple genotypes, although the grapevine genotype significantly influenced the technique efficiency.

The high biodiversity of the olive tree is an important opportunity to develop sustainable plans to control Xylella fastidiosa (Xf) through breeding programs. Olive tree breeding activities have been limited due to various features of this species including the long time required for seed germination caused by the inhibition effect of the woody endocarp, the seed integument, and the endosperm. Starting from F₁ seeds by cross-breeding, the embryo culture was compared with traditional seed germination, evaluating the effectiveness of in vitro multiplication of the plantlets for large-scale production. The isolated embryos were established on a new medium based on Rugini ‘84 macroelements, Murashige & Skoog ‘62 microelements, with Nitsch J. P. & Nitsch C. ‘69 vitamine and subcultured on Leva MSM modified. The results obtained confirmed that in vitro culture of olive embryos is a valid tool for increasing the percentage and speed of germination, helping to reduce the time of the olive breeding programs, offering the possibility to effectively propagate plantlets for further experiments.

The objective of this work was to evaluate the effectiveness of thermotherapy alone or combined with either shoot tip culture or in vitro micrografting treatments and shoot tip culture alone in eliminating olive leaf yellowing-associated virus (OLYaV) and strawberry latent ringspot virus (SLRSV) from naturally infected olive (Olea europaea L.) cultivars to obtain virus-free stock plants. Reverse-transcription polymerase chain reaction was used to determine the efficiency of virus elimination in the in vitro regenerated plants at 6 months following the acclimation to ex vitro conditions. All treatments proved effective in obtaining virus-free plants for all selected cultivars except for the heat therapy used alone which did not completely remove the virus from infected propagative material. The establishment of in vitro cultures of shoot tips from plants exposed to an alternating day/night temperature of 38/30°C or from vitroplants maintained at a constant temperature of 38°C resulted in OLYaV elimination rates of 67 to 100% and 60 to 100%, respectively. The combination of in vitro thermotherapy with shoot-tip grafting yielded up to 100% of OLYaV-negative plants, although grafting success rates were relatively low (29 to 33%). Instead, in vitro culture of shoot tip after eight consecutive cycles of subculturing without heat therapy led to the elimination of OLYaV/SLRSV from 17% of coinfected plants and OLYaV from 20% of single-infected plants. These results indicate that the combined application of treatments is an effective method for virus elimination in olive trees and could be used to ensure the production of healthy nursery stock plants.