Xanthomonas arboricolapv. pruni, the causal agent of bacterial spot disease of stone fruit, is considered a quarantine organism by the European Union and the European and Mediterranean Plant Protection Organization (EPPO). The bacterium can undergo an epiphytic phase and/or be latent and can be transmitted by plant material, but currently, only visual inspections are used to certify plants as beingX. arboricolapv. pruni free. A novel and highly sensitive real-time TaqMan PCR detection protocol was designed based on a sequence of a gene for a putative protein related to an ABC transporter ATP-binding system inX. arboricolapv. pruni. Pathogen detection can be completed within a few hours with a sensitivity of 10²CFU ml⁻¹, thus surpassing the sensitivity of the existing conventional PCR. Specificity was assessed forX. arboricolapv. pruni strains from different origins as well as for closely relatedXanthomonasspecies, non-Xanthomonasspecies, saprophytic bacteria, and healthyPrunussamples. The efficiency of the developed protocol was evaluated with field samples of 14Prunusspecies and rootstocks. For symptomatic leaf samples, the protocol was very efficient even when washed tissues of the leaves were directly amplified without any previous DNA extraction. For samples of 117 asymptomatic leaves and 285 buds, the protocol was more efficient after a simple DNA extraction, andX. arboricolapv. pruni was detected in 9.4% and 9.1% of the 402 samples analyzed, respectively, demonstrating its frequent epiphytic or endophytic phase. This newly developed real-time PCR protocol can be used as a quantitative assay, offers a reliable and sensitive test forX. arboricolapv. pruni, and is suitable as a screening test for symptomatic as well as asymptomatic plant material.

The number of described pathogenic and non-pathogenic Erwinia species associated with pome fruit trees, especially pear trees, has increased in recent years, but updated comparative information about their similarities and differences is scarce. The causal agent of the fire blight disease of rosaceous plants, Erwinia amylovora, is the most studied species of this genus. Recently described species that are pathogenic to pear trees include Erwinia pyrifoliae in Korea and Japan, Erwinia spp. in Japan, and Erwinia piriflorinigrans in Spain. E. pyrifoliae causes symptoms that are indistinguishable from those of fire blight in Asian pear trees, Erwinia spp. from Japan cause black lesions on several cultivars of pear trees, and E. piriflorinigrans causes necrosis of only pear blossoms. All these novel species share some phenotypic and genetic characteristics with E. amylovora. Non-pathogenic Erwinia species are Erwinia billingiae and Erwinia tasmaniensis that have also been described on pome fruits; however, less information is available on these species. We present an updated review on the phenotypic and molecular characteristics, habitat, pathogenicity, and epidemiology of E. amylovora, E. pyrifoliae, Erwinia spp. from Japan, E. piriflorinigrans, E. billingiae, and E. tasmaniensis. In addition, the interaction of these species with pome fruit trees is discussed.

Phytopathogenic bacteria represent a risk to global food production by impacting a variety of crops. The aim of this study was to characterize the contents of bioactive constituents in extracts from Ginkgo biloba L. leaves and fruits and test their activity against six phytopathogenic bacteria that affect horticultural crops. Gas chromatography–mass spectrometry (GC−MS) was used for the chemical profiling of the aqueous methanol extracts, and their bacteriostatic activity against Clavibacter michiganensis subsp. michiganensis, Pseudomonas cichorii, Pseudomonas syringae pv. pisi, Pseudomonas syringae pv. syringae, Pseudomonas syringae pv. tomato, and Xanthomonas vesicatoria (formerly Xanthomonas campestris pv. vesicatoria) was determined in vitro through the agar dilution method. The protective effect of the leaf extract was tested in vivo against the most relevant bacterial pathogens based on their economic/scientific importance, i.e., C. michiganensis subsp. michiganensis and P. syringae pv. pisi, in tomato (Solanum lycopersicum L.) and pea (Pisum sativum L.) plants, respectively, under greenhouse conditions. The GC−MS characterization of G. biloba extracts revealed the presence of dihydro-4-hydroxy-2(3H)-furanone, 2,4-dimethyl-3-hexanol, catechol, 3-O-methyl-D-fructose, 4,6-di-O-methyl-α-D-galactose, methyl 2-O-methyl-α-D-xylofuranoside, and 3-methyl mannoside. In vitro growth inhibition tests showed that, while the fruit extract had no activity, the leaf extract exhibited minimum inhibitory concentrations between 500 and 1000 μg mL⁻¹, which may be attributed to the presence of 2,4-dimethyl-3-hexanol and catechol. In vivo tests of the leaf extract demonstrated full protection in tomato and pea plants at 1000 and 1500 μg∙mL⁻¹, respectively. The results indicate that G. biloba leaves may be employed as a biorational source for integrated pest management in horticulture.