Plant bacterial diseases are routinely managed with scheduled treatments based on heavy metal compounds or on antibiotics; to reduce the negative environmental impact due to the use of such chemical compounds, as pollution or selection of antibiotic resistant pathogens, the integrated control management is required. In the frame of a sustainable agriculture the use of bacterial antagonists, biological agents, plant defence response elicitors or resistant host plant genotypes are the most effective approaches. In this work, cold atmospheric pressure plasma (CAP) was applied to sterile distilled water, inducing the production of a hydrogen peroxide, nitrite and nitrate, and a pH reduction. In particular, an atmospheric pressure dielectric barrier discharge (DBD) has been used to produce plasma activated water (PAW), that was firstly assayed in in vitro experiments and then in planta through application at the root apparatus of tomato plants, against Xanthomonas vesicatoria (Xv), the etiological agent of bacterial leaf spot. Moreover, the transcription abundance of five genes related to the plant defense was investigated in response to PAW treatment. PAW did not show direct antimicrobial activity against Xv in in vitro experiments, but it enhanced the tomato plants defenses. It was effective in reducing the disease severity by giving relative protections of ca. 61, 51 and 38% when applied 1 h, 24 h and 6 days before the experimental inoculation, respectively. In addition, the experiments highlighted the pal gene involvement in response to the PAW treatments and against the pathogen; its transcription levels resulted significantly high from 1 to 48 h until their decrease 192 h after PAW application.

ISHS VIII International Symposium on Kiwifruit VINE DECLINE IN KIWIFRUIT: CLIMATE CHANGE AND EFFECT ON WATERLOGGING AND PHYTOPHTHORA IN NORTH ITALY

Genera Pseudomonas and Xanthomonas include bacterial species that are etiological agents of several diseases of major vegetable crops, such as tomato, pepper, bean, cabbage and cauliflower. The bacterial pathogens of those genera may cause severe crop damage, leading to symptoms like leaf spots, wilting, blights, and rotting. These plant pathogens can affect propagation materials and spread rapidly through plant tissues, contaminated soils, or water sources, making them challenging to control using conventional chemical products alone. Biopesticides, such as essential oils (EOs), are nowadays studied, tested and formulated by employing nano- and micro-technologies as innovative biological control strategies to obtain more sustainable products using less heavy metal ions. Moreover, there is a growing interest in exploring new biological control agents (BCAs), such as antagonistic bacterial and fungal species or bacteriophages and understanding their ecology and biological mechanisms to control bacterial phytopathogens. These include direct competition for nutrients, production of antimicrobial compounds, quorum quenching and indirect induction of systemic resistance. Optimisation of the biocontrol potential goes through the development of nanoparticle-based formulations and new methods for field application, from foliar sprays to seed coatings and root inoculation, aimed to improve microbial stability, shelf life, controlled release and field performance. Overall, the use of biological control in horticultural crops is an area of research that continues to advance and shows promising potential. This review aims to provide an in-depth exploration of commercially accessible biocontrol solutions and innovative biocontrol strategies, with a specific focus on the management of bacterial diseases in vegetable crops caused by Pseudomonas and Xanthomonas species. In this article, we highlighted the advancements in the development and use of EOs and other BCAs, emphasizing their potential or shortcomings for sustainable disease management. Indeed, despite the reduced dependence on synthetic pesticides and enhanced crop productivity, variable regulatory frameworks, compatibility among different BCAs, and consistent performance under field conditions are among the current challenges to their commercialization and use. The review seeks to contribute valuable insights into the evolving landscape of biocontrol in vegetable crops and to provide guidance for more effective and eco-friendly solutions against plant bacterial diseases.

Chile is the largest producer of European hazelnut (Corylus avellana L.) in the southern hemisphere. Nowadays, there are established ca. 22,000 ha with a yield up 19,000 metric tons. Fungi reduce t...

Kiwifruit bleeding sap samples, collected in Italian and Chilean orchards from symptomatic and asymptomatic plants, were evaluated for the presence of Pseudomonas syringae pv. actinidiae, the causal agent of bacterial canker. The saps were sampled during the spring in both hemispheres, before the bud sprouting, during the optimal time window for the collection of an adequate volume of sample for the early detection of the pathogen, preliminarily by molecular assays, and then through its direct isolation and identification. The results of molecular analyses showed more effectiveness in the P. syringae pv. actinidiae detection when compared with those of microbiological analyses through the pathogen isolation on the nutritive and semiselective media selected. The bleeding sap analyses allowed the isolation and identification of two hypersensitive response (HR) negative and hypovirulent P. syringae pv. actinidiae strains from different regions in Italy. Moreover, multilocus sequence analysis (MLSA) and whole genome sequence (WGS) were carried out on selected Italian and Chilean P. syringae pv. actinidiae virulent strains to verify the presence of genetic variability compared with the HR negative strains and to compare the variability of selected gene clusters between strains isolated in both countries. All the strains showed the lack of argK and coronatine gene clusters as reported for the biovar 3 P. syringae pv. actinidiae strains. Despite the biologic differences obtained in the tobacco bioassays and in pathogenicity assays, the MLSA and WGS analyses did not show significant differences between the WGS of the HR negative and HR positive strains; the difference, on the other hand, between PAC_ICE sequences of Italian and Chilean P. syringae pv. actinidiae strains was confirmed. The inability of the hypovirulent strains IPV-BO 8893 and IPV-BO 9286 to provoke HR in tobacco and the low virulence shown in this host could not be associated with mutations or recombinations in T3SS island.

European hazelnut (Corylus avellana L.) is an emerging crop for export, mainly in southern Chile. Stem cankers and dieback of twigs on six-year-old European hazelnut cultivar Barcelona were observed during the 2012 growing season on plantations in Panguipulli (39° 38′ 37.12″ S and 72° 20′ 10.87″ W), Region de Los Rios, Chile. The incidence has been variable according to the place of plantation; it was estimated at approximately 15%. Cankers were characterized by brownish-gray and brown to reddish discoloration of the vascular stem system. Hazelnut plants between 1 and 3 years old developed stem basal canker, especially at conditions of high humidity and overpopulation of weeds; at critical conditions, the affected plants generally die. Small pieces of cankered stems, selected from 10 European hazelnuts, were surface sterilized in 0.5% sodium hypochlorite for 2 min and rinsed twice in sterile distilled water prior to incubation in a humid chamber for 7 days (25 ± 2°C) to stimulate production of reproductive bodies. Black sub-epidermal perithecia with unitunicate, cylindrical-clavate, 8-spored asci (n = 20) were obtained. Ascospores were septated, hyaline, multigutulate, and slightly constricted at the septum, the average measurements were (n = 20) 13.4 ± 0.6 μm × 3.9 ± 0.2 μm. The ascospores were transferred to potato dextrose agar (PDA) and incubated for 6 days at 25°C in the dark, then hyphal tips were transferred to fresh PDA and obtained a mycelia with white, cottony, and sparse colonies. Pycnidia and smooth, unicellular, hyaline, and biguttulate alpha conidia of 6.1 to 7.2 μm × 2.8 to 3.1 μm (n = 40) were observed. Beta conidia were not observed in culture media. Mature pycnidia were also detected on hazelnut shells remaining on the soil from the previous season. The identification of the species (isolate IMI-501237) was confirmed at CABI, United Kingdom, using an internal transcribed spacer (ITS), rDNA, BLASTn analysis of the 524-bp fragment, and showed 100% identity with Diaporthe australafricana Crous & J.M. van Niekerk (accessions KC343039, KC343038). These molecular and morphological characteristics were similar that reported from Vitis vinifera (2) and Chilean blueberry (3). The sequence obtained was deposited in GenBank (Accession No. JX316218.1). A pathogenicity test was conducted with isolate IMI-501237 on four 1-year-old plants from the hazelnut cultivar Barcelona. Plants were maintained in individual bags in greenhouse conditions (14/10 h dark/light, 20°C; 70% relative humidity). Prior to inoculation, plant tissues were surface disinfected with 2% sodium hypochlorite and rinsed with sterile distilled water. Each plant was inoculated at fresh wound sites on three stems and three vegetative buds on twigs. The inoculum consisted of an agar plug with mycelia (5 mm) from the edge of an actively growing colony cultured on PDA for 6 days. Each inoculation was covered with moistened cotton and sealed with Parafilm; a control plant was inoculated in the same way with agar only. After 30 days, necrotic lesions and discolored vascular tissue were only observed on inoculated stems and twigs. Symptomatic tissues were removed and incubated on PDA. D. australafricana was consistently recovered from these tissues, satisfying Koch's postulates. The control plant showed no symptoms of the disease. D. australafricana were previously reported on Vitis vinifera in Australia and South Africa (2,4), and Vaccinium corymbosum in Chile (1,3). To our knowledge, this is the first report of Diaporthe australafricana on Corylus avellana cultivar Barcelona in worldwide. References: (1) K. Elfar et al. Plant Dis. 97:1042, 2013. (2) R. Gomes et al. Persoonia 31:1, 2013. (3) B. Latorre et al. Plant Dis. 96:5, 2012. (4) J. M. van Niekerk et al. Australas. Plant Pathol. 34:27, 2005.