Immature walnut fruit inoculation for evaluation of Brenneria nigrifluens pathogenicity

A reliable, reproducible, rapid and specific test for the pathogenicity of Brenneria nigrifluens, the causal agent of shallow bark canker of Persian walnut, was developed. When the mesocarp of immature walnut fruits was infiltrated by syringe with bacterial suspensions (108 cells mL-1) of B. nigrifluens, necrosis and reddish brown exudates started to appear at the inoculation sites, as early as 2 days after inoculation. No symptoms were detected in control fruits or in fruits inoculated with other bacteria frequently associated with walnut cankers. This pathogenicity test saves time and space when compared with the plant stem inoculation technique, in which the canker symptoms do not appear until at least 1 month after inoculation.&nbsp

Erwinia oleae sp. nov., isolated from olive knots caused by Pseudomonas savastanoi pv. savastanoi

Three endophytic bacterial isolates were obtained in Italy from olive knots caused by Pseudomonas savastanoi pv. savastanoi. Phenotypic tests in combination with 16S rRNA gene sequence analysis indicated a phylogenetic position of these isolates in the genus Erwinia or Pantoea, and revealed two other strains with highly similar 16S rRNA gene sequences (> 99 %), CECT 5262 and CECT 5264, obtained in Spain from olive knots. Rep-PCR DNA fingerprinting of the five strains from olive knots with BOX, ERIC and REP primers revealed three groups of profiles that were highly similar to each other. Multilocus sequence analysis (MLSA) based on concatenated partial atpD, gyrB, infB and rpoB gene sequences, indicated that the strains constitute a single novel species in the genus Erwinia. The strains showed general phenotypic characteristic of Erwinia, and whole genome DNA-DNA hybridization data confirmed they represent a single novel Erwinia species. The strains showed a DNA G+C base composition ranging from 54.7 to 54.9 mol%. They could be discriminated from the phylogenetically related Erwinia species by their ability to utilise potassium gluconate, L-rhamnose and D-arabitol, but not glycerol, inositol and D-sorbitol. The name Erwinia oleae (type strain DAPP-PG 531T = LMG 25322T = DSM 23398T) is proposed for this new taxon

Zinc phosphate protects tomato plants against Pseudomonas syringae pv. tomato

AbstractThe purpose of this study was to determine whether zinc phosphate treatments of tomato plants (Solanum lycopersicum L.) can attenuate bacterial speck disease severity through reduction of Pseudomonas syringae pv. tomato (Pst) growth in planta and induce morphological and biochemical plant defence responses. Tomato plants were treated with 10 ppm (25.90 µM) zinc phosphate and then spray inoculated with strain DAPP-PG 215, race 0 of Pst. Disease symptoms were recorded as chlorosis and/or necrosis per leaf (%) and as numbers of necrotic spots. Soil treatments with zinc phosphate protected susceptible tomato plants against Pst, with reductions in both disease severity and pathogen growth in planta. The reduction of Pst growth in planta combined with significantly higher zinc levels in zinc-phosphate-treated plants indicated direct antimicrobial toxicity of this microelement, as also confirmed by in vitro assays. Morphological (i.e. callose apposition) and biochemical (i.e., expression of salicylic-acid-dependent pathogenesis-related protein PR1b1 gene) defence responses were induced by the zinc phosphate treatment, as demonstrated by histochemical and qPCR analyses, respectively. In conclusion, soil treatments with zinc phosphate can protect tomato plants against Pst attacks through direct antimicrobial activity and induction of morphological and biochemical plant defence responses

Occurrence of a soft rot of calla («Zantedeschia aethiopica») caused by «Pectobacterium carotovorum» subsp. «carotovorum» in central Italy

Pectobacterium carotovorum subsp. carotovorum causing soft rot of calla (Zantedeschia aethiopica) plants is reported in central Italy. Bacterial isolates were identified by biochemical, physiological and pathogenicity tests and characterized by the API 50 CHE Kit and rep-PCR

Race-specific genotypes of Pseudomonas syringae pv. tomato are defined by the presence of mobile DNA elements within the genome

Pseudomonas syringae pv. tomato is the causal agent of bacterial speck of tomato, an important disease that results in severe crop production losses worldwide. Currently, two races within phylogroup 01a (PG01a) are described for this pathogen. Race 0 strains have avirulence genes for the expression of type III system-associated effectors AvrPto1 and AvrPtoB, that are recognized and targeted by the effector-triggered immunity in tomato cultivars having the pto race-specific resistance gene. Race 1 strains instead lack the avrPto1 and avrPtoB genes and are therefore capable to aggressively attack all tomato cultivars. Here, we have performed the complete genome sequencing and the analysis of P. syringae pv. tomato strain DAPP-PG 215, which was described as a race 0 strain in 1996. Our analysis revealed that its genome comprises a 6.2 Mb circular chromosome and two plasmids (107 kb and 81 kb). The results indicate that the strain is phylogenetically closely related to strains Max13, K40, T1 and NYS-T1, all known race 1 strains. The chromosome of DAPP-PG 215 encodes race 1-associated genes like avrA and hopW1 and lacks race 0-associated genes like hopN1, giving it a race 1 genetic background. However, the genome harbors a complete ortholog of avrPto1, which allows the strain to display a race 0 phenotype. Comparative genomics with several PG01a genomes revealed that mobile DNA elements are rather involved in the evolution of the two different races

Comparative genomics to examine the endophytic potential of Pantoea agglomerans DAPP-PG 734

Pantoea agglomerans DAPP-PG 734 was isolated as endophyte from knots (tumors) caused by Pseudomonas savastanoi pv. savastanoi DAPP-PG 722 in olive trees. To understand the plant pathogen-endophyte interaction on a genomic level, the whole genome of P. agglomerans DAPP-PG 734 was sequenced and annotated. The complete genome had a total size of 5′396′424 bp, containing one circular chromosome and four large circular plasmids. The aim of this study was to identify genomic features that could play a potential role in the interaction between P. agglomerans DAPP-PG 734 and P. savastanoi pv. savastanoi DAPP-PG 722. For this purpose, a comparative genomic analysis between the genome of P. agglomerans DAPP-PG 734 and those of related Pantoea spp. was carried out. In P. agglomerans DAPP-PG 734, gene clusters for the synthesis of the Hrp-1 type III secretion system (T3SS), type VI secretion systems (T6SS) and autoinducer, which could play an important role in a plant-pathogenic community enhancing knot formation in olive trees, were identified. Additional gene clusters for the biosynthesis of two different antibiotics, namely dapdiamide E and antibiotic B025670, which were found in regions between integrative conjugative elements (ICE), were observed. The in-depth analysis of the whole genome suggested a characterization of the P. agglomerans DAPP-PG 734 isolate as endophytic bacterium with biocontrol activity rather than as a plant pathogen

Immature walnut fruit inoculation for evaluation of <I>Brenneria nigrifluens</I> pathogenicity

A reliable, reproducible, rapid and specific test for the pathogenicity of Brenneria nigrifluens, the causal agent of shallow bark canker of Persian walnut, was developed. When the mesocarp of immature walnut fruits was infiltrated by syringe with bacterial suspensions (108 cells mL-1) of B. nigrifluens, necrosis and reddish brown exudates started to appear at the inoculation sites, as early as 2 days after inoculation. No symptoms were detected in control fruits or in fruits inoculated with other bacteria frequently associated with walnut cankers. This pathogenicity test saves time and space when compared with the plant stem inoculation technique, in which the canker symptoms do not appear until at least 1 month after inoculation

The olive knot disease as a model to study the role of interspecies bacterial communities in plant disease

There is an increasing interest in studying interspecies bacterial interactions in diseases of animals and plants as it is believed that the great majority of bacteria found in nature live in complex communities. Plant pathologists have thus far mainly focused on studies involving single species or on their interactions with antagonistic competitors. A bacterial disease used as model to study multispecies interactions is the olive knot disease, caused by Pseudomonas savastanoi pv. savastanoi (Psv). Knots caused by Psv in branches and other aerial parts of the olive trees are an ideal niche not only for the pathogen but also for many other plant-associated bacterial species, mainly belonging to the genera Pantoea, Pectobacterium, Erwinia, and Curtobacterium. The non-pathogenic bacterial species Erwinia toletana, Pantoea agglomerans, and Erwinia oleae, which are frequently isolated inside the olive knots, cooperate with Psv in modulating the disease severity. Co-inoculations of these species with Psv result in bigger knots and better bacterial colonization when compared to single inoculations. Moreover, harmless bacteria co-localize with the pathogen inside the knots, indicating the formation of stable bacterial consortia that may facilitate the exchange of quorum sensing signals and metabolites. Here we discuss the possible role of bacterial communities in the establishment and development of olive knot disease, which we believe could be taking place in many other bacterial plant diseases.This research was supported by “Fondazione Cassa di Risparmio di Perugia,” Italy, project: “Indagini sul ruolo dei fenoli dell’olivo nello sviluppo della rogna, per individuare nuove strategie di lotta alla malattia” to CM. CR was supported by the Spanish Plan Nacional de I+D+I grants AGL2011-30343-C02-01 and AGL2014-53242-C2-1-R.Peer reviewedPeer Reviewe

Fondamenti di patologia vegetale

Svariate malattie di natura biotica e abiotica compromettono gravemente la produttivit\ue0 delle colture agrarie e forestali e provocano danni spesso irreversibili all\u2019ambiente ed al paesaggio. La trattazione degli aspetti scientifici e tecnici fondamentali di tali malattie, rivista e puntualmente aggiornata, \ue8 riproposta con arricchita veste tipografica in questa seconda edizione dei \u201cFondamenti di Patologia vegetale\u201d destinata soprattutto agli studenti dei corsi di laurea e di laurea magistrale in Scienze e Tecnologie Agrarie, Scienze Forestali e Ambientali, Viticoltura ed Enologia, Biotecnologie Agro-Alimentari, Scienze e Tecnologie Alimentari e ai tecnici e professionisti chiamati ad affrontare problemi fitopatologici sul territorio