1,721,007 research outputs found
Gli oli essenziali come agenti di controllo biologico delle batteriosi vegetali: il cancro batterico dell’actinidia
No full textIn agricoltura, la crescente necessità di limitare l’impiego di sostanze sintetiche per il controllo delle malattie delle piante ha reso sostanze naturali quali gli oli essenziali (OE) sempre più interessanti dal punto di vista applicativo per il minore impatto ambientale e per la sicurezza alimentare riscuotendo grande attenzione anche da parte dei consumatori. In particolare, il controllo delle batteriosi vegetali è tuttora affidato all’impiego di antibiotici, nei Paesi dove è permesso, e di prodotti rameici che tuttavia sono totalmente inefficaci nei confronti dei batteri patogeni endofiti in piante asintomatiche. La necessità di strategie alternative per il controllo e la gestione delle batteriosi, da adottare specialmente nelle coltivazioni biologiche, è sempre più impellente. Recenti studi sull’attività antimicrobica degli OE distillati da piante aromatiche hanno evidenziato il ruolo cruciale svolto dalla comunità microbica endofita biologicamente attiva nel controllo biologico di batteri fitopatogeni. L’ipotesi di somministrare alle piante OE o loro idrolati (Id) per interferire e bloccare la crescita di batteri fitopatogeni potrebbe costituire un importante strumento di controllo biologico. L’attività antimicrobica in vitro ed in planta di OE e Id ottenuti da Monarda didyma e M. fistulosa è stata valutata nei confronti di Pseudomonas syringae pv. actinidiae Takikawa et al. (Psa), batterio fitopatogeno da quarantena che causa il cancro batterico dell’actinidia. Infatti, gli OE distillati da piante di Monarda spp. sono caratterizzati da un elevato contenuto di monoterpeni, come ad esempio il timolo, il carvacrolo ed il loro precursore p-cimene, usati nell’industria alimentare come additivi per preservare gli alimenti. L’efficacia antimicrobica indotta dai trattamenti pre-infezionali con gli Id è molto incoraggiante per l’eventuale applicazione in campo finalizzato al controllo del cancro batterico dell’actinidia. Infatti, la loro composizione chimica è molto diluita rispetto ai corrispondenti OE e quindi l’azione protettiva nei confronti di Psa, senza causare effetti tossici indesiderati osservati in alcuni casi con gli OE, svolge un ruolo critico nella messa a punto di formulati a base di antimicrobici naturali. Le piante officinali, considerate quindi come sorgenti di nuovi agenti antimicrobici mediante l’impiego sia dei loro OE sia dei loro batteri endofiti, stanno offrendo approcci promettenti ed alternativi nel controllo biologico delle malattie batteriche delle piante degni di essere più approfonditamente studiati
Development of qPCR-based diagnostic assays for Xanthomonas arboricola pv. corylina early detection in Corylus avellana L.
No full textXanthomonas arboricola pv. corylina (Xac) is the causal agent of hazelnut bacterial blight, the most severe disease for coriliculture worldwide. Current Xac detection and identification methods rely on time-consuming diagnostic assays (e.g. microbiological, serological, biochemical and pathogenicity). Molecular diagnosis of Xac assay has been limited to a duplex PCR assay originally designed for X. arboricola pv. pruni, requiring modified thermal profiles to enhance sensitivity to the disadvantage of specificity. In 2023, efforts were made to develop a series of new molecular diagnostic methods (e.g. conventional PCR, qPCR and LAMP) based on the “region 2.4” specific to pathovar corylina. Despite that, to detect latent infections in asymptomatic tissues, the PCR assay typically used, although rapid, is not sufficiently specific. Furthermore, for the identification of X. arboricola, highly pathovar-specific and sensitive methods are not yet available except for pathogenicity testing on host plants. The study aimed to development and validated a reliable qPCR-based diagnostic protocol for the early and rapid detection of Xac in asymptomatic halzenut tissues, thereby improving disease prevention and management. Primers were designed based on ftsX and xopH genes, both specific for pv. corylina. Samples from symptomatic and asymptomatic hazelnut plant material were preliminarily tested. The qPCR assays demonstrated high sensitivity and specify, enabling consistent detection allowed to achieve encouraging results for Xac identification in asymptomatic and symptomatic plant material. However, it is necessary to deepen the genetic aspects on Xac virulence and to broaden the choice and type of molecular targets to prevent and control the disease
Presence of Pseudomonas syringae pv. actinidiae in buds of asymptomatic Actinidia chinensis var. deliciosa plants in late autumn and winter
No full textIn bacterial diseases, the latency period, during which there are no visible disease symptoms, can be prolonged depending on the conditions unfavorable for the growth of pathogens. As for Pseudomonas syringae pv. actinidiae (Psa), the causal agent of the bacterial canker of kiwifruit (BCK), the ability to survive several years in asymptomatic plants was recently highlighted. The Psa pluriannual latency in susceptible plants raises serious problems to control BCK for which it is necessary to consider defense strategies other than those based on spray treatments. Phytopatogenic bacteria can be hosted in buds of asymptomatic plants and their survival is regarded as a factor facilitating the overwintering of certain diseases caused by P. syringae. To clarify the bud epidemiological role, the Psa early detection in dormant buds (≈300) was carried out. In late autumn, 10 asymptomatic A. chinensis var. deliciosa plants were selected in an orchard located at the edge of a safety area that in the current year did not show BCK symptoms. At the beginning of dormancy (mid-December) and of “bleeding” (end of February), the buds were removed from a one-year old shoot. The Psa presence was determined by direct isolation and PCR analysis. At the end of the two surveys, the plant phytosanitary state was monitored to relate the orchard situation with the effective Psa absence/presence as pointed out by the early detection on bud samples. Psa was present in buds from 1 out of 10 and in 4 out of 10 plants in the first and in the second survey, respectively
Bacterial canker of kiwifruit: antimicrobial activity of Monarda spp. essential oils against Pseudomonas syringae pv. actinidiae
No full textIn agriculture, the economic losses due to plant diseases caused by infectious agents are constantly growing. In Italy, bacteria have recently caused outbreaks in crops of great economic impact: Pseudomonas syringae pv. actinidiae (Psa) for the bacterial canker of kiwifruit; Xylella fastidiosa, for the “Olive quick decline syndrome” and Erwinia amylovora (Ea) for the fire blight of pome-fruit trees. The control of these diseases relies almost exclusively on the use of copper compound sprays. It is therefore urgent to develop bactericidal products active in the plant or able to interfere with the growth of the pathogen already present as an endophyte in the host plant that can remain asymptomatic for years due to a long latent period. The idea to exploit the antimicrobial activity of essential oils (EO) to counteract the pathogens’ growth is increasingly taken into account. The antimicrobial effects of EO from Monarda spp. against Psa and Ea recently shown in vitro, allow to hypothesize their protection effect in planta against Psa. The EO and the hydrolate extracted by steam distillation from M. didyma flowering plants were tested to prevent the disease symptoms in Actinidia deliciosa cv. Tomouri plants induced by a Psa virulent strain. Four groups of plants were subjected to different pretreatments with: 1) sterile distilled water (positive control); hydrolate (14.7%); EO (0.3%) and streptomycin (negative control). 24 h later, they were inoculated with the Psa IPV-BO 8101 strain. Leaf spots characteristic of Psa were evidenced in the control plants starting from 8 days after the inoculation. The plants were monitored over the following two months to highlight the symptoms induced by Psa and any damages caused by each treatment. At the end of the trial, all leaves were collected from each plant to determine the number of spots/leaf/plant for statistical analysis. The protective effect of the EO/hydrolate, was correlated with their chemical compositions determined by GC/MS analysis. These results are encouraging for further research in this direction to safeguard health of plants and humans
Pseudomonas syringae pv. aptata HRP mutants which fail to produce periplasmic oligosaccharides
No full textPeriplasmic oligosaccharides, extracted from Pseudomonas syringae pv. aptata and purified by column chromatography, modify the homologous interaction between tobacco leaves and P. syringae pv. tabaci. The osmoregulating oligosaccharides can act as signal molecules to plant cells, but the molecular basis of this function is not known. Genetical analysis of pathogenicity determinants in P. s. pv. aptata strain NCPPB2664 allowed the identification of hrp genes which are essential in governing the ability of the bacteria to cause disease on host plants (such as sugar beet, lettuce), and the ability to induce the hypersensitive response on non-host plants (such as tobacco). The current study addresses whether a correlation between the pathogenicity and the production of oligosaccharides exists. To test the hypothesis that in the early stages of plant-bacteria interactions the hrp genes might be involved in the production of the periplasmic oligosaccharides, the latter has been studied in P. syringae pv. aptata Hrp- mutants
Fire blight in Emilia-Romagna and Veneto regions:virulence and genomic variability of Erwinia amylovora strains
No full textThe official cases of fire blight has been remarkable increased in host plants other than pear-tree in Emilia-Romagna (Northern Italy) beginning from 1997 when the first certified cases were also reported in the close Veneto. In this region the territorial distribution of the new foci in the following years and the genomic characteristics of the Erwinia amylovora (Ea) isolates based on the AFLP analysis pointed out the spread of the pathogen from the Emilia-Romagna border to north-west. Moreover, the AFLP genomic analysis of Venetian and Emilian strains revealed that all of them belong to the same clone that had caused the primary foci in 1994 in Emilia-Romagna. Adaptation to host plants other than pear may modify genetic frequencies in Ea sub-populations with possible effects even on virulence. In this study the AFLP fingerprints of the Emilian isolates from different host plants were very similar (SD3 0.987). The virulence analysis of the strains from the two regions revealed two homogeneous groups not correlated to the host plant or the province. The majority of the strains had a virulence slightly lower than that of the reference strain OMP-BO 1077/7, associated to the primary foci in 1994, and only 7 strains had a virulence higher not correlated to the host plant or the province
HOST-PATHOGEN INTERACTION IN ACTINIDIA-BACTERIAL CANKER PATHOSYSTEM: INVESTIGATION ON THE LATENCY PERIOD IN ASYMPTOMATIC PLANTS (vol 96, pg 38, 2014)
No full textBacterial canker of kiwifruit caused by Pseudomonas syringae pv. actinidiae (Psa) still results in serious yield losses in Italy and, despite the studies conducted hitherto to deal with this devastating disease, some epidemiological aspects are still to be clarified. In particular, the available information on life-cycle of Psa is still incomplete on the latency period of Psa within the susceptible host plant. To elucidate this dangerous endophytic latent phase, the survival of a virulent Psa gfp-expressing/Rif-resistant strain (Psa::gfp) within asymptomatic Actinidia spp. plants was studied. The results were obtained both in adult plants of Actinidia chinensis cv. Hort16A four years after inoculation with Psa::gfp at low inoculum dose, and in Actinidia deliciosa cv. Hayward plants obtained from micropropagated shoots similarly inoculated more than three years before. Both types of plant were in toto analyzed to re-isolate Psa::gfp on selective media, and to check its ability to induce disease symptoms in host plants and hypersensitivity reaction in tobacco plants. PCR analysis was carried out to confirm the identity of the re-isolate Psa::gfp. On the fourth year following inoculation, the data confirmed that Psa can colonize plants for a long time staying latent at very low concentrations. In the pathosystem Actinidia-Psa the pathogen appears to have achieved a high degree of pathoadaptation which is witnessed in a pluriannual latency period. The implications of what reported are especially important for its impact on the nursery industry, and control strategies in kiwifruit orchards to prevent the spread of the pathogen present in asymptomatic plants
Endophytic distribution of Pseudomonas syringae pv. actinidiae after a five-year latency into Actinidia chinensis var. chinensis plants: a real-time-PCR analysis
No full textThe ability of phytopathogenic bacteria to survive for long time within asymptomatic host plants represents one of the main critical factors to control outbreaks. The epidemiological role of the bacterial latency phase is very important since the control strategies are based on preventive chemical treatments by spraying on plant surfaces. In seven-year-old plants of Actinidia chinensis var. chinensis ‘Hort16A’ inoculated five years before with a virulent Pseudomonas syringae pv. actinidiae gfp-expressing/rifampicin-resistant strain (Psagfp-Rifres) at low inoculum dose, the dangerous latency phase of Psagfp-Rifres was studied dissecting the whole plants by cutting, from the apex to the root collar, the shoots/stems in segments of 20 cm (approx. 10-15/plant). In this study, to better clarify the endophyte distribution in asymptomatic plants and the preference of the pathogen for certain portions of the plant stem, the data previously obtained from microbiological (direct isolation on selective media, DI), biological (pathogenicity/HR assay) and PCR (Bio- and Nested) analyses were compared with those from Real-time PCR (RT-PCR) analysis. In the pathosystem Psa–Actinidia, the pathogen reached a high degree of pathoadaptation which is highlighted by the pluriannual latency period of Psa. The RT-PCR of the DNA extracted and quantified by the different segments of each entire plant confirmed the results previously obtained from microbiological and Bio/Nested PCR analyses and allowed to detect Psagfp-Rifres in segments of the stem that in Bio/Nested PCR analyses were Psagfp-Rifres-negative. Direct isolation revealed the Psagfp-Rifres presence in accordance with the RT-PCR data. The long time required for DI of Psagfp-Rifres from plant samples five years after the plant inoculation was largely compatible with the low concentrations of Psagfp-Rifres detected by RT-PCR
Survival of Erwinia amylovora on pears and on fruit containers in cold storage and outdoors
No full textThe survival of Erwinia amylovora during cold storage or in the open air might be a relevant factor in the spread of fire blight. Pear fruits, the wooden or plastic container surfaces and the packaging paper may be vehicles for the spread over short, medium and long distances associated with the marketing of fruit, the movement of bins and trays, and the disposal of packaging paper after storage. Survival in cold storage (-0.5°C) and/or in the open air of a rifampicin-resistant strain was studied on pears, bins, trays and packaging paper. The surfaces of highly standardised samples were contaminated with a bacterial suspension. The washing liquid was centrifuged and the final concentrate was quantitatively streaked on selective medium. Although it was no longer possible to isolate the bacteria from the pear skin after 24 hours, survival in the calycine cavity reached at least 101 days. Survival was (considerable) on oak (20–30 days) and poplar wood (40–60 days); maximum survival was estimated at 60–70 days and 70–80 days respectively. After 24 hours the bacteria could no longer be isolated from polyvinyl chloride. Survival on packaging paper was 14-24 days. The grey paper used to line the sides was less conducive to survival than that used for the bottom. The survival curves were calculated for each type of material. An estimation of phytosanitary risk periods for the transmission of Ea based on the critical time of survival is hypothesised
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