Dissemination of Pseudomonas syringae pv. actinidiae through pollen and its epiphytic life on leaves and fruit

The role of pollen in disseminating Pseudomonas syringae pv. actinidiae (Psa) in kiwifruit orchards was investigated and the survival of the pathogen as an epiphyte on leaves and fruits was followed, from pollination time until the pre-harvest season. Pollen with natural inoculum was obtained from an infected orchard and pollen harvested without any contamination by Psa was experimentally inoculated at approximately the same contamination level. Two pollination techniques were used in glasshouse experiments: dusting and spraying. In parallel, field trials in commercial orchards were carried out: two plots were designed in two orchards, where bacterial canker was present at low incidence. From petal fall to 3 weeks before harvesting, leaf and fruit samples were taken and analysed for the presence of Psa, using two different PCR protocols and direct isolation. Results confirmed the dissemination of Psa through pollen, especially when using the aqueous suspensions. Both in glasshouse experiments and in the orchards Psa was found as an epiphyte for several weeks after pollination. Pathogen populations on leaves were, initially, 10 to 100 times less than on fruitlets. As the summer continued, the epiphytic contamination levels of fruits decreased constantly, being no more detectable from early August, whereas Psa was present at detectable levels on leaves until early October, approx. 20 days before harvesting time. Our results confirmed the role of pollen in disseminating Psa, the long epiphytic survival of the pathogen on kiwifruit leaves and the increasing unsuitability of fruits to harbour detectable, epiphytic populations of the bacterium through the summer season in commercial orchards with low disease incidence, when they are reaching the final development stage. Thus, kiwifruit surfaces do not appear to be a suitable niche for a long term survival of Psa as an epiphyte and, therefore, kiwifruits should not represent a pathway for Psa dissemination and pose a negligible risk for the introduction of the pathogen into new areas

Le malattie batteriche emergenti o riemergenti delle colture agrarie in Italia e nel bacino del Mediterraneo

Vengono descritte alcune malattie batteriche emergenti, o riemergenti, che potrebbero diventare un serio fattore limitante le produzioni ortofrutticole italiane e mediterranee

Pollen as a possible pathway for the dissemination of Pseudomonas syringae pv. actinidiae and bacterial canker of kiwifruit

Pollen collected in a kiwifruit orchard with symptoms of bacterial canker and naturally contaminated by Pseudomonas syringae pv. actinidiae (Psa), was used to pollinate an experimental orchard, in order to confirm its role, under commercial orchard conditions, in disseminating the pathogen and, possibly, contributing to disease spread. A pollen lot, certified free from Psa, was used with the same methods as a control. Two pollination techniques were used: dusting (dry pollen) and spraying (pollen suspension in water). The orchard was monitored during 2 years from experimental pollination, with regular sampling of flowers, fruits, leaves, and vines, to check for Psa as an epiphyte or endophyte, and for bacterial canker symptoms. Psa was recovered from flowers, fruitlets and leaves during the first season, mainly in plots where contaminated pollen had been sprayed in water suspension. From early August until harvesting time (mid-October), Psa detection was possible only on leaves. No symptoms developed during the first season after pollination. No endophytic Psa was detected in pruned vines in the following winter. During the second season, detection and isolation of Psa was erratic, but direct isolation was achieved from four plots. During the second season after pollination, typical leaf symptoms were observed on a few vines, and Psa was isolated and identified. Our results suggest that Psa could be disseminated via contaminated kiwifruit pollen as a pathway for spread of bacterial canker. However, further pollination experiments are needed to establish, beyond any doubt, whether contaminated pollen may contribute to possible disease outbreaks

Plant Growth Promoting and Biocontrol Activity of Streptomyces spp. as Endophytes

There has been many recent studies on the use of microbial antagonists to control diseases incited by soilborne and airborne plant pathogenic bacteria and fungi, in an attempt to replace existing methods of chemical control and avoid extensive use of fungicides, which often lead to resistance in plant pathogens. In agriculture, plant growth-promoting and biocontrol microorganisms have emerged as safe alternatives to chemical pesticides. Streptomyces spp. and their metabolites may have great potential as excellent agents for controlling various fungal and bacterial phytopathogens. Streptomycetes belong to the rhizosoil microbial communities and are efficient colonizers of plant tissues, from roots to the aerial parts. They are active producers of antibiotics and volatile organic compounds, both in soil and in planta, and this feature is helpful for identifying active antagonists of plant pathogens and can be used in several cropping systems as biocontrol agents. Additionally, their ability to promote plant growth has been demonstrated in a number of crops, thus inspiring the wide application of streptomycetes as biofertilizers to increase plant productivity. The present review highlights Streptomyces spp.-mediated functional traits, such as enhancement of plant growth and biocontrol of phytopathogens

In vitro characterization of plant growth promoting and biocontrol activity of beneficial microorganisms

Plant roots are associated with numerous and diverse types of beneficial and pathogenic microorganisms. Among them, plant growth\u2013promoting (rhizo)bacteria (PGPB or PGPR) are isolated from plants crops worldwide, and many of them are used as agricultural inoculants. Agricultural biofertilization and biocontrol of pathogens are eco-friendly alternatives to chemical usage and have less energy, environmental, and economic costs. PGPB isolation and evaluation are essentials steps for determining bacteria that could improve plant development and productivity. In the present study three Streptomyces sp. strains SB14, SA51 & SL81, two Pseudomonas sp. strains PT65 & PN53, an Agrobacterium sp. strain AR39 and an internal control (IC) Pseudomonas synxantha were evaluated in vitro for different plant growth promoting and biocontrol activities. The results were aimed to identify possible antagonists able to inhibit different plant bacterial (Xanthomonas vesicatoria, Clavibacter michiganensis subsp. michiganensis, Clavibacter michiganensis subsp. sepedonicus, Acidovorax citrulli and Ralstonia solanacearum) and fungal (Rhizoctonia solani, Sclerotium sp., Fusarium oxysporum, Alternaria solani and Monilia laxa) pathogens. All the strains were screened for biocontrol activity on three different media\u2019s and AIA (average inhibition area) was calculated. Among the isolates, each strain showed different ability to inhibit the pathogens: Streptomyces sp. strain SA51 was found to be most active. The most prospective strains SA51, AR39 and DLS65 were further evaluated in the field, as possible biocontrol agents for the tomato spot disease (X. vesicatoria), singularly and as a consortium. Results will improve our understanding on the use of such microbial biocontrol agents and will implement innovative biocontrol strategies to bacterial diseases

Growth Promotion and Biocontrol Activity of Endophytic Streptomyces spp.

There has been many recent studies on the use of microbial antagonists to control diseases incited by soilborne and airborne plant pathogenic bacteria and fungi, in an attempt to replace existing methods of chemical control and avoid extensive use of fungicides, which often lead to resistance in plant pathogens. In agriculture, plant growth-promoting and biocontrol microorganisms have emerged as safe alternatives to chemical pesticides. Streptomyces spp. and their metabolites may have great potential as excellent agents for controlling various fungal and bacterial phytopathogens. Streptomycetes belong to the rhizosoil microbial communities and are efficient colonizers of plant tissues, from roots to the aerial parts. They are active producers of antibiotics and volatile organic compounds, both in soil and in planta, and this feature is helpful for identifying active antagonists of plant pathogens and can be used in several cropping systems as biocontrol agents. Additionally, their ability to promote plant growth has been demonstrated in a number of crops, thus inspiring the wide application of streptomycetes as biofertilizers to increase plant productivity. The present review highlights Streptomyces spp.-mediated functional traits, such as enhancement of plant growth and biocontrol of phytopathogens

Xylella fastidiosa: il patogeno, le malattie e l’attuale situazione fitosanitaria

Xylella fastidiosa è un batterio fitopatogeno Gram negativo che appartiene alla famiglia delle Xanthomonadaceae. È l’agente causale di numerose malattie d’importanti colture arboree, erbacee, forestali e ornamentali e, a differenza di quanto molta parte dell’opinione pubblica crede, non è un problema di recente comparsa, ma ha una lunga storia che affonda le sue radici ancora alla fine del diciannovesimo secolo. L’etimologia e la semantica del nome assegnato al patogeno da parte dei ricercatori che per primi lo isolarono in coltura pura svelano due aspetti fondamentali della sua biologia: Xylella rivela la nicchia biologica del patogeno all’interno delle sue piante ospiti, cioè lo xilema; fastidiosa indica la grande difficoltà che il batteriologo incontra durante il processo d’isolamento e purificazione della coltura pura

Dissemination of Pseudomonas syringae pv. actinidiae through pollen and its epiphytic life on leaves and fruits

The role of pollen in disseminating Pseudomonas syringae pv. actinidiae (Psa ) in kiwifruit orchards was investigated and the survival of the pathogen as an epiphyte on leaves and fruits was followed, from pollination time until the pre-harvest season. Pollen with natural inoculum was obtained from an infected orchard and pollen harvested without any contamination by Psa was experimentally inoculated at approximately the same contamination level. Two pollination techniques were used in glasshouse experiments: dusting and spraying. In parallel, field trials in commercial orchards were carried out: two plots were designed in two orchards, where bacterial canker was present at low incidence. From petal fall to 3 weeks before harvesting, leaf and fruit samples were taken and analysed for the presence of Psa, using two different PCR protocols and direct isolation. Results confirmed the dissemination of Psa through pollen, especially when using the aqueous suspensions. Both in glasshouse experiments and in the orchards Psa was found as an epiphyte for several weeks after pollination. Pathogen populations on leaves were, initially, 10 to 100 times less than on fruitlets. As the summer continued, the epiphytic contamination levels of fruits decreased constantly, being no more detectable from early August, whereas Psa was present at detectable levels on leaves until early October, approx. 20 days before harvesting time. Our results confirmed the role of pollen in disseminating Psa, the long epiphytic survival of the pathogen on kiwifruit leaves and the increasing unsuit­ability of fruits to harbour detectable, epiphytic populations of the bacterium through the summer season in commercial orchards with low disease incidence, when they are reaching the final development stage. Thus, kiwifruit surfaces do not appear to be a suitable niche for a long term survival of Psa as an epiphyte and, therefore, kiwifruits should not represent a pathway for Psa dissemination and pose a negligible risk for the introduction of the pathogen into new areas