Abstract
This study included eight bacterial isolates originating from the apple phyllosphere or soil environment that were previously selected using the pear fruitlet test (Mikiciński 2017). Identification of these isolates based on phenotypic assays and DNA analysis showed that five of them belonged to species for which an antagonistic activity against Erwinia amylovora and the protective capacity of apple and pear against fire blight were not previously demonstrated. These were L16 identified as Pseudomonas vancouverensis, 3 M as Pseudomonas chlororaphis subsp. aureofaciens, 35 M – Pseudomonas congelans, 43 M – Enterobacter ludwigii, and 59 M – Pseudomonas protegens. Investigation of the biotic relationships between the tested strains and E. amylovora showed that 3 M, 35 M and 59 M inhibited the growth of the pathogen on five out of six media used (NAS, KB, LB, R2A, NAG), but 43 M did not do so on any of these media. Strain L16 did not inhibit the growth of the pathogen on LB or R2A medium. In contrast, all strains grown on medium 925 stimulated the growth of the pathogen, which showed no growth without co-cultivation with these strains. The experiments on apple trees and detached apple branches showed the ability of the tested bacteria to protect flowers at medium to high levels, depending on the experiment (55–93%). In some cases, this protection was even higher than that of the copper product used for comparison. In studies assessing the bacterial ability to protect shoots of M.26, the highest efficacy was observed for strains 35 M (96%) and 43 M (93%) but on ‘Gala Must’ all tested strains showed 100% of efficacy.
Highlights
Fire blight (Erwinia amylovora) is one of the most harmful diseases in apple and pear orchards and nurseries (Vanneste 2000)
Due to the regulations enforced by the European Union related to the status of E. amylovora as a quarantine organism when it occurs on propagation material (Directive 2000/29/EC), appropriate procedures are needed to eliminate the disease and to prevent its spread
The identification of tested bacterial isolates showed that five of them (L16 identified as Pseudomonas vancouverensis, 3 M as Pseudomonas chlororaphis subsp. aureofaciens, 35 M – Pseudomonas congelans, 43 M – Enterobacter ludwigii, 59 M – Pseudomonas protegens) belonged to species in which an antagonistic activity to Erwinia amylovora and a protective capacity of apple and pear against fire blight were not previously demonstrated
Summary
Fire blight (Erwinia amylovora) is one of the most harmful diseases in apple and pear orchards and nurseries (Vanneste 2000). Protection of plants against fire blight includes the use of chemical, agrotechnical, biological, and quarantine methods (Psallidas and Tsiantos 2000; Steiner 2000). Because none of these methods is fully effective, attention is paid to their proper integration (Steiner 2000; Norelli et al 2003; Sobiczewski 2011). In some countries (e.g., the USA, New Zealand, Israel, Canada, Mexico), treatments with antibiotics are recommended (Stockwell and Duffy 2012) Their use in plant protection within the European Union is prohibited (Fried et al 2013). In regions where fire blight is endemic, it is recommended to choose cultivars with higher resistance for new orchard establishment
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