amylovora are flowers, biological control of fire blight is based on the establishment of antagonist bacteria on blossoms prior to the arrival of the pathogen ( Wilson et al., 1992 Johnson et al., 1993 Wilson & Lindow, 1993). Therefore, new strategies of fire blight management are increasingly being used, such as biological control ( Wilson & Lindow, 1993 Johnson & Stockwell, 2000 Stockwell et al., 2002).īecause the organs most susceptible to infection by E. amylovora ( Moller et al., 1981 Loper et al., 1991 Jones & Schnabel, 2000 Vanneste & Voyle, 2002), which may cause the failure of disease control and the persistence of such chemicals in the environment and food. Nevertheless, the wide use of chemicals has important drawbacks, such as the appearance of antibiotic-resistant strains of E. copper hydroxide, copper oxychloride, copper sulphate) ( Psallidas & Tsiantos, 2000). streptomycin, oxytetracycline) or copper compounds (e.g. amylovora on blossoms by means of spray treatments with antibiotics (e.g. The control of fire blight has been mainly based on interfering with multiplication of E. Erwinia amylovora infections usually start in blossoms, where the pathogen multiplies rapidly and enters into plant host tissues, where the infection progresses, being able to kill trees within a single growing season ( Vanneste & Eden-Green, 2000). This disease has a worldwide distribution, causing important economic losses ( Van der Zwet & Keil, 1979 Van der Zwet & Beer, 1995 Vanneste, 2000). The combined use of real-time PCR and CFU-counting methods of analysis permitted the identification of three physiological states for EPS62e in the field, which consisted of active colonization, survival and entry into a viable but nonculturable state, and cell death.īiological control, fire blight, Pseudomonas fluorescens EPS62e, real-time PCR monitoring, population dynamics, spread Introductionįire blight is a serious disease caused by Erwinia amylovora that affects several plant species, mainly belonging to the rosaceous family, such as fruit trees ( Pyrus spp., Malus spp.) and ornamentals ( Cotoneaster spp., Crataegus spp., Pyracantha spp.). EPS62e spread moderately in the orchard, being detected in nontreated flowers of trees 15–35 m from the inoculation site. With inoculated leaves, the EPS62e population decreased to nondetectable levels 30 days after treatment according to both methods used. The plant host species did not influence the colonization rate, and the biocontrol agent dominated the microbial communities of blossoms, representing up to 100% of the total cultivable population. With inoculated flowers, weather conditions were optimal for colonization, and EPS62e established high and stable population levels around 10 8 CFU per organ, according to both methods of analysis. Population dynamics were assessed by real-time PCR and CFU-counting methods. The trials studied the influence of weather conditions, plant host species, presence of indigenous microbial community and spread from treated to nontreated trees on colonization and survival. The behaviour of Pseudomonas fluorescens EPS62e was investigated in apple and pear orchards under Mediterranean climatic conditions.
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