Biological Control Of Fire Blight Research Articles

Biological Control of Fire Blight of Hawthorn (Crataegus monogyna) with Fluorescent Pseudomonas spp. under Protected Conditions

AbstractNaturally‐occurring epiphytic fluorescent pseudomonads were isolated and characterized in terms of their potential to control fire blight infection of hawthorn, caused by Erwinia amylovora.Preliminary testing and selection of antagonists using an immature pear fruit assay gave some inconsistency in the amount of pathogen suppression on the pear tissue and also in the prediction of biocontrol effectiveness on the intact plant.Selected antagonists provided significant but variable control of fire blight under protected (polythene tunnel and glasshouse) conditions, with isolates HL83 and HL99 giving control of both blossom‐blight and shoot‐blight. In some cases the degree of control was equal to that of chemical treatments, including agrimycin 17 and experimental bactericides, and was achieved without any numerical advantage of applied control agent over pathogen. The timing of pseudomonad application in relation to pathogen inoculation was found to have a significant effect on the level of control of blossom‐blight.

Dissemination of Bacteria Antagonistic toErwinia amylovoraby Honey Bees

Foraging honey bees (Apis mellifera) were tested for ability to disseminate bacteria antagonistic to Erwinia amylovora to apple and pear flowers in commercial orchards. The bacteria, Pseudomonas fluorescens and E. herbicola, previously known to provide biological control of fire blight, were placed on apple or cattail pollen at populations of 10 9 and 10 8 bacteria per gram, respectively. There was no significant decline in viable bacteria on either pollen over 3 wk at 4 C. These bacteria-treated pollens were placed in pollen inserts in the entrances of beehives (.)

Biological control of fire blight of hawthorn (Crataegus monogyna) with Erwinia herbicola under protected conditions

Isolates of Erwinia herbicola, obtained from flowers and leaves of hawthorn (Crataegus monogyna), were screened as potential control agents of fire blight disease (caused by Erwinia amylovora) using an immature pear fruit assay. Selected isolates were subsequently tested for disease control by infection of hawthorn blossom in the laboratory, and by shoot infection of hawthorn plants grown under controlled (glasshouse) and fluctuating (polythene tunnel) environmental conditions.Although the immature pear fruit assay provided a general screen for the selection of antagonists for the control of both blossom and shoot blight, it had two major limitations when quantitatively applied. Firstly there were inconsistencies in the relative effects of different isolates on the pear‐slice surface, with some isolates being more suppressive than the standard antagonist Eh252 in the first screening and less in the second. Secondly the assay was not able to predict accurately the level of control in the intact plant‐as no correlation occurred between the level of control in the pear fruit assay and the percentage control of either blossom blight or shoot blight.Two isolates of E. herbicola, WL9 and WL40, reduced both blossom‐ and shoot‐blight. WL9 provided over 80% control of blossom blight, equivalent to that provided by chemical agents, and also gave total control of shoot blight when applied at a WL9: pathogen ratio of 10:1.