Progress 09/15/03 to 09/14/05
Outputs
Fire blight caused by Erwinia amylovora is the most serious bacterial disease of apple and pear trees. Streptomycin sprays gave excellent control of fire blight, but now the pathogen is resistant. Growers now rely on less effective products like the antibiotic oxytetracycline (Mycoshield) or the biological control product BlightBan A506 (Pseudomonas fluorescens A506) for disease control. We discovered that iron can trigger A506 to produce a compound that kills the fire blight pathogen. Our WRIPM research focuses on how to integrate iron with A506 for disease control. In repeated trials, some iron-nutrition products such as Metalosate-Fe (a registered organic formulation) or ferrous sulfate burned flowers and unacceptably marked the surface of pear and apple fruit. In contrast, the iron chelate FeEDDHA (Sequestrene 138) did not damage flowers or fruit in repeated field trials, even when sprayed twice on flowers at high doses. We tested disease control with different
combinations of BlightBan A506 and iron (FeEDDHA) treatments. BlightBan A506 alone reduced the incidence of fire blight by an average of 22% in three field trials compared disease on water-treated trees. Adding FeEDDHA to A506 significantly decreased the incidence of fire blight by an average of 52% in five field trials. We tested 5 different iron-timing strategies and found that the timing of iron application did not influence disease control greatly, except that spraying flowers with a mixture of iron with A506 provided better disease control than applying A506 during bloom and later spraying trees with iron after petal fall. In our laboratory experiments, ionic forms of iron (e.g. ferric chloride or ferrous sulfate) inactivate oxytetracycline. Oxytetracycline combined with water or chelated forms of iron (eg. FeDTPA or FeEDDHA) remained active and inhibited growth of the fire blight pathogen; thus, iron chelates are compatible with the antibiotic. We evaluated integrated control of
fire blight in five orchard trials in 2004 and 2005. Two applications of oxytetracycline reduced the incidence of fire blight by an average of 45%. A single bloom application of A506 followed by a single post-bloom spray of oxytetracycline improved control and reduced the incidence of fire blight by an average of 54%. We obtained excellent disease control in five orchard trials by spraying a combination of BlightBan A506 with FeEDDHA during bloom, followed by a single post-bloom spray of oxytetracycline. This integrated treatment program reduced the incidence of fire blight by an average of 70% and was not statistically different than two sprays of streptomycin (75% disease control against a streptomycin-sensitive pathogen). This research indicates that the iron-enhanced biological control technology using chelated forms of iron can be combined safely with oxytetracycline. Applying BlightBan A506 with FeEDDHA followed by a single application of oxytetracycline provided excellent
protection of trees to fire blight and reduced the number of applications of the antibiotic to achieve significant disease control.
Impacts
Fire blight is the most serious bacterial disease of pear and apple trees. During severe epidemics, entire orchards can be lost. In the western states, multiple sprays of oxytetracycline (an antibiotic) or BlightBan A506 (a biocontrol bacterium) are used for disease management, but these products reduce the incidence of disease only by 45% and 22%, respectively. We showed that adding iron to A506 improves control of fire blight to an average of 52%, but the form of iron is important. Ferric chloride, ferrous sulfate, and Metalosate-Fe (registered organic formulation) inactivates oxytetracycline, burns flowers, and damages the pear and apple fruit surface. The iron chelate FeEDDHA (Sequestrene 138) did not damage flowers or fruit or interfere with oxytetracycline. Our new integrated program using iron-enhanced biological control technology (chelated iron combined with A506) followed by a single treatment with oxytetracycline reduced the incidence of fire blight by 70%.
This integrated strategy provided superior disease control in orchard trials and reduced the number of antibiotic treatments needed for disease suppression. This research should provide growers a new and effective integrated management strategy for the suppression of fire blight of pear and apple.
Publications
- Stockwell, V.O., Temple, T. N., Johnson, K. B., and Loper, J. E. 2005. Effect of the iron chelate FeEDDHA on control of fire blight by Pseudomonas fluorescens A506. Phytopathology 95:S100.
- Stockwell, V.O., and Stack, J. 2005. Using Pseudomonas spp. for integrated biological control. Phytopathology 95:S145.
- Temple, T.N., Stockwell, V.O., Johnson, K.B., and Loper, J.L. (2005). Relative availability of iron to Pseudomonas fluorescens A506 on pome fruit blossoms. Acta Hort (in press).
- Stockwell, V.O., Johnson, K.B., and Loper, J.E. (2005). Enhancement of biocontrol of fire blight by combining Pseudomonas fluorescens A506 with the iron chelate FeEDDHA. Acta Hort (in press).
- Temple, T.N., Stockwell, V.O., Loper, J.E. and Johnson, K.B. 2004. Bioavailability of iron to Pseudomonas fluorescens A506 on flowers of pear and apple. Phytopathology 94:1286-1294.
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Progress 01/01/04 to 12/31/04
Outputs
Fire blight caused by Erwinia amylovora is the most serious bacterial disease of apples and pears trees. Streptomycin sprays gave excellent control of fire blight, but now the pathogen is resistant. Growers now rely on less effective products like the antibiotic oxytetracycline (Mycoshield) or the biological control product BlightBan A506 for disease control. BlightBan A506 (the bacterium Pseudomonas fluorescens strain A506) suppresses disease by competing with the pathogen in infection sites on pear and apple flowers. We discovered that iron can trigger A506 to produce a compound that kills the fire blight pathogen. Our WRIPM research will provide answers about how to best combine iron with A506 for disease control in orchards. We will study safety of iron sprays on fruit trees in bloom, when iron should be sprayed, and if iron will interfere with the activity of oxytetracycline for disease suppression. We found that some iron-nutrition products can be sprayed onto
flowers safely, whereas others damage flowers and fruits. Metalosate-Fe (a registered organic formulation) or ferrous sulfate burned flowers and unacceptably marked the surface of pear and apple fruit. The chelate FeDTPA (Sequestrene 330) marked flowers only at high concentrations. The iron chelate FeEDDHA (Sequestrene 138) did not damage flowers or fruit in repeated field trials, even when sprayed twice on flowers at high doses. In three field trials, we tested disease control with different combinations of BlightBan A506 and iron (FeEDDHA) treatments. Treatment with BlightBan A506 alone reduced the incidence of fire blight by 0%, 33%, and 37% compared disease on water-treated trees. Adding FeEDDHA to A506 significantly decreased the incidence of fire blight by 70%, 51%, and 43% compared to water-treated trees. We tested 5 different iron-timing strategies and found that varying timing of iron application did not influence disease control greatly, except that early applications of
iron tended to provide better disease control than post-bloom applications. We tested activity of oxytetracycline (Mycoshield) with iron. We found that ionic forms of iron (e.g. ferric chloride or ferrous sulfate) inactivate oxytetracycline. Oxytetracycline combined with water or chelated forms of iron (eg. FeDTPA or FeEDDHA) remains active and inhibits growth of the fire blight pathogen. Thus, iron chelates are compatible with the antibiotic. In three field trials, we obtained excellent disease control by spraying a combination of BlightBan A506 with FeEDDHA during bloom, followed by a post-bloom spray of Mycoshield combined with FeEDDHA. This integrated treatment program reduced the incidence of fire blight by 84%, 74%, and 45% compared to water-treatment and provided the best control of all treatments in two of three trials. This research indicates that the iron-enhanced biological control technology using chelated forms of iron can be combined safely with oxytetracycline. This
research to provide integrated management strategies for the suppression of fire blight of pear and apple will be repeated in laboratory and field trials in 2005.
Impacts
Fire blight is the most serious bacterial disease of pear and apple trees. During severe epidemics, entire orchards can be lost. In the Pacific Northwest, oxytetracycline and BlightBan A506 (a biocontrol bacterium) are used to control the disease. We showed that adding iron to A506 improves control of fire blight but the form of iron is important. Ferric chloride, ferrous sulfate, and Metalosate-Fe (registered organic formulation) inactivates oxytetracycline, burns flowers, and ruins the pear and apple fruit surface. The iron chelate FeEDDHA (Sequestrene 138) did not damage flowers or fruit or interfere with oxytetracycline. Our new integrated program using iron-enhanced biological control technology (chelated iron combined with A506) followed by treatment with oxytetracycline provided superior disease control in orchard trials in 2004. If similar results are obtained in 2005, then growers may have a new and effective integrated management strategy for the suppression
of fire blight of pear and apple.
Publications
- No publications reported this period
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Progress 09/15/03 to 12/31/03
Outputs
The western region of the U.S. is a major production area for apples and pears. Fire blight caused by Erwinia amylovora is the most serious bacterial disease of these crops. Antibiotics (streptomycin and oxytetracycline) are applied routinely during bloom to control this disease, but the emergence of streptomycin-resistant strains of the pathogen has compromised effectiveness of antibiotics. In 1996, the biocontrol bacterium Pseudomonas fluorescens strain A506 was registered for fire blight management. Suppression of fire blight by A506 was attributed to competitive exclusion of E. amylovora from colonization sites on flowers. In our field trials, A506 reduces the incidence of fire blight by 30%. We discovered that A506 could be induced to produce an antibiotic that is highly toxic to E. amylovora. The production of this antibiotic by A506 is triggered by high concentrations of iron. In field trials, we found that spraying an iron chelate (FeEDDHA) on flowers provided
iron to A506, and that combining this iron chelate with the biocontrol agent significantly improved control of fire blight to ca. 53%. In some trials, control from A506 plus iron was similar to antibiotic sprays; but in a few trials, the addition of FeEDDHA did not significantly increase disease control compared to A506 alone. Thus, this is a promising method to improve biological control of fire blight, but more information is needed to obtain more consistent levels of disease control. At stakeholder forums, we have been asked practical questions related to the use of iron with A506. Our research is concerned with questions of how to best utilize, refine, and implement iron-enhanced biocontrol of fire blight with A506. In the spring of 2004, we will study if an application of iron during late bloom improves control of fire blight. All of our research to date has utilized iron attached to EDDHA. In spring of 2004, we will evaluate other iron chelates for their suitability for this
technology. In experiments in 2003, we found that the iron chelate FeDPTA provides iron to A506 on flowers, as measured with iron-biosensors. We did not observe injury to flowers or fruit sprayed during bloom with 3 mM FeDPTA. We are evaluating an iron-amino acid complex sold as Metalosate-Iron, which is registered for use in organic-certified crops. In preliminary tests, this complex provided iron to A506, but high concentrations of sprayed during bloom injured flowers and young leaves of apple. We will determine if Metalosate-Iron can be used safely at lower concentrations on flowers. Finally, in clinical studies, it has been shown that iron can inactivate the bacteriostatic properties of tetracyclines. Because oxytetracycline is used for fire blight suppression on trees, we are starting studies to determine if iron chelates significantly reduce the ability of oxytetracycline to control disease. Through this work, we will evaluate the pallet of iron compounds that may be used
effectively and safely in combination with BlightBan A506 and oxytetracycline for control of fire blight.
Impacts
Fire blight is the most serious bacterial disease of pear and apple trees. During severe epidemics, entire orchards can be lost. In the Pacific Northwest, oxytetracycline and BlightBan A506 (a biocontrol bacterium) are used to control the disease. We showed that adding iron to A506 can improve control of fire blight. This project will evaluate if the chemical form of iron is important and if iron decreases the activity of oxytetracycline. Through this research we hope to develop management recommendations on the implementation of this new technology.
Publications
- No publications reported this period
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