Source: OREGON STATE UNIVERSITY submitted to
EPIDEMIOLOGY AND CONTROL OF DISEASES OF FRUIT CROPS IN WESTERN OREGON
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0205269
Grant No.
(N/A)
Project No.
ORE00380A
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Oct 1, 2004
Project End Date
Sep 30, 2009
Grant Year
(N/A)
Project Director
Johnson, K.
Recipient Organization
OREGON STATE UNIVERSITY
(N/A)
CORVALLIS,OR 97331
Performing Department
BOTANY AND PLANT PATHOLOGY
Non Technical Summary
Fire blight is a serious disease of pear and apple that impacts productivity of orchards, and prohibits export of these fruits to countries that do not have the disease. Our first purpose is to improve control of fire blight of pear and apple. Our second purpose is to evaluate the risk of movement of the fire blight pathogen in association with pear fruit.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
2121110116010%
2121115116010%
2121219116010%
2124010116010%
2124020116010%
2151199116015%
2151219116010%
2161199116015%
2161219116010%
Goals / Objectives
1. Improve control of fire blight of pear and apple. 2. Evaluate the risk of movement of the fire blight pathogen in association with pear fruit.
Project Methods
Objective 1: We will address hypotheses concerned with the addition of avirulent strains of E. amylovora to already effective antagonist mixtures for fire blight suppression. We propose to evaluate the role of avirulent strains of E. amylovora with specific mutations in the hrp gene cluster for their potential to influence the domination of epiphytic populations of the pathogen by an antagonist mixture. We hypothesize that avirulent strains of E. amylovora will effectively contribute to antagonist mixtures by enhancing preemptive occupation of microsites currently colonized by virulent strains (but not by P. fluorescens or P. agglomerans), and by enhancing the relative competitive ability of the mixture, particularly at higher temperatures when E. amylovora has a growth rate advantage over P. fluorescens and P. agglomerans. Objective 2: We will 1) determine the frequency which viable cells of E. amylovora can be detected on mature fruit of DAnjou pear in growing districts of Washington and Oregon, and 2) evaluate in experiments the capacity of Erwinia amylovora to colonize or persist on pear fruit surfaces; apple fruit will be used as a comparative control in these experiments. Results of this study are expected to form a foundation for assessing the risk of introduction of fire blight into a new geographic region via shipments of commercial pear fruit.

Progress 10/01/04 to 09/30/09

Outputs
OUTPUTS: Experimental activities were conducted on the following objectives. 1. Integrated chemical and biological control of fire blight: We evaluated combinations of biological control agents with oxytetracycline or kasugamycin in orchard trials inoculated with an antibiotic-sensitive strain of Erwinia amylovora. 2. Early detection of the fire blight pathogen: Detection of DNA of Erwinia amylovora by a loop-mediated isothermal amplification protocol (LAMP) was evaluated in laboratory assays and field experiments. 3. Comparison of the epiphytic fitness of a pathogenic and an avirulent strain of Erwinia amylovora: We investigated the dynamics of growth suppression of E. amylovora by comparing the ability of virulent and avirulent strains of E. amylovora to compete with each other on stigmas of pear and apple, and to compete with a co-inoculated mixture of effective bacterial antagonists. 4. Evaluation of likelihood of co-occurrence of Erwinia amylovora with mature fruit of winter pear: Over a four year period, we evaluated the potential for co-occurrence of E. amylovora with mature symptomless winter pear fruit by inoculation experiments and by survey of commercial orchards. 5. Understanding impacts of blackberry rust in the Pacific Northwest: The following subobjectives were addressed. a) Determine when infection cycle of Phragmidium violaceum is initiated in spring; b) identify the kind of weather and host developmental stages that allow for initial host infection; c) develop an efficient chemical control program; d) examine the effects leaf wetness and temperature interactions on the infection frequency of P. violaceum. Workshop held: Convened the '11th International Workshop on Fire Bight', Portland, OR, August 2007. The workshop was attended by 108 international scientists. We made five research presentations at this meeting (see Abstracts). Dissemination: Management of blackberry rust, N. Willamette Horticultural Soc., Wilsonville,OR, Jan. 2007; Integrated control of fire blight; Orchard Pest and Disease Management Conference, Portland, OR, January 2007; Understanding the significance of the new rust on blackberry,Orchard Pest and Disease Management Conference, January 2007; Charactering risk of the fire blight pathogen to associate with healthy pear fruit; Pear Research Review, Hood River, OR, February 2007; Overview of disease concerns in caneberry production,Raspberry Blackberry Preseason Workshop, Aurora, OR,February 2007. PARTICIPANTS: Individuals: K. Johnson (principle investigator); Virginia Stockwell (assistant professor senior research); Teresa Sawyer (senior faculty research assistant); Todd Temple (faculty research assistant). Partner Organizations: Oregon State University Extension Service, USDA ARS, Fresh Pear Committee, Washington Tree Fruit Research Commission, PNW Center for Small Fruits Research, Oregon Raspberry and Blackberry Commission. Collaborators: Larry Pusey, USDA ARS Wenatchee; Walt Mahaffee, USDA ARS Corvallis; Tim Smith, WSU Extension, Wenatchee; Steve Castagnoli, OSU Extension, Hood River; Diane Kaufman, OSU Extension, N. Willamette, AREC. Training and professional development: a) see 'Dissemination' above;, b) K. Johnson teaches 'Introductory Plant Pathology' annually to 55 undergraduates and 10 graduates students; K. Johnson co-teaches 'Plant Disease Management' every other year to 10-12 graduate students. TARGET AUDIENCES: This project generates both basic and applied knowledge related to the biology and management of diseases that affect fruit crops grown in western Oregon. The target audience for applied research results includes: growers, farm advisors, extension specialists/agents, and crop consultants in the western region of the United States. The target audience for basic research results includes: scientists, regulators, and policy makers (national and international) who have an interest in the crop diseases and specific objectives undertaken in our research. PROJECT MODIFICATIONS: We continue to address fundable questions and objectives that relate to mitigating the impacts of diseases of fruit crops grown in western Oregon.

Impacts
Changes in knowledge: 1. Integrated chemical and biological control of fire blight: Biological and chemical methods of fire blight suppression appear to be complimentary, and consequently, an integrated strategy consisting of a biological control agent sprayed early in bloom, followed by oxytetracycline or kasugamycin treatment at mid- to late bloom provides improved disease control with a reduced number of antibiotic applications. Nonetheless, an integrated biological and chemical strategy involving kasugamycin requires further investigation to determine the feasibility of selecting biological agents with greater tolerance to this material, and within the chemical component, to evaluate mixtures of antibiotics where kasugamycin is applied at a lower rate. 2. Early detection of the fire blight pathogen: A loop-mediated isothermal amplification protocol (LAMP) represents a sensitive, low cost method for detection of E. amylovora. A LAMP assay can be subjected to quantitative monitoring of DNA amplification, and may be adapted for use in the field. When coupled with disease forecasting models, the ability to rapidly detect epiphytic populations of E. amylovora with LAMP could improve fire management. 3. Comparison of the epiphytic fitness of a pathogenic and an avirulent strain of Erwinia amylovora: Results were consistent with the hypothesis that virulent E. amylovora modifies the epiphytic habitat presented by the stigma through the expression of pathogenesis-related genes, which increases resources available to itself and coincidentally to nonpathogenic competitors. The degree of biological control achievable with an avirulent strain of E. amylovora likely is limited by its inability to utilize the stigmatic habitat to the same degree as a virulent strain. 4. Evaluation of likelihood of co-occurrence of Erwinia amylovora with mature fruit of winter pear: We conclude that epiphytic E. amylovora has similar survival characteristics on both pear and apple fruit, that it is not an endophytic within mature symptomless pear fruit, its presence is exceptionally rare on commercially-produced fruit, and that epiphytic survival of E. amylovora through a postharvest chilling period is unlikely given the unrealistically high population size required for persistence. 5. Understanding impacts of blackberry rust in the Pacific Northwest: We determined that the blackberry rust pathogen is very sensitive to environmental conditions during the transition from the overwintering phase (in teliospores) to the active phase (as infections producing urediniospores). The degree to which the pathogen can make this transition determines whether or not the disease will be important in a given season. Delayed dormant treatments with lime sulfur significantly impact this transition; the developed weather-based infection models aid timing of early season scouting efforts and fungicide treatments.

Publications

  • Temple, T. N., Stockwell, V. O., Pusey, P. L., and Johnson, K. B. 2007. Evaluation of likelihood of co-occurrence of Erwinia amylovora with mature fruit of winter pear. Phytopathology 97:1263-1273.
  • Temple, T.N., Stockwell, V.O., Pusey, P.L. and Johnson, K.B. 2007. Evaluation of likelihood of co-occurrence of Erwinia amylovora with mature fruit of winter Pear. (Abstract) 11th International Workshop on Fire Bight, Portland, OR, August 2007.
  • Temple, T.N., Stockwell, V.O., and Johnson, K.B. 2007. Development of a rapid detection method for Erwinia amylovora by loop-mediated isothermal amplification (LAMP). (Abstract) 11th International Workshop on Fire Bight, Portland, OR, August 2007.
  • Johnson, K.B., Stockwell, V.O., and Temple, T.N. 2007. Evaluation of kasugamycin as a component of an integrated biological and chemical strategy for suppression of blossom blight. (Abstract) 11th International Workshop on Fire Bight, Portland, OR, August 2007
  • Johnson, K.B., Sawyer, T.L., Stockwell. V.O., and Temple, T.N. 2007. Comparison of the epiphytic fitness of a pathogenic and an avirulent strain of Erwinia amylovora on pear and apple flowers as it relates to biological control. (Abstract) 11th International Workshop on Fire Bight, Portland, OR, August 2007.
  • Stockwell, V.O. Temple, T.N., Johnson, K.B., and Loper, J.E. 2007. Integrated control of fire blight. (Abstract) 11th International Workshop on Fire Bight, Portland, OR, August 2007.


Progress 01/01/06 to 12/31/06

Outputs
Objective 1. Antagonistic, beneficial bacteria are being investigated for their ability to suppress fire blight. Previously, we found that Pseudomonas fluorescens A506 produces an extracellular protease that inactivates antibiotics of the antagonist Pantoea agglomerans C9-1. Using a mutant of A506 (A506 AprX-) deficient in extracellular protease, we have observed that mixtures of A506 AprX- and C9-1 reduced the incidence of fire blight to levels surpassing control with oxytetracycline alone. Currently, we are investigating what we term an integrated strategy, which is one treatment of A506 AprX- with C9-1 followed by one oxytetracycline treatment. In orchard trials in 2005 and 2006, the integrated strategy was similar to the long term average of two applications of streptomycin. Objective 2. This objective is evaluating the potential for E. amylovora to co-occur with mature, symptomless fruit of winter pears grown in the Pacific Northwest. This potential has led to phytosanitary concerns that restrict the export of Northwest-grown winter pears into countries where fire blight does not occur. In this multi-year study, four sub-objective were invegated: 2.1 Evaluate capacity of E. amylovora to colonize or persist on healthy pear fruit surfaces; 2.2 Determine if E. amylovora can be detected in mature (apparently disease-free) symptomless dAnjou pear fruit on trees diseased with fire blight; 2.3 Estimate incidence of contamination of E. amylovora on commercially-produced, mature symptomless dAnjou pear fruit, and 2.4 Evaluate postharvest survival of E. amylovora on calyx ends and in micro-wounds of mature symptomless dAnjou pear fruit. Overall results indicate that E. amylovora has a very low potential to be associated (on or in) mature symptomless winter pear fruit, and that the risk of association is no different than the very low risk associated with mature symptomless apple fruit. Objective 3. Blackberry rust, caused by the pathogen Phragmidium violaceum was first confirmed in western Oregon in June 2005. The rust is already impacting the productivity of some commercial blackberry plantings. Fields experiments were initiated at two locations in western Oregon to evaluate appropriate timing and application intervals of fungicides. Fungicides treatments provided excellent control of blackberry rust in 2006. Lime sulfur applied as a delayed dormant (early April) apparently provided excellent suppression of teliospore germination. Growth chamber experiments determined the effects of temperature and leaf wetness duration on infection of blackberry by urediniospores of P. violaceum. The resulting models will be used to forecast infection infection events, particularly in April and early May when cold or intermittent wetness may be insufficient for infection to occur. Similarly, a rotational trap plant study involving 600 potted blackberry plants was initiated and completed at two locations in western Oregon. Specific infection events were identified in this study. Decision rules based on these results will be field tested in 2007.

Impacts
Fire blight caused by Erwinia amylovora is the most serious bacterial disease of pear and apple in many regions of the world. In North America, antibiotics have been used for fire blight suppression, but resistance in the pathogen to these chemicals has reduced the effectiveness of antibiotic treatment. Selected strains of nonpathogenic, bacterial epiphytes provide suppression of the blossom blight phase of fire blight. Our results are demonstrating that biological control of fire blight can be enhanced and can become a reliable and widely used management strategy provided that cost-effective formulations of the selected biocontrol agents can be developed. Our results continue to add to the base of knowledge concerned with epidemiology of bacterial diseases of plants and the efficiency of control. In addition, our risk assessment project concerned with the low likelihood of association of the fire blight pathogen with mature, symptomless pear fruit has the potential to increase exports of this commodity. Blackberry rust represents a new and important problem for the Pacific Northwest's $36 million blackberry industry, with the full impact of the disease expected to occur in future years. Because this is a new disease, very little is known about its biology and management under PNW conditions. Gray mold impacts dozens of fruit, vegetable and ornamental crops grown in western Oregon. Management of this disease could be improved with greater knowledge of spore production and movement within the region.

Publications

  • Johnson, K.B., Sawyer, T. L., and T. N. Temple. 2006. Rates of epiphytic growth of Erwinia amylovora on flowers common in the landscape. Plant Dis. 90:1331-1336.


Progress 01/01/05 to 12/31/05

Outputs
Objective 1. We continue to investigate fire blight suppression by beneficial bacteria optimized for compatibility of their biological mechanisms. Previously, we found that Pseudomonas fluorescens A506 produces an extracellular protease that inactivates antibiotics of the antagonist Pantoea agglomerans C9-1. Using a mutant of A506 (A506 AprX-) deficient in extracellular protease, we have observed that mixtures of A506 AprX- and C9-1 reduced the incidence of fire blight to levels surpassing control with oxytetracycline alone . Currently, we are investigating what we term an integrated strategy, which is one treatment of A506 AprX- with C9-1 followed by one oxytetracycline treatment. In three 2005 orchard trials, the integrated strategy was similar to the long term average of two applications of streptomycin. Objective 2. This objective is evaluating the potential for E. amylovora to be associated with mature, symptomless fruit of winter pears grown in the Pacific Northwest. This potential has led to phytosanitary concerns that restrict the export of Northwest-grown winter pears into countries where fire blight does not occur. In a multi-year study initiated in 2004, the following four sub-objectives are being investigated: 2.1 Evaluate capacity of E. amylovora to colonize or persist on healthy pear fruit surfaces; 2.2 Determine if E. amylovora can be detected in mature (apparently disease-free) symptomless dAnjou pear fruit on trees diseased with fire blight; 2.3 Estimate incidence of contamination of E. amylovora on commercially-produced, mature symptomless dAnjou pear fruit, and 2.4 Evaluate postharvest survival of E. amylovora on calyx ends and in micro-wounds of mature symptomless dAnjou pear fruit. Results to date indicate that E. amylovora has a very low potential to be associated (on or in) mature symptomless winter pear fruit, and that the risk of association is no different than the very low risk associated with mature symptomless apple fruit. Objective 3. Blackberry rust, caused by the pathogen Phragmidium violaceum was first confirmed in western Oregon in June 2005. The rust is already impacting the productivity of some commercial blackberry plantings. Fungicide trials were initiated in fall 2005, with the goal of developing a chemical control program for the 2006 season. Epidemiological studies are being planned for the 2006 season to better understand when the pathogen becomes active in spring, and its potential impact on both cultivated and weedy blackberry hosts. Objective 4. Studies were initiated in summer 2005 to develop a PCR-based method for quantification of spore loads of the gray mold pathogen, Botrytis cinerea, on the surfaces of plant hosts grown in western Oregon. Snap bean and blackberry plants were sampled periodically through the summer, and spore loads on these surfaces were measured by dilution plating. DNA was extracted from recovered spores, and PCR-based methods are being evaluated to estimate the amount of Botrytis DNA in these samples.

Impacts
Impact : Fire blight caused by Erwinia amylovora is the most serious bacterial disease of pear and apple in many regions of the world. In North America, antibiotics have been used for fire blight suppression, but resistance in the pathogen to these chemicals has reduced the effectiveness of antibiotic treatment. Selected strains of nonpathogenic, bacterial epiphytes provide suppression of the blossom blight phase of fire blight. Our results are demonstrating that biological control of fire blight can be enhanced and can become a reliable and widely used management strategy provided that cost-effective formulations of the selected biocontrol agents can be developed. Our results continue to add to the base of knowledge concerned with epidemiology of bacterial diseases of plants and the efficiency of control. In addition, our risk assessment project concerned with the low likelihood of association of the fire blight pathogen with mature, symptomless pear fruit has the potential to increase exports of this commodity. Blackberry rust represents a new and important problem for the Pacific Northwest's $36 million blackberry industry, with the full impact of the disease expected to occur in future years. Because this is a new disease, very little is known about its biology and management under PNW conditions. Gray mold impacts dozens of fruit, vegetable and ornamental crops grown in western Oregon. Management of this disease could be improved with greater knowledge of spore production and movement within the region.

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. (Abstract) Phytopathology 95:100.
  • Temple, T.N., Stockwell,, V.O., and Johnson, K.B. Culturable populations of Erwinia amylovora do not persist on mature symptomless winter pear fruit. APS Pacific Division Annual Meeting, Portland, OR June 2005.
  • Temple, T.N., Stockwell V.O., Johnson, K.B., and Loper, J.E. 2005. Bioavailability of iron to Pseudomonas fluorescens Strain A506 on flowers of pear. Acta Hortic. (in press).
  • Stockwell, V.O., Johnson, K.B., and Johnson, V.W. 2005. Colonization of flowers by Pseudomonas fluorescens A506 formulated in a biopolymer gel. Acta Hortic. (in press).