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United States Department of Agriculture

Agricultural Research Service

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Location: Physiology and Pathology of Tree Fruits Research

2009 Annual Report

1a. Objectives (from AD-416)
The fundamental goal of this research program is the development of sustainable methods fro the control of soilborne diseases of fruit trees. Thus, the objectives are to define the mechanism(s) of action for brassicaceae seed meals in the control of the pathogen/parasite complex which incites orchard replant disease, and develop and evaluate in the field novel formulations or integrated systems to attain the necessary spectrum of pathogen/parasite suppression for control of orchard replant disease.

1b. Approach (from AD-416)
This program will develop a systems approach to disease management which exploits the biological resources resident to orchard ecosystems and utilizes minimal inputs beyond that commonly employed during orchard renovation or management. This will be achieved through acquiring an understanding of the biological and chemical mechanisms involved in the brassicaceae seed meal induced suppression of the pathogen complex contributing to apple replant disease. New tools will be developed to efficiently monitor fungal community structure in these soils to garner a more complete understanding of the functional elements contributing to disease suppression and the temporal nature of the response. Enhanced efficacy of bio-active plant residues for the control of soilborne pathogens will be obtained by clarifying the role of soil microbial communities in eliciting the inhibitory activity of these plant tissues. Information from these studies will be utilized to develop and field validate biologically sustainable management strategies for control of replant diseases in conventional and organic production systems. Replacing 5350-22000-012-00D (11/07).

3. Progress Report
Orchards were established on replant sites to evaluate the efficacy of individual and composite mustard seed meal amendments for the control of apple replant disease (ARD). All seed meals when utilized individually in concert with the highly susceptible apple root stock M26 failed to provide ARD control to the level attained with pre-plant soil fumigation based upon growth increment and an assessment of the pathogen population colonizing tree roots. However, when used in concert with a post-plant application of mefenoxam, all seed meals dramatically improved tree growth and yield relative to the control, and some yields were equivalent to Telone-C17 soil fumigation. Mefenoxam alone did not improve tree growth or provide significant disease control. A novel seed meal formulation when applied in an organic orchard replant site significantly enhanced growth of ‘Gala’ apple on the highly susceptible rootstock M26 relative to the non-treated control and to date growth in response to this amendment is equivalent to pre-plant soil fumigation. In this instance, the seed meal formulation provided effective disease control without a post-plant application of mefenoxam. A population of bacteria which are thought to function in the mustard seed meal-induced control of root rot were analyzed in an attempt to determine the mechanism responsible for disease control. The bacteria initially isolated from roots of apple grown in seed meal amended soils elicited a range of responses ranging from suppression to promotion of root rot. Screening of a number of bacterial isolates indicated many with high production of nitric oxide gas provided disease control. Different mustard seed meals have dramatically different effects on the composition of bacterial populations native to orchard soils. Thus, knowledge of these diverse interactions between the seed meal-modified bacterial community and apple will be of value in managing this bacterial population for the suppression of disease. Mustard seed meal amendments increased populations of other organisms known as protozoa that prey on beneficial bacteria that suppress root rot. Studies demonstrated that some beneficial bacteria produce proteins that protect them against protozoan grazing.

4. Accomplishments
1. Bacterial anti-predation mechanism. Certain soil dwelling bacteria produce cyclic lipopeptides (CLPs) that inhibit plant pathogenic fungi and provide biological control disease. Researchers at the Tree Fruit Research Laboratory in Wentachee, Washington, in collaboration with a partner at Wageningen University, the Netherlands, examined whether the production of cyclic lipopeptides served as a means by which bacteria could prevent predation by soil organisms, including protozoa, that feed on bacteria. CLP production was shown to be essential for the survival of producing bacterium and protozoa resulted in altered gene expression in the bacterium including increased production of the cyclic lipopeptides. This research indicates that selection of potential biocontrol organisms that produce anti-predator compounds will survive longer in soil environments, which will ensure superior control of soil borne plant diseases.

5. Significant Activities that Support Special Target Populations
Contacts with orchardists and nursery operators regarding non-fumigant alternatives for control of soilborne plant pathogens, and in particular apple replant disease, occur on a regular basis. Contacts included the establishment of a demonstration in a small family operated organic orchard, interaction with growers at industry sponsored meetings, and frequent contact with small growers and nursery operators around the nation via electronic or voice communication. Information provided to growers is based upon findings from this project concerning the development of novel non-fumigant methods for the management of replant disease that can be utilized in organic and conventional orchard production systems.

Review Publications
Mazzola, M., Brown, J., Zhao, X., Izzo, A., Fazio, G. 2009. Interaction of brassicaceous seed meal and apple rootstock on recovery of Pythium spp. and Pratylenchus penetrans from roots grown in replant soils. Plant Disease. 93:51-57.

Izzo, A., Mazzola, M. 2009. Hybridization of an ITS-based macroarray with ITS community probes for characterization of complex communities of fungi and fungal-like protists. Mycological Research. 113:802-812.

Pusey, P.L., Stockwell, V.O., Mazzola, M. 2009. Epiphytic bacteria and yeasts on apple blossoms and their potential as antagonists of Erwinia amylovora. Phytopathology. 99:571-581.

Last Modified: 06/23/2017
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