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United States Department of Agriculture

Agricultural Research Service


Location: Horticultural Crops Research

2010 Annual Report

1a. Objectives (from AD-416)
Evaluate the etiology and epidemiology of soilborne diseases of small fruit and nursery crops and the biology of causal pathogens. Develop, evaluate, and enhance strategies for the management of soilborne diseases of horticultural crops. Develop knowledge of mechanisms contributing to biological control of soilborne plant diseases.

1b. Approach (from AD-416)
Dose-response relationships between propagule density in irrigation water and disease. Identification of factors influencing pathogen dispersal and disease spread among containers in a nursery. A systematic survey of blueberry fields throughout the PNW will be conducted to identify nematode pathogens. Greenhouse and microplot experiments will be employed to determine the effects of a range of population densities of nematode species found in the survey on the health of a widely planted blueberry cultivar. Test the Electrocatalytic Oxidation/precipitation (EO) method. Identify factors influencing the efficacy of the EO method. Test the EO method in an experimental nursery setting. Use the recently-described genomisotopic approach to purify the two cryptic metabolites from cultures of Pf-5. Derive mutants of Pf-5. Assess the role of novel metabolites in biological control. Test toxicity of the purified metabolites. Evaluate gene expression by Pf-5 on seed surfaces using RNA isolation, labeling and hybridization. Characterize the nutritional composition of seed exudates. Generate derivatives of Pf-5 with mutations in selected genes. Test mutants for spermosphere colonization and biological control of Pythium damping off. Replaced 5358-12220-001-00D (3/03). FY03 $73,538 Program Increase. FY06 $133,650 Program Increase (memo #44). Replacing 5358-12220-002-00D (3/07). FY09 perm F/T from 5358-21000-037-00D (6/08).

3. Progress Report
The genomic sequences of seven strains of Pseudomonas spp. that suppress plant disease were compared and mined to identify genes with potential roles in biological control. Type III secretion systems were found in five genomes and insect toxin genes were found in all seven genomes. Many orphan gene clusters were identified, providing avenues for the future discovery of novel natural products, including those contributing to biocontrol of plant disease. Pseudomonas fluorescens Pf-5 was found to be toxic to the insect Drosophila melanogaster when injested. Commercial and experimental plantings of blueberry were monitored over a nine month period for populations of P. syringae and symptoms of die back and leaf spot caused by the pathogen. Observations and quantitative data are being integrated to develop knowledge of the population dynamics and life cycle of this pathogen on blueberry. We completed analysis of environmental data for field experiments demonstrating that plastic shelters provide an excellent cultural control method for suppression of bacterial blight of lilac caused by Pseudomonas syringae. Final data for the large-scale, replicated methyl bromide alternatives field trial were collected and analyzed. Efficacy of a new, low-permeability plastic to retain fumigants was as effective at disease control as standard plastic. Four lower-dose fumigant chemistries were as effective at disease control as standard methyl bromide applications. Pathogen impact to seedling production was quantified; approximately 8-17% additional seedling loss if fumigation is not used. Methods for estimating pathogen populations were evaluated and the best method was selected for future work. Costs of fumigant alternatives were calculated and compared to methyl bromide standard. Final report for project was prepared. Pathogenicity studies of Pythium species on Douglas-fir are continuing. A new field trial to evaluate biocontrol agents is beginning. Surveys of Verticillium dahliae in woody ornamental nurseries are continuing. Greenhouse studies to evaluate host response to different amounts of the pathogen are in progress. To determine where and when root lesion nematodes, Pratylenchus spp., are associated with blueberry plantings, an in-depth sampling effort was undertaken. Over 50% of the blueberry and weed samples contained root lesion nematodes; however, population densities of this nematode were 4 to 8 times higher in weed roots than blueberry roots. Initial results indicate that more than one species of root lesion nematode is present in PNW blueberry fields. A microplot trial was established to evaluate the impact of the root-knot nematode, Meloidogyne hapla, on grape rootstock establishment and productivity. Currently little is known about the relative resistance/susceptibility of rootstocks to this nematode. Over the next four to five years the following data will be collected: nematode population densities in soil and roots, vine establishment, pruning weights, yield, and vine nutrient status.

4. Accomplishments
1. Pythium species of Pacific Northwest forest nurseries. Pythium species are economically important soilborne pathogens that stunt or kill tree seedlings produced for reforestation. However, the identity of these species in forest nurseries has been largely ignored. ARS researchers at Corvallis, OR surveyed field soils at three nurseries and discovered 19 Pythium species. Each nursery was associated with a different predominate species. The results are significant because the use of nonselective disease management practices, such as fumigation, are becoming increasingly restricted by state and federal regulations. Knowledge of pathogen identity is the first step required to develop more targeted and integrated pathogen control measures.

2. The impact of ring nematode (Mesocriconema xenoplax) on grapevines grafted to different rootstocks. The ring nematode (Mesocriconema xenoplax) is an economically important, common root parasite of grapevines worldwide, however, little is known about how and when this nematode affects vine growth and productivity. ARS researchers in Corvallis, OR discovered that the first effect of this nematode on plant growth occurred below ground with decreased root growth, and that above-ground impact of the nematode on plant productivity was not apparent until the third year of the four-year study. In addition, the apparent ring nematode resistance of the rootstocks 101-14 and 420A broke down in year three, with only the rootstock 420A remaining highly resistant to the nematode. These results are significant because they will guide growers in rootstock selection and direct the timing of management practicing to minimize the impact of ring nematode on vine establishment and productivity.

Review Publications
Gross, H., Loper, J.E. 2009. Genomics of secondary metabolism in Pseudomonas spp. Natural Product Reports. 26:1408-46.

Walters, T.W., Pinkerton, J.M., Riga, E., Zasada, I.A., Particka, M., Yoshida, H., Ishida, H. 2009. Managing plant-parasitic nematodes in established red raspberry fields. HortTechnology. 19:762-768.

Stocking, L.A., Weil, R., Zasada, I.A., Momen, B., Sardanelli, S. 2010. Brassicaceous and rye cover crops altered free-living soil nematode community composition. Applied Soil Ecology. 45:1-12.

Buyer, J.S., Teasdale, J.R., Roberts, D.P., Zasada, I.A., Maul, J.E. 2010. Factors Affecting Soil Microbial Community Structure in Tomato Cropping Systems. Soil Biology and Biochemistry. 42:831-841.

Zasada, I.A., Meyer, S.L., Morra, M.J. 2010. Brassicaceous seed meals as soil amendments to suppress the plant-parasitic nematodes Pratylenchus penetrans and Meloidogyne incognita. Journal of Nematology. 41:221-227.

Hassan, K., Johnson, A., Shaffer, B.T., Ren, Q., Kidarsa, T.A., Elbourne, L.H., Hartney, S., Duboy, R., Goebel, N., Zabriskie, M.T., Paulsen, I.T., Loper, J.E. 2010. Inactivation of the GacA response regulator in Pseudomonas fluorescens Pf-5 has far-reaching transcriptomic consequences. Environmental Microbiology. 12(4):899-915.

Zasada, I.A., Halbrendt, J.M., Burelle, N.K., Lamondia, J., Mckenry, M.V., Noling, J. 2010. Managing Nematodes without Methyl Bromide. Annual Review of Phytopathology. 48:311-328.

Zasada, I.A., Pinkerton, J., Forge, T. 2010. Occurrence and distribution of plant-parasitic nematodes in Pacific Northwest blueberry production systems . International Journal of Fruit Science. 10:123-133.

Last Modified: 2/23/2016
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