Location: Horticultural Crops Research
2009 Annual Report
We manually updated the existing annotation of approximately 70% of the genome of the biocontrol agent Pseudomonas fluorescens Pf-5, which serves as an important resource for the scientific community.
We completed microarray experiments identifying genes expressed by Pf-5 on surfaces of pea seed under the control of two global regulators, GacA and RpoS.
Using a collection of mutants of Pf-5 with stacked mutations in 10 antibiotic biosynthesis pathways, we identified the antibiotics responsible for Pf-5’s suppression of Fusarium spp. and Pseudomonas syringae, and its phytotoxicity to rice and wheat.
We completed field experiments demonstrating that plastic shelters provide an excellent cultural control method for suppression of bacterial blight of lilac caused by Pseudomonas syringae.
A plant-parasitic nematode survey of blueberries was continued in Washington and expanded to include Oregon. During a survey conducted in 2008, it was discovered that Pratylenchus spp. was present in > 50% of the fields surveyed. However, in a greenhouse pathogenicity study where six blueberry genotypes were exposed to P. penetrans, very little or no reproduction of this nematode occurred on these genotypes. To determine where and when Pratylenchus spp. are associated with blueberry plants, a more in-depth sampling was undertaken to include blueberry roots and rhizosphere soil as well as weed roots.
Field microplots (a pot-in-pot system) were established to study the effects of the ring nematode, Mesocriconema xenoplax, on physiology and growth ‘Pinot noir’ grapevines. The first impact of M. xenoplax on grape production that we detected was fewer fine roots but higher root-soil respiration in self-rooted vines and vines on ‘3309C’ rootstock than in tolerant or resistant rootstocks in 2007. By 2008, M. xenoplax no longer altered root-soil respiration, but affected aboveground performance of the vines.
A greenhouse study was conducted and is being repeated to study the pathogenicity of plant-parasitic nematodes on a range of blueberry genotypes. All genotypes except for rabbit-eye blueberry were excellent hosts for Paratrichodorus renifer.
Surveys of Verticillium dahliae in woody ornamental nurseries in Oregon are continuing. Evaluation of methods for isolation of pure cultures of V. dahliae are in progress. Greenhouse studies to evaluate suitable inoculation methods are in progress.
Efficacy of low doses of four alternative fumigants in reducing Pythium populations was compared to populations from nonfumigated plots and plots treated with methyl bromide. Three methods for isolation of Pythium species from soils were selected and have been used throughout the study. Quantification of prefumigation and 2 postfumigation Pythium populations have been completed from 3 forest nurseries. Isolates have been put into a culture collection and are currently being identified to species. Pathogenicity studies on Dougfir have been initiated.
Loper, J.E., Bruck, D.J., Pechy-Tarr, M., Maurhofer, M., Keel, C., Gross, H. 2008. Genomic Analysis of Secondary Metabolite Production by Pseudomonas fluorescens Pf-5. In: Lorito, M., Woo, S.L., Scala, F., editors. Biology of Molecular Plant-Microbe Interactions. Volume 6. [CD-ROM]. St. Paul, MN. International Society for Molecular Plant-Microbe Interactions. Chapter 101.
Mavrodi, D.V., Loper, J.E., Paulsen, I.T., Thomashow, L.S. 2009. Mobile genetic elements in the genome of the beneficial rhizobacterium Pseudomonas fluorescens Pf-5. BMC Microbiology. 9:8.
Stockwell, V., Hockett, K., Loper, J.E. 2009. Role of RpoS in stress tolerance and environmental fitness of the phyllosphere bacterium Pseudomonas fluorescens 122. Phytopathology. 99:689-695.
Zasada, I.A., Masler, E.P., Rogers, S.T., Halbrendt, J.M. 2009. Behavioral response of Meloidogyne incognita to benzyl isothiocyanate. Nematology. 11:603-610.
Meyer, S.L., Rice, C., Zasada, I.A. 2009. DIBOA: Fate in Soil and Effects on Root-knot Nematode Egg Numbers. Soil Biology and Biochemistry. 41:1555-1560.
Hagen, M., Stockwell, V., Whistler, C., Johnson, K.B., Loper, J.E. 2009. Stress tolerance and environmental fitness of Pseudomonas fluorescens A506, which has a mutation in rpoS. Phytopathology. 99:689-695.