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United States Department of Agriculture

Agricultural Research Service

Research Project: Exotic and Emerging Plant Diseases of Horticultural Crops

Location: Horticultural Crops Research

2013 Annual Report


1a.Objectives (from AD-416):
Objective 1: Describe the pathogen biology of exotic and emerging plant pathogens affecting horticultural crops. Objective 2: Apply knowledge of biology, ecology, and epidemiology of economically important plant pathogens to the development of improved integrated disease management approaches.


1b.Approach (from AD-416):
The biology of exotic, emerging, and re-emerging plant pathogens is either poorly understood or inadequate to enable economic and environmentally sustainable management. Objective 1: We will develop and test methods for monitoring pathogen dispersion and describe the evolutionary history, population structure, genetics, epidemiology, and ecology of these pathogens. Objective 2: This knowledge will then be used to develop decision support tools for producers of horticultural crops. Once an increased understanding of a pathogen’s biology has been developed, this knowledge needs to be translated into disease management strategies that are continually optimized and/or improved based on new knowledge. We will develop and improve disease management strategies for select pathogens affecting horticultural crops. While this objective cannot be achieved directly for quarantine pathogens (e.g. P. ramorum), concepts and approaches can be tested by using proxy pathosystems that are similar in the event of an exotic pathogen introduction or quarantines are lifted. In addition, development and improvement of integrated disease management strategies for endemic pathogens will improve our ability to respond to changing climatic conditions while enhancing the economic and sustainable production of horticultural crops.


3.Progress Report:
Objective 1A: We conducted routine analysis to determine population structure and emergence of new strains of Phytophthora ramorum by genotyping isolates received from new findings across the US using microsatellite genotyping. We have also sampled isolates of P. syringae and P. plurivora that are being characterized using genotyping-by-sequencing.

Objective 1C: We have compared the ability of different Phytophthora species to infect the host plant Rhododendron. Two pathogens, P. plurivora and P. syringae appear to be the most aggressive under warm and cold temperatures, respectively.

Objective 1D: We developed a novel spore trapping system that can be used to capture airborne spores released after specific temperature and wetness periods. We developed techniques to simulate grape bark wetting and drying that will allow for greater experimental control and flexibility than using grape trunks to experimentally manipulate overwintering conditions and test their impact on cleistothecia. These advances will allow us to better determine the exact conditions required for ascospore release and improve disease forecasting.

Objective 2A: We sampled foliar infections of Rhododendron to assess which species of Phytophthora are dominant. P. syringae and P. plurivora are the two dominant species causing foliar Phytophthora disease on Rhododendron in the Pacific Northwestern US.

Objective 2C: We demonstrated that leaf removal occurring as early as BBCH growth 53 did not reduce yield or grape quality but reduced severity powdery mildew and bunch rot. These results indicate the growers can pull leaves earlier in the season improve disease control without increasing production costs.

Objective 2D: We demonstrated that loop mediated isothermal amplification can be used by growers to detect the grape powdery mildew pathogen and time fungicide applications. The significantly lower capital costs and simplicity of the technique indicate that this tool could be commercially viable for disease management.


Review Publications
Parke, J.L., Grunwald, N.J. 2012. A systems approach for management of pests and pathogens of nursery crops. Plant Disease. 96(9):1236-1244.

Utro, F., Haiminen, N., Livingstone Iii, D., Cornejo, O.E., Royaert, S., Schnell, R.J., Motamayor, J.C., Kuhn, D.N., Parida, L. 2013. iXora1: exact haplotype inferencing and trait association. BioMed Central (BMC) Genetics. 14:48.

Faukner, J., Rawles, S.D., Proctor, A., Sink, T.D., Chen, R., Philips, H., Lochmann, R.T. 2013. The effects of diets containing standard soybean oil, soybean oil enhanced with conjugated linoleic acids, menhaden fish oil, or an algal docosahexaenoic acid supplement on channel catfish performance, body composition, sensory evaluation, and storage characteristics. North American Journal of Aquaculture. 75:252–265.

Fry, W.E., Mcgrath, M.T., Seaman, A., Zitter, T.A., Mcleod, A., Danies, G., Small, I.M., Myers, K., Everts, K., Gevens, A.J., Gugino, B.K., Johnson, S.B., Judelson, H., Ristaino, J., Roberts, P., Secor, G., Seebold, K., Snover-Clift, K., Wyenandt, A., Grunwald, N.J., Smart, C.D. 2013. The 2009 late blight pandemic in eastern USA – causes and results. Plant Disease. 97:296-306.

Berbegal, M., Perez-Sierra, A., Armengol, J., Grunwald, N.J. 2013. Evidence for multiple introductions and clonality in Spanish populations of Fusarium circinatum. Phytopathology. 103:851-861.

Gent, D.H., Mahaffee, W.F., Mcroberts, N., Pfender, W.F. 2013. The use and role of predictive systems in disease management. Annual Review of Phytopathology. 51:267-89.

Last Modified: 9/1/2014
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