Location: Horticultural Crops Research
2012 Annual Report
Under objective 1A, we demonstrated and transferred technology for the detection of airborne inoculum for grape powdery mildew and the use of this information to time fungicide applications. The research resulted in the savings of 2.3 fungicide applications on average over the past 5 years in commercial vineyards. We are extending this research by developing methods for growers to perform their own molecular detection assays.
Under objective 1B, we described the migration patterns of Phytophthora ramorum. We demonstrated that the EU1 clonal lineage emerged via migration from Europe to the Pacific Northwestern United States and Canada.
Under objective 1C, progress has been made in terms of documenting the existence of two distinct small RNA classes describing previously unknown genetic mechanisms in the genus Phytophthora. We have characterized biogenesis effectors involved in processing of small RRNAs.
In objective 1D, we examined the impact of leaf wetness and temperature on the epidemiology of blackberry rust, grape powdery mildew, and ramorum blight. These data were then used to develop or refine disease forecasting models or best management practices. For blackberry rust, we demonstrated that most growing seasons will not be conducive to disease development. For grape powdery mildew, modifications to the Gubler/Thomas infection risk model were developed and tested in Oregon and California in collaboration with the research scientists. These results indicate that our model rules for the impact of temperatures above 30C (86F)reduce pesticide usage without impacting disease development, thus further reducing fungicide usage.
Under objective 2, variation in resistance in viburnum and lilac to P. ramorum has been characterized, and scientists continue to study the diversity of Phytophthora spp. in nursery environments as a function of plant genotype, season, and cultural practice.
Under objective 3, we identified the errors associated with weather data interpolation and demonstrated that these errors have minimal impact on disease management decisions for grape powdery mildew. The larger collaborative group has demonstrated similar results for multiple pathosystems.
Vercauteren, A., Larsen, M.M., Goss, E.M., Grunwald, N.J., Maes, M., Heungens, K. 2011. Identification of new polymorphic microsatellite markers in the NA1 and NA2 lineages of Phytophthora ramorum. Mycologia. 103:1245-1249.
Cardenas, M.E., Tabima, J., Fry, W.E., Grunwald, N.J., Bernal, A.J., Restrepo, S.O. 2012. Defining species boundaries in the genus Phytophthora: the case of Phytophthora andina. A response to “Phytophthora andina sp. nov., a newly identified heterothallic pathogen of solanaceous hosts in the Andean highlands." Plant Pathology. 61(2):215-220.
Grunwald, N.J., Garbelotto, M., Goss, E.M., Heungens, K., Prospero, S. 2012. Emergence of the sudden oak death pathogen Phytophthora ramorum. Trends in Microbiology. 20:131-138.
Pfender, W.F., Gent, D.H., Mahaffee, W.F., Coop, L.B., Fox, A. 2011. Decision Aids for Multiple-Decision Disease Management as Affected by Weather Input Errors. Phytopathology. 101:644-653.
Pfender, W.F., Gent, D.H., Mahaffee, W.F. 2012. Sensitivity of disease management decision aids to temperature input errors associated with out-of-canopy and reduced time-resolution measurements. Plant Disease. 96:726-736.