Theodore M. DeJong, Pomologist
Ph.D., University of California, Davis, 1977

Phone (530) 752-1843    FAX (530) 752-8502
E-mail: tmdejong@ucdavis.edu

Department of Pomology
University of California, Davis

Areas of Specialty:
Environmental plant physiology, photosynthetic efficiency of tree crops relative to the utilization of nitrogen, water, and solar radiation

Research Statement
The research in my laboratory is primarily field-oriented and directed toward gaining a better understanding of the environmental physiology of tree crops. We are interested in elucidating the factors that determine, enhance, or limit both the photosynthetic efficiency of fruit trees and the allocation of assimilates toward various fruit tree components. On the basis of this research we are attempting to develop improved, physiologically sound, horticultural practices that increase production efficiency of tree crops.

The primary approach that we have been using in these studies is the development of a computer model that simulates seasonal tree carbon assimilation and partitioning on a daily basis. This model is based on simple concepts of carbon supply and demand for maintenance, growth and storage functions of various organs. The concepts developed in the model permit new approaches to studying the integrated effects of environmental stresses such as temperature, water and nutrients on canopy photosynthesis and partitioning of assimilates to vegetative vs. reproductive plant parts. Some of the horticultural systems that we are currently evaluating are: various conformations of high density hedgerow orchards, optimization of fruit thinning practices, adjustments in fertilizer and irrigation application rates and timing, and rootstock selection or tree size control. The crops that we are most closely associated with are peaches, nectarines, plums, and prunes.

Selected Publications

1997.  Berman, M.E., and T.M. DeJong.   Diurnal patterns of stem extension growth in peach (Prunus persica): Temperature and fluctuations in water status determine growth rate. Physiologia Plantarum 100:361-370.

1997.  Berman, M.E., and T.M. DeJong.  Crop load and water stress effects on daily stem growth in peach (Prunus persica). Tree Physiology 17:467-472.

1997.  Saenz, J.L., T.M. DeJong, and S..A. Weinbaum.  Nitrogen stimulated increases in peach yields are associated with extended fruit development period and increased fruit sink capacity. Journal of the American Society for Horticultural Science 122(6):772-777.

1996.  Berman, M.E., and T.M. DeJong.  Water stress and crop load effects on fruit fresh and dry weights in peach (Prunus persica). Tree Physiology 16:859-864.

1996.  Retzlaff, William, William W. Barnett, Larry E. Williams, and Theodore M. DeJong.  Ozone air pollution increases spray oil phytotoxicity. California Agriculture 50(2):21-23.