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United States Department of Agriculture

Agricultural Research Service

Principal Investigators of CPGRU
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Kendra Baumgartner, Research Plant Pathologist

Phone: (530)754-7461   FAX: (530)754-7195



Dr. Baumgartner's research is focused on developing vineyard practices that reduce chemical inputs, while achieving production and quality demands. Her research on the epidemiology of Armillaria root disease in Californiavineyards led to the development of nonchemical control practices that enhance colonization of grapevine roots by naturally-occurring, beneficial root fungi, known as mychorrhizal fungi. Her research on mycorrhizal fungi includes basic studies into quantifying nutrient exchange among grapevines and vineyard cover crops connected by mycorrhizal networks. Dr. Baumgartner's research on Pierce's disease in the NorthCoastshows that two invasive weeds, periwinkle and Himalayan blackberry, may contribute to long-term survival of the pathogen, Xylella-fastidiosa, in areas with low overwinter survival of the sharpshooter vector. Her studies on weed control are aimed at developing integrated weed management strategies. She is working towards improving the application timing of alternative practices and learning how they can compliment conventional weed control programs.  

Kendra Baumgartner




Greg Browne, Research Plant Pathologist

Phone: (530)754-9351   FAX: (530)754-7195



Dr. Browne's research program examines the biology and integrated management of soilborne diseases that affect deciduous tree crops and strawberries. The research is designed to contribute to development of chemical, cultural, and biological alternatives to methyl bromide. A major focus of the lab is determining causes and practical control measures for Prunus replant disease (PRD), that causes stunting and replant failure in almond, peach, and other species of Prunusin absence of plant parasitic nematodes. Evidence to date suggests that PRD has biological cause(s), that it exhibits specificity between peach and grape, and that it can be managed using short-term cover crop rotations as well as several alternative pre-plant fumigants. Additional projects include evaluation of almond and walnut rootsocks and strawberry cultivars for resistance to Phytophthoraspp., evaluation of phosphonate treatments for prevention of perennial cankers and crown rot caused by Phytophthoraspp. on almond and walnut, and detection and genetic characterization of populations of   Phytophthoraspp. that affect these crops.     Greg Browne




Cai-Zhong Jiang, Plant Physiologist

Phone:   (530)752-7060   FAX:   (530)754-7195



Dr. Jiang's research project is on post-harvest biology and technology of floricultural/ornamental crops.   An array of research approaches will be used to develop sustainable production systems that enhance productivity while reducing loses due to post harvest disease, longevity and quality issues.   The project will focus on 1) To understand the molecular basis of plant senescence and abscission; 2) To address how environmental factors such as water, temperature and diseases, effect on the performance of ornamental crops; 3) To develop improved methods and technologies for harvesting, handling, pretreating and storing floricultural crops.   One of the basic research programs is the exploitation of virus-induced gene silencing (VIGS) to identify which transcription and regulatory factors that control floral senescence, abscission and other important agronomic traits.   This basic research may result in the development and commercialization of flowering plants with enhanced flower colors, improved disease, and stress tolerance and longer flower life time.   Such plants are of great interest to the horticulture industry and its consumers.  Cai-Zhong Jiang




Dan Kluepfel, Supervisory Research Plant Pathologist

Phone:   (530)752-1137   FAX:   (530)754-7195



Dr. Kluepfel's research program explores the interaction between plants and bacteria at the interface between roots and the surrounding soil called the rhizosphere. The aim of the research is to characterize both individual bacterial species and the microbial community which occupy the rhizopshere of important fruit and nut crops such as walnut, almonds and grapes and understand how they interact and communicate with their plant hosts. Toward this end, different model plant-bacteria systems are being examined.   In particular, the laboratory is examining, the behavior and pathogenecity of Agrobacterium tumefaciens, the cause of Crown Gall Disease, on walnut. In addition, a project to detect and characterize the bacterial pathogen, Brenneria rubrifaciens, that causes deep bark canker on walnut is underway. These projects are all supported by our effort to isolate and characterize all the bacterial genes whose expression is modulated by plant-root exudates during bacterial growth in the rhizosphere.   This information is being used to identify individual microbial species and/or microbial communities that are beneficial to plant health and antagonistic to disease causing pathogens in the soil in an effort to develop ecologically sustainable disease control methods employing naturally occurring soil bacteria. Dan Kluepfel



Andrew McElrone, Research Plant Physiologist

Phone:   (530) 754-9763   FAX:   (530)754-7195



Dr. McElrone's research focuses on the development of and evaluation of irrigation practices for vineyard systems that optimally produce grapes while minimizing water usage and negative environmental impacts.   Research efforts will focus on understanding of the effects of irrigation practices and water quality on environmental factors that may affect vine physiology, yield, and grape quality in different rootstock/scion combinations.   This research is expected to lead to irrigation practices that can be integrated with other sustainable vineyard practices to enhance the competitive ability of California's wine industry.   Dr. McElrone plans to apply his research experience in ecohydrology, whole tree sap flow, and root structure and physiology to address these research goals. Andrew McElrone



Kerri Steenwerth, Soil Scientist

Phone:   (530)752-7535   FAX:   (530)752-0382



Dr. Steenwerth's research goal is to develop ecological approaches for sustainable vineyard floor management and determine impacts of management practices on weeds, grapevines, soil microbial communities, and soil quality for Californiaviticulture as part of the Sustainable Viticulture program. In order to accomplish these goals, three objectives have been defined: 1) effects of vineyard floor practices on soil organic matter dynamics and grapevine health, 2) effects of weed management practices and soil disturbance on soil microbial communities, and 3) alternatives to traditional pre-emergent chemicals for weed control. These initial subject areas will be broadened to include such issues as off-site effects of management practices (i.e., erosion, dust production), interactions of cover crops and weed management practices with beneficial insects and pests, and identifying mechanisms for competition of weeds and cover crops with grapevines, especially in newly established vineyards. The program will also address economic costs of these various practices to identify those that enhance the competitive ability of California's wine industry. Kerri Steenwerth




Tom Tai, Research Geneticist

Phone:   (530)752-4342   FAX: (530)752-4631



The goal of Dr. Tai's research program is to develop improved rice germplasm for temperate environments and solve problems facing the U.S.rice industry through the application of molecular genetics and genomics approaches. California's temperate climate is unique among U.S.rice growing states and presents distinct challenges to the rice industry here. Environmental concerns have also resulted in changes in production practices that threaten the long-term sustainability of rice farming. To address these problems, a better understanding of the genetic basis of important agronomic traits is needed and new sources of genetic material for incorporation into adapted cultivars must be identified. Research topics include seedling and reproductive stage cold tolerance, resistance to stem rot disease, nutritional quality of rice, and development of enhanced germplasm for use in breeding improved temperate rice varieties. This research contributes to the development of new cultivars by state breeding programs to ensure that the rice industry in Californiacontinues to be competitive. Tom Tai




Jerry Uyemoto, Research Plant Pathologist

Phone:   (530)752-0309   FAX:   (530)754-7195


Dr. Uyemoto's research focuses on the etiology and biology of grapevine virus diseases including virus characterization and development of assays and control. Dr. Uyemoto has projects with stone fruits on almond leaf scorch incitant Xylella fastidiosa; necrotic union of pluot trees (cause unknown); and stunt of Tieton sweet cherry trees (cause unknown).  With grapevines, new viruses are detected using a differential set of hybrid rootstocks.  In addition, new stem markings attributed to graft-transmissible pathogens are being investigated. All are lethal conditions. Jerry Uyemoto





Takao Kasuga, Molecular Geneticist

Phone:  (530)752-0766  FAX:  (530)754-7195


Dr. Kasuga's research is focused on the molecular genetics of Phytophthora ramorum, the causal agent of Sudden Oak Death.  In recent years in California alone, over a million oak trees have been killed by P. ramorum. The pathogen also infects ornamentals, which serve as an inoculum source and means of spread to forest ecosystems. Due to its significance, a genome sequence of the pathogen was published in 2006.   Taking full advantage of the genome data, his group conducts comparative genomics and transcriptomics, which will help us to decipher the mechanism of plant-P. ramorum interactions and to facilitate management of the pathogen. 

Takao Kasuga



Mysore R.Sudarshana, Research Plant Pathologist   

Phone:  (530)752-3621  FAX:  (530)754-7195


Dr. Sudarshana has projects on black line disease of walnut, grape leaf roll-associated viruses and necrotic union disorders of stone fruits and grapes.  His program includes both applied and molecular biology with emphasis on detection and characterization of new viruses.








Last Modified: 10/6/2016
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