Project Number: 5306-22000-014-00
Project Type: Appropriated

Start Date: Jul 13, 2007
End Date: Jul 12, 2012

Objective:
1. Improve management strategies for key soil borne diseases of tree fruit and nut crops. 1A. Develop economical alternatives to preplant use of methyl bromide (MB). 1B. Identify and characterize available walnut and almond rootstock germplasm for resistance to key soil borne pathogens. 2. Characterize the etiology of key soil borne diseases of tree fruit and nut crops, and examine the molecular microbial ecology of both pathogenic and beneficial plant-associated microorganisms. 2A. Determine the etiology of Prunus replant disease (PRD). 2B. Characterize the genetic diversity and ecology of Agrobacterium tumefaciens. 3. Develop enhanced traditional and culture-independent molecular detection methods for key pathogens of fruit and nut crops. 3A. Develop enhanced detection protocols for Agrobacterium tumefaciens. 3B. Develop enhanced detection protocols for Brennaria rubrifaciens. 3C. Develop enhanced detection protocols for Phytophthora cactorum. 4. Examine etiology, epidemiology, and control strategies for systemic/graft transmissible pathogens of fruit and nut trees. 4A. Identify and characterize graft-transmissible pathogens(GTP)in fruit and nut trees with an emphasis on determining the etiology of emerging diseases such as Tieton cherry stunt (TCS) and Plum necrotic union (PNU). 4B. Epidemiology and molecular characterization of PBNSPaV. 4C. Evaluate Marianna 2624 rootstock for tolerance to Xyllela fastidiosa in almond. 5. Examine the structural and functional genomics of Phytophthora ramorum, the causal agent of Sudden Oak Death. 6. Identify and characterize rhizobacterial genes whose expression is mediated by plant root exudates and evaluate involvement of these genes in such ecologically important phenotypes as root colonization, infection, competition, and persistence in the environment. 7. Characterize the biology, genetic diversity, and ecology of key plant pathogenic agents of fruit/nut trees including A. tumefaciens strains, and examine the ecology and significance of molecular microbe-microbe and plant-microbe interactions of key plant associated microorganisms.

Approach:
1. Chemical and crop-rotation-based alternatives to methyl bromide will be tested for control of Prunus replant disease (PRD), and genetic resistance to Phytophthora spp. and Agrobacterium tumefaciens will be explored in promising almond and walnut rootstocks. 2. Examine shifts in soil borne microbial communities associated with PRD incidence using culture-based and culture-independent approaches and complete Koch's postulates for organisms linked to the disease. Examine the molecular microbial ecology of A. tumefaciens under both orchard and nursery conditions in an effort to design effective crown gall control strategies. Examine Ti-plasmid ecology under commercial orchard conditions. Assess the genetic diversity of A. tumefaciens in California. 3. Described and novel PCR primers will be tested for specific amplification of ribosomal and mitochondrial DNA from P. cactorum. Enhance described and develop novel PCR primers for species-specific detection and quantification of A. tumefaciens in soil and inplanta. Develop PCR primers and define the extraction and cycling parameters for the detection and quantification of Brennaria rubrifaciens. 4. Epidemiological studies and molecular characterization of Plum bark necrosis-stem pitting associated virus (PBNSPaV) will be performed. Discarded and healthy almond trees on M2624 plum and peach rootstocks will be compared for tree performance, nut set, nut quality and decline symptoms as a function of X. fastidiosa infection. 5. Structural and functional genomics and/or a proteomics approaches will be used to examine the biochemical and molecular mechanisms of pathogenesis. Analysis of the P. ramorum genome also will focus on gene identification, assignment of putative gene function, and comparative genomics studies using the currently sequenced genomes of Phytophthora spp. FORMERLY CRIS PROJECT #5306-22000-013-00D