THE MOST NOTORIOUS AND DEVASTATING PATHOGENS FOR AGRICULTURE BELONG TO THE PHYTOPHTHORA GENUS (SO-CALLED PLANT DESTROYERS). PHYTOPHTHORA CINNAMOMI (PC) IS ONE OF THE WORLD'S MOST INVASIVE PATHOGEN PRESENT IN SOIL, IRRIGATION WATER, AND IN INFECTED PLANTS. THIS PATHOGEN CAUSES PHYTOPHTHORA ROOT ROT (PRR) AND CANKER IN OVER 5,000 PLANT SPECIES THREATENING NATURAL ECOSYSTEMS, BIODIVERSITY, FORESTRY, AND AGRICULTURE. UNFORTUNATELY, ONCE THIS PATHOGEN IS INTRODUCED IN A NEW AREA CANNOT BE ERADICATE IT, FOR THIS REASON THE ABILITY TO RAPIDLY AND ACCURATELY DETECT PC AND DEVELOP CHEMICAL PRODUCTS AND RESISTANT PLANTS BECOMES MORE COMPELLING TO EFFECTIVELY MANAGE THIS PATHOGEN. PHYTOPHTHORA ROOT ROT (PRR) IS A MAJOR PRODUCTION CHALLENGE FOR SEVERAL ECONOMICALLY IMPORTANT SPECIALTY CROPS SUCH AS AVOCADO, BLUEBERRY, PINEAPPLE, PEACH, MACADAMIA, AND ALMONDS. LOSSES DUE TO THIS PATHOGEN INCLUDE NOT ONLY DECREASES IN CROP YIELD AND PRODUCT VALUE, BUT ALSO SIGNIFICANT EXPENDITURES FOR CONTROL MEASUREMENTS. CURRENTLY, STAKEHOLDERS RELY ON FUNGICIDES SUCH AS POTASSIUM PHOSPHITE (PP), MEFENOXAM, AND TOLERANT ROOTSTOCKS FOR CONTROL. HOWEVER, THE EFFECTIVENESS OF THESE METHODS HAS DECREASED DUE TO A NEW PP RESISTANT AND MORE VIRULENT PC POPULATIONS RECENTLY IDENTIFIED IN CA.DESPITE THE IMPORTANCE OF THIS PATHOGEN, STUDIES AIMING TO CHARACTERIZE AND UNDERSTAND THE GENETIC AND PHENOTYPIC DIVERSITY OF THE PC POPULATIONS ARE LIMITED. MOREOVER, THE MOLECULAR BASIS OF THE PATHOGEN VARIABILITY, PATHOGENICITY, AND OTHER KEY PHENOTYPIC TRAITS ARE COMPLETELY UNKNOWN. THUS, THERE IS AN IMPERATIVE NEED NOT ONLY TO CHARACTERIZE THE PATHOGEN POPULATIONS BUT ALSO TO FILL THE KNOWLEDGE GAPS REGARDING THE UNDERSTANDING OF IMPORTANT KEY PC PHENOTYPIC TRAITS, WHICH IS CRITICAL FOR DEVELOPING NEW EFFECTIVE AND DURABLE PC CONTROL METHODS. THIS PROJECT WILL COMBINE GENOMICS, TRANSCRIPTOMICS, AND PHENOTYPIC DATA REGARDING PC FUNGICIDE SENSITIVITY AND VIRULENCE TO IDENTIFY GENOME REGIONS ASSOCIATED WITH THESE PHENOTYPIC TRAITS AND TO ELUCIDATE THE FACTORS CONTRIBUTING TO THE INVASIVENESS, GENOME EVOLUTION, AND ADAPTATION OF THIS DESTRUCTIVE SOIL-BORNE PATHOGEN. THE IDENTIFICATION OF GENETICALLY AND PHENOTYPICALLY DIVERSE ISOLATES WILL AID TO THE DESIGN OF ISOLATE/CLADE/PHENOTYPIC-SPECIFIC DIAGNOSTIC TOOLS TO MONITOR THE SPREAD AND DISTRIBUTION OF MORE VIRULENT AND FUNGICIDE RESISTANT ISOLATES, WHICH CAN BE DETRIMENTAL FOR AGRICULTURE, FORESTRY, NATURAL COMMUNITIES, AND BIODIVERSITY. MOREOVER, THESE ISOLATES CAN BE USED TO SELECT AND DEVELOP PLANT MATERIAL THAT IS RESISTANT AGAINST A MORE GENETICALLY AND PHENOTYPICALLY DIVERSE PC POPULATION. OUTREACH AND EXTENSION TO STAKEHOLDERS, SCIENTISTS, AND GENERAL PUBLIC WILL BE CONDUCTED THROUGH PUBLICATIONS, SEMINARS, AND BY USING SOME OF THE PROJECT RESULTS AS PART OF THE LECTURES FOR THE UCR COURSE INTRODUCTION TO PLANT PATHOLOGY.