TOMATO IS RANKED FIRST IN THE VALUE OF UTILIZED VEGETABLE PRODUCTION IN USA. TOMATOES ARE SUSCEPTIBLE TO A DISORDER CALLED BLOSSOM-END ROT (BER) WHICH DEVELOPS DURING EARLY FRUIT GROWTH PERIOD. THIS DISORDER INITIATES AT THE BLOSSOM-END OF THE FRUIT AS WATER SOAKED SPOTS WHICH EVENTUALLY BECOME DRY, SUNKEN AND BROWN, AND IN SEVERE CASES CAN ENCOMPASS THE ENTIRE FRUIT. THE ROT MAY OCCUR DUE THE INADEQUATE CALCIUM IN THE FRUIT OR DUE TO VARIOUS STRESSES IMPOSED ON THE FRUIT. IN SEVERE CASES, LOSSES OF UP TO 50% OF THE TOTAL YIELD CAN OCCUR WHICH RESULTS IN A SIGNIFICANT ECONOMIC LOSS. CURRENTLY, THE UNDERLYING CAUSE OF BER IS NOT KNOWN AND GENERATING MORE INFORMATION ON THIS DISORDER WILL HELP WITH BREEDING CULTIVARS THAT ARE BER-RESISTANT OR PROVIDE INFORMATION ON CERTAIN MANAGEMENT STRATEGIES TO MINIMIZE THIS DISORDER. IN THIS WORK WE PLAN TO CHARACTERIZE TOMATO LINES THAT HAVE CONTRASTING PHENOTYPES, ONE WHICH IS BER-SUSCEPTIBLE AND THE OTHER BER RESISTANT. IF TWO SUCH PARENTAL LINES ARE CROSSED THEN THE RESULTING PROGENY WILL HAVE EITHER ONE OF THESE PHENOTYPES, SOME MAY BE RESISTANT TO BER AND OTHER LINES MORE SUSCEPTIBLE. USING AN APPROACH CALLED GENETIC MAPPING WE SHOULD BE ABLE TO IDENTIFY CERTAIN REGIONS IN THE GENOME (REFERRED TO AS LOCI) THAT UNDERLIE BER. HOWEVER IF THESE GENOMIC REGIONS ARE VERY LARGE WE NEED TO BREAK IT UP INTO SMALLER CHUCKS TO IDENTIFY THE SMALLEST GENOMIC INTERVAL THAT IS RESPONSIBLE FOR BER RESISTANCE. ULTIMATELY THIS APPROACH MAY HELP TO IDENTIFY THE BER-CAUSATIVE GENE, THE ULTIMATE TARGET RESPONSIBLE FOR CAUSING THIS DISORDER. USING A COMPLEMENTARY APPROACH, WE WILL STUDY OTHER DEVELOPMENTAL CAUSES OF BER. WE WILL DETERMINE IF BER CAN OCCUR IN FRUIT THAT GROW RELATIVELY FAST DURING THEIR DEVELOPMENT AND THEREFORE HAVE HIGHER DEMAND FOR CALCIUM. FRUIT RECEIVE THEIR CALCIUM THROUGH VASCULAR TISSUES SUCH AS XYLEM, AND THEREFORE INVESTIGATING HOW THE XYLEM DEVELOPS DURING FRUIT DEVELOPMENT MAY BE CRITICAL IN UNDERSTANDING CALCIUM TRANSLOCATION INTO THE FRUIT. WE ALSO PLAN TO DETERMINE IF APPLICATIONS OF CERTAIN PLANT HORMONES THAT ALTER CALCIUM TRANSPORT INTO THE FRUIT WILL MINIMIZE THIS DISORDER. OVERALL THE PROPOSED WORK USES MULTIPLE APPROACHES TO FIND THE UNDERLYING CAUSE OF BER IN TOMATOES. THIS DISORDER AFFECTS OTHER VEGETABLES AND FRUITS SUCH AS PEPPER, WATERMELON, SQUASH AND EGGPLANT, WHICH IMPLIES THAT THE FINDINGS FROM THIS PROPOSED PROJECT WILL BE USEFUL TO OTHER CROPS. THIS PROJECT IN THE FUTURE WILL HELP DEVELOP MARKERS FOR BREEDING CROPS THAT ARE RESISTANT TO BER AND PROVIDE MANAGEMENT STRATEGIES TO MINIMIZE THIS DISORDER IN THE FIELD.