THE U.S. FRESH-MARKET BLACKBERRY INDUSTRY HAS EXPERIENCED RAPID GROWTH AND CHANGE DURING THE PAST 15 YEARS DRIVEN BY INCREASED CONSUMER DEMAND, NEW CULTIVARS, ADVANCED PRODUCTION METHODS, AND YEAR-ROUND PRODUCT AVAILABILITY. THE ENTIRE BERRY INDUSTRY IS EXPANDING, AND BLACKBERRIES IN PARTICULAR HAVE BEEN DRIVING THIS GROWTH WITH AN INCREASE IN SALES OF 14.7% BETWEEN 2015 AND 2016. FRESH-MARKET BLACKBERRIES ACCOUNTED FOR $549 MILLION IN SALES DURING 2016 AND ARE CURRENTLY THE FOURTH-MOST IMPORTANT DOMESTIC BERRY CROP, BEHIND STRAWBERRIES, BLUEBERRIES, AND RASPBERRIES (CA STRAWBERRY COMMISSION, 2017).DESPITE RECENT GROWTH, THE BLACKBERRY INDUSTRY CONTINUES TO BE PLAGUED BY SHORT SHELF LIFE AND LOSS OF FRUIT QUALITY DURING SHIPPING. BLACKBERRIES ARE CONSIDERED ONE OF THE MOST DIFFICULT FRUITS TO SHIP DUE TO THEIR SUSCEPTIBILITY TO MANY CONDITIONS THAT REDUCE MARKETABILITY, SHELF LIFE, AND FRUIT QUALITY INCLUDING DECAY, JUICE LEAKAGE, BERRY SOFTENING, AND WEIGHT. RED DRUPELET REVERSION IS A PARTICULARLY PROBLEMATIC POSTHARVEST PHYSIOLOGICAL DISORDER AFFECTING FRESH MARKET BLACKBERRIES. BLACKBERRIES HARVESTED WHEN COMPLETELY BLACK AND FULL RIPE OFTEN DEVELOP RED DISCOLORATION AFTER THEY ARE RETURNED TO ROOM TEMPERATURE FOLLOWING COLD STORAGE. THIS DISCOLORATION LIMITS FRUIT MARKETABILITY AS CONSUMERS PERCEIVE IT AS UNATTRACTIVE. FURTHERMORE, EXCESSIVE REVERSION CAN RESULT IN REJECTION OF WHOLE SHIPMENTS OF BERRIES AS LOTS OF BLACKBERRIES WITH GREATER THAN 10% OF FRUIT LACKING FULL BLACK COLORATION ARE NOT CONSIDERED PERMISSIBLE BY USDA MARKETING STANDARDS (USDA-AMS 2016). RED DRUPELET REVERSION IS LIKELY A FORM OF CHILLING INJURY EXPERIENCED AS RAPID TEMPERATURE CHANGES WEAKEN CELL WALLS AND MEMBRANES AND THE ANTHOCYANINS THAT GIVE BERRIES THEIR BLACK COLOR ARE DEGRADED IN A LESS ACIDIC ENVIRONMENT.THE UNIVERSITY OF ARKANSAS SYSTEM DIVISION OF AGRICULTURE (UA) IS HOME TO THE LARGEST PUBLIC-SECTOR FRESH-MARKET BLACKBERRY BREEDING PROGRAM IN THE US. SINCE ITS INCEPTION IN 1964, THE UA BLACKBERRY BREEDING PROGRAM HAS PUBLICLY RELEASED 16 CULTIVARS THAT HAVE TRANSFORMED THE INDUSTRY. TWO MAJOR ACHIEVEMENTS HAVE BEEN THE DEVELOPMENT OF ERECT, THORNLESS CULTIVARS AND PRIMOCANE-FRUITING CULTIVARS THAT PRODUCE A FALL CROP ON FIRST YEAR CANES. THE IMPROVEMENT OF FRUIT FIRMNESS IS AN IMPORTANT OBJECTIVE IN THE UA BLACKBERRY BREEDING PROGRAM, AS FIRM FRUIT GENERALLY PERFORM BETTER FOR MANY POSTHARVEST QUALITY PARAMETERS. SIGNIFICANT IMPROVEMENTS IN FIRMNESS HAVE BEEN MADE THROUGH CLASSICAL BREEDING, WITH SUBSTANTIAL VARIATION IN FIRMNESS OBSERVED AMONG UA SELECTIONS AND CULTIVARS. A DRAMATIC ADVANCE IN FIRMNESS WAS ACHIEVED WITH THE DISCOVERY OF A VERY DISTINCT 'CRISPY' TEXTURE IN A THORNY, FLORICANE FRUITING SELECTION. CRISPY SELECTIONS ARE CONSIDERABLY MORE FIRM THAN OTHER UA BREEDING SELECTIONS AND CULTIVARS AT HARVEST AND AFTER SEVEN DAYS OF COLD STORAGE AND EXPERIENCE SIGNIFICANTLY LESS RED DRUPELET REVERSION. CRISPY-TEXTURED BLACKBERRIES HAVE THEPOTENTIAL TO INCREASE THE PROFITABILITY OF THE US BLACKBERRY INDUSTRY BECAUSE OF THEIR SUPERIOR POSTHARVEST PERFORMANCE AND RESISTANCE TO RED DRUPELET REVERSION. HOWEVER, THE UNDERLYING BIOLOGY OF CRISPY TEXTURE IS NOT UNDERSTOOD AND THE TRAIT HAS BEEN DIFFICULT TO RECOVER IN CROSSES BETWEEN CRISPY AND NON-CRISPY SELECTIONS IN THE UA BREEDING PROGRAM. GENES AND ENZYMES ASSOCIATED WITH CELL WALL METABOLISM AND SOFTENING DURING RIPENING IN OTHER FRUITS ARE WELL UNDERSTOOD AND DIAGNOSTIC MARKERS ASSOCIATED WITH FIRMNESS HAVE BEEN IDENTIFIED AND IMPLEMENTED IN OTHER FRUIT CROPS INCLUDING APPLE AND PEACH. THE DEVELOPMENT OF GENETIC MARKERS FOR CRISPY TEXTURE IN BLACKBERRY WOULD GREATLY EXPEDITE BREEDING FOR THIS TRAIT AND FACILITATE THE STACKING OF GENES FOR CRISPY TEXTURE, THORNLESSNESS, AND PRIMOCANE FRUITING IN ELITE CULTIVARS. THE IMPLEMENTATION OF MOLECULAR BREEDING IN BLACKBERRY HAS BEEN DELAYED BY COMPLICATIONS INCLUDING POLYPLOIDY, MULTISOMIC INHERITANCE, AND HETEROZYGOSITY. HOWEVER, RECENT ADVANCES IN COMPUTATIONAL TOOLS FOR POLYPLOIDS AND DEVELOPMENT OF GENOMIC RESOURCES FOR RELATED SPECIES HAVE REMOVED MANY OF THESE BARRIERS.OUR LONG-TERM GOAL IS TO DEVELOP NEW CRISPY BLACKBERRY CULTIVARS WITH ENHANCED FIRMNESS AND SUPERIOR POSTHARVEST PERFORMANCE. THE PRIMARY OBJECTIVE OF THIS PROPOSAL IS TO IMPLEMENT MARKER-ASSISTED SELECTION FOR TEXTURE IN THE UA FRUIT BREEDING PROGRAM TO REDUCE BREEDING CYCLE TIME AND EXPEDITE THE PROCESS OF COMBINING CRISPY TEXTURE WITH OTHER DESIRABLE TRAITS. BASED ON PRELIMINARY RESULTS IN BLACKBERRY AND STUDIES IN OTHER FRUIT CROPS, WE HYPOTHESIZE THAT VARIATION IN FRUIT FIRMNESS IN FRESH-MARKET BLACKBERRIES IS DETERMINED BY MUTATIONS IN A FEW GENE(S) RELATED TO RIPENING AND CELL WALLS. THE SPECIFIC OBJECTIVES OF OUR PROPOSAL ARE:OBJECTIVE 1. MEASURE FRUIT FIRMNESS AND RED DRUPELET REVERSION IN A PANEL OF 400 BREEDING SELECTIONS FROM THE UA BLACKBERRY BREEDING PROGRAM FOR FRUIT FIRMNESS AND RED DRUPELET REVERSION AND GENOTYPE THE PANEL TO IDENTIFY MOLECULAR MARKERS FOR FIRMNESS AND RED DRUPELET REVERSION.OBJECTIVE 2. STUDY THE BIOLOGY BEHIND SOFTENING DURING RIPENING IN BLACKBERRIES WITH SOFT, FIRM, AND CRISPY TEXTURE BY MEASURING THE CELL WALL COMPONENTS AT DIFFERENT STAGES OF FRUIT DEVELOPMENT.OBJECTIVE 3. DEVELOP A MAPPING POPULATION SEGREGATING FOR CRISPY TEXTURE THAT WILL BE EVALUATED FOR TEXTURE AND RED DRUPELET REVERSION AND GENOTYPED TO IDENTIFY MOLECULAR MARKERS FOR FIRMNESS AND RED DRUPELET REVERSION.THE NOVEL CRISPY BLACKBERRY PHENOTYPE RESULTS FROM A NATURALLY OCCURRING GENETIC MUTATION (NON-GMO) AND IS LIKELY TO BE DEPLOYED IN FARMERS' FIELDS, POTENTIALLY EXTENDING THE SHELF LIFE OF FRESH-MARKET BLACKBERRIES AND REDUCING LOSSES FROM RED DRUPELET REVERSION. THIS PROPOSAL WILL HAVE SUBSTANTIAL IMPACT FOR THE US BLACKBERRY INDUSTRY BECAUSE MOLECULAR MARKERS DEVELOPED IN THIS PROJECT WILL BE IMPLEMENTED IN APPLIED BREEDING PROGRAMS AND WILL EXPEDITE THE DEVELOPMENT OF ELITE CRISPY CULTIVARS.