Ripening physiology in 'Navaho' thornless blackberries: Color, respiration, ethylene production, softening, and compositional changes

Fruit were harvested from an erect, thornless blackberry (Rubus L. subgenus Rubus Watson,'Navaho' to study ripening changes, Soluble solids content in creased between the red (unripe) and dull-black (overripe) stages of ripeni ng while titratable acidity decreased sharply between the mottled and shiny -black ripeness stages. Anthocyanin content increased sharply between the m ottled and shiny-black stages, Firmness of drupelet and receptacle tissues decreased between the mottled and shiny-black stages of ripeness, In whole blackberries, total uronic acids decreased, and water soluble uronic acids increased between the green-red and shiny-black ripeness stages. Volatile p roduction paralleled ripening changes, and was highest in dull-black fruit, with alcohols and aldehydes predominating. Respiration of intact fruit mai ntained in water decreased between the green and red ripeness stages and in creased at the mottled (part-black) and black ripeness stages. Ethylene pro duction remained below 10 nmol . kg(-1). h(-1) until the dull-black (overri pe) stage of maturity. Free 1-aminocyclopropane-1-carboxylic acid (ACC) and ACC oxidase did not increase in berries until the shiny-black stage, corre sponding with the onset of detectable ethylene production. ACC oxidase acti vity decreased in the drupelet tissue (0.5 to 0.01 mu mol . kg(-1) . h(-1)) and increased in the receptacle tissue (2 to 3.8 mu mol . kg(-1) . h(-1)) as fruit changed from red to dull black. These results indicate that ripeni ng in blackberries may be initiated in the receptacle tissue. Ripening in b lackberries is likely independent of ethylene, but ethylene may regulate be rry detachment from pedicels. thus controlling timing of fruit harvests.