DIFFERENCES IN SUCROSE METABOLISM RELATIVE TO ACCUMULATION OF BIRD-DETERRENT SUCROSE LEVELS IN FRUITS OF WILD AND DOMESTIC VACCINIUM SPECIES

We examined variability in sucrose levels and metabolism in ripe fruit s of wild and domestic Vaccinium species and in developing fruits of c ultivated blueberry (V. ashei and V. corymbosum). The objective was to determine if sufficient variability for fruit sucrose accumulation wa s present in existing populations to warrant attempts to breed for hig h-sucrose fruit, which potentially would be less subject to bird preda tion. Threefold differences in fruit sucrose concentration were found among Vaccinium species, ranging from 19 to 24 mg (g fresh weight)(-1) in V. stamineum and V. arboreum to approximately 7 mg (g fresh weight )(-1) in cultivated blueberry (V. ashei and V. corymbosum) and V. darr owi. Hexose levels were similar among species, ranging from 90 to 110 mg (g fresh weight)(-1), and glucose and fructose were present in equa l amounts. Soluble acid invertase (EC 3.2.1.26) activity was negativel y correlated with fruit sucrose concentration. There was no apparent c orrelation between fruit sugar concentration and either sucrose syntha se (EC 2.4.1.13) or sucrose phosphate synthase (EC 2.4.1.14) activitie s, both of which were low for all species studied. Developmental incre ases in fruit sugar levels of cultivated blueberry followed a pattern similar to that observed in fruit fresh weight accumulation. Hexose co ncentrations ranged from 6 to 30 mg (g fresh weight)(-1) during the fi rst 60 days after anthesis. Between 60 days and fruit ripening (80 day s), hexose levels rose from 30 to 80 mg (g fresh weight)(-1). Sucrose was not detected in fruits until ripening, when low levels were found. Insoluble acid invertase activity was relatively high early in fruit development, decreasing as soluble acid invertase activity increased. Between 60 days and fruit ripening, soluble acid invertase activity in creased from 3 to 55 mu mol (g fresh weight)(-1) h(-1). Both sucrose s ynthase and sucrose phosphate synthase activities were low throughout development. The extent of sucrose accumulation in fruits and the degr ee of variability for this trait among Vaccinium species support the f easibility of developing high sucrose fruits, which would be a potenti ally valuable addition to current strategies of minimizing crop losses to birds.