No abstract

We examined variability in sucrose levels and metabolism in ripe fruits of wild and domestic Vaccinium species and in developing fruits of cultivated blueberry (V. ashei and V. corymbosum). The objective was to determine if sufficient variability for fruit sucrose accumulation was present in existing populations to warrant attempts to breed for high‐sucrose fruit, which potentially would be less subject to bird predation. 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. darrowi. Hexose levels were similar among species, ranging from 90 to 110 mg (g fresh weight)–1, and glucose and fructose were present in equal amounts. Soluble acid invertase (EC 3.2.1.26) activity was negatively correlated with fruit sucrose concentration. There was no apparent correlation between fruit sugar concentration and either sucrose synthase (EC 2.4.1.13) or sucrose phosphate synthase (EC 2.4.1.14) activities, both of which were low for all species studied. Developmental increases in fruit sugar levels of cultivated blueberry followed a pattern similar to that observed in fruit fresh weight accumulation. Hexose concentrations ranged from 6 to 30 mg (g fresh weight)−1 during the first 60 days after anthesis. Between 60 days and fruit ripening (80 days), 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 increased from 3 to 55 μmol (g fresh weight)–1 h–1. Both sucrose synthase and sucrose phosphate synthase activities were low throughout development. The extent of sucrose accumulation in fruits and the degree of variability for this trait among Vaccinium species support the feasibility of developing high sucrose fruits, which would be a potentially valuable addition to current strategies of minimizing crop losses to birds.

To determine if multiple applications of GA3 would increase size of parthenocarpic fruit, and to assess the interaction between GA3 applications and pollination, `Beckyblue' rabbiteye blueberry (Vaccinium ashei Reade) flowers were treated with single or multiple applications of GA3 alone or in combination with full or partial pollination. Single or multiple applications of GA3 resulted in similar or increased fruit set compared with pollination, and increased fruit set compared with no pollination. GA3 applications decreased fruit mass and increased the fruit development period in comparison with pollination alone. Multiple, late applications of GA3 were ineffective in overcoming these effects. Partial (nonsaturating) pollination resulted in an average fruit set of 60%, while set following GA3 treatment in combination with full or partial pollination averaged 85%. Fruit mass was greater in the full pollination ±GA3 treatments than in all other treatments. The number of large seeds and seed mass per fruit were greatest in the full pollination treatment, and were significantly decreased by all treatments in which GA3 and/or partial pollination were used; however, there were no concomitant effects of GA3 in delaying the fruit development period. Our results indicate that under optimal pollination conditions, no detrimental effects of GA3 applications on fruit set, fruit size, or fruit development period in blueberry are to be expected, even though GA3 reduces seed number and seed mass. Furthermore, GA3 applications appear to be beneficial in increasing fruit set under suboptimal pollination conditions, although smaller fruit are to be expected under such conditions. Chemical name used: gibberellic acid (GA3).

Sucrose metabolism and fruit growth in parthenocarpic vs seeded blueberry (Vaccinium ashei) fruits. -Physiol. Plant. 99: 439-446.Although fruit set and development are induced hy applications of gibberellins, final friiit weight of gibberellin-induced parthenocarpic fruit is often less than that of pollinated fruit. We examined changes in the activities of sucrose-metabolizing enzymes and sugar accumulation in developing fruits of cultivated bluebeny (Vaccinium ashei Reade) and their correlation with fruit growth upon pollination or exogenous apphcations of gihberellic acid (GA3). The objective was to detennine if differences in fruit growth could he attributed to differences in enzyme activities and subsequent sugar accumulation in fruits. The fhiit development period of GAj-treated fruits was 15 days longer than that of pollinated fruits. At maturity, GAj-treated fruit accumulated an average of 180 mg dry weight while poUinated fruit accumulated 390 mg dry weight. Dry weigh! accumulation in nonpollinated fruits was negligible and these fruits abscised hy 45 days after bloom (DAB). The total carbon (C) cost (dry weight C + respiratory C) for fruit development was 109 and 244 mg C ftuir' for GAj-treated and pollinated fruits, respectively. Hexose concentration increased to 100 mg (g fresh weight)"' at ripening in both GA3-treated and pollinated fruits. Nonpollinated fruits reached a maximum hexose concentration at 45 DAB. Sucrose phosphate synthase (EC 2.4.1.14) and sucrose synthase (EC 2.4.1.13) activities reached a maximum of <5.0 junol (g fresh weight)"' h"' in both GA3-treated and pollinated fniits. Soluble acid invertase (EC 3.2.1.26) activity increased to about 60 (imol (g firesh weight)"' h"' in both GA3-treated and pollinated fruits at ripening, while in nonpollinated fruits, a maximum solubleacidinvertaseactivity of 0.12 (imol (g fresh weight)"' h"'was measured at 24 DAB. Insoluble acid invertase activity decbned during the early stages of fiiiit growth and remained relatively low throughoat fruit development. Neutral invertase activity was low throughout development, increasing to 5 ^mol (g fresh weight)"' h ' al ripening is GA3-treated and pollinated fruits. Our studies demonstrate that blueberry fruit development does not appear to be limited by sucrose metabolizing enzyme activity and/or the ability to accumulate sugars in either GA3-treated or pollinated fruits. Key words -Blueberry, cariiohydrate metabolism, fruit growth, gibberellie acid, invertase, sucnose phosphate synthase, sucrose synthase, Vaccinium ashei. R. 56230 Edomex, Mexico) andR.L. Damell