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Two cultivars of southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid), ‘Sharpblue’ and ‘Wannabe’, were container-grown outside in either a dormant or nondormant production system to determine how the two production systems affected carbohydrate (CH2O) status, growth, and development. Plants were maintained in the nondormant condition by continuous N fertilization throughout winter (average maximum/minimum temperatures of 17/5 °C). Plants in the nondormant system retained their foliage longer into the winter compared with plants in the dormant system. Flower bud number, density, fruit number, and total fruit fresh weight (FW) per plant were greater in the nondormant compared with the dormant system plants for both cultivars. Mean fruit FW was greater in dormant compared with nondormant ‘Wannabe’ plants, while in ‘Sharpblue’, mean fruit FW was similar in both systems. Cane and root CH2O concentrations in nondormant system plants were generally similar to or lower than those measured in dormant system plants. Assuming that longer leaf retention in nondormant system plants increased CH2O synthesis compared with dormant system plants, the patterns of reproductive/vegetative development and root/shoot CH2O concentrations indicate that the increased CH2O in nondormant system plants was allocated to increased reproductive growth in lieu of CH2O reserve accumulation. It is probable that this increased CH2O availability, combined with longer perception of short days due to longer leaf retention, were major factors in increasing flower bud initiation and yield in the nondormant compared with the dormant system plants. and winter, compared with plants in the dormant production system. However, differences in growth and yield between the two systems are unknown since side-by-side comparisons have not been made. It is likely that the longer photosynthetic season experienced by nondormant compared with dormant system plants would alter the carbohydrate (CH2O) status of plants (e.g., timing or extent of reserve accumulation), which in turn, may affect vegetative and/or reproductive growth. In warm winter climate areas, either production system can be used, thus, it is important to compare blueberry growth and yield between the two systems. The hypothesis tested in the present experiment was that the increased length of the photosynthetic season in the nondormant plants will increase CH2O availability and therefore increase fruit yield the following season, compared with plants in the dormant system. The specific objectives were to 1) compare vegetative and reproductive development between the two systems, and 2) determine the effect of production system on the CH2O status at various phenological stages. Chilling accumulation is a major limitation to extending deciduous fruit production into subtropical and tropical areas. In traditional deciduous fruit production areas, plants enter endodormancy in the fall and accumulate chill hours during the winter. Upon chilling satisfaction, floral and vegetative buds are released from endodormancy and budbreak occurs when environmental conditions permit. Insufficient chilling results in delayed, protracted, and reduced budbreak and fruit development. Blueberry plants (Vaccinium sp.) can be prevented from entering endodormancy if they are fertilized continuously with N and protected from freezing temperatures (Reeder et al., 1994, 1998). Under these conditions, flowering and fruit development occur in the spring without a dormant period or chilling (Reeder et al., 1998; Sharpe and Sherman, 1971). This nondormant production system for blueberry has been used in the subtropics to avoid endodormancy and the concomitant chill requirement (Reeder et al., 1998). In the nondormant production system, year-round N fertilization enables blueberry plants to maintain their foliage longer into the fall Table 1. Calendar dates and phenological stages for whole-plant harvests of ‘Sharpblue’ and ‘Wannabe’ southern highbush blueberry ‘Sharpblue’ ‘Wannabe’ Phenological stage Dormant Nondormant Dormant Nondormant Pre-FBI 3 Oct. 1996 3 Oct. 1996 12 Oct. 1996 12 Oct. 1996 FBI 27 Dec. 1996 27 Dec. 1996 28 Dec. 1996 28 Dec. 1996 50% Bloom 1 Feb. 1997 17 Jan. 1997 no harvest no harvest 50% Fruit set 6 Apr. 1997 5 Mar. 1997 16 Apr. 1997 17 Apr. 1997 Fruit harvest 10 June 1997 11 June 1997 27 May 1997 28 May 1997 zPre-FBI = before flower bud initiation and differentiation, FBI = after flower bud initiation and differentiation, bloom = 50% of the flower buds were open, fruit set = 50% of the flower buds that opened set fruit, and fruit harvest = immediately after final fruit harvest. Table 3. Vegetative growth of ‘Wannabe’ southern highbush blueberry in the dormant (D) and nondormant (ND) production systems at each whole-plant phenological harvest (n = 4); DNT = data not taken. Phenological Harvest Leaf area (cm) Leaf dry wt (g) New cane Root dry Plant vol stage System date Old New Old New Length (cm) DW (g) wt (g) (m) Pre-FBI None 12 Oct. 1996 10,162.0 a --127.6 a 125.1 a 0.90 a FBI D 28 Dec. 1996 1,848.2 c B --21.4 c B 204.3 a A DNT ND 28 Dec. 1996 6,842.6 b A --77.5 b A 178.0 a A DNT 50% Bloom D ND 50% Fruit set D 16 Apr. 1997 43.4 c A 3,879.0 a A 0.6 d A 26.2 a A ----161.7 a A 0.93 a A ND 17 Apr. 1997 195.8 c A 1,044.0 a A 2.8 d A 6.4 a A ----127.6 a A 1.10 a A Fruit harvest D 27 May 1997 2.2 c A 7,570.0 a A 0.0 d A 82.2 a A 994.5 a A 24.1 a A 147.5 a A 1.00 a A ND 28 May 1997 255.9 c A 7,574.0 a A 2.8 d A 61.0 a A 849.0 a A 18.1 a A 146.1 a A 0.90 a A zPre-FBI = before flower bud initiation and differentiation, FBI = after flower bud initiation and differentiation, bloom = 50% of the flower buds were open, fruit set = 50% of the flower buds that opened set fruit, and fruit harvest = immediately after final fruit harvest. yLower case letters indicate mean separation within columns across phenological stages and production systems by Duncan’s multiple range test, P ≤ 0.05. xDashes indicate no new growth at these phenological stages. wUpper case letters indicate mean separation between production systems within a phenological stage by paired t test, P ≤ 0.05. Table 2. Vegetative growth of ‘Sharpblue’ southern highbush blueberry in the dormant (D) and nondormant (ND) production systems at each wholeplant phenological harvest (n = 4); DNT = data not taken. Phenological Harvest Leaf area (cm) Leaf dry wt (g) New cane Root dry Plant vol stage System date Old New Old New Length (cm) DW (g) wt (g) (m) Pre-FBI None 3 Oct. 1996 9,659.4 a --88.1 a 95.8 a 0.40 b FBI D 27 Dec. 1996 2,097.1 cd B --22.3 c B 136.5 a A DNT ND 27 Dec. 1996 5,496.2 b A --63.1 b A 134.2 a A DNT 50% Bloom D 1 Feb. 1997 522.5 de B 9.2 d A 5.5 cd B 0.1 d A ----127.3 a A 0.70 a A ND 17 Jan. 1997 3,721.8 bc A 0.0 d B 45.5 b A 0.0 d B ----128.0 a A 0.48 b B 50% Fruit set D 6 Apr. 1997 67.1 e B 4,050.4 c A 0.7 d B 32.4 c A ----128.7 a A 0.65 a A ND 5 Mar. 1997 1,235.0 de A 812.3 d B 13.0 cd A 4.4 d A ----101.0 a A 0.63 a A Fruit harvest D 10 June 1997 41.7 e A 7,389.9 b B 0.4 d A 62.7 b A 731.8 A 19.0 B 127.8 a A 0.77 a A ND 11 June 1997 26.9 e A 10,555.5 a A 0.3 d A 99.8 a A 1,110.0 A 37.4 A 102.0 a B 0.77 a A zPre-FBI = before flower bud initiation and differentiation, FBI = after flower bud initiation and differentiation, bloom = 50% of the flower buds were open, fruit set = 50% of the flower buds that opened set fruit, and fruit harvest = immediately after final fruit harvest. yLower case letters indicate mean separation within columns across phenological stages and production systems by Duncan’s multiple range test, P ≤ 0.05, except for plant volume, where P ≤ 0.10. xDashes indicate no new growth at these phenological stages. wUpper case letters indicate mean separation between production systems within a phenological stage by paired t test, P ≤ 0.05. Table 4. Comparison of flowering and fruiting between the dormant and nondormant production systems in ‘Sharpblue’ and ‘Wannabe’ southern highbush blueberry. ‘Sharpblue’ ‘Wannabe’ Parameter Dormant Nondormant Dormant Nondormant Flower bud number 239 b 297 a 412 b 454 a Flower bud density (no./cm) 0.15 b 0.18 a 0.19 a 0.22 a Floral budbreak (%) 71.0 a 80.2 a 26.5 b 42.0 a Fruit number/plant 464 b 627 a 241 b 574 a Fruit fresh weight (g/plant) 576 b 722 a 460 b 836 a Mean fruit fresh weight (g/fruit) 1.26 a 1.16 a 1.93 a 1.47 b zFlower bud number recorded between 15 and 31 Dec. 1996. yMean separation within rows and cultivar by paired t test, P = 0.05. xTotal number of flower buds that opened/total number of flower buds. Materials and Methods VEGETATIVE AND REPRODUCTIVE DEVELOPMENT. In June 1996, two container-grown southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrid) cultivars, Sharpblue and Wannabe, were obtained from two commercial nurseries. These cultivars were selected based on their different patterns of vegetative and floral budbreak. Floral and vegetative budbreak occur concomitantly in ‘Sharpblue’, whereas floral budbreak precedes vegetative budbreak in ‘Wannabe’. The ‘Sharpblue’ plants were 18 months old and 60 cm tall, and the ‘Wannabe’ plants were 24 months old and 90 to 120 cm tall. Root balls on each plant were pruned to about a 12-L volume and planted in 22-L containers with a medium of 1 peat : 1 perlite (by volume). Plants were acclimated in a 60% shade house for 2 weeks, then placed outdoors in full sun for the remainder of the experiment. Broken canes and canes growing parallel to the ground were pruned at this time. Between June and Sept. 1996, plants in both systems were fertilized twice weekly with 2.0 L of Peters 20N– 8.8P–16K water soluble fertilizer at 1 g·L (Grace-Sierra Hort. Products, Co., Milpitas, Calif.). In Sept. 1996, canopy volumes of 40 plants of each cultivar were determined by measuring height, widest width and a third measurement perpendicular t

Differences in Phenology and Reserve Carbohydrate Concentrations Between Dormant and Nondormant Production Systems in Southern Highbush Blueberry