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  • Author or Editor: Jeffrey G. Williamson x
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Experiments were conducted with `Misty' southern highbush blueberry (Vaccinium corymbosum L. interspecific hybrid) to test the effects of high temperature on flower bud initiation and carbohydrate accumulation and partitioning. Plants were grown under inductive short days (SDs = 8 hour photoperiod) or noninductive SDs with night interrupt (SD-NI = 8 hour photoperiod + 1 hour night interrupt), at either 21 or 28 °C for either 4 or 8 weeks. Flower bud initiation occurred only in the inductive SD treatments and was significantly reduced at 28 °C compared with 21 °C. The number of flower buds initiated was not significantly different between 4- and 8-week durations within the inductive SD, 21 °C treatment. However, floral differentiation appeared to be incomplete in the 4-week duration buds and bloom was delayed and reduced. Although plant carbohydrate status was not associated with differences in flower bud initiation between SD and SD-NI treatments, within SD plants, decreased flower bud initiation at high temperature was correlated with decreased whole-plant carbohydrate concentration. These data indicate that flower bud initiation in southern highbush blueberry is a SD/long night phytochrome-mediated response, and plant carbohydrate status plays little, if any, role in regulating initiation under these experimental conditions.

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Some physiological and biochemical properties of melting flesh (MF) and non-melting flesh (NMF) peaches [Prunus persica (L.) Batsch] were determined during ripening for 5 days at 20 °C. Respiration rates and ethylene production of MF ‘Flordaprince’, MF ‘TropicBeauty’, NMF ‘UFSun’, and NMF ‘Gulfking’ were measured at different harvest skin ground color-based maturity stages. The MF cultivars at harvest were mostly preclimacteric or at the onset of ripening. The NMF cultivars generally had higher ethylene production at harvest and throughout ripening than the MF cultivars; thus, the NMF fruit had started ripening on the tree before harvest. Some of the NMF fruit harvested at more advanced stages quickly became postclimacteric during the storage period. Quality determination after fruit ripening showed that MF ‘TropicBeauty’ had the highest soluble solids content (SSC), but also the highest titratable acidity (TA). The NMF cultivars had lower TA than the MF cultivars. NMF ‘Gulfking’ consistently had high SSC/TA, which was the result of it having the lowest TA. The NMF cultivars retained firmer texture than the MF cultivars during ripening. The flesh firmness of the NMF cultivars was four to five times greater than that of the MF cultivars. To investigate the reason for this significant textural difference, the activities of the cell wall modification enzymes pectin methylesterase (PME) and polygalacturonase (PG) were quantified in all four cultivars at advanced ripeness stages. PME activity appeared to be more directly related with peach fruit softening than PG activity.

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Experiments were conducted in north Florida and south Georgia to determine the effects of H2CN2 sprays on vegetative and reproductive growth of blueberry. In Florida, mature, field-grown `Misty' southern highbush (Vaccinium corymbosum L. hybrid) blueberry plants were sprayed to drip with 0, 10.2, or 20.4 g·L-1 of H2CN2 [hereafter referred to as 0%, 1.0%, and 2.0% (v/v) H2CN2] on 20 Dec. 1996 and 7 Jan. 1997. During the following winter, mature `Misty' southern highbush and `Climax' rabbiteye (V. ashei Reade) plants were sprayed to drip with 0, 7.6, or 15.3 g·L-1 of H2CN2 [hereafter referred to as 0%, 0.75%, and 1.5% (v/v) H2CN2] on 17 Dec. 1997 and 6 Jan. 1998. For all experiments, plants were dormant and leafless, with slightly swollen flower buds, at the time of spray applications. Generally, H2CN2 sprays increased the extent and earliness of vegetative budbreak and canopy establishment and advanced flowering slightly. The number of vegetative budbreaks usually increased linearly with increasing spray concentrations. In Florida, H2CN2 [0.75% to 1.0% (v/v)] sprays increased mean fruit fresh weight and yield, and shortened the fruit development period (FDP) compared to controls. However, H2CN2 sprays ranging in concentration from 1.5% to 2.0% (v/v) resulted in significant flower bud injury and reduced total fruit yield compared to controls. In south Georgia, 27 of 37 field trials conducted between 1991 and 1998 on several rabbiteye and southern highbush cultivars indicated that leaf development was significantly enhanced by H2CN2. H2CN2 shows potential for increasing early fruit maturity, fruit size, and yield of southern highbush and rabbiteye blueberry cultivars with poor leaf development characteristics in low-chill production regions. Chemical name used: hydrogen cyanamide (H2CN2).

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Nonweighing drainage lysimeters were used to measure seasonal water use of mature ‘Emerald’ southern highbush blueberry (SHB; Vaccinium corymbosum interspecific hybrid) plants grown in pine bark beds and in pine bark amended soil in north central Florida. In the absence of rain, irrigation was applied daily with microsprinklers at ≈120% to 175% of reference evapotranspiration as either single or split applications. Leachate was collected and its volume determined from each lysimeter at 6- to 10-day intervals throughout the study. Water use, expressed as L/plant, was calculated as the difference between the amount of irrigation/rain added to lysimeters and the amount of leachate collected from lysimeters during each measurement period. Average daily water use was calculated for monthly intervals beginning in Apr. 2010 and ending in Sept. 2012. Water use increased rapidly during spring through the final stages of fruit ripening and harvest (May) with peak water use occurring during mid to late summer (July, August, and September). Plants grown in pine bark beds used more water than plants in pine bark amended soil during Apr., May, and Dec. 2010, Feb. 2011, and Mar. 2012, but there were no differences during the periods of highest water use. No differences in water use were observed between single or split-application irrigation treatments. Monthly averages for daily water use during the 30-month period ranged from ≈1.75 L/plant in January to ≈8.0 L/plant in mid to late summer. Mean monthly crop coefficient values during the 30-month period ranged from 0.44 in February to 0.86 in September. Canopy volume, yield, and mean berry weight were unaffected by soil or irrigation treatments.

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Four low-chill peach cultivars were evaluated for vegetative and reproductive growth, fruit quality, and yield in north central and central Florida. Twenty-trees (five of each cultivar) were planted at each site in Feb. 2002. Prior to budbreak in the spring of 2004 and 2005, three shoots of average length and diameter were selected at a height of 1.5–2.0 m and the number of vegetative and flower buds was recorded for each shoot. Percentage of bloom was estimated, and the number of open flowers on selected shoots was measured weekly. Trees were harvested twice per week starting in mid-April in central Florida, and in late April in north central Florida. Total number and weight of marketable fruit was measured for each tree. Ten representative fruits were selected from each tree at each harvest. Fruit were measured for blush, weight, and size. Soluble solids, TAA, and pressure were determined for five fruit from each 10-fruit sample. Preliminary results indicate a higher mean number of blind nodes in central Florida and a higher mean number of flower buds in north central Florida. In central Florida, 90% bloom was about 4 days earlier than north central Florida. Fruit number and individual fruit size, weight, and marketable yield were higher in north central Florida than in central Florida. Fruit blush was higher in central Florida than in north central Florida and tended to increase as the season progressed. In north central Florida, blush decreased slightly throughout the season.

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The effect of climate was observed on fruit quality of four low-chill peach cultivars (Flordaprince, Flordaglo, UFGold, and TropicBeauty). The cultivars were evaluated in three locations (north–central, central, and southwest Florida). Soluble solids content (SSC), titratable acidity (TA), SSC:TA ratio, fruit weight, blush, and fruit development period (FDP) were determined. Longer FDPs were observed at the north–central location than at the southwest location. Fruit development and the expression of quality attributes were affected by location during fruit growth with higher color and SSC and shorter FDP occurring under warmer conditions. Within locations, ‘UFGold’ had the shortest FDP except at the southwest location where its chilling requirement may not have been met. At the central and southwest locations, ‘UFGold’ also tended to have lower TA values and higher SSC;TA ratios than the other cultivars.

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Fruit shape of four low-chill peach [Prunus persica (L.) Batsch] cultivars was evaluated in north-central, central, and southwest Florida. During 2005, measurements were taken at all locations for cheek diameter, suture diameter, and tip protrusion. A suture deformation index was calculated (suture diameter/cheek diameter) to determine suture deformation. Fruit had more protruding tips and suture deformation was more pronounced at the southwest location than at the north-central or central locations. Overall, ‘TropicBeauty’ had more protruding tips than the other cultivars. It was concluded that warmer temperatures at the southwest location during fruit development affected fruit shape by increasing the incidence of protruding tips and pronounced sutures.

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The effect of climate was observed on the relative frequency of vegetative and floral buds in four low-chill peach cultivars (‘Flordaprince’, ‘Flordaglo’, ‘UFGold’, and ‘TropicBeauty’). The trees were planted in north–central, central, and southwest Florida. The percentage of blind nodes, mixed nodes (nodes with vegetative and floral buds), and nodes with only vegetative buds were determined from three representative shoots per tree at each location. In general, higher percentages of blind nodes were observed in central and southwest Florida and higher percentages of mixed nodes were observed in north–central Florida. ‘TropicBeauty’ tended to have a greater percentage of blind nodes than the other cultivars. Higher temperatures during bud formation most likely contributed to the increased amounts of blind nodes observed in the central and southwest locations and to the reduced amounts of mixed nodes. However, stresses imposed by bacterial spot and hurricanes may have contributed to the higher incidence of blind nodes in 2005. Our results indicate that certain genotypes have a predisposition for the formation of blind nodes. Advanced selections having low chilling requirements and potentially being adapted to a wide diversity of tropical or subtropical climates need to be tested in multiple locations to evaluate blind node formation.

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Blueberry (Vaccinium spp.) summer pruning can increase yield by promoting healthy fall foliage to support the reproductive development. However, there has been little research to examine the effects of timing and intensity of summer pruning in subtropical conditions. The objective of this study was to determine the effects of summer pruning timing and intensity on reproductive traits of mature ‘Jewel’ and ‘Emerald’ southern highbush blueberry (SHB) plants (V. corymbosum L. interspecific hybrid) in subtropical Florida. The effect of pruning time was evaluated by removing 30% of the canopy in June or July. The effect of intensity was evaluated by pruning either 30% or 60% of the canopy in June, followed by removal of the upper 5 cm of regrowth (“tipping”) in July. Both timing and intensity used nonpruned plants as a control. The same plants were evaluated over three consecutive seasons (June 2011–May 2014). Main effects of pruning time, intensity, and tipping were evaluated. Tipping did not affect the reproductive traits evaluated. ‘Emerald’ reproductive traits were unaffected by either summer pruning time or intensity over the 3-year study. ‘Jewel’ yield was unaffected in the first year, but was increased by 48% and 65% in years 2 and 3, respectively, in the 30% pruning treatment compared with the nonpruned control. Lack of pruning in ‘Jewel’ decreased inflorescence bud number compared with moderate pruning likely due to more diseased foliage that increased defoliation. Thus, pruning effects on reproductive traits were cultivar dependent. Leaving ‘Jewel’ plants unpruned for two or more seasons reduced inflorescence bud number and yield.

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The profitability of the fresh market blueberry industry in many areas is constrained by the extensive use and cost of soil amendments, high labor requirements for hand harvesting, and the inefficiencies of mechanical harvesters. Vaccinium arboreum Marsh is a wild species that has wide soil adaptation and monopodial growth habit. It has the potential to be used as a blueberry rootstock, expanding blueberry production to marginal soil and improving the mechanical harvesting efficiency of cultivated blueberry. The objectives of this research were to compare yield, berry quality, and postharvest fruit storage of own-rooted vs. grafted southern highbush blueberry (SHB) cultivars (Farthing and Meadowlark) grown on amended vs. nonamended soil and either hand or mechanical harvested. Yields of hand-harvested SHB during the first two fruiting years were generally greater in own-rooted plants grown on amended soil compared with own-rooted plants on nonamended soil or grafted plants on either soil treatment. However, by the second fruiting year, hand-harvest yields of grafted SHB were ≈80% greater than own-rooted plants when grown in nonamended soil. Yields of mechanical-harvested SHB grafted on V. arboreum and grown in either soil treatment were similar to yields of mechanical-harvested own-rooted plants in amended soil the second fruiting year, and greater than yields of own-rooted plants in non-amended soil. In general, mechanical harvesting reduced marketable yield ≈40% compared with hand harvesting. However, grafted plants reduced ground losses during harvest by ≈35% compared with own-rooted plants for both cultivars. Mechanical-harvested berries had a greater total soluble solids:total titratable acidity ratio (TSS:TTA) than hand-harvested berries, and berries harvested toward the end of the harvest season had a greater TSS:TTA than those from early-season harvests. As postharvest storage time increased, berry appearance ratings decreased and berry softness and shriveling increased, particularly in mechanical-harvested compared with hand-harvested berries. Firmness of mechanical-harvested berries decreased during storage, whereas firmness of hand-harvested berries remained relatively stable. However, fruit quality at harvest and during postharvest storage was unaffected by V. arboreum rootstocks or lack of pine bark amendment. This study suggests that using V. arboreum as a rootstock in an alternative blueberry production system has the potential to decrease the use of soil amendments and increase mechanical harvesting efficiency.

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