Jeffrey G. Williamson

Effects of exogenous abscisic acid on fruit quality, antioxidant capacities, and phytochemical contents of southern high bush blueberries

Abscisic acid (ABA) is a plant growth regulator that has a potential to increase antioxidant capacity and phenolic content of fruits and vegetables. The objective of this study was to examine whether an exogenous ABA application can positively affect fruit quality, antioxidant capacity, and phytochemical content of southern high bush blueberries (Vaccinium darrowii). Two varieties, namely Star and Windsor, were tested with ABA water solutions of three concentrations (0, 200, and 400ppm) using a randomised complete block design. Results showed that ABA significantly increased the firmness of berries in both varieties, suggesting a ripening delay effect. Such effect was more pronounced in Windsor variety as reflected by a lower percentage of ripe berries and smaller sized berries on ABA treated bushes. In conclusion, ABA delayed the ripening of blueberries, but did not affect total phenolic content, antioxidant capacity, or the content of individual phytochemicals in ripe blueberries.

Night temperature and source–sink effects on overall growth, cell number and cell size in bell pepper ovaries

BACKGROUND AND AIMS Ovary swelling, and resultant fruit malformation, in bell pepper flowers is favoured by low night temperature or a high source-sink ratio. However, the interaction between night temperature and source-sink ratio on ovary swelling and the contribution of cell size and cell number to ovary swelling are unknown. The present research examined the interactive effects of night temperature and source-sink ratio on ovary size, cell number and cell size at anthesis in bell pepper flowers. METHODS Bell pepper plants were grown in growth chambers at night temperatures of either 20 °C (HNT) or 12 °C (LNT). Within each temperature treatment, plants bore either 0 (non-fruiting) or two developing fruits per plant. Ovary fresh weight, cell size and cell number were measured. KEY RESULTS Ovary fresh weights in non-fruiting plants grown at LNT were the largest, while fresh weights were smallest in plants grown at HNT with fruits. In general, mesocarp cell size in ovaries was largest in non-fruiting plants grown at either LNT or HNT and smallest in fruiting plants at HNT. Mesocarp cell number was greater in non-fruiting plants under LNT than in the rest of the night temperature/fruiting treatments. These responses were more marked in ovaries sampled after 18 d of treatment compared with those sampled after 40 d of treatment. CONCLUSIONS Ovary fresh weight of flowers at anthesis increased 65 % in non-fruiting plants grown under LNT compared with fruiting plants grown under HNT. This increase was due primarily to increases in mesocarp cell number and size. These results indicate that the combined effects of LNT and high source-sink ratio on ovary swelling are additive. Furthermore, the combined effects of LNT and low source-sink ratio or HNT and high source-sink ratio can partially overcome the detrimental effects of LNT and high source-sink ratio.

Blueberry Producers’ Attitudes toward Harvest Mechanization for Fresh Market

The availability and cost of agricultural labor is constraining the specialty crop industry throughout the United States. Most soft fruits destined for the fresh market are fragile and are usually hand harvested to maintain optimal quality and postharvest longevity. However, because of labor shortages, machine harvest options are being explored out of necessity. A survey on machine harvest of blueberries (Vaccinium sp.) for fresh market was conducted in 2015 and 2016 in seven U.S. states and one Canadian province. Survey respondents totaled 223 blueberry producers of various production sizes and scope. A majority (61%) indicated that their berries were destined for fresh markets with 33% machine harvested for this purpose. Eighty percent said that they thought fruit quality was the limiting factor for machine-harvested blueberries destined for fresh markets. Many producers had used mechanized harvesters, but their experience varied greatly. Just less than half (47%) used mechanical harvesters for fewer than 5 years. Most respondents indicated that labor was a primary concern, as well as competing markets and weather. New technologies that reduce harvesting constraints, such as improvements to harvest machinery and packing lines, were of interest to most respondents. Forty-five percent stated they would be interested in using a modified harvest-aid platform with handheld shaking devices if it is viable (i.e., fruit quality and picking efficiency is maintained and the practice is cost effective). Overall, the survey showed that blueberry producers have great concerns with labor costs and availability and are open to exploring mechanization as a way to mitigate the need for hand-harvest labor.

Mechanical Harvesting and Postharvest Storage of Two Southern Highbush Blueberry Cultivars Grafted onto Vaccinium arboreum Rootstocks

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 ofmechanical harvesters.Vaccinium arboreum Marsh is a wild species that has wide soil adaptation andmonopodial 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 handharvested 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 byV. 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. Highbush blueberries grown for fresh market are typically hand harvested; however, hand harvesting is labor intensive and costly, resulting in low production efficiency and profitability (Takeda et al., 2008, 2013). In addition, unpredictable labor supplies affect a large number of specialty crops, and are becoming a major issue in blueberry production (Zhang and Wilhelm, 2011). To decrease harvesting costs in blueberry production, mechanical harvesters have been developed, tested, and manufactured since the late 1950s (Hedden et al., 1959; Peterson and Brown, 1996; Takeda et al., 2008, 2013; van Dalfsen and Gaye, 1999), but have been primarily used to harvest berries for processing or at the end of the harvest season (Williamson et al., 2012; Yu et al., 2012). However, growers’ concerns about handharvesting costs and labor availability have increased interest in adopting mechanical harvesters for fresh market blueberries. Brown et al. (1996) reported an increase of 60-fold in labor efficiency and a cost reduction of 85% when using over-the-row mechanical blueberry harvesters. However, mechanical harvesting causes excessive fruit bruising (Sargent et al., 2013) and harvest losses. Bruising occurs when berries hit canes, other fruits, and interior surfaces of the harvester or catch plates while falling through the bush after detachment (Takeda et al., 2008), and as fruit moves from the catch plates to the lugs (Yu et al., 2012). Harvest losses may occur due to harvesting of unripe or damaged berries, reducing packout efficiency by 4% to 30% (Peterson and Brown, 1996; Takeda et al., 2013; van Dalfsen and Gaye, 1999). Harvest losses may also occur due to the design of the machine, which allows berries to fall to the ground because the catch plates do not fit closely around the multicaned crown of the bush. Estimates of ground losses from mechanical harvesting range from 10% to 50% of the total fruit harvested (Brown et al., 1996; Peterson and Brown, 1996). Blueberries are very perishable (Vicente et al., 2007), thus, adequate and efficient harvesting methods (Sargent et al., 2013), handling and packing (Jackson et al., 1999), and postharvest storage strategies (Schotsmans et al., 2007) are needed to increase the storage and shelf life of fresh blueberries. Several studies have compared fruit quality of mechanicalvs. hand-harvested blueberry fruit immediately after harvest and during postharvest storage. The increased fruit bruising associated with mechanical harvest reduces berry firmness compared with hand harvest (Li et al., 2011). During postharvest storage, mechanical-harvested berries exhibit a decrease in overall appearance, fresh weight, and firmness, and an increase in shriveling (Sargent et al., 2013) and respiration (Nunez-Barrios et al., 2005) compared with hand-harvested berries. Efficient harvesting systems are needed to reduce fruit losses during harvest and maintain good fruit quality during postharvest storage, since fresh-market berries must maintain acceptable fruit quality for 2 or 3 weeks after harvest (Sargent et al., 2013). Vaccinium arboreum is a wild species native to the southeastern United States that exhibits a single-trunk growth habit (Brooks and Lyrene, 1998). If used as a rootstock for cultivated Vaccinium, the monopodial treelike architecture of V. arboreum could improve mechanical harvesting efficiency of blueberries. A blueberry plant with a single trunk could eliminate much of the yield losses that occur with multicaned plants, as well as reduce the need to prune the bushes to fit the harvest machines. Along with the desired characteristics for mechanical harvesting, V. arboreum tolerates high pH (above 6.0) and low organic matter soils (below 2.0%) (Brooks and Lyrene, 1998), conditions that cultivated V. corymbosum tolerates poorly. Thus, it may be useful in reducing use of soil amendments that are necessary for successful blueberry production in many areas. Received for publication 2 Sept. 2016. Accepted for publication 22 Sept. 2016. This material is based on work that is supported by the National Institute of Food and Agriculture, U.S. Department of Agriculture, under award number 2009-51181-06021 and by the Florida Department of Agriculture and Consumer Services award number 00120479. Current address: Department of Horticulture, The University of Georgia, 1111 Plant Sciences Building, Athens, GA 30602. Corresponding author. E-mail: jgrw@ufl.edu. HORTSCIENCE VOL. 51(12) DECEMBER 2016 1503 Although there is currently research investigating mechanical vs. hand harvesting of blueberry, there are no reports of studies comparing grafted vs. own-rooted plants to assess yield losses due to mechanical harvesting. Further, there are no other reports examining the potential of using V. arboreum as a rootstock to reduce or eliminate soil amendments while maintaining yield and postharvest fruit quality in blueberry. The hypotheses tested in the present research are that 1) yield and fruit quality at harvest and during postharvest storage of handor mechanical-harvested grafted SHB are greater compared with own-rooted SHB and 2) fruit ground losses during harvest are decreased in grafted plants that are mechanical harvested compared with mechanicalharvested own-rooted plants. The specific objectives were to evaluate the effects of root (own rooted vs. grafted), soil (amended vs. nonamended), and harvest method (hand vs. mechanical) treatments on marketable fruit yield, berry weight, harvest losses, and berry quality at harvest and during postharvest storage. Materials and Methods The research was located at Straughn Farms, LLC in Archer, FL (29 32# 56

Crop Water Requirements of Mature Southern Highbush Blueberries

N, 82 29# 11

Nitrogen Uptake and Allocation at Different Growth Stages of Young Southern Highbush Blueberry Plants

W) using ‘Meadowlark’ and ‘Farthing’ SHB. Both cultivars have potential for mechanical harvesting (Williamson et al., 2014); however, they exhibit different plant architectures. ‘Farthing’ is bushy with numerous lateral shoots (Lyrene, 2008), whereas ‘Meadowlark’ is tall with upright shoots (Lyrene, 2010). Four scion/rootstock combinations were tested: 1) own-rooted ‘Farthing’, 2) ‘Farthing’ grafted onto V. arboreum, 3) ownrooted ‘Meadowlark’, and 4) ‘Meadowlark’ grafted onto V. arboreum. Scions and rootstocks were propagated as previously described by Casamali et al. (2016). Briefly, own-rooted plants were propagated by stem cuttings at a commercial nursery in Summer 2010. Vaccinium arboreum seedlings used as rootstocks for grafted plants were germinated from open-pollinated seeds of native V. arboreum plants in northeast Florida, and from 1-year-old seedlings purchased from a native plant nursery (Ornamental Plants and Trees, Inc., Hawthorne, FL). For grafted plants, scions were veneer grafted onto V. arboreum seedling rootstocks in Summer 2010. Own-rooted plants and their grafted counterparts were field planted in May 2011. Plant spacing was 0.9 m in the row and 3.3 m between rows. The soil is a well-drained, typically dry, Arredondo sand, pH 5.5–6.0, with very low organic matter. Each scion/rootstock combination was grown in two different soil treatments 1) pine bark amended soil and 2) nonamended soil. The amended soil consisted of a mixture of pine bark (primarily Pinus elliottii) and native soil, where a 10-cm layer of pine bark was rototilled into the top 20 cm of the native soil. Nonamended soil consisted of native soil. Planting occurred in rows 90 cm wide. All treatment combinations were either han

Classification of blueberry fruit and leaves based on spectral signatures

Measures of crop water use for mature blueberry plantings could offer improved irrigation management by growers, reducing irrigation diversions. The objective of this research was to provide crop coefficients for mature southern highbush blueberry plants. Measures of crop water requirements were made using a water balance enabled by suction lysimeters. Eight established, mature plants were instrumented for water balance. Irrigation was managed to ensure well-watered conditions. Monthly crop coefficients ranged from 0.59 to 1.10 with an annual mean of 0.84.

Flower bud density affects vegetative and fruit development in field-grown Southern Highbush Blueberry

Southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrid) is the major species planted in Florida because of the low-chilling requirement and early ripening. The growth pattern and nitrogen (N) demand of SHBmay differ from those of northern highbush blueberry (NHB, V. corymbosum L.). Thus, the effect of plant growth stage on N uptake and allocation was studied with containerized 1-year-old SHB grown in pine-bark amended soil. Five ‘Emerald’ plants were each treated with 6 g 10% N labeled (NH4)2SO4 at each of 12 dates over 2 years. In the first year, plants were treated once in late winter, four times during the growing season, and once in the fall. In the second year, treatment dates were based on phenological stages. After a 14-day chase period following each N treatment, plants were destructively harvested for dry weight (DW) measurements, atom% of N, and N content of each of the plant tissues. Total DW increased continuously frommid-May 2015 to Oct. 2015 and fromMar. 2016 to late Sept. 2016. From August to October of both years, external N demand was the greatest and plants absorbed more N during the 2-week chase period, about 0.53 g/plant in year 1 and 0.67 g/plant in year 2, than in chase periods earlier in the season. During March and April, N uptake was as low as 0.03 g/plant/2 weeks in year 1 and 0.21 g/plant/2 weeks in year 2. Nitrogen allocation to each of the tissues varied throughout the season. About half of the N derived from the applied fertilizer was allocated to leaves at all labeling times except the early bloom stage in 2016. These results suggest that young SHB plants absorb greater amounts of N during summer and early fall than in spring. Blueberry (Vaccinium spp.) plants in Florida are typically grown on sandy soils where the risk of N loss via leaching is greater than on clay soils (Whitehead and Raistrick, 1993). Although cultivated blueberry grows optimally with ammonium as the N source, and ammonium is typically not as readily leachable as nitrate, significant leaching of both N forms occurs on coarse-textured sandy soils (Vitosh et al., 1995). In addition, the rainy season in Florida is from late spring through early fall, which coincides with the time when commercial blueberry growers apply N fertilizer. It is commonly understood that heavy rainfall increases N leaching (Gheysari et al., 2009; Wild and Cameron, 1980). In addition, blueberry plants are shallow-rooted, with roots concentrated mostly in the top 0.15 m (Williamson and Miller, 2009). Thus, there is a high risk for N leaching and an increased potential for ground or surface water contamination where blueberry is grown on sandy soils in humid, subtropical climates. Split applications of N may extend the time of N bioavailability for plant uptake and have been reported to promote yield or plant growth compared with a single application. For example, mature blueberry plants had a 10% yield increase (Hanson and Retamales, 1992), red raspberry (Rubus idaeus L.) ended up with a significantly greater berry yield (Rempel et al., 2004), and lowbush blueberry (V. angustifolium) plants increased both growth and berry yield significantly (Percival et al., 2002). Storage and remobilization of N in perennial woody species such as blueberry help plants reduce dependency on fertilizer N (Geßler et al., 1998; Millard, 1996). Remobilization of storage N accounted for 65% of the total N in new vegetative growth of ‘Climax’ rabbiteye blueberry (V. virgatum Ait.) at vegetative budbreak (Birkhold and Darnell, 1993). Cheng and Fuchigami (2002) found that 50% of reserve N in apple (Malus domestica Borkh.) trees was remobilized to support new growth of shoots and leaves. Some species of woody plants can remobilize up to 90% of reserve N to new leaf growth (Millard, 1996). Thus, with sufficient N storage, plants can be less dependent on N fertilizer. However, N remobilization is closely related to plant phenology (Millard and Grelet, 2010). Banados (2006) concluded that N uptake in mature NHB (V. corymbosum L.) is more dependent on plant demand than on N availability in the soil. Thus, an effective N fertilization program requires a clear understanding of the times when N fertilizer is most needed. Previous studies have found that the effect of application date on N absorption by blueberry plants is significant (Banados, 2006; Hanson and Retamales, 1992; Throop and Hanson, 1997). However, these studies used the midseason NHB cultivar ‘Bluecrop’. Southern highbush blueberry (V. corymbosum L. interspecific hybrid) cultivars that are adapted to Florida’s mild winter climate ripen fruit earlier in the season and have a longer postfruit harvest vegetative growth period than NHB cultivars. Therefore, seasonal growth and N demand of SHB may differ from NHB. However, there is no literature available for the seasonal growth and N demand pattern of young SHB plants. This study was conducted to 1) determine seasonal growth of SHB by measuring organ DW at various growth stages, 2) identify the growth stages of young SHB that exhibit the greatest N uptake, and 3) determine N allocation patterns within plant tissues. Materials and Methods Plant material. Sixty one-year-old ‘Emerald’ (SHB) plants (average height 0.19 m) were obtained from a north Florida nursery and individually planted in 57-L containers on 6 Feb. 2015 and grown outdoors at the Horticultural Greenhouse Complex at the University of Florida, Gainesville, FL (29 38#N latitude and 82 21#W longitude). The growingmedium consisted of Arredondo sandy soil (Thomas et al., 1979) mixed with fresh pine bark at the ratio of 1:1 (v/v). Owing to the potential for fresh pine bark to immobilize fertilizer N, it was pretreated 2 months before planting with a liquid fertilizer UAN32 (32N–0P–0K) at the rate of 0.15 g/L N (Krewer and Ruter, 2009). Treatments. Treatments consisted of applying 10% N labeled fertilizer as ammonium sulfate [(NH4)2SO4] at six different growth stages during each of the two growing seasons. In the first growing season (2015), flowers were removed to encourage vegetative growth. Vegetative growth occurred Received for publication 9 Jan. 2017. Accepted for publication 8 May 2017. This studywas financially supported byUSDA-AMS through 2014 Florida Specialty Crop Block Grant program (Contract no. 00096225). We thank professors Ed Hanlon and Don Huber at the University of Florida for reviewing the article. We would appreciate Island Grove Ag Products: Nursery Division for providing free blueberry plants and pine bark, Eric Ostmark for his help in managing the trial and James Colee for his assistance on statistical analysis. Corresponding author. E-mail: guodong@ufl.edu. HORTSCIENCE VOL. 52(6) JUNE 2017 905 continuously from early March to late September, and individual growth flushes were not evident. Thus, treatment dates were not based on plant phenology. The N treatment dates were 3 Mar. (25 d after budbreak), 2 Apr., 11 May, 18 July, 21 Aug., and 30 Sept. (after vegetative growth stopped). In the second growing season (2016), the N treatments were applied on 26 Feb. (early bloom), 5 Apr. (early green fruit stage), 25 May (10 d after the final fruit harvest), 1 July (between growth flushes), 22 July (midgrowth flush), and 9 Sept. (after the final vegetative flush). Each growth flush ceased when the uppermost bud aborted, and the next flush began when buds burst near the tip. On each of the six dates either year, five plants were treated with 6 g N labeled (NH4)2SO4 (1.26 g N), and the other plants were treated with the same amount of N from unlabeled (NH4)2 SO4. The five N treated plants were destructively harvested for analysis after 14 d. The treatments were arranged in a randomized complete block design with five singleplant replications. In the first year, there was a long period between the third fertilization date (11 May) and the fourth date (18 July); therefore, unlabeled N was applied on 16 June. Thus, the rate of N fertilization was equivalent to 38 kg/ha N (0.85 m · 2.74 m spacing) in year 1 and 33 kg/ha N in year 2. Both labeled and unlabeled N fertilizers were dissolved in water and applied manually and evenly on soil around the root systems. At the same time as the N applications, 3.6 g triple superphosphate (0N–19.6P–0K) and 6.8 g sulfate of potash (0N–0P–41.5K) were applied to each pot (49 kg P/ha and 103 kg K/ha in year 1 and 42 kg P/ha and 88 kg K/ha in year 2). The plants were irrigated by microsprinklers at 250 mL/min, and the irrigation run times were determined by multiplying the in situ evapotranspiration (ET) by 1.2 (based on 120% ET level). The ET data were downloaded twice a month from the Florida Automated Weather Network (FAWN) Alachua station (http://fawn.ifas. ufl.edu). Measurements. Harvested plants were separated into leaves, new (current season’s) stems, 1-year-old stems, roots, and flowers/ fruits when available. The roots were carefully excavated from the containers. Then, they were pressure washed (up to 80 pounds per square inch, PSI) using a Melnor 5Pattern Watering Nozzle (Model no.: 20101GT; BFG Supply, Burton, OH) to remove the soil and pine bark. Tissues were individually oven-dried at 65 C to a constant weight which was recorded. Total DW was the sum of the DW of each of the tissues. The tissues were ground with a laboratory mill (Arthur H. Thomas Company, Philadelphia, PA) into a powder passing a 2-mm mesh screen. Subsamples of leaf (1 mg), flower and fruit (3 mg), stem (4 mg), and root (4 mg) tissues were submitted to the Soil and Water Science Biogeochemistry Core Laboratory (University of Florida, Gainesville, FL) to determine atom% of N and N concentration by using an isotope ratio mass spectrometer (Finnigan DELTAplus XP; Thermo Fisher Scientific, Bremen, Germany). Nitrogen derived from fertilizer (NDFF) represented the total amount of N from labeled fertilizer absorbed by plants during a 14-d chase period after N treat