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Elizabeth Conlan, Tatiana Borisova, Erick Smith, Jeffrey Williamson, and Mercy Olmstead

Freeze events between January and April can result in major crop and economic losses for growers of low-chill, early-ripening varieties of blueberry (Vaccinium sp.) in Florida and Georgia. The objective of this research was to determine current responses by blueberry growers to freeze events. Blueberry growers in Florida and Georgia were surveyed about frost protection decision criteria. Growers had differing opinions on when to make the decision to frost-protect blueberry crops. Almost all (98.9%) of the respondents (n = 94) who reported using at least one method of active frost protection reported using irrigation. Farm size, as measured by blueberry acreage, did not influence decisions regarding the use of active frost protection measures. Blueberry growers, on average, reported that a loss of up to 30% to 39% of their crop could be tolerated and still produce a marketable crop. However, they may have been overly cautious at the early bud stages, with ≈40% and 55% of respondents protecting at the bud swell and tight cluster stages, respectively. Understanding the use of irrigation as a frost protection practice in the southeastern United States can aid in improving frost protection recommendations, helping growers maximize yield and saving water and money.

Open access

R. F. Korcak, G. J. Galletta, and A. Draper


The growth and elemental composition of a range of blueberry (Vaccinium sp.) progenies was greenhousetested on 5 unmulched soils. Three of the soils, low in pH and fertility, represented the physiographic regions of the eastern United States; Coastal Plain, Piedmont, and Appalachian Highlands; also included were a high-pH, high-fertility Piedmont soil and a commercial blueberry Coastal Plain soil. Two studies, 10 and 20 weeks in duration, were made with seedlings of crosses of blueberry clones of hybrid origin. Growth was significantly higher for seedlings grown on the commercial blueberry soil in both studies. V. ashei (rabbiteye) seedlings grew significantly larger than all others when measured over all soil types in one experiment but not the other. There were no significant differences in growth among the 4 progenies when averaged over all soil types. Percent sand was positively correlated with growth while both percent silt and clay were negatively correlated with growth. Plant composition was generally within acceptable levels for Ca, Mg, K, Fe, and Zn. Plant Mn and Al, although variable, tended to be higher than reported values. Soil Mn was significantly and negatively correlated with growth. It was possible to select individual seedlings which grew well on each of the mineral soils represented in the study.

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Lisa J. Rowland, Anik L. Dhanaraj, James J. Polashock, and Rajeev Arora

Expressed sequence tag-polymerase chain reaction (EST-PCR) markers for DNA fingerprinting and mapping in blueberry (Vaccinium sp.) had previously been developed from expressed sequence tags (ESTs) produced from a cDNA library, derived from RNA from floral buds of cold acclimated plants. Because EST-PCR markers are derived from gene coding regions, they are more likely to be conserved across populations and species than markers derived from random regions of DNA, such as randomly amplified polymorphic DNA (RAPD) or amplified fragment length polymorphism (AFLP) markers. In this study, we tested whether many of the EST-PCR primer pairs developed for blueberry are capable of amplifying DNA fragments in other members of the family Ericaceae. In addition, we cloned and sequenced a selection of 13 EST-PCR fragments to determine if they showed homology to the original blueberry cDNA clones from which the EST-PCR primer pairs were derived. Closely related cranberry genotypes (two wild selections of V. oxycoccus L. and two cultivars of V. macrocarpon Aiton, `Early Black' and `Stevens') and more distantly related rhododendron genotypes (one wild selection each of Rhododendron arboreum Marsh, R. maximum L., and R. ponticum L. and three complex species hybrids, `Sonata', `Grumpy Yellow', and `Roseum elegans') were used. Of 26 primer pairs tested in cranberry, 23 (89%) resulted in successful amplification and eight of those (35%) amplified polymorphic fragments among the cranberry genotypes. Of 39 primer pairs tested in rhododendron, 29 (74%) resulted in successful amplification and 21 of those (72%) amplified polymorphic fragments among the rhododendron genotypes. Approximately 50% of the 13 sequenced EST-PCR fragments were found to be homologous to the original blueberry cDNA clones. These markers should be useful for DNA fingerprinting, mapping, and assessing genetic diversity within cranberry and rhododendron species. The markers which are shown to be homologous to the blueberry cDNA clones by DNA sequencing should also be useful for comparative mapping and genetic diversity studies between some genera of the family Ericaceae.

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Tripti Vashisth and Anish Malladi

Fruit abscission in blueberry (Vaccinium sp.) occurs at the pedicel/peduncle junction (PPJ). Growth regulators such as methyl jasmonate (MeJa) and ethephon accelerate the progression of abscission at this zone. It is not known whether the abscission zone at the PPJ is sufficient to perceive and respond to these growth regulator applications or if the fruit and leaf tissues are required to elicit these responses. Furthermore, the effects of injury to the fruit and leaves on fruit detachment responses have not been previously reported in blueberry. In this study, the requirement of the fruit and leaves to respond to MeJa and ethephon applications was investigated through organ removal treatments in rabbiteye blueberry. Removal of the fruit or the fruit and leaves on the branch followed by MeJa application delayed the progression of abscission at the PPJ suggesting that the fruit tissue is required only to accelerate the progression of fruit detachment in response to MeJa. Interestingly, the extent of fruit/pedicel detachment in response to ethephon applications was higher in the organ removal treatments compared with the control indicating that the PPJ was sufficient to perceive and respond to ethephon and that wounding caused by organ removal synergistically enhanced fruit abscission in response to ethephon. Mechanical wounding of the fruit by removing the distal half of the berry resulted in accelerated fruit detachment at the PPJ. Detachment of non-injured fruit was unaffected by mechanical wounding of adjacent fruit. These data suggest that wounding generates a local signal capable of accelerating fruit abscission at the PPJ. This information may have implications for fruit retention or drop in response to injury to the fruit as caused by herbivore feeding or as a result of insects and pathogens.

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R. Karina Gallardo, Eric T. Stafne, Lisa Wasko DeVetter, Qi Zhang, Charlie Li, Fumiomi Takeda, Jeffrey Williamson, Wei Qiang Yang, William O. Cline, Randy Beaudry, and Renee Allen

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.

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David C. Diehl, Nicole L. Sloan, Christine M. Bruhn, Amarat H. Simonne, Jeffrey K. Brecht, and Elizabeth J. Mitcham

As part of a larger project to show how fresh fruits and vegetables with enhanced flavor can be successfully handled to improve consumer satisfaction without compromising food safety, key informant interviews were conducted with fruit industry leaders dealing with melons (Cucumis melo and Citrullus lanatus), peaches and nectarines (Prunus persica), pears (Pyrus communis), tomatoes (Solanum lycopersicum), strawberries (Fragaria ×ananassa), and blueberries (Vaccinium sp.). The interview was designed to collect information on industry attitudes and practices related to postharvest handling of more mature fruit, harvest timing, preconditioning, cold chain management, and shipping and handling procedures throughout the supply chain. The current analysis focuses on two key questions from the interviews: 1) To what extent do industry experts believe that better fruit handling and shipping procedures contribute to better taste quality in fruit? 2) To what extent do industry experts believe that better fruit quality will lead to more consumer purchasing? In response to the first question, the majority of respondents (70%) agreed that postharvest handling affects fruit flavor with the most cited themes related to agreement being gentle handling, cold chain management, and harvest timing. Of the respondents who expressed disagreement most acknowledged the importance of postharvest handling, but felt other factors were also important, mainly the variety grown, the shelf life requirements, and the growing conditions. For the second question, 95% of respondents agreed that increased taste quality of fruit would mean increased purchasing and consumption. The primary theme related to agreement was that consumers would repeat purchase after positive eating experiences. Other important factors were the price point of fruit, retail display, product identity, and fruit appearance. With increasing consumer attention to fruit quality and a generally accepted belief among industry representatives that fruit flavor and quality drives consumer demand, there is an opportunity to shift industry practices toward postharvest handing that is conducive to consistently delivering better-tasting fruit to consumers.

Open access

Jaysankar De, Aswathy Sreedharan, You Li, Alan Gutierrez, Jeffrey K. Brecht, Steven A. Sargent, and Keith R. Schneider

Cooling procedures used by blueberry (Vaccinium sp.) growers often may include delays up to 24 hours that can damage the fruit through rough handling and adverse temperatures, thereby potentially compromising quality and, subsequently, safety. The objectives of this experiment were to compare forced-air cooling (FAC) compared to hydrocooling without sanitizer (HW) and hydrocooling with sanitizer (HS) regarding the quality and shelf life of southern highbush blueberry [SHB (Vaccinium corymbosum)] and to determine the efficacy of these treatments for reducing Salmonella in SHB. Freshly harvested SHB that were inoculated with a five-serovar cocktail of rifampin-resistant Salmonella were rapidly chilled by FAC or hydrocooling (HW and HS) using a laboratory model system. FAC did not show any significant reduction (P > 0.05) in Salmonella or in the effects on the microbiological quality of blueberries. HW and HS reduced Salmonella by ≈2 and >4 log cfu/g SHB, respectively, on day 0. These postharvest treatments were also evaluated for their ability to help maintain fruit quality throughout a storage period of 21 days at 1 °C. Hydrocooling (both HS and HW) provided more rapid cooling than FAC. Hydrocooled blueberries showed significant weight gain (P < 0.05), whereas FAC resulted in a slight, but insignificant (P > 0.05), reduction in final weight. The results of hydrocooling, both HS and HW, shown in this study could help to extend the shelf life while maintaining or increasing the microbiological quality of fresh market blueberries. Information obtained by this study can be used for developing the best temperature management practices to maintain the postharvest safety and quality of blueberries.

Free access

Qin Yang, Er Liu, Yan Fu, Fuqiang Yuan, Tingting Zhang, and Shu Peng

After nearly a decade of development, the scale of blueberry (Vaccinium sp.) cultivation has increased, particularly in south China; however, this region is becoming increasingly challenged by temperature changes during the flowering phenophase. Understanding the effects of temperature on pollen germination and pollen tube growth in blueberry is thus important. Using the rabbiteye blueberry (V. ashei) ‘Brightwell’, different temperature treatments were carried out during open pollination and cross-pollination with the pollen from rabbiteye blueberry ‘Gardenblue’ in field, greenhouse, and controlled temperature experiments over two consecutive years. The differences in pollen germination, pollen tube dynamics, and ovule viability following different treatments were analyzed, and the critical temperatures were calculated using quadratic and modified bilinear equations to quantify the developmental responses to temperature. The results showed that the fruit set of the artificially pollinated plants inside the greenhouse was significantly higher than that outside the greenhouse. Furthermore, pollen germination and pollen tube growth gradually accelerated under the appropriate high-temperature range, resulting in reduced pollen tube travel time to the ovule. However, the percentage of the style traversed by the pollen tube did not increase at temperatures greater than 30 °C, and a high-temperature range could accelerate ovule degeneration. Therefore, impairment of pollen tube growth in the upper half of the style following pollen germination and ovule degeneration constituted important factors leading to reduced fruit setting under short periods of high temperature during the flowering phenophase in rabbiteye blueberry. This work advances our understanding of the effect of temperature on pollen germination, pollen tube growth, ovule longevity, and fruit setting in rabbiteye blueberry, and provides a foundation for continued cultivation and breeding enhancement. The findings propose that the tolerance of rabbiteye blueberry to a certain high-temperature range in the flowering phenophase should inform breeding strategies for temperature resistance and that temperature range is also an important indicator of suitable environments for cultivation to mitigate potential temperature stress.

Free access

Carolyn DeMoranville

The american cranberry (Vaccinium macrocarpon) is a wetland plant native to North America. The plant is adapted to sandy, nutrient-poor, low pH soils and thus, like blueberry (Vaccinium sp.), its nutritional requirements are low compared with many other perennial fruit crops. Research conducted over the past 30 years has defined the annual requirements for nitrogen [N (20–60 lb/acre)], phosphorus [P (<20 lb/acre)], and potassium (40–120 lb/acre) based on tissue testing, plant growth demands, potential for remobilization, and determination of removal in the crop. These three nutrient elements are those most commonly applied to the crop in fertilizers. However, much of the work on nutrient rate requirements was conducted on native cultivars and there is an expectation that requirements of newer hybrid cultivars are greater. In Massachusetts, cranberries are grown in coastal watersheds and often depend on small lakes as their water source for irrigation, harvest, and winter flooding. Since cranberry production is heavily dependent on water use, the interaction of nutrient management and water management has become a primary focus area for research and extension, particularly for N and P, the nutrient elements most frequently associated with environmental pollution. Recent preliminary research examining cranberry farms with varied configurations (e.g., water passes through the bog and exits via a long channel, water recirculates back into the supply water body) has indicated that the cranberry bogs may act as either a source or sink for N depending on configuration and management activities. In a study of cranberry farms where P use was reduced to an average of <10 lb/acre, P concentration in harvest flood water declined by as much as 85% while crop production was sustained. Site variation in output of N and P in cranberry drainage and flood waters indicates the need for further research into the variables that control these processes, including soil types, site hydrology, nutrient application rates and forms, and water-management activities.

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David R. Bryla and Bernadine C. Strik

Northern highbush blueberry (Vaccinium corymbosum) is well adapted to acidic soils with low nutrient availability, but often requires regular applications of nitrogen (N) and other nutrients for profitable production. Typically, nutrients accumulate in the plant tissues following the same pattern as dry matter and are lost or removed by leaf senescence, pruning, fruit harvest, and root turnover. Leaf tissue testing is a useful tool for monitoring nutrient requirements in northern highbush blueberry, and standards for analysis have been updated for Oregon. Until recently, most commercial plantings of blueberry (Vaccinium sp.) were fertilized using granular fertilizers. However, many new fields are irrigated by drip and fertigated using liquid fertilizers. Suitable sources of liquid N fertilizer for blueberry include ammonium sulfate, ammonium thiosulfate, ammonium phosphate, urea, and urea sulfuric acid. Several growers are also applying humic acids to help improve root growth and are injecting sulfuric acid to reduce carbonates and bicarbonates in the irrigation water. Although only a single line of drip tubing is needed for adequate irrigation of northern highbush blueberry, two lines are often used to encourage a larger root system. The lines are often installed near the base of the plants initially and then repositioned 6–12 inches away once the root system develops. For better efficiency, N should be applied frequently by fertigation (e.g., weekly), beginning at budbreak, but discontinued at least 2 months before the end of the growing season. Applying N in late summer reduces flower bud development in northern highbush blueberry and may lead to late flushes of shoot growth vulnerable to freeze damage. The recommended N rates are higher for fertigation than for granular fertilizers during the first 2 years after planting but are similar to granular rates in the following years. More work is needed to develop fertigation programs for other nutrients and soil supplements in northern highbush blueberry.