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Kimberly L. Morgan and Mercy A. Olmstead

Florida has a large and diverse horticulture industry, with large quantities of fruit and vegetables produced from November to February. Diversification strategies have come to the forefront in perennial horticulture sectors, such as citrus (Citrus sp.), where several diseases have reduced productivity and acreage. Many growers are considering diversification of their groves to other fruit crops, such as peach (Prunus persica). To understand the state of the industry and provide perspective for transitional Florida growers to mitigate risk, a survey was conducted in 2011. A total of 27 completed survey questionnaires were returned which represented 68% of 2011 Florida peach orchard owners and managers. On average, responding peach orchard size was 18 acres, ranging from 1 to 100 acres, with ‘TropicBeauty’, ‘UFSun’, ‘UFOne’, and ‘UFBeauty’ comprising the main varieties. Production and marketing challenges were key issues identified by growers as they sought to mitigate risk in an uncertain economic climate. Key sources of production information were university personnel, followed by fellow growers, indicating that stone fruit (Prunus sp.) extension programs are effective in information delivery. Tree production expertise combined with geographic proximity to concentrated market segments, access to established fresh fruit distribution routes, and existing relationships with retail market customers are expected to provide the Florida tree-ripened peach grower with unique marketing opportunities. Findings from this survey effort will be used by the project team to develop educational materials and outreach programs, designed to better address the production and marketing risks facing Florida peach growers. In addition, project results will provide new information for regional and national perennial crop producers who are interested in diversifying production practices to meet increased consumer demand for access to locally sourced horticultural products.

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Tripti Vashisth, Mercy A. Olmstead, James Olmstead, and Thomas A. Colquhoun

Producing temperate-zone fruit crops in subtropical environments requires alterations in fertilizer application and rates. Nitrogen (N) is a critical mineral nutrient required in high amounts by the tree; however, it is often over- or under-applied for optimal fruit quality and can affect the phytochemical composition of fruits. The effects of different N fertilizer rates and harvest date on total phenolic content, total flavonoid content, total anthocyanins, total antioxidant capacity, total soluble solids, titratable acidity, and organic acids (citric and malic acid) of two subtropical peach (Prunus persica) cultivars, TropicBeauty and UFSharp, were investigated. N rate did not affect total soluble solids in ‘TropicBeauty’, although total soluble solids decreased as N rate increased in ‘UFSharp’. Titratable acidity and organic acid content was significantly higher in ‘UFSharp’ as compared with ‘TropicBeauty’, although there was no effect of N rate on titratable acidity. An overall increase in phenolic content, flavonoid content, anthocyanins, and antioxidant capacity were observed with decreasing N rates in both subtropical peach cultivars. A stronger genotype × N treatment interaction was observed for ‘TropicBeauty’ for phenolic content, flavonoid content, and antioxidant capacity than for ‘UFSharp’. In ‘TropicBeauty’, among the treatments with no N and highest N, an almost 100% increase in phenolic content, 200% increase in flavonoid content, 50% increase in anthocyanin content, and 80% increase in antioxidant activity was observed. A positive correlation among phenolic content, flavonoid content, and antioxidant capacity was observed in both ‘TropicBeauty’ and ‘UFSharp’. Late harvest date decreased phenolic content in ‘TropicBeauty’, ranging from 6% to 32% among different N treatments. Late harvest increased anthocyanin content as compared with fruit that were harvested on early dates. The results suggest that subtropical peach phytochemical composition can be affected by different cultivars and tree age, and can be manipulated with cultural practices like N fertilization and harvest time to produce fruit with altered or desired nutritional composition for consumers.

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Mercy A. Olmstead, Robert Wample, Stephanie Greene, and Julie Tarara

Traditionally, vegetative cover has been subjectively assessed by visual assessment. However, visual assessment is thought to overestimate percent vegetative cover. Thus, a repeatable method to objectively quantify percent cover is desirable. In two vineyards near Prosser, Wash., the percentage of ground surface covered by up to 15 different cover crops was assessed both visually and by computer-assisted digital image analysis. Quadrats in the cover crop were photographed digitally and the images analyzed with commercially available software. Areas of green vegetation in each image were identified and measured. Weeds in some images were differentiated from the cover crop by user-defined thresholds. Subjective visual estimates of percent vegetative cover were generally higher than those digitally estimated. Values for the visual estimates ranged from 5% to 70% in 1998 (mean = 52.4%) and 7.5% to 55% in 1999 (mean = 30.7%), compared to digital readings ranging from 0.5% to 24% (mean = 11.1%) and 10.3% to 36.6% cover (mean = 20.1%), respectively. The visual assessments had lower coefficients of variability in 1998 (cv 28.1) than the digital image analysis (cv 52.3), but in 1999, the values for the two techniques were similar (cv 41.2 vs. cv 45.7). Despite initial variations between the two methods, the accuracy of digital image analysis for measuring percentage vegetative cover is superior.

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Skyler Simnitt, Tatiana Borisova, Dario Chavez, and Mercy Olmstead

The study focuses on frost protection for early-season (early-ripening) peach (Prunus persica) varieties, which are an important crop for producers in the southeastern United States. Using in-depth interviews with four major Georgia peach producers, we explore their frost protection management strategies. This information is the first step in developing a comprehensive research agenda to advise cost-effective frost protection methods for peach cultivation. We found that peach producers are concerned about frost impacts on their crops. Although early-season peach varieties are particularly susceptible to frost impacts, producers still dedicate significant acreage to these varieties, aiming to extend the market window, satisfy sales contracts, and meet obligations for hired labor. However, early-season varieties do not result in high profits, so producers prefer to concentrate on frost protection for mid- and late-season varieties. Producers employ a variety of frost protection methods, including passive methods (such as planting sensitive varieties in areas less susceptible to frost and adjusting pruning/thinning schedules) and active methods (such as frost protection irrigation and wind machines). The choice among active frost protection methods is based on factors such as the planning horizon, initial investment needs, frequency of frost events, and the effectiveness of the frost protection method. Problem areas that producers identified included improving the effectiveness of frost protection methods; reducing initial investments required to install frost protection systems; and employing better spatial targeting and configuration of frost protection strategies (to reduce investment costs while maintaining or improving the effectiveness of frost protection). Although the initial investment costs of enhanced protection systems may limit producers from actually adopting such methods, the operating costs of such systems are relatively low and have a limited effect on the decision to employ frost protection during a particular frost event. However, producers use information about critical temperatures for different bud stages, and hence, improving the quality of information regarding frost susceptibility can help producers make better frost protection decisions (and potentially reduce electricity costs and water use for frost protection).

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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.

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Lisa Tang, Shweta Chhajed, Tripti Vashisth, Mercy A. Olmstead, James W. Olmstead, and Thomas A. Colquhoun

To determine how the dormancy-breaking agent hydrogen cyanamide (HC) advances budbreak in peach (Prunus persica), this study compared the transcriptome of buds of low-chill ‘TropicBeauty’ peach trees treated with 1% (v/v) HC and that of nontreated trees at 3 and 7 days after treatment (DAT), respectively, using an RNA sequencing analysis. The peak of total budbreak occurred 6 weeks earlier in the HC-treated trees (at 32 DAT) than the nontreated trees (at 74 DAT). There were 1312 and 1095 differentially expressed genes (DEGs) at 3 and 7 DAT, respectively. At 3 DAT, DEGs related to oxidative stress, including the response to hypoxia, lipid oxidation, and reactive oxygen species (ROS) metabolic process, were upregulated in HC-treated buds. Additionally, DEGs encoding enzymes for ROS scavenging and the pentose phosphate pathway were upregulated at 3 DAT but they were not differently expressed at 7 DAT, indicating a temporary demand for defense mechanisms against HC-triggered oxidative stress. Upregulation of DEGs for cell division and development at 7 DAT, which were downregulated at 3 DAT, suggests that cell activity was initially suppressed but was enhanced within 7 DAT. At 7 DAT, DEGs related to cell wall degradation and modification were upregulated, which was possibly responsible for the burst of buds. The results of this study strongly suggest that HC induces transient oxidative stress shortly after application, leading to the release of bud dormancy and, subsequently, causing an increase in cell activity and cell wall loosening, thereby accelerating budbreak in peach.

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Julie M. Tarara, Paul E. Blom, Bahman Shafii, William J. Price, and Mercy A. Olmstead

Estimates of canopy and fruit fresh mass are useful for more accurate interpretation of data from the Trellis Tension Monitor, a tool for real-time monitoring of plant growth and predicting yield in trellised crops. In grapevines (Vitis labruscana Bailey), measurements of shoot and fruit fresh mass were collected at frequent intervals (14 to 21 days) over 5 years, and these data were correlated with variables that could be obtained nondestructively: shoot length, number of leaves per shoot, and number of clusters per shoot. Shoot length provided a good estimator of shoot fresh mass in all years. Nonlinear logistic regression models described the dynamics of canopy growth from bloom to the early stages of ripening, which often is poorly represented by simple linear regression approaches to seasonal data. A generalized function indicated a lower bound of ≈600 degree-days, after which an increase in shoot fresh mass could be considered on average to contribute only slightly to further increases in trellis wire tension. The dynamics of fruit mass were captured adequately by a nonlinear function, but not as well as vegetative mass because of larger variances in fruit mass. The number of clusters per shoot was associated with fruit mass only after the accumulation of ≈550 degree-days or, equivalently, the time at which fruit mass exceeded ≈25 g per shoot. Seasonal dynamics of the ratio of fruit to vegetative fresh mass were not sufficiently discernable by the logistic models because of the dominance of fruit mass and its large interannual variation.

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Mercy A. Olmstead, N. Suzanne Lang, Gregory A. Lang, Frank W. Ewers, and Shirley A. Owens

Dye transport through vascular pathways was examined in tissues surrounding the graft union of second-leaf, field-grown trees of `Lapins'/Gisela 5 (`Gi 5') (dwarfing) and `Lapins'/'Colt' (nondwarfing). Excavated, intact trees were allowed to take up xylemmobile dye via transpiration for 6 h before sectioning the tree into scion, graft union, and rootstock tissue. `Lapins'/'Gi 5' had a significantly larger stem cross-sectional area in the central graft union than did `Lapins'/'Colt'. Per unit cross section, dye transport of both `Lapins'/'Gi 5' and `Lapins'/'Colt' was significantly less in the graft union than in rootstock sections, with still less transported to scion tissues in `Lapins'/'Gi 5'. `Lapins'/'Gi 5' had a tendency to produce vascular elements oriented obliquely to the longitudinal axis of the tree. Dye was distributed more uniformly axially and radially across the graft union in `Lapins'/'Colt' than in `Lapins'/'Gi 5', with an apparent accumulation of dye in `Lapins'/'Gi 5' graft union. Xylem vessel diameters and vessel hydraulic diameters (VDh) were smaller overall in `Lapins'/'Gi 5' than in `Lapins'/'Colt'; however, graft unions in both had smaller VDh than did rootstock sections. These observations suggest reduced transport efficiency of xylem vessels in the graft union in `Lapins'/'Gi 5' may be due to smaller vessels, vascular abnormalities and/or increased amounts of callus and parenchyma tissue.

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Mercy A. Olmstead, N. Suzanne Lang*, Frank W. Ewers, and Shirley A. Owens

Dwarfing rootstocks in sweet cherry (Prunus avium L.) have been planted worldwide. No single theory has emerged to answer why scion dwarfing occurs in fruit trees. This research examines the vascular pathway in a dwarfing cherry system to determine if physical limitations alter water transport as a possible dwarfing mechanism. Second-leaf `Lapins' trees grafted onto Gisela 5 (Gi5; dwarfing) and Colt (vigorous) rootstocks were field-grown in East Lansing, Mich. During maximum shoot elongation, trees were dug, placed into containers with safranin dye solution (0.1% w/v) for 6 hours and then removed for division (3-5 cm in length) based on location in scion, graft union, and rootstock tissue. Tissues were sectioned using a sliding microtome (120 μm) for examination with a laser confocal microscope (Zeiss LSM Pascal). Mean stem area and vessel diameter were measured; and mean hydraulic diameter was calculated for vessels in the area of dye translocation. Overall, Lapins/Gi5 stem area in the graft union was larger compared to Lapins/Colt; however dye translocation in Lapins/Gi5 was reduced compared to other tissues in the tree. Confocal microscopy indicated dye uptake through the grafted region was more uniformly distributed in Lapins/Colt than in Lapins/Gi5, with dye accumulation in areas of maximum translocation. Vessel diameter did not differ in these areas of translocation. However, in both combinations there was a reduction in mean hydraulic diameter of graft union sections, suggesting a reduction in vessel efficiency to translocate water in this region. Vascular system anomalies were more frequent in Lapins/Gi5, disrupting acropetal dye translocation. This suggests the greatest reduction in vascular transport is in Lapins/Gi5.

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Mercy Olmstead, Timothy W. Miller, Callie S. Bolton, and Carol A. Miles

Consumer demand for organic and sustainably produced products has increased the interest in organic wine grape (Vitis vinifera) production. However, organic production can be challenging, and weed management is a critical issue during the establishment of an organic vineyard. In 2009, the effectiveness of five cover crop treatments and cultivation regimes was evaluated for two years for weed control in a newly established organic vineyard of ‘Pinot noir précoce’ and ‘Madeleine angevine’ grape cultivars in northwestern Washington State. Alleyway management treatments were cultivation in alleyways with hand weeding in the vine row (control), grass cover crop which included perennial ryegrass (Lolium perenne ssp. perenne) and red fescue (Festuca rubra ssp. arenaria) seeded in the alleyway and in-row tillage with a specialty offset-type cultivator, winter wheat (Triticum aestivum) cover crop with in-row string-trimming, austrian winter pea (Pisum sativum ssp. sativum var. arvense) cover crop with in-row string-trimming, and winter wheat–austrian winter pea cover crop mix with in-row string-trimming. In 2009, weed dry biomass was lowest in the alleyway of the control (0.8 g·m−2) and offset cultivator treatments (6.3 g·m−2) on 3 Aug. and tended to be lowest in the alleyway of the control (4.8 g·m−2) and offset cultivator treatments (16.0 g·m−2) on 27 Sept. In the second year of establishment (2010), winter wheat and austrian winter pea were eliminated from the plots by mid-July, and white clover (Trifolium repens) and perennial ryegrass were the dominant weed species and accounted for a majority of the total weeds. On average over the two-year period, the control treatment required the most time for alleyway management (92 h·ha−1) followed by the offset cultivator treatment (64 h·ha−1), while the winter wheat, austrian winter pea, and winter wheat–austrian winter pea mixture required 32 to 42 h·ha−1. ‘Madeline angevine’ produced more shoot growth than ‘Pinot noir précoce’ in Sept. 2010 (42.3 and 25.9 cm respectively), and shoot growth of both cultivars in the control treatment was significantly longer (125.0 cm) than under any other treatment (55.4 to 93.0 cm), illustrating the importance of weed control during vineyard establishment. In this study, the most effective weed management regime, although also the most time consuming, included a vegetative-free zone around the vines (e.g., in-row) maintained by hand weeding and a cultivated alleyway.