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Patrick J. Conner and Dan MacLean

Anthocyanin content and composition and CIE 1976 (L*, a*, b*) color space (CIELAB) color coordinates were examined for the skin of 22 muscadine grape (Vitis rotundifolia Michx.) cultivars and Muscadinia Planch germplasm. Analysis of berry skin extracts by high-performance liquid chromatography (HPLC) determined that anthocyanin content varied from less than 100 μg·g−1 in bronze and pink berries to over 5500 μg·g−1 in highly pigmented black berries. The anthocyanins delphinidin, cyanidin, petunidin, pelargonidin, peonidin, and malvidin were detected in their 3,5-diglucosidic forms. Analysis of berry color with a colorimeter revealed chroma (C*) ranged from 2.4 to 22.8 with the highest values occurring in bronze- and red-colored berries. As anthocyanin concentration increased, lightness (L*) decreased to a low of 20 to 23 in black-colored berries. Pink and red skin colors were primarily a result of lower levels of total anthocyanins, although there was also a shift away from delphinidin and petunidin production toward more cyanidin and peonidin. Malvidin, the most important anthocyanin for muscadine wine and juice color stability, was only abundant in a few clones, all of which had V. munsoniana (Simpson ex Munson) Small or V. popenoei (Fennell) Small in their pedigree. The interspecific hybrid ‘Fennell’s 3-way Hybrid’ had the largest proportion of malvidin, contributing ≈58% of the total anthocyanin content. This clone also had low levels of delphinidin and high total levels of anthocyanin, making it a promising source for the improvement of muscadine grape pigment profiles.

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Dan D. MacLean and D. Scott NeSmith

A postharvest 1-methylcyclopropene (1-MCP) treatment was evaluated for its ability to maintain firmness and delay the ripening of rabbiteye blueberries. Three cultivars, Austin, Brightwell, and Premier, were harvested by hand from the UGA Alapaha Blueberry Farm and treated overnight with 1 μL·L−1 1-MCP as field heat was being removed [0 to 1 °C, 90% to 95% relative humidity (RH)]. Fruit were evaluated for firmness, total soluble solids (TSS), total acidity (TA), ethylene production, and other quality attributes at 0, 1, and 2 weeks after harvest as well as 1 or 4 days post-removal evaluations at room temperature (≈21 °C). In general, the 1-MCP treatment resulted in the stimulation of ethylene production in all three cultivars but had minimal effect on TSS and TA content. Furthermore, the treatment resulted in an accelerated loss of firmness in ‘Brightwell’. The lack of inhibition of fruit ripening likely related to the fact that blueberries were harvested, and subsequently treated with 1-MCP, at a post-climacteric stage of development. Based on current results, more information is required regarding ethylene production during rabbiteye blueberry fruit maturation before establishing a 1-MCP treatment recommendation for use by the rabbiteye blueberry industry.

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Dan D. MacLean*, Dennis P. Murr and Jennifer R. DeEll

Glutathione S-transferase (GST) is a ubiquitous and constitutive enzyme that is involved in numerous cellular activities including the amelioration of oxidative stresses caused by the presence of xenobiotics and reactive oxygen species. In the present study, a glutathione S-transferase was extracted, purified, and partially characterized from two types of pome fruits. Pear (Pyrus × communis L., cultivar D'Anjou) and apple (Malus × domestica Borkh., cultivar Delicious) fruit were tested. The glutathione S-transferase was extracted using traditional methods, and purified using a combination of ammonium sulfate precipitation, dialysis, and GST-specific affinity chromatography. The GST enzyme was subsequently eluted from the column and concentrated prior to characterization studies. A purified fraction from the column was loaded onto an SDS-PAGE gel, and resulted in a single band with an apparent molecular weight of ≈26 kDa. This band was excised and used for MALDI-TOF/MS peptide mass fingerprint studies, and also served to confirm the apparent mass of the protein (25969 Da). The ExPASy software was used for the peptide mass fingerprint study, where the digest of the GST using trypsin was compared to a theoretical digest of an Arabidopsis GST, and resulted in two peptides of significant mass homology. The purified GST was also tested for enzyme activity using the standard assay substrate of 1-chloro-2,4-dinitrobenzene and reduced glutathione. Total GST protein extracted from `D'Anjou' pear was 0.532 mg·mL-1, while `Delicious' apple contained 0.127 mg·mL-1. The activity of GST enzymes may play a role in minimizing oxidative stress injury in stored pear and apple tissues.

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Dan D. MacLean, Dennis P. Murr, Jennifer R. DeEll and Eugene Kupferman

The ethylene antagonist 1-methylcyclopropene (1-MCP) was investigated for its potential impact on the transcription of key flavonoid biosynthetic (PAL and CHS) and ethylene perception (ERS1) genes during the postharvest storage of pear (Pyrus × communis L.). Optimally harvested red and green `d'Anjou' fruit were treated with 1 μL·L-1 1-MCP for 24 h at 0 °C to 1 °C, and subsequently placed in cold storage (0–1 °C, 90–95% RH). Fruit were removed every 21 days for 126 days, and evaluated for firmness, TSS, and ethylene and volatile production for up to 10 days (≈21 °C). Tissue samples were collected for Northern blot analysis and determination of flavonoid and chlorogenic acid content. PAL content increased during the 1-week simulated marketing period irrespective of storage duration, which coincided with an increase in respiration and ethylene content. Although it was still detectable, total PAL content was dramatically reduced by the 1-MCP treatment. CHS was abundant immediately after harvest and after removal from storage, but declined rapidly thereafter, and was not detectable after 1 week at room temperature. The 1-MCP treatment further exacerbated this decreasing trend in CHS content. ERS1 content appears to be stable throughout storage and the simulated marketing period, with levels lower in 1-MCP-treated fruit. These results suggest that 1-MCP significantly inhibits the transcription of key flavonoid and ethylene regulatory enzymes, possibly compromising the nutraceutical content of pear fruit. The increase in PAL with the concomitant decrease of CHS after removal from storage suggests a diversion of carbon from flavonoid compounds into simple phenols, such as chlorogenic acid.

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Cecilia McGregor, Vickie Waters, Savithri Nambeesan, Dan MacLean, Byron L. Candole and Patrick Conner

Developing high levels of resistance to Phytophthora blight (Phytophthora capsici Leonian) of pepper (Capsicum annuum L.) is a goal of many pepper breeding programs. Genetic diversity and plant characteristics were evaluated on 21 pepper accessions previously identified as having high levels of Phytophthora root rot resistance. Accessions were evaluated for plant height, fruit size and shape, pericarp thickness, and pungency. Accessions varied widely from very unadapted material to those with more obvious breeding potential. Genetic diversity among the accessions was estimated using 22 simple sequence repeat (SSR) loci. Phytophthora capsici resistant accessions were identified that were not closely related to previously described sources of resistance. This information will allow breeders and researchers to further identify and incorporate novel sources of resistance to P. capsici into breeding programs. Accessions PI 201237 and PI 640532 appear to have the most potential for introgressing P. capcisi resistance into bell pepper.

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Juan C. Díaz-Pérez, Dan MacLean, Smiljana Goreta, Sarah Workman, Erick Smith, Harwinder Singh Sidhu, Gunawati Gunawan, Anthony Bateman, Jesús Bautista, William Lovett, Maja Jukić Špika, Gvozden Dumičić and Mira Radunić

Pomegranate (Punica granatum L.) is a nonclimacteric fruit sold fresh as whole fruit or arils (fleshy seeds). It is also used for the production of juice, wine, and syrup. Pomegranate is popular due to its numerous health benefits. In the United States, it is grown primarily in California and other semi-arid regions, with Wonderful being the most widely grown cultivar. However, preliminary research has shown that ‘Wonderful’ produces low yields in Georgia, thus indicating the need to identify cultivars better suited for warm and humid conditions, such as those of the southeastern United States. The objective of this study was to determine the physical and chemical quality attributes of pomegranate cultivars grown in Georgia. Pomegranate fruit from 40 cultivars were harvested during 2012 to 2017. Individual fruit weight varied from 124 g for ‘Utah Sweet’ to 631 g for ‘C1’. The total fruit weight percentage accounted for by fresh aril weight (aril fraction) ranged from 22% for ‘C8’ to 70% for ‘JC’. Individual aril weight ranged from 174 mg for ‘Utah Sweet’ to 638 mg for ‘Cloud’. Across cultivars, individual fruit weight increased linearly with the increasing number of arils. Aril color varied from white to deep red. The arils L* value ranged from 15.7 (dark arils) for ‘Crown Jewel’ to 46.1 (light arils) for ‘Utah Sweet’. The a* values ranged from 0.6 (white arils) for ‘Cloud’ to 20.5 (red arils) for ‘Crab’. The b* values ranged from 8.7 for ‘DJ Forry’ (from a store) to 62.5 for ‘R9’. The Chroma* values ranged from 13.4 for ‘Cloud’ to 24.3 for ‘Crab’. The hue° values ranged from 29.7 for ‘Wonderful’ (from a store) to 87.1 for ‘Cloud’. Rind color was related to the color of the arils; high a* values in the rind and arils were associated with the red color. The fruit juice content ranged from 174 mL·kg−1 fruit for ‘Utah Sweet’ to 638 mL·kg−1 fruit for ‘Cloud’. Cultivars varied from tart to sweet. The fruit soluble solids concentration (SSC) ranged from 10.8% for ‘Sin Pepe’ to 16.4% for ‘Crown Jewel’. Fruit titratable acid (TA) ranged from 0.27% for ‘Sin Pepe’ to 6.20% for ‘Utah Sweet’. The juice maturity index measured as the SSC/TA ratio ranged from 1.9 for ‘Utah Sweet’ to 39.5 for ‘Sin Pepe’. The juice total phenols (measured as gallic acid equivalents) ranged from 463 mg·L−1 for ‘JC’ to 2468 mg·L−1 for ‘Wonderful’ (Georgia). Trolox equivalent antioxidant capacity values of juice ranged from 10,001 µM for ‘King’ to 59,821 µM for ‘I11’. Cupric reducing antioxidant capacity values in juice ranged from 7471 µM for ‘Azadi’ to 20,576 µM for ‘Wonderful’ (Georgia). Juice total anthocyanins varied from 1.7 mg·L−1 for ‘R19’ to 50.0 mg·L−1 for ‘Wonderful’ (Georgia). Pomegranate cultivars showed large variability in physical and chemical attributes. Such pomegranate variability represents opportunities for breeding, for the retail market, and for the development of different products by the food industry.