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  • Author or Editor: Xu Lu x
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`Pam' is a popular muscadine grape (Vitis rotundiforia) used for the fresh fruit market. It is characterized with large berry, nice appearance, good texture and flavor, and high disease resistance. This cultivar, however, requires pollinators because it is pistillate. To select a better pollinator for this pistillate cultivar, a 2-year study was conducted at Florida A&M University in 2003 and 2005. Fresh pollen of muscadine grape `Alachua', `Nesbitt', and `Noble' was used for pollination. `Nesbitt' pollen resulted in 100% of the pollinated clusters setting fruits in both years, while pollination with `Alachua' yielded 70% (2003) to 87% (2005) of fruiting clusters, and `Noble' pollen yielded 72% (2003) and 97% (2005) fruiting clusters, respectively. Fruit numbers per fruiting cluster also varied among pollen sources. `Alachua' pollen resulted in 7.2 (2003) and 8.1 (2005) fruits per cluster, while `Nesbitt' produced 10.1 (2003) to 10.5 (2005) fruits per cluster, and `Noble' produced 8.3 (2003) and 9.0 (2005) berries per cluster. Open pollinated `Pam' had 100% clusters set fruits, averaging about 11 fruits per cluster in both seasons. No difference of berry size was observed among fruits produced from different pollen sources. Both sugar contents and acids levels were a little bit higher in 2005 than that in 2003. However, no differences of sugar content and acid level were found among the fruits derived from different controlled pollen sources. These data suggested that `Nesbitt' is a better pollinator than `Alachua' and `Noble' for `Pam' muscadine grape.

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Low frequency of in vitro regeneration has hampered the adoption of genetic engineering technique for improving the quality of muscadine grape. This study is to develop a straightforward method for high-frequency regeneration of muscadine grapes in vitro. Leaves, petioles, and immature ovules of muscadine grapes were cultured on various media. Embryogenic callus, somatic embryos were formed after 9 weeks inoculated on embryo rescue (ER) medium. The somatic embryos were isolated and subcultured on fresh medium to promote enlargement and increase the number of uniformly sized somatic embryos. Of the medium tested (MS, NN, and ER), the ER medium was the best for somatic embryo growth and multiplication. The somatic embryogenic lines were maintained by transferring the embryos to the fresh ER medium every 4 weeks. Germination was achieved by transferring these embryos to woody plant medium or NN medium. The frequency of somatic embryogenesis of embryo germination appeared to be genotype dependent. The establishment of the somatic embryogenesis system in this study should be a step forward in directly transferring a foreign gene into muscadine grape.

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Pierce's Disease (PD) is a major factor limiting grape production in the southeast United State. This disease is caused by a bacterium, Xylella fastidiosa Wells et al., which is transmitted to the xylem system of the grapevines primarily by glassy-winged sharpshooters (Homalodisca coagulata Say). Once it is in the xylem, the X. fastidiosa will use the xylem sap as a nutrient source to multiply, colonize, and eventually plug the xylem vessels and cause the PD in susceptible cultivars. On the other hand, symptoms of PD in tolerant cultivars do not appear until fruit maturation, and symptoms are rarely observed in PD resistant cultivars. In order to understand the correlation between X. fastidiosa and PD symptom development, a study was initialed to monitor X. fastidiosa in xylem of resistant, tolerant, and susceptible vines on a monthly basis. Presence of X. fastidiosa was detected directly from xylem sap of field-grown vines by medium culture and confirmed by polymerase chain reaction (PCR). Xylella fastidiosa was detectable throughout the growing season in PD susceptible cultivar `Chardonnay', PD tolerant Florida hybrid grape `Blanc du Bois', and muscadine cultivar `Carlos'. The bacteria were also appeared in the dormant vines with high density in cultivars `Chardonnay' and `Blanc du Bios'. Although X. fastidiosa was also found in dormant canes of `Carlos', the density decreased throughout the late fall and winter months, and they were hardly found before June. The results indicated that X. fastidiosa were carried over from previous season in cultivars `Chardonnay' and `Blanc du Bois', while in PD tolerant cultivar `Carlos', they were newly acquired from the sharpshooter feedings during the growing season.

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Muscadine grape industry in the southeastern United Sates is expanding in recent years. To provide necessary information for the growing industry, 50 muscadine grape cultivars were evaluated for vigor and fruit characteristics at Florida A&M Univ., Tallahassee, Fla. Vine vigor was measured by winter pruning weight and varied from 5.4 lb/vine to 35.7 lb/vine. Among these cultivars, Triumph, Summit, and Tara were the least vigorous, while `Carlos', `Fry Seedless', and `Gold Isle' produced the most pruning weight. Dry scar ranged from 60.6% (Darlene) to 97.7% (Dixie Red). Among the most important table grapes, `Nesbitt', `Alachua', `Jumbo', `Fry', `Triumph', and `Scarlete' showed more than 70% of dry scars. Fruit rot ranged from 0.3% (Gold Isle) to 31.8% (Dixie Land). `Noble', `Scarlet', `Nesbitt', and `Carlos' were the important cultivars with less than 5% rotted fruits. Commercial fruit index were different significantly among the cultivars, ranged from 45.5% to 96.4%. Higher commercial fruit index of table grapes were found with `Magnolia', `Rosa', `Scarlet', and `Tara', while `Dixie Land' (45.5%) was the least. Seeds per fruit varied among the cultivars, ranging from 2.4 to 4.9. Fewer fruit seeds were found in `Fry' and `Nesbitt', while `Granny Val', `Senoria', `Darlene' and `Triumph' had more seeds per fruit than the others. Seed size also differed among the cultivars. `Sugar Pop' had the largest seeds (0.144 g/seed), which was twice as the size of the smallest seeds of `Welder' (0.056 g/seed). Fruit soluble solids content (SSC) ranged from 11.7% to 16.9% among the cvs. evaluated. Higher SSCs were found in `Welder', `Fry Seedless', `Scarlet', and `Cowart', while `Senoria' and `Jumbo' had relatively low SSC.

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Ploidy level in grapevines varies, especially since in vitro techniques are employed in the breeding process and after plants are treated with either chemicals or radiation. Detection of ploidy level in grapevines by microscopic chromosome counting is complicated by their high number and the small size of chromosomes. Flow cytometry provides an accurate and rapid method in determining the ploidy level in plant tissue by measuring the nuclear DNA content in living cells and thus is a very useful tool in plant breeding or genetic studies. The objective of this research was to analyze the ploidy level of a selected group of muscadine vines that were different from normal diploid vines in morphology. These grapes were derived from either chemical treatment of known varieties or from controlled/open pollinations. Among the 26 grapevines investigated, 8 were found to be diploids, 11 were tetraploids, and 7 were chimeric aneuploids. Results of this study indicate that flow cytometry is a quick, reliable tool for determining ploidy levels of grapevines.

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Susceptibility to mechanical injury and fast decay rates are currently two main problems of litchi fruit after harvesting. To achieve better postharvest management of litchi fruit, this study aimed to find an effective method of litchi fruit supervision during the circulation process that included mechanical injury detection and storage quality detection. For mechanical injury detection, injury-free litchis without any treatment and litchis with mild and severe mechanical injuries were dropped from 80 and 110 cm high, respectively. The electronic nose (E-nose) response, total soluble solid (TSS), and titratable acidity (TA) of samples were tested on days 0, 1, 2, 3, 4, and 5 after injury at room temperature. For storage quality detection, normal litchis were stored in a cold environment. The E-nose response, TSS, and TA of samples were tested on storage days 0, 3, 6, 10, 15, 19, and 24. The experimental results showed that mechanical injury not only accelerated pericarp browning but also accelerated flavor (TA and TSS) loss. The browning index quickly increased during storage, and the TSS and TA of defect-free litchis changed only barely at room temperature and during cold environment storage. After feature extraction, mechanical injury of litchi can be well-detected by E-nose from day 1 to day 4 after injury. The best mechanical injury detection time of litchi fruit is at day 4 after injury under room temperature storage conditions. After singular sensor elimination and comprehensive feature extraction, the storage time and browning degree, but not TSS and TA, of litchi fruit can be detected by E-nose. E-nose data preprocessing should differ according to the litchi variety and detection target.

Open Access
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Ethephon [ETH (2-chloroethylphosphonic acid, an ethylene-releasing compound)] has been used as a plant growth regulator in turfgrass management. The aim of the study was to assess the effects of ETH seed treatment on drought tolerance of kentucky bluegrass (Poa pratensis) seedlings. Seeds of two kentucky bluegrass cultivars, Midnight and Nuglade, were exposed to ETH treatment or untreated as controls. Seedlings were then exposed to two water regimes: well-watered conditions and polyethylene glycol (PEG)–induced drought conditions. ETH-treated plants exhibited better turf performance relative to the untreated control under PEG-stressed conditions illustrated by higher relative water content (RWC) and lower lipid peroxidation and lower electrolyte leakage (EL). In both cultivars, ETH treatment increased enzyme activity of ascorbate peroxidase (APX), peroxidase (POD), and catalase (CAT); proline content; and soluble protein content under PEG-induced drought conditions. The results suggest that ETH seed treatment can improve drought tolerance in kentucky bluegrass seedlings.

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Visible/near-infrared (VIS/NIR) spectroscopy is a powerful tool for rapid, nondestructive fruit quality detection. This technology has been widely applied for quality detection of small thin-peel fruit, although less so for large thick-peel fruit because of the low signal-to-noise ratio of the spectral signal, resulting in a reduction of accuracy. More modeling work should be focused on solving this problem. This research explored a method of spectroscopy for the total soluble solid (TSS) content and acidity detection of ‘Shatian’ pomelo, which are two major parameters of fruit internal flavor. VIS/NIR spectral signal detection of 100 pomelo samples during storage was performed. Detection based on raw data, signal jitter, and scattered light noise removal, feature extraction, and deep learning were performed and combined with modeling detection to achieve an accurate step-by-step detection. Our results showed that 600 W is the optimal light intensity for detecting the internal flavor of pomelo. The TSS content of pomelo is optimally detected using Savitzky-Golay (SG) + multiplicative scatter correction (MSC) + genetic algorithm (GA) + principal component analysis (PCA) + convolutional neural network (CNN) + partial least squares regression (PLSR); however, acidity of pomelo is optimally detected using SG + MSC + GA + PLSR. With the optimal detection method, the coefficient of determination and root mean squared error (RMSE) of the validation set for TSS detection are 0.72 and 0.49, respectively; and for acidity detection are 0.55 and 0.10, respectively. Even though the accuracy is not high, the data are still acceptable and helpful in nondestructive quality grading of large quantities postharvest fruit. Therefore, our results demonstrated that VIS/NIR was feasible for detecting the TSS content and acidity of postharvest pomelo, and for providing a possible method for the nondestructive internal quality detection of other large thick-peel fruit.

Open Access

Biotechnology has great potential for grape genetic improvement. However, successful implementations of grape biotechnologies, such as transformation and in-vitro selection, are based on a high yield productivity of synchronized somatic embryos as well as an efficient single-cell regeneration system. Suspension culture has been known as an ultimate approach to provide those requirements. We recently developed the highly repeatable protocol for PEM suspension culture of `Autumn Royal Seedless' (Vitis vinifera L.). In a following experiment, three factors, including activated charcoal (AC), darkness, and full- or half-strength MS medium were tested for their impact on grape embryogenesis of PEM suspension cells. All three factors proved to be important for grape somatic embryogenesis. Darkness was the most-influenced factor among the three. After 4 weeks on full-strength MS medium plus AC, suspension cells mostly grew friable callus and somatic embryos were rarely observed under 16-h light conditions, whereas numerous somatic embryos were fully developed in darkness. Strength of MS medium and AC also affected grape somatic embyogenesis. In every combination tested, full-strength MS media was all superior to half-strength, which was more obvious under darkness. The AC had a positive effect for promoting of somatic embryogenesis.

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Amplified fragment length polymorphism (AFLP) was used to analyze genetic diversity of 100 accessions of Chinese bayberry (Myrica rubra Sieb. et Zucc.), one of the widely cultivated fruit tree crops in southern China. Six E-NN/M-NNN primer combinations were selected and a total of 236 bands were obtained, of which 177 were polymorphic (75.01%). An unweighted pair-group method of the arithmetic averages (UPGMA) was used to analyze the genetic relationships. The Dice's similarity coefficient among the Chinese bayberry accessions ranged from 0.75 to 1.00 and was 0.49 between Chinese bayberry and wax myrtle (M. cerifera L.). The 100 accessions of Chinese bayberry were clustered into two groups and seven subgroups. Subgrouping of Chinese bayberry was not related to the sex of the plant and color or size of the ripe fruit, but to some extent the region where the accession originated. However, the accessions from the same region did not necessarily belong to the same group or subgroup, which suggested the presence of extensive gene flow among different regions. Furthermore, close relationships between some morphologically similar accessions were found.

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