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Andrew S. Wang

Friable embryogenic callus of American ginseng (Panax quinquefolium L.) was induced from root pith on Murashige and Skoog medium supplemented with 2 mg 2,4-D and 1 mg KIN/liter. Optimal callus growth occurred on medium containing 1.5 mg dicamba/liter. Plants were regenerated on MS medium supplemented with various concentrations of plant growth regulators (PGRs); the best PGR combination was 0.5 mg IBA and 0.1 mg NAA/liter. Chemical names used: (2,4-dichlorophenoxy) acetic acid (2,4-D); 3,6-dichloro-o-anisenic acid (dicamba); 6-benzylaminopurine (BA); gibberellic acid (GA); indole-3-butyric acid (IBA); kinetin (KIN); and naphthaleneacetic acid (NAA).

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Yan Wang and S.J. Kays

Breeding sweetpotatoes [Ipomoea batatas (L.) Lam.] for improved flavor would be greatly facilitated by understanding the flavor chemistry of the crop. To ascertain the chemical composition of the aroma, an aroma extract of baked `Jewel' sweetpotatoes was obtained using a cold solvent trap system and analyzed by gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS) and gas chromatography olfactometry (GCO) using aroma extract dilution analysis (AEDA). GC with a flame ionization detector (GC-FID) revealed ≈60 compounds presented in the aroma extract, of which 48 were identified. Olfactory evaluation of the eluted compounds using GC with a thermal conductivity detector (GC-TCD) indicated the presence of 37 odor-active peaks in the aroma extract. Three compounds, phenylacetaldehyde (perfume), maltol (caramel), and methyl geranate (2,6-octadienoic acid, 3,7-dimethyl-, methyl ester) (sweet candy) possessed the highest flavor dilution (FD) values (1500) via AEDA. 2-Acetyl furan (baked potato), 2-pentyl furan (floral), 2-acetyl pyrrole (sweet, caramel), geraniol (sweet floral), and β-ionone (violet) had FD values of 1000. These compounds are thought to be the most potent odorants in baked `Jewel' sweetpotatoes. Additionally, 1,2,4-trimethyl benzene, 2-furmethanol, benzaldehyde, 5-methyl-2-furfural, linalool, isopulegone, n-decanal, 2,4-decadienal, octyl ketone, α-copaene, 4-decanolide, and one unidentified compound were also contributors to the aroma. There was not a character impact compound that comprised the basic baked sweetpotato aroma. The aroma appeared to be made up of a relatively complex mixture of compounds. Maillard and/or caramelization reactions, Strecker degradation of phenylalanine, lipid and carotenoid degradation, and the thermal release of glycosidically bound terpenes appear to be involved in the formation of the characteristic aroma of baked `Jewel' sweetpotatoes.

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Shiow Y. Wang and Kim S. Lewers

Fruit of the cultivated strawberry (Fragaria ×ananassa Duchesne ex Rozier) are a good source of natural antioxidants, which play an important role in protecting human health. Antioxidant levels vary considerably among strawberry genotypes. The cultivated strawberry is a hybrid of two very different wild progenitor species: F. virginiana Mill. and F. chiloensis (L.) Mill. The progenitor species are valued by strawberry breeders as sources of novel traits, but have not been evaluated for antioxidant capacity or levels of antioxidant compounds. The objectives of this study are 1) to evaluate the antioxidant contents and antioxidant activities in representatives of F. virginiana and F. chiloensis in comparison with representatives of the cultivated strawberry species (F. ×ananassa), 2) to determine which strawberry compounds are most closely correlated with antioxidant capacity among these three species, and 3) to identify wild strawberry genotypes with high antioxidant activity and bioactive compounds for use in cultivar development. Fruit of 19 accessions from each of the three species, cultivated strawberry plus the two progenitor species (F. ×ananassa, F. virginiana, and F. chiloensis), were evaluated for levels of antioxidant capacity (oxygen radical absorbance capacity), total phenolics, total anthocyanins, ellagic acid, quercetin 3-glucoside plus quercetin 3-glucuronide, kaempferol 3-glucoside, kaempferol 3-rutinoside, p-coumaryl–glucose, pelargonidin 3-glucoside, pelargonidin 3-glucoside–succinate, cyanidin 3-glucoside, and cyanidin 3-glucoside–succinate. Fruit of the 13 accessions tested from the wild progenitor species F. virginiana had significantly higher antioxidant capacity, total phenolics, and total anthocyanins than did the fruit of three accessions tested from the cultivated strawberry F. ×ananassa, or the three accessions tested from the other wild progenitor species (F. chiloensis), and will be valuable as a source of parent material for developing more nutritious strawberry cultivars. The high correlation with antioxidant capacity, relative efficiency, and lack of genotype-by-year interaction in this study suggests that the measurement of total phenolics may be the better assay to use for the later selection stages in a strawberry cultivar development program. Of the evaluated F. virginiana accessions, NC 95-19-1, JP 95-1-1, CFRA 0982, NC 96-5-3, and RH 30 fruit were highest in antioxidant capacity and should prove useful toward development of strawberry cultivars with high antioxidant capacities.

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Wang Koon-Hui, Brent S. Sipes, and Adelheid R. Kuehnle

Radopholus similis distribution in Anthurium plant tissue was determined in a greenhouse experiment. Two thousand mixed life stages of R. similis per plant were inoculated onto Anthurium cultivars `Alii' and `Midori'. Nine months later, nematodes per gram of tissue were determined from stem sections (0-3, 3-6, and above 6 cm from the base), the lowest leaf petiole, and root tissue. R. similis occurred in all stem sections, leaf petioles, and roots in both `Alii' and `Midori'. Nematode distribution differed between the two cultivars. `Midori' had higher numbers of nematode in the roots whereas `Alii' had higher numbers of nematode in the stem sections and first leaf petiole. Anthurium apical stem cuttings could be contaminated with R. similis and may not be a nematode-free propagation material.

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George F. Kramer, Chien Yi Wang, and William S. Conway

Pressure infiltration of `Golden Delicious' and `McIntosh' apples (Malus domestica Borkh.) with polyamides resulted in an immediate increase in firmness. `Golden Delicious' apples were 2.7 N (0.25 mM spermidine) to 6.7 N (1.0 mM spermine) firmer, while `McIntosh' apples were 2.2 N (0.25 mM spermidine) to 5.3 N (1.0 mM spermine) firmer than the water-treated control. During 28 weeks of storage at 0C, the differences between the polyamine-treated and water-treated apples were even larger. Similar results were observed with a 3% Ca treatment, but the Ca treatment reduced the rate of softening to a greater extent than did the polyamine treatments in `Golden Delicious'. Polyamides increased the endogenous levels of the polyamides infiltrated; however, the levels declined rapidly with time in storage. Both polyamine and Ca inhibited the development of chilling injury symptoms (brown core) in `McIntosh'. The influence of polyamines on ethylene production was negligible in both cultivars. The Ca treatment, however, inhibited ethylene evolution in `Golden Delicious'. Polyamides, thus, may affect apple softening through rigidification of cell walls rather than through interactions with ethylene metabolism.

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H. Wang, S. Parent, A. Gosselin, and Y. Desjardins

Micropropagated plantlets of Gerbera jamesonii H. Bolus ex Hook. F. `Terra Mix', Nephrolepis exaltata (L.) Schott `Florida Ruffles', and Syngonium podophyllum Schott `White Butterfly' were inoculated with two vesicular-arbuscular mycorrhizal (VAM) fungi, Glomus intraradices Schenck and Smith and G. vesiculiferum Gerderman and Trappe. They were potted in three peat-based media to determine the effects of mycorrhizal peat substrate on acclimatization and subsequent growth of micropropagated plantlets under greenhouse conditions. Symbiosis was established between the three ornamental species and VAM fungi within 4 to 8 weeks of culture in the greenhouse, but not during acclimatization. Mortality of Gerbera and Nephrolepis mycorrhizal plantlets was reduced at week 8 compared to the noninoculated control. A peat-based substrate low in P and with good aeration improved VAM fungi spread and efficiency. Mycorrhizal substrates had a long-term benefit of increasing leaf and root dry weight of Gerbera and Nephrolepis. Mycorrhizal Gerbera plants flowered significantly faster than non-mycorrhizal plants.

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Yuefang Wang, Carol D. Robacker, and S.K. Braman

Azalea lace bug is the most serious pest of cultivated azalea. Though deciduous azaleas are generally considered to be more resistant to lace bug than are evergreen azaleas, some variation in resistance has been reported. The identification of the genetic and physiological basis of resistance is important to eventual development of resistant cultivars of both the deciduous and evergreen azaleas. The first step in this program is to evaluate a wide range of deciduous azaleas for level of resistance. Laboratory evaluations were conducted on nine species and two hybrid cultivars of deciduous azalea and a known susceptible cultivar of evergreen azalea, `Delaware Valley White'. Oviposition rate, rate of egg hatch, number of nymphs surviving, and percent damaged leaf area were evaluated for each of the tested genotypes. Results indicated a wide range of susceptibility, with R. canescens and R. periclymenoides plants highly resistant to infection, while R. atlanticum and R. viscosum were highly susceptible.

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F.D. Moore III, S.R. Nath, and Y-C Wang

Duration of growth is dependent on morphological events or changes in growth rate. It is the latter that is associated with phasic development. The most productive phase of plant growth is the linear or constant rate phase, primarily because it endures longer than the exponential phase. The purpose of our research was to objectively determine the true tree-height growth pattern, the linear and stationary phases of height growth, and to mathematically derive the maximum slope (maximum growth rate) of the growth curve, its location (inflection point), and the maximum slope of the logarithmic form (maximum relative growth rate) of the growth curve. The data were composed of 333 tree-height records covering 240 years from 200 beechwoods in the U.K. Height-age data were fitted using a splined function (S) and the Chapman-Richards function (CR). The growth curve and critical points on the curve were derived from the CR model. The linear phase began when trees were 9 and lasted 43 years. However, the stationary phase did not begin until age 162. Anecdotal evidence suggests that very little fruiting occurs before age 50. Based on derived critical points and anticipated source-sink dynamics, the reproductive stage should have taken place during the progressive “deceleration phase” when trees were between 31 (location of the maximum slope, also inflection point) and 162 (from quadratic root). The linear phase ended at 52 years, (coinciding with minimum acceleration) and may prove a more accurate estimate than 31. Maximum slope was 1.2 m per year occurring at age 31. Maximum slope of the log curve was 0.14 m·m–1 per year. The advantage of the CR function and the importance of the derived quantities and growth phases will be discussed.

Open access

Mohamed S. Elmongy, Xiuyun Wang, Hong Zhou, and Yiping Xia

Auxins and humic acid (HA) were investigated for their roles in adventitious root induction in azalea microshoots in our previous study. To reveal the regulatory mechanisms of auxins and HA in this process, measurements of the levels of reactive oxygen species (ROS), carbohydrates, and phenolic compounds and gene expression during in vitro root development were performed. During the adventitious root induction process, ROS levels in shoots treated with auxins and HA increased compared to untreated shoots, especially during the earliest period after transfer to the media. Media supplemented with NAA experienced increases in H2O2 contents by 480%and 250%, respectively, after 7 and 14 days of culture. The phenolic compound levels were also enhanced in the shoots treated with auxins and HA, reflecting the different rooting-promoting abilities of both auxins and HA. The highest levels of total phenolic [68.6 mg·g−1 fresh weight (FW)], polyphenolic acids (121.72 μg caffic acid/g FW), and total flavonols (162.42 μg quercetin/g FW) were recorded after 21 days for NAA media, but the maximum levels of anthocyanins (49.76 μg cyanindin/g FW) were recorded after 21 days for IBA medium. Soluble carbohydrate, starch, and soluble protein levels were increased in the shoots treated with all treatments; however, the influence of NAA treatments was stronger than that of other treatments for most investigated parameters. The NAA significantly enhanced soluble carbohydrates by 30%, 37%, and 25%, respectively, at 14, 21, and 28 days compared with untreated microshoots. Expression of the POD1 gene increased in the shoots submitted to HA treatment media. Expression levels of auxin response factors (ARFs) increased with IBA- and NAA-treated explants, suggesting that ARFs may have diverse regulatory roles in adventitious root induction in evergreen azalea. Moreover, the profiles of the IAA1, IAA9, IAA14, and IAA27 transcripts were analyzed to reveal their roles in the adventitious rooting of evergreen azalea microshoots. These results indicate that auxins and HA promote adventitious root induction in Rhododendron plants through their impact on ROS, carbohydrate contents, phenolic compound levels, and expression levels of different genes related to root development in evergreen azalea plants.

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Yuefang Wang, Carol D. Robacker, and S. Kristine Braman

The susceptibility of seventeen deciduous species or cultivars and one evergreen cultivar of azalea (Rhododendron spp.) to azalea lace bug (Stephanitis pyrioides Scott) was evaluated in field and laboratory experiments. Rhododendron canescens Michx. and R. periclymenoides (Michx.) Shinners were the most resistant species, followed by R. prunifolium (Small) Millais. Ratings were based on oviposition rate, percentage emergence from the egg, feeding damage, and nymphal growth rate. The most susceptible genotypes were TNLV1, R. oblongifolium (Small) Millais, R. alabamense Rehder, R. serrulatum (Small) Millais, R. viscosum (L.) Torr., `Buttercup', and `My Mary'. Leaf water content and leaf pubescence were significantly different among taxa. However, leaf water content was not significantly correlated with azalea lace bug performance, and insufficient evidence was available to conclude that leaf pubescence was involved in azalea lace bug resistance.