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Yan Wang

Alternatives to ethoxyquin (Etq) are needed for controlling superficial scald of ‘Anjou’ european pears (Pyrus communis) during long-term storage. The current commercial standard storage conditions [Etq + −1 °C + controlled atmosphere (CA) with 1.5 kPa O2] reduced scald occurrence compared with control fruit (−1 °C + CA) during 6–8 months storage. At 1 °C in air, 1-methylcyclopropene (1-MCP) fumigation at 0.15 µL·L−1 at harvest was more efficient on reducing scald than Etq but did not prevent scald during 6–8 months storage. The 1-MCP-treated fruit at 1 °C in air developed their ripening capacity at 20 °C following 6–8 months storage but had deceased shipping ability (softening and yellowing of fruit). Although Etq inhibition of scald was associated with the inhibition of α-farnesene oxidation to conjugated trienols (CTols); 1-MCP reduced α-farnesene synthesis and thereby the availability of substrate to oxidize to CTols. CA storage at 1.5 kPa O2 totally prevented scald and retarded the loss of shipping ability without affecting the ripening capacity of 1-MCP-treated fruit at 1 °C through further decreases in the syntheses of ethylene, α-farnesene and CTols during 6–8 months storage. In addition, 1-MCP prevented a CA-induced disorder, pithy brown core (PBC), in ‘Anjou’ pears possibly through enhancing an oxidative/reductive metabolic balance during extended storage. In conclusion, the combinations of 1 °C + 1-MCP + CA is a potential commercial alternative to Etq for scald control while allowing the 1-MCP-treated ‘Anjou’ pears to recover ripening capacity during the shelf life period after 6–8 months storage.

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Yan Xu and Yuejin Wang

Expressed sequence tags (ESTs) constitute a rapid and informative strategy for studying gene-expression profiles of specific stages of annual and perennial plant species. Compared with annual plants, the NCBI database has very little sequence information from perennial plant species. To date, only ∼145 ESTs of Vitis pseudoreticulata W.T. Wang have been deposited in databases. This is insufficient to understand the biology and development of this species. In this report, a cDNA library constructed from young leaf inoculated with powdery mildew pathogen [Uncinula necator (Schw.) Burr.] of Chinese wild Vitis pseudoreticulata. Leaf was harvested at various times after inoculation for total RNA extraction, which was used to generate ESTs. In our study, 107 cDNA clones were sequenced either from 5' or 3' end of the cDNAs. Among them, 60 unigenes (56%) were functionally characterized by the BLASTX matches to known function proteins, and 20 unigenes (18.6 %) matched significantly with those having unknown function in the public databases. The remaining 27 unigenes (25.2%) failed to show significant homology to any proteins in the public databases, suggesting that they represent novel sequences. Some functional genes identified from the cDNA library to be potentially associated with plant defence-related responses are discussed.

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Stanley J. Kays and Yan Wang

Using the sweetpotato as a model, we identified precursors of critical flavor volatiles by fractionating, based upon solubility, raw roots into major groups of constituents. Volatile thermophyllic products from the individual fractions were analyized and compared to those from non-extracted root material. Volatile components were seperated and identified using GC-MS and quantified using internal standard methodology. Mechanisms of synthesis of flavor volatiles via thermophyllic reactions will be discussed, as will postharvest treatments that can modulate eventual aromatic properties of cooked plant products.

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Yan Wang and Stanley J. Kays

The sweetpotato weevil is the single most critical insect pest of the sweetpotato worldwide. While male weevils can be lured to traps using a synthetic female pheromone, crop losses are not adequately reduced since damage is caused by the larvae arrising from eggs laid by female weevils in the storage roots. Identification of a female attractant could greatly enhance the control of the insect. The leaves and storage roots are known to emit volatiles that attract the female and in the following tests, we demonstrate that feeding by female weevils stimulates the synthesis of a volatile attractant which attracts additional females to the root. Undamaged, artificially damaged, and female weevil feeding damaged periderm were tested in dual-choice and no-choice olfactometers. Volatiles from feeding damaged roots were significantly more attractive than undamaged and artificially damaged roots. To test whether the volatile attractant was of weevil or root origin, volatiles were collected in MeCl2 after removal of the weevils and fractionated on a megabore DB-1 capillary column using a GC fitted with a TC detector. Fractions were collected from the exit port and their activity index (AI) determined using dual choice and no choice olfactometry. The active fraction was ascertained and active components identified via GC-MS.

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Stanley J. Kays and Yan Wang

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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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Yan Wang and Stanley J. Kays

The sweetpotato weevil (SPW) [Cylas formicarius elegantulus (Summers) (Coleoptera: Curculionidae)] is the single most devastating pest of the sweetpotato [Ipomoea batatas (L.) Lam.] worldwide. Attempts to develop host-plant resistance have been only moderately successful due in part to deficiencies in parent and progeny selection methods. Host-plant phytochemicals play critical roles in insect behavior, modulating a cross-section of key behavioral decisions. Thus, identification of the phytochemicals the female weevil uses in decision making could greatly facilitate development of host-plant resistance. The volatile chemistry of the sweetpotato was studied in relation to the host-finding behavior of the female weevil. Critical biologically active volatiles were determined via isolation (Tenax trapping), fractionation (gas chromatography-thermal conductivity detector), identification (gas chromatography and gas chromatography-mass spectroscopy), and bioassay (olfactometry). Differences in volatile chemistry among sweetpotato clones that may relate to differences in resistance or susceptibility to the female SPW were assessed. Volatile extracts from storage roots (site of oviposition) and aerial plant parts were attractive to female SPW, the former being substantially greater. In total, 33 compounds were identified from storage roots and aerial plant parts, including 23 terpenes. Three oxygenated monoterpenes (nerol, Z-citral, and methyl geranate), found in storage roots but not aerial plant parts, were identified as attractants. The sesquiterpene volatile fraction was repellent to female SPW with α-gurjunene, α-humulene, and ylangene active in the concentration range emanating from storage roots. The aerial plant parts emanated a higher composite concentration of sesquiterpenes than storage roots. Differences in the relative attraction among four sweetpotato cultivars to female SPW was inversely correlated with the composite concentration of headspace sesquiterpenes. Selection of clones with decreased volatile attractants and/or increased deterrents using an analytical means of quantification may significantly facilitate developing resistance to the SPW.

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Yan Wang and Stanley J. Kays

Flavor quality is one of the most difficult traits to select in plant breeding programs due to the large number of sensory panelists required, the small number of samples that can be evaluated per day, and the subjectivity of the results. Using sweetpotato [Ipomoea batatas (L.) Lam.] as a model, clones exhibiting distinctly different flavors were analyzed for sugars, nonvolatile acids, and aroma chemistry to identify the critical flavor components. Differences in sugars, sucrose equivalents, nonvolatile acids, and 19 odor-active compounds were identified that accounted for differences in flavor among the clones. Using the intensity of the aroma per microliter for each of the 17 most important aroma-active compounds (maltol, 5-methyl-2-furfural, 2-acetyl furan, 3-furaldehyde, 2-furmethanol, benzaldehyde, phenylacetaldehyde, β-ionone, 1,2,4-trimethyl benzene, 2-pentyl furan, 2,4-decadienal, 2,4-nonadienal, linalool, geraniol, cyperene, α-copane and a sesquiterpene) and the relative sweetness of individual sugars × their respective concentrations, multivariate (principal component and cluster) analysis allowed accurate classification of the clones according to flavor type without sensory analysis. The level of precision was such that sweetness, starch hydrolysis potential, and the concentration of β-carotene could be accurately predicted by quantifying specific volatiles. Analytical assessment of flavor would greatly facilitate the accurate evaluation of large numbers of progeny, the simultaneous selection of multiple flavor types, and the development of superior new cultivars for a wide cross-section of food crops.

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Todd C. Einhorn, Yan Wang and Janet Turner

Sweet cherry (Prunus avium L.) producers in the Pacific Northwest have devoted considerable acreage to late-maturing cultivars. By using these cultivars to extend the harvest window, producers avoid lower returns associated with cherries harvested during the peak period (i.e., midseason) when supplies are overly abundant. Over several years, we evaluated preharvest applications of gibberellic acid (GA3) between 10 and 100 ppm (a.i.) on the late-maturing sweet cherry cultivars Lapins, Skeena, Staccato, and Sweetheart. Individual trials examined the timing of GA3 applications and/or rate on fruit quality attributes at harvest and after 4 weeks of cold storage at 0 °C. The influence of GA3 timing and/or rate on sweet cherry skin color and harvest delay was also evaluated. Multiple applications split between the end of Stage II (pit hardening) and mid-Stage III (final fruit swell) of fruit development did not improve fruit quality attributes or delay skin color development of ‘Skeena’ and ‘Sweetheart’ compared with equivalent concentrations applied once at the end of Stage II. Low concentrations (between 10 and 25 ppm) consistently improved fruit firmness (FF) of all cultivars by 10% to 43%. No further improvements in FF were observed when rates exceeded 25 ppm. Skin color development was retarded by GA3 but did not respond in a consistent manner to increasing rate. Fruit size was not uniformly increased by GA3. In trials where GA3 had a positive effect on fruit size, the effect was observed at low concentrations and was not further improved with increasing rate. A cultivar-dependent response to GA3 was observed for return bloom. ‘Skeena’ reproductive buds per fruiting spur and flowers per floral bud in years after treatment were unaffected by GA3 concentration. On the contrary, the number of flowers per bud of ‘Lapins’ was significantly reduced to 79% and 38% of control levels for 50 and 100 ppm GA3, respectively. At 100 ppm, GA3 additionally limited the number of reproductive buds returning on fruiting spurs of ‘Lapins’. GA3 reduced stem browning and surface pitting disorder of ‘Sweetheart’ and ‘Lapins’ after 4 weeks of cold storage at 0 °C; however, these effects were optimized at 25 ppm. Respiration rate and weight loss were unaffected by GA3 at harvest or after 2 and 4 weeks of cold storage. Unidentified endogenous factors that regulate FF and are inducible by GA3 appear to be largely responsible for improved resistance to pitting. Collectively, the results demonstrate high sensitivity of cherry FF and skin color to GA3. Split applications did not provide further harvest delays or affect any of the attributes evaluated, possibly because low rates (20 ppm) applied at the first timing were sufficient to saturate the response. In general, fruit quality of late-maturing cultivars of sweet cherry was improved by low rates of GA3 applied in a single application at the end of pit hardening.

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Xingbin Xie, Congbing Fang and Yan Wang

Bosc is a winter cultivar of european pear (Pyrus communis) that has a relatively short storage life partially due to a high ethylene production rate (EPR) during cold storage. ‘Bosc’ pears were harvested at commercial maturity and treated with gas 1-methylcyclopropene (1-MCP) at 0, 0.15, and 0.3 µL·L−1 and stored at −1.1 °C for 8 months. Results indicated that all 1-MCP treatments inhibited EPR and respiration rate (RR), retarded the degradation of chlorophyll and titratable acidity (TA), and extended storage quality; but inhibited ripening capacity. 1-MCP at 0.15 and 0.3 µL·L−1 had the same efficacy on keeping fruit quality although its higher rate was more efficient on inhibiting EPR and RR. The expression of ethylene synthesis genes (PcACS1, PcACS2, PcACS4, PcACS5, and PcACO1) and receptor genes (PcETR1, PcETR2, and PcERS1) was upregulated in control fruit during storage and they were downregulated significantly by 1-MCP treatments. In contrast, the ethylene receptor genes of PcETR5 and PcCTR1 were downregulated in control fruit during storage and were unaffected by 1-MCP treatments. Although the transcription levels of chlorophyll degradation genes PcPPH, PcNOL, PcSGR, PcRCCR, PcNYC, and PcPAO were all upregulated in control fruit during storage and downregulated by 1-MCP; only PcCHL was downregulated in the control and 1-MCP had no consistent effect on it. The relationship of ethylene biosynthesis/perception with chlorophyll degradation and storage quality in european pears was discussed.