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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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C.K. Wan and F.G. Dennis Jr.

The roles of inhibitors in the seedcoat and locules and of seed water content in fruit-induced dormancy of apple (Malus domestics Borkh.) seeds were investigated. Seeds were after-ripened at 5C for various periods up to 12 weeks: 1) in the locules of intact fruits or half-fruits, 2) on wire mesh over moist filter paper, which simulated the locule in preventing leaching, or 3) on moist filter paper. The seeds were subsequently germinated in the locules of half-fruits, on screen, or on moist paper. In some experiments, the seeds were soaked in distilled water before or after after-ripening, or the embryos were excised before germination. The results indicate that fruit volatiles are unlikely to inhibit germination of seeds after-ripened in the fruit. Although limited water content reduced the ability of the seeds to germinate, it did not prevent after-ripening. An unidentified inhibitor(s) present in the locule and on the surface of the seed appears to be the major factor(s) preventing germination in the fruit, as seeds after-ripened on moist paper germinated well on paper or screen but poorly in the locule. The inhibitor(s) appears to be metabolized or to break down spontaneously when seeds are after-ripened on a screen, suggesting that the locule serves as a reservoir of the inhibitor as long as the seed remains in the fruit.

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Elizabeth A. Baldwin, Myrna O. Nisperos-Carriedo, and Manuel G. Moshonas

Whole tomato fruit (Lycopersicon esculentum Mill.), cvs. Sunny and Solarset, were analyzed at 5 different ripening stages for ethylene and CO2 production. Homogenates from the same fruit were prepared for determination of color, flavor volatiles, sugars and organic acids. Of the flavor volatiles measured, only eugenol decreased during ripening in both varieties and 1-penten-3-one in `Sunny' tomatoes. Ethanol, and trans-2-trans-4-decadienal levels showed no change or fluctuated as the fruit matured while all other volatiles measured (cis-3-hexenol, 2-methyl-3-butanol, vinyl guiacol, acetaldehyde, cis-3-hexenal, trans-2-hexenal, hexanal, acetone, 6-methyl-5-hepten-2-one, geranylacetone and 2-isobutylthiazole) increased in concentration, peaking in the later stages of maturity. Synthesis of some volatile compounds occurred simultaneously with that of climacteric ethylene and color. `Solarset' fruit exhibited higher levels of sugars and all flavor components except ethanol, vinyl guiacol, hexanal and 2-methyl-3-butanol in the red stage. There were no differences between these varieties for acids

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J.P. Mattheis and D.A. Buchanan

Apple fruit storage lie is prolonged by low-oxygen cold storage, however, ethanol accumulates when oxygen concentration is reduced below the Pasteur point, Upon return to aerobic conditions, dissipation of ethanol occurs due to physical (evaporation) and biochemical processes. Oxidation of ethanol by apple fruit occurs at a slow rate, but ethanol also serves es a substrate for fruit volatile synthesis. This study was conducted to determine changes in concentrations of ethanol and other non-ethylene apple fruit volatiles following periods of anaerobiosis. `Delicious' apples were obtained from a commercial warehouse and stored at 0.05% O2, 0.2% CO2 and 1 C. One day following return to ambient oxygen conditions, several volatiles were identified from anaerobic fruit that were nor produced by the control fruit. All were eaters that contained an ethyl group as the alcohol-derived portion, These included ethyl acetate, ethyl butyrate, ethyl 2-methyl butyrate, ethyl hexanoate and ethyl octanoate. Several esters produced by the controls were not detectable from anaerobic fruit including butyl butyrate, butyl 2-methyl butyrate, propyl hexanoate and 3-methyl butyl hexanoate. After 7 days ripening at 20 C, the amount of ethanol and the additional ethylesters was reduced in anaerobic fruit. Synthesis of esters produced by control fruit but nor by anaerobic fruit during the initial volatile sampling had resumed after 7 days.

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Mung Hwa Yoo, Youn Jung Kwon, Ki-Cheol Son, and Stanley J. Kays

Foliage plants of Hedera helix L. (english ivy), Spathiphyllum wallisii Regal (peace lily), Syngonium podophyllum Schott. (nephthytis), and Cissus rhombifolia Vahl. (grape ivy) were evaluated for their ability to remove two indoor volatile organic air pollutants, benzene and toluene. Removal was monitored when the aerial portion of plants was exposed singly to 1 μL·L-1 or to 0.5 μL·L-1 of each gas in a closed environment over 6-hour periods during the day and the night. Selected physiological processes were assessed before and immediately after treatment to determine the effect of the gases on the plants. The effectiveness of plants in the removal of air pollutant(s) varied with species, time of day, and whether the gases were present singly or as a mixture. When exposed to a single gas, S. wallisii, S. podophyllum, and H. helix displayed higher removal efficiencies (ng·m-3·h-1·cm-2 leaf area) of either gas than C. rhombifolia during the day. The efficiency of removal changed when both gases were present; H. helix was substantially more effective in the removal of either benzene or toluene than the other species, with the removal of toluene more than double that of benzene. When exposed singly, the removal of both compounds was generally higher during the day than during the night for all species; however, when present simultaneously, H. helix removal efficiency during the night was similar to the day indicating that stomatal diffusion for english ivy was not a major factor. The results indicated an interaction between gases in uptake by the plant, the presence of different avenues for uptake, and the response of a single gas was not necessarily indicative of the response when other gases are present. Changes in the rates of photosynthesis, stomatal conductance, and transpiration before and after exposure indicated that the volatiles adversely affected the plants and the effects were not consistent across species and gases. Deleterious effects of volatile pollutants on indoor plants may be critical in their efficacy in improving indoor air quality and warrant further study.

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Meny Benady, Amots Hetzroni, James E. Simon, and Bruce Bordelon

We have developed an electronic sensor (“sniffer”) that measures fruit ripeness rapidly and nondestructively by measuring the aromatic volatiles that are naturally emitted by ripening fruit. In this study, we evaluated the potential of using the fruit ripeness sniffer in the quality sorting of blueberries. Blueberries were first visually classified into four distinct ripeness classes: unripe; half-ripe; ripe; and over-ripe and quantitatively measured for color, firmness, TSS, and sugar acid ratio. Ripeness classification accuracy with the sniffer matched or exceeded that of all other ripeness indices. The sniffer differentiated unripe, ripe and over-ripe berries within one second, but could not distinguish between the unripe and half-ripe class. Detection of l-2 damaged or 1-2 soft fruit spiked within a large container of 24-37 high quality ripe fruit was also achieved, but required a response time of 10 seconds. Electronic sensing of aromatic volatiles may be a useful new technique in the grading and sorting of blueberries.

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Craig S. Charron, Daniel J. Cantliffe, Raymond M. Wheeler, Ara Manukian, and Robert R. Heath

A system and methodology were developed for the nondestructive qualitative and quantitative analysis of volatile emissions from hydroponically grown `Waldmann's Green' leaf lettuce (Lactuca sativa L.). Photosynthetic photon flux (PPF), photoperiod, and temperature were automatically controlled and monitored in a growth chamber modified for the collection of plant volatiles. The lipoxygenase pathway products (Z)-3-hexenal, (Z)-3-hexenol, and (Z)-3-hexenyl acetate were emitted by lettuce plants after the transition from the light period to the dark period. The volatile collection system developed in this study enabled measurements of volatiles emitted by intact plants, from planting to harvest, under controlled environmental conditions.

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J. Song, N. Rubinstein, and R.M Beaudry

Banana [Musa sp.9AAA group0, Cavendish] fruit are climacteric in nature, undergoing a rapid rise in ethylene production and respiration. Ethylene production can peak within 8 h of a detectable rise in production and respiration peaks within 24 h. These rapid changes permit precise timing for events related to or dependent on ethylene presence. Using rapid analytical methodology, we investigated the dynamic changes in volatile biosynthesis and its relation to other ripening parameters. Ungassed, mature-green banana fruit were placed individually at 23°C in flow through glass chambers. Ethylene production, respiration, chlorophyll fluorescence, skin color (hue angle) and volatile production were monitored. The climacteric rise and subsequent fall in ethylene production was found to be complete within 20 h. The respiratory rise peaked 20 h after the initial rise in ethylene production. The onset of the decline in chlorophyll fluorescence, skin color (hue angle) were coincident with the rise of ethylene and respiration, which indicated that the chlorophyll fluorescence may be used to monitor the banana fruit ripening. Volatile production was found to begin ≈60 h after the onset of the ethylene climacteric, peaking 3 to 4 days later. The ester precursors butyric acid and 3-methylbutanol were used in feeding experiments at different developmental stages for pulp and peel. Full ester-forming capacity was found to exist well before the onset of volatile biosynthesis. There were also different biosynthetic capacities for pulp and peel. Low aroma production in pre-climacteric fruit is apparently limited by the supply of precursors, which may be derived from the ethylene-induced enhancement of fruit respiratory metabolism.

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Ali A. Ramin, P. Gordon Braun, Robert K. Prange, and John M. DeLong

Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.

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J. Song, M.S. Tian, D.R. Dilley, and R.M. Beaudry

Aroma production by apple fruit is an important quality criterion and has been found to be a fruit-ripening-related process. 1-Methylcyclopropene (1-MCP), an effective ethylene action inhibitor, was used to study the relationship between volatile biosynthesis, ethylene action, and fruit ripening in `Golden Delicious' apple fruit. Pre-climacteric fruit were treated with 1-MCP vapors at a concentration of 500 parts per billion (v/v) at 23°C. 1-MCP prevented the climacteric rise of ethylene production, respiration, and volatile production, while untreated fruits developed typical climacteric changes in ethylene production, respiration and volatile production. Applying ethylene at 15–20 parts per million for 24 hr 11 days after 1-MCP treatment could not overcome the effect of 1-MCP, suggesting that 1-MCP inhibited ethylene action irreversibly. Interestingly, when 1-MCP-treated tissue were fed butanol and butyric acid, they converted these compounds to their corresponding esters butylacetate and butylbutanoate. Thus precursor supply is apparently limiting and appears to be ethylene-dependent.