Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: D. P. Murr x
Clear All Modify Search
Authors: and

Recent advances in technology have made the snapdragon, Antirrhinum majus L., a promising florist crop in North America and potentially on the Ontario market. CO2 is a known inhibitor of ethylene action, but its effects tend to be difficult to interpret based on the variable responses of plants to this gas. Recently, a gaseous ethylene analog has been shown to inhibit certain ethylene responses of cut flowers, such as wilting in carnations and flower abscission of cut phlox. This cyclic olefin, 1-methylcyclopropene (1-MCP), is thought to bind irreversibly to the ethylene receptor sites, thereby preventing or delaying ethylene responses. In the experiments undertaken, the potential of CO2 and 1-MCP were investigated for their ability to enhance vase life and to reduce shattering and wilting of snapdragons. Flowers were sealed in ≈0.2-m3 chambers encased in 6-mil polyethylene and exposed to elevated CO2 (5% or 10%) or 1-MCP (20-200 nL/L) for 6 to 24 h at 20 °C. The flowers were then exposed to continuous ethylene of 0-20 μL/L. Following exposure to 5 or 20 μL/L ethylene, 1-MCP reduced shattering ≈2- to 3-fold compared to CO2 treatment. 1-MCP did not prevent the wilting response but delayed it by ≈2 days. CO2-treated flowers exhibited a more rapid decline in net percent open florets from days 3 to 5 post-treatment. Despite the ability of 1-MCP to reduce shattering, in the absence of exposure to continuous ethylene, it has limited effectiveness on wilting compared to CO2.

Free access
Authors: and

Benzyladenine (100 or 200 mg.litre-1) was applied to mature Empire/M.26 apple trees as dilute sprays 2, 4, 9, 11, 13, 15, 17, 20, 25, 27, 29 or 31 days after full bloom (DAFB). The most effective time of thinning was 25-29 DAFB (king fruit diameter 8.94-13.91 mm), and the thinning response to BA concentration was linear. Benzyladenine (BA) did not reduce fruit set when king fruit diameter was less than 5.35 mm, but BA significantly increased fruit weight, diameter (D), length (L) and L:D ratio compared to unsprayed controls and later BA treatments. BA - treated fruitlets had higher ethylene production, 24 hours and 7 days after spraying compared to untreated controls. We suggest that the response of apple fruitlets to BA applied as a thinner is mediated by ethylene. High fruit quality was obtained when BA was applied at 17-31 DAFB. Timing of BA sprays had no effect on seed number, though BA significantly increased seed number, fruit size, weight and L:D ratio. These results suggest that BA has the potential to substitute for the use of carbaryl as a thinner of apples in Ontario orchards.

Free access

`McIntosh' apples were treated at 20 °C with 0.0, 0.01, 0.1, 1.0, 10, and 100 ppm 1-methylcyclopropene (1-MCP; EthylBloc™) a day after harvest for 18 h and stored at 0 °C in air. Apples were also continuously exposed to 0.0 and 25 ppm 1-MCP under controlled atmosphere (CA; 0 °C in 4.5 kPa CO2 and 3 kPa O2) by re-establishing the initial concentration at week 9 and 17. The threshold concentration of 1-MCP at 20 °C to inhibit de novo ethylene production in apple fruit was determined to be 1.0 ppm. Interestingly, the ethylene antagonist completely inhibited (99.67%) ethylene production in apples, which were removed from 0 °C in air and CA after 9 weeks and held at 20 °C up to 6 days. Overall, ethylene production was 10- to 100-fold less in apples treated with 1 ppm and above 1-MCP than in untreated apples. 1-MCP-treated apples showed less softening; fruit firmness was 2-4 Lb higher compared to untreated apples. Total soluble solids of apples was not affected by 1-MCP treatment. Total hydrophobic volatiles, including the sesquiterpene hydrocarbon α-farnesene, from apples measured by SPME/GC showed an inverse relation to 1-MCP concentration. Contents of α-farnesene and its putative superficial scald-causing catabolite, conjugated triene alcohol, in the skin were reduced 60% to 90% by 1-MCP. However, 1-MCP did not suppress the incidence of scald or other disorders, e.g., stem cavity, browning and brown core, in `McIntosh' apples.

Free access

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the surface wax of apples (Malus domestica Borkh.). Although, oxidation products of α-farnesene have been implicated in the development of the physiological disorder superficial scald in apple, the mechanism of α-farnesene biosynthesis has not been studied in detail. We are currently investigating α-farnesene biosynthesis in relation to superficial scald development in apples. Radiolabelled feeding experiments using isolated tissue segments indicated that α-farnesene is derived from trans,trans-farnesyl pyrophosphate (FPP), mainly in the skin rather than cortex. Among the other labeled products detected, farnesol level was over a hundred-fold higher compared to α-farnesene. However, [1-3H] trans,trans-Farnesol was not incorporated into α-farnesene. Feeding radiolabelled FPP to skin tissue segments of scald-developing and normal apples showed differential incorporation of radiolabel into various products. Though the incorporation into α-farnesene was nearly the same, there was higher levels of incorporation into farnesyl esters in normal apples. As well, the levels of radiolabelled in the farnesol fraction was three times higher in scald-developing regions. These results indicate that there are potential difference in the biosynthesis and metabolism of farnesyl components between scald-developing and normal apples. In studies using cell-free extracts, farnesol formation was observed from labeled FPP and was two-fold higher in crude membrane extract compared to crude cytosol. Our results indicate that α-farnesene formation in apple fruit tissue is through FPP and is possibly catalyzed by a single sesquiterpene synthase enzyme. Purification and characterization of this enzyme are in progress.

Free access

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the volatile components and the surface wax of apples (Malus ×domestica Borkh.). Although oxidation products of α-farnesene have been implicated in the development of superficial scald in apples, the relation between α-farnesene biosynthesis and scald development is not well understood. In vivo labeling studies using isolated tissue segments showed that α-farnesene is derived from trans,trans-[1,2-14Cor 1-3H]-farnesyl pyrophosphate (FPP) mostly in the skin rather than cortex tissue. Among other labeled products, farnesol was >100-fold higher compared to α-farnesene. However, HPLC analysis of hexane-extractable components from apple skin revealed farnesol is not a predominant natural constituent of apple skin tissue. In addition, trans,trans-[1-3H]-farnesol was not converted to α-farnesene by apple skin tissue. Our results indicate that biosynthesis of α-farnesene in apple tissue occurs through the isoprenoid pathway, and the conversion of FPP to α-farnesene is catalyzed by a single sesquiterpene synthase enzyme, trans,trans-α-farnesene synthase, rather than via farnesol as an intermediate. A comparison of α-farnesene biosynthesis between scald-developing and scald-free regions of the same apple showed that incorporation of radiolabel into α-farnesene from trans,trans-[1-3H]-FPP was nearly 3-fold lower in scald-developing skin tissue than in scald-free skin tissue.

Free access

Apple fruits (Malus domestica Borkh. cv. `Red Delicious') stored for 6 months at 2°C in air were analyzed for headspace volatiles by SPME-GC and for surface components by HPLC of hexane extracts. Analysis of headspace volatiles evolved from whole fruit showed five major volatiles that were identified previously as: acetic acid, hexyl ester; hexanoic acid, butyl ester; octanoic acid, propyl ester; hexanoic acid, hexyl ester; and the sesquiterpene, α-farnesene. No significant differences existed in these volatiles between scald-developing and non-scald developing apples. To explore potential differences in volatile evolution, fruit developing scald were cut (axial plane) into scalding and non-scalding halves for analysis. In all cases, volatile emission was much higher from the non-scalding side of the fruit, and the ratio of volatile levels from non-scalding to scalding averaged greater that 2. Various regions of tissue from the same fruit were extracted in hexane for estimation of levels of α-farnesene and its potential catabolites by HPLC. The levels and proportions of the components were nearly identical to those observed during headspace volatile analysis of half fruit. The results suggest that there are potential differences in α-farnesene metabolism an/or permeability of apple cuticle to volatiles between scald-developing and non-scald developing regions of apple fruit.

Free access

Abstract

Controlled atmosphere (CA) storage has proven notably successful for storing some apple cultivars and has been adopted on a wide commercial scale. However, CA storage of other crops has had variable success (39). Since the inception of CA storage, the only major innovation in storage practices with a potential broadscale application is the use of sub-atmospheric pressures (hypo-baric storage, low pressure storage, LPS). The inventor has coined the name hypobaric for this method (20). We prefer the term low pressure storage because it is less “medicinal” in implication and is readily shortened to LPS. Although LPS has been discussed in textbooks (1, 21, 71, 75), commercial use is still restricted to a few mobile vans. In the belief that LPS is technically possible on a large scale and may offer advantages over current methods, this review undertakes to examine the potential application of LPS to selected horticultural crops.

Open Access

1-Methylcyclopropene (1-MCP), a gaseous synthetic cyclic hydrocarbon, has been shown to have potential to become an important new tool in controlling the response of plants sensitive to ethylene. Due to its irreversible binding to the ethylene receptor(s) and its subsequent prevention of the physiological action of ethylene for extended periods, 1-MCP may prove also to have effective commercial application in the control of ethylene effects in detached organs such as fruit. Our objective was to investigate the effectiveness of 1-MCP in controlling ripening in pear. Two commercial cultivars (Bosc, Anjou) and one numbered cultivar from Agriculture and Agri-Food Canada's breeding program (Harrow 607) were harvested at commercial maturity. Immediately after harvest, fruit were exposed for 24 h at 20 °C to 1-MCP ranging from 0 to 100 μL•L-1 then placed in air at 0 °C and 90% relative humidity for 5 and 10 weeks. Following treatment and after 5 weeks storage plus a 7- or 14-day post-storage ripening period, fruit softening and ethylene evolution were inhibited and fruit volatile evolution was reduced significantly by exposure to 1-MCP at or above 1.0 μL•L-1 in all three cultivars. Concentrations exceeding 1.0 μL•L-1 were required to maintain initial firmness and inhibit ethylene production after 10 weeks storage in air. Evolution of alpha-farnesene and 6-methyl-5-hepten-2-one was related to low temperature stress and chlorophyll loss as a result of ripening, respectively, and were affected by 1-MCP exposure. The pattern of evolution and amounts of other volatiles was also affected by 1-MCP treatment. These results indicate a huge potential for commercial use and application of 1-MCP in controlling fruit ripening and senescence.

Free access

Abstract

Wall-bound β-galactosidase activity within the cortical flesh of ‘McIntosh’ apples (Malus domestica Bork.) increased in storage, but was independent of fruit ripening. There was less activity in fruits held in low pressure storage than in those held in controlled atmosphere or in refrigerated storage, and less activity in fruits held at 0.5 than at 3.5°C. Fruit field-treated with butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) had more β-galactosidase activity than control fruits at harvest, and maintained higher β-galactosidase activity in storage, but did not soften more rapidly than control fruits. Storage treatments that led to rapid softening coincided with the highest enzyme activity that developed in storage, but low enzyme activity was not consistently related to low softening rates.

Open Access

Abstract

In situ measurements of impedance and resistance of fruits have not found general use in measuring fruit maturation, senescence, and physiological condition despite some advantages over measurements of electrolyte leakage (exosmosis) from excised tissue. The advantages are ease and rapidity of techniques and preservation of the fruit for other analyses. The disadvantages or difficulties are the small measurable differences, cost and suitability of instrumentation for rapid measurements, choice of frequency of imposed current, suitable placement of electrodes to compensate for variation, and interpretation of data in physiological terms relating to membrane permeability or other developmental changes. With proper selection of methods and instrumentation, in situ impedance and resistance measurements have a potential not yet exploited.

Open Access