Malus Sylvestris Mill Research Articles

Ultrastructural Changes in the Cell Walls of Ripening Apple and Pear Fruit

Ultrastructural changes in the cell walls of "Calville de San Sauveur" apples (Malus sylvestris Mill) and "Spadona" pear (Pyrus communis L.) fruit were followed during ripening. In apple, structural alterations in cell walls became apparent at advanced stages of softening and showed predominantly dissolution of the middle lamella. In pears softening was also associated with the dissolution of the middle lamella, and in addition a gradual disintegration of fibrillar material throughout the cell wall. In fully ripe fruit almost all of the fibrillar arrangement in the cell wall was lost. Application of enzyme solutions containing polygalacturonase and cellulase to tissue discs from firm pear fruit led to ultrastructural changes observed in naturally ripening pears. In apple polygalacturonase alone was sufficient to dissolve the middle lamella region of the cell walls, as was also found to occur in naturally ripening fruit. In both apple and pear the cell wall areas containing plasmodesmata maintained their structural integrity throughout the ripening process. At advanced stages of ripening vesicles appeared in the vicinity of plasmodesmata.

Methionine Metabolism in Apple Tissue

If S-adenosylmethionine (SAM) is the direct precursor of ethylene as previously proposed, it is expected that 5'-S-methyl-5'-thioadenosine (MTA) would be the fragment nucleoside. When [Me-(14)C] or [(35)S]methionine was fed to climacteric apple (Malus sylvestris Mill) tissue, radioactive 5-S-methyl-5-thioribose (MTR) was identified as the predominant product and MTA as a minor one. When the conversion of methionine into ethylene was inhibited by (l)-2-amino-4-(2'-aminoethoxy)-trans-3-butenoic acid, the conversion of [(35)S] or [Me(14)C]methionine into MTR was similarly inhibited. Furthermore, the formation of MTA and MTR from [(35)S]methionine was observed only in climacteric tissue which produced ethylene and actively converted methionine to ethylene but not in preclimacteric tissue which did not produce ethylene or convert methionine to ethylene. These observations suggest that the conversion of methionine into MTA and MTR is closely related to ethylene biosynthesis and provide indirect evidence that SAM may be an intermediate in the conversion of methionine to ethylene.When [(35)S]MTA was fed to climacteric or preclimacteric apple tissue, radioactivity was efficiently incorporated into MTR and methionine. However, when [(35)S]MTR was administered, radioactivity was efficiently incorporated into methionine but not MTA. This suggests that the sulfur of MTA is incorporated into methionine via MTR. A dual label experiment with [(35)S, Me-(3)H]MTA indicates that the CH(3)S group of MTA was transferred as a unit to form methionine.A scheme is presented for the production of ethylene from methionine, the first step being the activation of methionine by ATP to give SAM. SAM is fragmented to give ethylene, MTA, and other products. MTA is then hydrolyzed to MTR which donates its methylthio group to a four-carbon acceptor to reform methionine.

MATURITY STUDIES ON RED SPORTS OF DELICIOUS APPLES

A 2-yr study of Gardiner, Hardispur, Harrold Red, Hi-Early, Redspur, Starkrimson, Starking and Wellspur indicated little or no difference in the rate of maturation among the sports of Delicious apples (Malus sylvestris Mill.). The pattern of CO2 production immediately after harvest among the sports was quite similar and the time of the onset of ethylene production indicated a slight difference in stage of maturation only for three sports in one harvest of the 1st yr. Values for internal flesh chlorophyll intensity and soluble solids showed some small and inconsistent differences. Acidity levels and the incidence of scald were not significantly different among the sports in either year.

Sorbitol and other carbohydrates in dormant apple shoots as influenced by controlled temperatures

The influence of controlled temperatures on levels of sorbitol and other carbohydrates was determined to provide further information on dormancy of apple trees ( Malus sylvestris Mill.). For 3 years, 2-year-old “Red Delicious” apple shoots were collected from mature trees in an orchard at intervals during the autumn and winter, and shoots were stored for 6 hr to 1 week at temperatures from 18 to −60 °C. Sorbitol and other carbohydrates were estimated in the sap or wood by gas chromatography. Controlled temperatures had a marked influence on the carbohydrate content of excised 2-year-old apple shoots. Levels of sorbitol in the sap were maximum at −0.6 °C. The increase was greatest at the earliest sampling before complete hardening had occurred in each of the 3 years tested. Total sorbitol in the wood was less influenced by storage at various controlled temperatures than sorbitol in the sap. Levels of fructose, glucose, and sucrose in the wood were higher at temperatures below −0.6 °C than at warmer temperatures. Levels of starch were usually inversely related to soluble sugars.

EFFECTS OF CARBON DIOXIDE TREATMENT ON CONTROLLED ATMOSPHERE STORAGE BEHAVIOR OF McINTOSH APPLES

McIntosh apples (Malus sylvestris Mill.) were treated with different levels of CO2 for various lengths of time prior to controlled atmosphere storage. Beneficial effects of CO2 treatment on retardation of softening were observed in 1973 and in a commercial trial in 1974, but not in the 1974 and 1975 experiments. There was no effect of CO2 treatment on soluble solids or acid levels. Extensive surface and internal injury was found in apples treated with 15 or 20% CO2 for 10 or more days. In the limited commercial trial, CO2-treated fruit was significantly firmer than untreated fruit, but the difference in firmness was not considered sufficient to warrant application of the treatment for McIntosh apples.

ABSCISIC ACID LEVELS AND GENETIC COMPACTION IN APPLE SEEDLINGS

Apple (Malus sylvestris Mill.) seedlings arising from controlled crosses involving McIntosh Wijcik segregate reliably into normal and compact growth types. The compact or spur-type seedlings have shorter, thicker stems; shorter internodes; and a strong upright, nonbranching growth habit. They contained less free ABA per shoot tip than normal seedlings. A reliable and rapid method for extracting and measuring ABA is described.

The Effect of Leaf Water Potential, Leaf Temperature and Light Intensity on Leaf Diffusion Resistance and the Transpiration of Leaves of Malus sylvestris

AbstractThe relationship between leaf resistance to water vapour diffusion and each of the factors leaf water potential, light intensity and leaf temperature was determined for leaves on seedling apple trees (Malus sylvestris Mill. cv. Granny Smith) in the laboratory. Leaf cuticular resistance was also determined and transpiration was measured on attached leaves for a range of conditions.Leaf resistance was shown to be independent of water potential until potential fell below — 19 bars after which leaf resistance increased rapidly. Exposure of leaves to CO2‐free air extended the range for which resistance was independent of water potential to — 30 bars.The light requirement for minimum leaf resistance was 10 to 20 W m−2 and at light intensities exceeding these, leaf resistance was unaffected by light intensity.Optimum leaf temperature for minimum diffusion resistance was 23 ± 2°C. The rate of change measured in leaf resistance in leaves given a sudden change in leaf temperature increased as the magnitude of the temperature change increased. For a sudden change of 1°C in leaf temperature, diffusion resistance changed at a rate of 0.01 s cm−1 min−1 whilst for a 9°C leaf temperature change, diffusion resistance changed at a rate of 0.1 s cm−1 min−1.Cuticular resistance of these leaves was 125 s cm−1 which is very high compared with resistances for open stomata of 1.5 to 4 s cm−1 and 30 to 35 s cm−1 for stomata closed in the dark.Transpiration was measured in attached apple leaves enclosed in a leaf chamber and exposed to a range of conditions of leaf temperature and ambient water vapour density. Peak transpiration of approximately 5 × 10−6 g cm−2 s−1 occurred at a vapour density gradient from the leaf to the air of 12 to 14 g m−3 after which transpiration declined due presumably to increased stomatal resistance. Leaves in CO2‐free air attained a peak transpiration of 11 × 10−6 g cm−2 s−1 due to lower values of leaf resistance in CO2 free air. Transpiration then declined in these leaves due to development of an internal leaf resistance (of up to 2 s cm−1). The internal resistance was masked in leaves at normal CO2 concentrations by the increase in stomatal resistance.

CURRENT SEASON AND HOLDOVER EFFECTS OF LOW CONCENTRATIONS OF SADH APPLIED AS SPLIT OR SINGLE SPRAYS ON PREHARVEST DROP, FIRMNESS AND OTHER RESPONSES OF MCINTOSH APPLE

In two experiments, succinic acid 2,2-dimethylhydrazide (SADH) at low to moderate rates (62.5–1,000 ppm, 0.93–4.32 kg/ha (0.82–3.84 lb/acre)) increased fruit firmness and decreased fruit drop of McIntosh apples (Malus sylvestris Mill.) proportionately to amount applied. Split and single sprays that applied the same total amount of SADH were equally effective. Addition of Tween 20 at 0.025% (vol/vol) had no significant effect on response. None of the treatments affected cropping over three seasons, fruit color or fruit size in the year of application. Fruit size in the year following application showed a threshold effect in that earlier dates and lower rates had no measurable effect.

FACTORS AFFECTING SHAPE OF MCINTOSH APPLE FRUIT

McIntosh apple (Malus sylvestris Mill.) fruit shape was influenced by position in the blossom cluster, rootstock and strain and was correlated with Mg content of leaf tissue. High Mg content of leaves was associated with large length to diameter (L/D) ratios of fruit. The effects of rootstock and strain were conditional; in years of short apples, the L/D ratio of fruit approached a common small value regardless of rootstock or strain; in years of more elongate apples, the L/D ratio of fruit was more influenced by rootstock or strain. In general, large L/D ratios were associated with shallow stem-cavities.

Xylem cavitation in excised leaves of Malus sylvestris Mill. and measurement of leaf water status with the pressure chamber

A change occurs in the relationship between xylem water potential (Ψx) measured with the pressure chamber and leaf water potential ((Ψw)) when a period of post-excision water loss is allowed before measurement of (Ψx) and (Ψx). When this occurs, water stress is over-estimated by the pressure chamber measurement. Over the same period of water loss, cavitation vibrations have been detected acoustically in excised leaves. It is suggested that the measurement of (Ψx) is affected by emptying of some of the xylem vessels due to cavitation. This would require that additional pressure be applied to a leaf in the pressure chamber in order to measure (Ψx).

SEASONAL CHANGES IN THE EPIPHYTIC POPULATION OF ERWINIA AMYLOVORA ON APPLE AND PEAR

Erwinia amylovora (Burr.) Winsl. et al., the pathogen causing fireblight, was readily isolated from symptomless leaves in blocks of Lodi apple (Malus sylvestris Mill.), Bartlett pear (Pyrus communis L.) and a multicultivar pear block. The frequency of positive assays appeared to be related to the incidence of fireblight symptoms. However, the percent positive samples was highly variable, making prediction of blight outbreaks difficult. The bacterial population was highest from mid-July to the end of August. Before and after this period numbers of E. amylovora were relatively low. The pathogen was isolated from apparently healthy dormant buds of Lodi apple and Flemish Beauty pear.

COLOR, FIRMNESS, STARCH CONTENT, AND PERSISTENCE OF 2-CHLOROETHYLPHOSPHONIC ACID IN McINTOSH APPLES

Ethephon plus 2,4,5-TP stimulated color development and fruit softening of McIntosh (Malus sylvestris Mill.) apples after 7–10 days. Most of the large differences in fruit pressure observed 10 or more days after treatment were lost after 2 or 3 mo storage at 1 C. Analysis for residual ethephon indicated that its breakdown in McIntosh apples occurred at the same rate at room temperature, on the tree or in storage at 1 C. The rate of breakdown was rapid for the first 17 days but decreased to a much slower rate after 30 days. The lack of color response with ethephon and 2,4,5-TP in some seasons was attributed to factors other than a slow breakdown of ethephon in the fruit.

Calcium Concentration of ‘Spartan’ Apple in Relation to Amount of Senescent Breakdown in Individual Fruits1

Abstract The concentration of Ca in the flesh was closely related to the amount of breakdown in individual apples in 5 lots of ‘Spartan’ apple (Malus sylvestris Mill.) collected over 2 years. Correlation coefficients of 0.9 were obtained using log Ca and linear breakdown or log Ca and log breakdown. The amount of breakdown calculated for the 5 lots by the 2 equations was 100 percent at 70 ppm Ca, from 46 to 100 percent at 100 ppm Ca, from 3 to 12 percent at 150 ppm Ca and less than 2 percent at 200 ppm.

The Water Conductivity of Defective Graft Unions in Pome and Stone Fruits1

Abstract Using heat pulses the apparent velocity of the transpiration stream was measured in apple (Malus sylvestris Mill.) grafted on French seedlings (M. baccata Desf.), and several cultivars of peach (Prunus persica Sieb. and Zucc.) and Japanese plum (Prunus triflora Roxb.) grafted on almond (Prunus amvgdalus Batsch.) rootstock. The trees varied in compatibility with their respective rootstocks, as established by visual observation and gross morphology of the zone of union. Velocity of the transpiration stream was measured in 3 regions of each tree: the rootstock stem, the zone of union, and the scion stem. In definitely defective unions velocity of the transpiration stream in the zone of union exceeded that in both rootstock and scion. The possible use of this method as a tool for identifying poor graft unions in orchards is evaluated.

EFFECTS OF ETHEPHON AND SADH ON COLOR, QUALITY AND SHELF-LIFE OF CRIMSON GRAVENSTEIN APPLES

The effects of ethephon (2-chloroethylphosphonic acid) from Ethrel at 0.62 and 1.25 liters/ha (0.5 and 1.0 pints/acre) applied at two dates, and of SADH (succinic acid 2,2-dimethyl hydrazide) from Alar 85W at 13.2 kg/ha were tested on Crimson Gravenstein apples (Malus sylvestris Mill.). SADH and ethephon treatments intensified red overcolor when compared with untreated controls. Ethephon at the 0.62-liter/ha rate was almost as effective as at the 1.25-liters/ha rate. Fruit ripening, following harvest, was slowed by early harvest and by the application of SADH and was accelerated by ethephon. However, no significant interaction was found between the effects of applying both chemicals to the same fruit.

LEVELS OF DEICING SALT PRODUCING INJURY ON APPLE TREES

A suppression of flowering and dieback of terminal shoots in apple (Malus sylvestris Mill.) trees was associated with increased levels of Na and Cl in the twigs. These symptoms were observed on both roadside trees exposed to salt spray, and trees sprayed experimentally with 2% aqueous solutions of road salt. Concentrations of Na and Cl exceeding 0.20 and 0.50%, respectively, of the dry weight were associated with injury to the trees.

The Metabolism of Abscisic Acid to a Water Soluble Complex in Apple1

Abstract When apple (Malus sylvestris Mill) seedlings are fed abscisic acid (ABA), a water soluble complex of ABA and glucose is rapidly formed. This may be a mechanism for inactivating ABA. Similarly, the trans isomer of ABA (trans-ABA) gives rise to a water soluble complex, which is also presumed to be a glucose complex. Apple seedlings did not convert ABA to trans-ABA during feeding experiments, suggesting that small amounts of trans-ABA occasionally found in apple seedling extracts may be artifacts.

Postharvest Decay Control of Apple by Acetaldehyde Vapor1

Abstract Decay of apples (Malus sylvestris Mill.) inoculated with Penicillium expansum was controlled by acetaldehyde vapor concentrations (v/v) of 0.5% for 180 min, 1% for 120 min, 2% for 60 min, and 3% for 30 min. The above treatments did not produce lenticel or skin injury. Fumigated conidia did not germinate in 21 days at 21°C on artificial media and failed to induce decay in stem-punctured apples. The pathogen could not be re-isolated from fumigated inoculated punctures, however, the pathogen was obtained from inoculated punctures not exposed to acetaldehyde vapor. Fungicidal action of acetaldehyde vapor was a function of concentration and exposure period. Objectional off-flavors were not detected in fumigated apples, although appreciable amounts of acetaldehyde vapor were absorbed.

SURVIVAL OF ERWINIA AMYLOVORA IN ASSOCIATION WITH MATURE APPLE FRUIT

Mature fruit from naturally infected apple (Malus sylvestris Mill. ’Wealthy’) trees was free from a detectable population of Erwinia amylovora in the calyx, stem, peel and cortex. The pathogen failed to survive for 24 h on the surface of artificially inoculated fruit of Red and Golden Delicious apple in the orchard. In the laboratory, survival of the bacterium was excellent on the surface of apples when applied as natural ooze, or in a water suspension. Bacteria injected into the cortex of fruit of several cultivars survived as long as the apples were physiologically sound. Apples even from resistant cultivars developed symptoms of fireblight in storage. However, the absence of E. amylovora from symptomless fruit of naturally infected trees suggests that mature fruit presents a negligible risk for dissemination of fireblight bacteria.

BACTERICIDAL TREATMENT OF APPLES FOR ELIMINATION OF SURFACE-BORNE ERWINIA AMYLOVORA

A bactericidal dip for mature apple (Malus sylvestris Mill.) was developed as a precaution against possible dissemination of Erwinia amylovora on fruit surfaces to fireblight-free areas. Several common bactericides including sodium hypochlorite, panacide, 8-hydroxyquinolinol sulfate, stretptomycin sulfate and acetic acid showed activity against E. amylovora in a filter paper disc bioassay. None of these compounds completely eliminated E. amylovora from the surface of apples inoculated by swabbing with bacterial ooze. Streptomycin sulfate 250 ppm and actetic acid 1.0 M were most effective as dips. Several combinations of compounds killed all bacterial cells on the surface. When apples were inoculated with a water suspension of bacterial ooze (8.2 × 106 cells/ml) a 10-min dip in 1.0 M acetic acid was completely effective.