W.B. McGlasson

Ripening behaviour and responses to propylene in four cultivars of Japanese type plums

Abstract The aim of this study was to determine the physicochemical changes in highly coloured cultivars of plums that could be used as a guide to assessing optimum harvest maturity. The patterns of fruit growth and maturation were investigated in the cultivars: Gulfruby, Beauty, Shiro and Rubyred. Changes in the rates of respiration and ethylene production, skin colour, firmness, soluble solids concentration and titratable acidity were recorded at intervals from pit-hardening until the fruit were tree ripe. In order to evaluate the role of ethylene in the ripening process, propylene was applied to harvested fruit. Internal ethylene concentrations in the cv. Rubyred were also measured at intervals after pit-hardening either in harvested fruit or fruit attached to the tree. Studies of the changes in the physiological parameters associated with ripening showed that none were suitable for the assessment of harvest maturity in all cultivars of plums. However, this analysis revealed two distinct patterns of ripening behaviour in the cultivars studied. Gulfruby and Beauty showed a typical climacteric pattern of development, whilst Shiro and Rubyred exhibited a suppressed-climacteric phenotype. This phenotype appears to result from an inability of the fruit to produce sufficient quantities of ethylene to co-ordinate ripening. However, treatment with propylene showed that fruit displaying the suppressed-climacteric phenotype should still be placed in the climacteric class. This suppressed-climacteric character could be incorporated into plum breeding programs to produce new varieties with improved storage properties.

Induction of ethylene synthesizing competency in Granny Smith apples by exposure to low temperature in air

Abstract Preclimacteric Granny Smith apples ( Malus domestica , Borkh.) were held in air at 20°C or in air at 0°C for periods of 2, 4, 8, 16, or 32 days before transfer to air at 20°C and assessed periodically for rates of C 2 H 4 and CO 2 production and for 1-aminocyclopropane-1-carboxylic acid (ACC) content. Fruits kept in air continuously at 20°C entered the autocatalytic phase of C 2 H 4 production after 22 days while fruits chilled for 2, 4, 8, 16 or 32 days before ripening at 20°C began autocatalytic C 2 H 4 production after 16, 14, 2, 0 and 0 days, respectively. ACC levels in peel tissue from fruits kept at 0°C in air for 8 days or less remained at low levels when transferred to air at 20°C, then the ACC level increased greatly. Beyond 8 days in air at 0°C, fruits accumulated low ACC levels which were rapidly converted to C 2 H 4 as indicated by a high and sustained C 2 H 4 production rate.

The effects of short heat-treatments on the induction of chilling injury in avocado fruit (Persea americana Mill)

Abstract The ripening of avocado fruit and the development of chilling injury in relation to short heat-treatments has been studied in the cv. ‘Mass’. The minimal conditions needed to induce maximal production of heat shock proteins (HSP) in samples of mesocarp tissue were an exposure to 38 °C for 4 h. Short heat-treatments applied during the ripening process reduced the maximum rate of ethylene production during the climacteric period, but this was not correlated with lower levels of 1-aminocyclopropane-1-carboxylic acid (ACC). Heat-treatment also hastened the occurrence of the climacteric in fruit treated in the early pre-climacteric period. A similar regime applied to fruit immediately prior to this event delayed the onset of the climacteric. The use of short heat-treatments to overcome the effects of chilling injury was investigated by subjecting the fruit to 38 °C for 0, 6, 12, 24, 36 or 48 h prior to transferring them to 0 °C for 7, 14 or 21 days. Heating for 6–12 h provided a significant degree of protection from chilling injury and therefore may have potential for extending the period of cold storage.

A comparison of ethylene production, maturity and controlled atmosphere storage life of Gala, Fuji and Lady Williams apples (Malus domestica, Borkh.)

Abstract Gala and Lady Williams apples have distinct climacteric patterns of ethylene production but ethylene production remains low during ripening of Fuji apples. The Induced Ethylene Climacteric (IEC) method was found to accurately predict optimum harvest maturity for long-term CA storage of Gala apples. Alternative maturity indices are reported for Fuji and Lady Williams apples. Samples of the apple cultivars Gala, Fuji and Lady Williams were picked over a three week period around the commercial harvest time for each cultivar in the Harcourt area (Victoria, Australia). The fruit were stored under controlled atmosphere (CA) conditions (1.5% O 2 at 0–1 °C). Samples were removed for analysis at 0, 3 or 4, 5, 7 and 9 months. Ethylene production rates were measured at harvest, and internal ethylene levels after various storage intervals. Firmness was assessed at harvest and after 7 and 9 months of CA storage and 18 or 25 days at 20 °C. Gala and Lady Williams cultivars showed climacteric ethylene patterns with ripening, but this was much less obvious with the cultivar Fuji. Gala apples maintained a higher level of firmness if put into CA storage in a preclimacteric state. For the other cultivars, edible quality after CA storage was much less affected by pick date. Consumer tests have suggested that Fuji and Lady Williams apples were improved by being harvested later than the presently used commercial harvest dates, and explanations for those findings are put forward.

The effects of copper and calcium foliar sprays on cherry and apple fruit quality

Abstract The effects of post-bloom applications of calcium hydroxide (3000 g per 100 1) either alone or mixed with copper hydroxide (150 g Kocide ® , 50% Cu per 100 1) on fruit quality of sweet cherry and apple were studied. The sprays were applied to sweet cherry trees within 6 weeks of flowering and to apple trees within 8 weeks of flowering. Calcium hydroxide alone had no effect on the quality parameters measured except that russet was decreased on ‘Golden Delicious’. Application of copper plus calcium mixture to ‘Bing’ and ‘Van’ cherries improved fruit resistance to cracking and firmness. This spray mixture also improved the flesh firmness of ‘Golden Delicious’ apples.

Normal ripening cultivars of Pyrus serotina are either climacteric or non-climacteric

Abstract The climacteric status has been investigated in two cultivars of Pyrus serotina (Rehder). Both cultivars are chance seedlings. The fruit displayed a high respiration rate early in development that declined as fruit matured. Both ripened, as seen by skin degreening and softening, at similar times after flowering. Yet only in cultivar ‘Chojuro’ were the ripening changes associated with increased rates of ethylene and carbon dioxide production. In cultivar ‘Nijisseiki’ ethylene and carbon dioxide did not increase as fruit ripened. Continuous exposure of fruit to propylene accelerated skin degreening in cultivar ‘Nijisseiki’ but did not induce ethylene production or a climacteric peak of respiration. Whereas, in ‘Chojuro’, skin degreening, and ethylene and carbon dioxide production were all advanced after exposure to propylene. We conclude that although fruit development and ripening of both cultivars are similar, ‘Chojuro’ ripens with an associated respiratory climacteric, whereas ‘Nijisseiki’ does not.

Relationship between production of ethylene and α-farnesene in apples, and how it is influenced by the timing of diphenylamine treatment

Abstract The relationship between ethylene and peel α -farnesene concentrations was examined by applying diphenylamine (DPA) and the ethylene analogue, propylene at varying times after harvest to superficial scald (scald) susceptible ‘Granny Smith’ apples ( Malus domestica Borkh.) stored at 10°C. Delaying DPA application after harvest had no large effect on ethylene or on peel α -farnesene production. Propylene advanced fruit ripening and promoted an increase in peel α -farnesene concentration before endogenous internal ethylene production, suggesting that ethylene has an important regulatory role in α -farnesene production, but their biosynthetic pathways are controlled independently. The effect of delayed DPA application (4 and 7 days after harvest) on the relationship between ethylene and peel α -farnesene was further examined at both a scald-inducing temperature (0°C) and a non-scald-inducing temperature (10°C) with ‘Granny Smith’ and the scald resistant ‘Crofton’ cultivar. Similarly a delayed DPA application had only minor effects on internal ethylene and peel α -farnesene concentrations. The relationship between internal ethylene and peel α -farnesene concentration was dependent on storage temperature, and the type of relationship was independent of cultivar. However, the magnitude of the relationship between cultivars was significantly different (‘Granny Smith’ produced significantly more α -farnesene than ‘Crofton’) and may be related to scald development.

Does Inhibition of Aco Activity in Japanese-Type Plums Account for the Suppression of Ethylene Production in Attached Fruit by the Tree Factor and the Suppressed Climacteric?

Abdi et al. [1] reported that the ripening of attached fruit of some cultivars of Japanesetype plums is delayed compared to harvested fruit. This phenomenon has been reported in other species, notably apples, and is ascribed to the presence of an unknown ‘tree factor’. Abdi et al. [1] also described two classes of plums: one class, represented by the cvv Gulfruby and Beauty, expresses a typical climacteric pattern of respiration and ethylene production, while the second class, represented by cvv Shiro and Rubyred, has a suppressed-climacteric phenotype. In this latter phenotype, levels of ethylene production are low compared to normal, climcateric types. To further elucidate the physiology of the tree factor and the suppressed-climacteric behaviour we treated fruit of defined maturity stages with 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, and propylene [2]. Measurements of ethylene production and respiration were made within 24 h of harvest and on the 5 subsequent days storage at 20°C.