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Apple fruit (Malus domestics Borkh. cv. Cox's Orange Pippin) were harvested in four orchards from trees growing under the same conditions but differing in crop load. Regardless of fruit size, apples from light-cropping trees had lower Ca and higher K concentrations and more bitter pit than did fruit from trees with heavy crop loads. The inverse relationship between Ca concentration in the fruit and the incidence of bitter pit also varied according to crop load and could affect the ability to predict incidence of bitter pit from Ca measurements. Differences in fruit maturity that would influence bitter pit incidence were not associated with crop load. The enhanced susceptibility to storage disorders, such as bitter pit, in fruit of all sizes from light-cropping trees suggests the need to handle fruit from such trees differently for postharvest storage.

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Abstract

Inheritance of the bitter pit disorder was determined in the field on fruiting seedlings resulting from crosses between the highly susceptible cultivar ‘Prima’, Coop 11 (a scab-resistant advanced selection), and 3 other scab-resistant selections. Segregation ratios indicated that 2 major genes controlled resistance. Both dominant genes, designated Bp-1 and Bp-2, were required to confer resistance. Analysis of leaf and peeled fruit tissues for Ca, Mg, K, and B indicated the presence of higher levels of Ca and B, and lower levels of Mg and K on a dry weight basis in resistant seedlings. A gradient was observed through the flesh on the fruit for all elements tested. Ca content was elevated at the base, but dropped rapidly towards the apex in susceptible fruits. Mg was reduced at the base and increased towards the apex in all fruits, but its level increased sharply in susceptible fruits.

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Abstract

Spraying ‘Northern Spy’ apple trees with 50 ppm TIBA 2 weeks after petal fall reduced the accumulation of Ca in the fruit and increased the amount of bitter pit. The greatest incidence of bitter pit was associated with the Ca content of the fruit during the middle of the growing season. Calcium accumulated rapidly during the period of cell division and seed development, and again 2 to 3 weeks before harvest. The late influx of Ca may explain the development of less bitter pit in storage in late harvested apples than in apples harvested immature.

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Abstract

Addition of 1% lecithin (phosphatidyl choline) to 4% Ca dips increased internal CO2 levels and decreased O2 levels in fruit of apple (Malus domestica Borkh.) stored at 3°C. This effect was greater than that found with lecithin alone. At 18°, respiration and ethylene production by the fruit were reduced slightly by Ca, but to a much greater extent by lecithin. A further reduction of the production of both gases was found with Ca and lecithin. The climacteric rise was also delayed by lecithin treatments. At 3°, ethylene production was both delayed and reduced by lecithin treatments, but no influence on CO2 production was detected. Although differences in Ca concentration of the fruit caused by the addition of lecithin to Ca could not be detected when bulked samples of fruit were analysed, use of 45Ca showed that both the initial rate of Ca uptake and the final Ca content of the fruit flesh after 6 weeks at 3° were increased by lecithin. The beneficial effects of lecithin plus Ca in bitter pit control probably result from rapid modification of gas exchange together with increased Ca uptake.

Open Access

Abstract

Equations were developed that could predict the incidence of senescent breakdown, bitter pit, and decay in ‘Cox's Orange Pippin’ apples and senescent breakdown and bitter pit in ‘Bramley's Seedling’ apples. The parameters used to predict the incidences of disorders included fruit Ca, P, and K concentrations; fruit weight; respiration rate; and fruit maturity. Each disorder and each cultivar had a unique prediction equation. Such equations must be established individually for a disorder, cultivar, and, probably, growing region. Given an appropriate data base, this method seems to have broad applicability as a predictive tool for these disorders. However, core flush and low temperature breakdown could not be predicted using the parameters measured in this study.

Open Access

A study was undertaken to identify key factors associated with storage disorders in three commercially important apple cultivars in British Columbia and to determine how early in the season associations could be measured. Fruit mass, density, and concentrations of N, P, K, Ca, Mg, and dry matter were determined for `McIntosh', `Spartan', and `Golden Delicious' apples (Malus ×domestica Borkh) from ≈30 commercial orchards 9, 6, 3, and 0 weeks before harvest. Storage samples were collected at commercial harvest and evaluated for the development of internal breakdown (`McIntosh' and `Spartan') or bitter pit (`Golden Delicious') after 4 and 6 months of 0 °C air storage. Mass and [Ca] and the mass/[Ca] and [K]/[Ca] ratios were the factors most often significantly correlated with storage disorders within each year for all three cultivars. Correlations were as frequently significant 6 and 3 weeks before harvest as they were at harvest. Mass of `McIntosh' and `Spartan' was the only variable consistently related with breakdown in all 3 years of the study. There were no variables with a consistent relationship to bitter pit in `Golden Delicious'. Fruit [Ca] was associated with the relative levels of disorders within years but could not be associated with specific levels of disorders across all years.

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Abstract

‘Delicious’, ‘Golden Delicious’, and ‘Stayman’ apple trees (Malus domestica Borkh.) were summer pruned in late June or mid-August. Fruit were smaller on June- or August-pruned ‘Stayman’ trees than on comparable dormant-pruned control trees. Summer pruning had little effect on the size of ‘Delicious’ and ‘Golden Delicious’ fruit. Soluble solids were suppressed within 2 weeks after summer pruning on all cultivars, but fruit firmness was unaffected. Summer pruning slowed the rate of starch disappearance from fruit flesh. Preharvest drop, severity of watercore, and bitter bit were suppressed by summer pruning. Calcium concentration of fruit flesh was not significantly increased by summer pruning. Yield, expressed as total fruit weight or number of fruit per tree, was not consistently influenced by summer pruning over a 2-year period.

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Abstract

‘Golden Delicious’ apple trees sprayed with 50 ppm 2,3,5-triiodobenzoic acid (TIBA) 28 days after bloom had pitted fruit at harvest, but comparable control trees had none. The appearance of the pits on the fruit was similar to bitter pit. TIBA decreased the fruit Ca content and increased fruit B content. Decrease in Ca content by TIBA probably caused the development of bitter pit on the fruit.

Open Access

Abstract

Calcium (Ca) level of leaves sampled in mid- or late summer was closely related to peel Ca levels of mature apples (Malus pumila Mill. cv. Baldwin). Ca content of fruit was directly related to fruit yield of the tree, cycling with biennial bearing. In 1971 bitter pit incidence could be predicted from either leaf or peel Ca; internal breakdown and decay were less predictable. In 1972 leaf Ca and peel Ca averaged, respectively, 27 and 17% higher than in 1971, accompanying increased yield. Little bitter pit, internal breakdown, or decay occurred, even at Ca levels correlated with high incidence rates the previous year. We concluded that Ca must be only 1 among several factors regulating these occurrences.

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`Gardiner Delicious'/MM.lO6 apple (Malus domestics Borkh.) trees were initially sprayed in 1985 with paclobutrazol (PB) at 250 mg.liter-1 at tight cluster and again on 10 and 25 June and 29 July. From 1986 through 1988, PB sprays of 85 or 100 mg·liter-1 were applied at either petal fall (PF) + 2 or PF + 4 weeks and one to two additional sprays were applied per year when growth resumed. Promalin was applied to one group of trees that received PB starting at PF + 2 weeks. PB reduced terminal, lateral, and total shoot growth the year of application and in subsequent years. Although average shoot length of lateral and terminal shoots was reduced, the greatest reduction in growth occurred because PB prevented spurs from growing into lateral and terminal shoots. Compared to unsprayed trees, PB reduced pruning time in all 4 years by 23% to 70%. PB increased bloom only the first year after application, but increased fruit set for 2 years due to a carryover effect. Application of PB in 1985 caused a reduction in fruit size, sometimes in soluble solids concentration, length: diameter (L : D) ratio, and pedicel length. Promalin either overcame the reduction in the ratio or increased it in 1986. Reduced rates of PB in subsequent years caused few adverse effects on the fruit. PB increased flesh firmness when applied at PF + 2 weeks but not at PF + 4 weeks. Trees treated with PB produced fruit with higher flesh Ca and less bitter pit, cork spot, and senescent breakdown following regular air storage. Chemical names used: ß -(4 -chlorophenyl)methyl α -(1,1-dimethylethyl) -1H-l,2,4-triazole-1-ethanol (paclobutrazol, PB); gibberellins A4+7 plus N-(phenylmethyl) -1H-purine-6-amine (Promalin).

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