Storage temperature, diphenylamine, and pre-storage delay effects on soft scald, soggy breakdown and bitter pit of ‘Honeycrisp’ apples

Postharvest Biology and Technology 32 (2004) 213–221

Storage temperature, diphenylamine, and pre-storage delay effects on soft scald, soggy breakdown and bitter pit of ‘Honeycrisp’ apples Christopher B. Watkins a,∗ , Jacqueline F. Nock a , Sarah A. Weis b , Sastry Jayanty c , Randolph M. Beaudry c b

a Department of Horticulture, Cornell University, Ithaca, NY 14853, USA Department of Plant and Soil Sciences, University of Massachusetts, Amherst, MA 01003, USA c Department of Horticulture, East Lansing, MI 48824, USA

Received 30 April 2003; accepted 8 November 2003

Abstract ‘Honeycrisp’ apple [(Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit are susceptible to the storage disorders soggy breakdown, soft scald, and bitter pit. The effects of low and high temperature storage regimes (0 or 0.5 ◦ C and 2.2, 2.8 or 3 ◦ C, respectively), diphenylamine (DPA) treatment, and delays at 10 or 20 ◦ C before storage, were investigated. Soggy breakdown and soft scald incidence is highest at the lowest temperatures of 0 or 0.5 ◦ C and reduced or eliminated by storage at the higher temperatures. DPA sometimes reduced, but did not eliminate, soft scald. Both soggy breakdown and soft scald were markedly reduced or eliminated however, by keeping fruit at 10 or 20 ◦ C before storage regardless of storage temperature. Bitter pit incidence was sometimes increased by delay treatments and storage at higher temperatures. Little effect of any treatment on firmness, soluble solids content, internal ethylene concentration (IEC), background color and titratable acidity was detected. © 2003 Elsevier B.V. All rights reserved. Keywords: Malus sylvestris var. domestica; Soft scald; Storage disorders; Ethylene; Firmness

1. Introduction The ‘Honeycrisp’ apple, released by the Minnesota Agricultural Experiment Station in 1991, has been widely planted in the US with approximately 950,000 trees planted as of January 2001 (Tong et al., 2003). The cultivar has outstanding flavor charac∗ Corresponding author. Tel.: +1-607-255-1784; fax: +1-607-255-0599. E-mail address: [email protected] (C.B. Watkins).

teristics, and it has been reported to remain crisp during air storage for 9 months (Luby and Bedford, 1992; Tong et al., 1999). However, industry confidence in ‘Honeycrisp’ has been negatively affected by the development of high incidences of bitter pit, soft scald and soggy breakdown in the fruit (Greene and Weis, 2001; Rosenberger et al., 2001). Bitter pit is a calcium-related disorder (Ferguson and Watkins, 1989) that can occur on the tree or develop during storage, but can be managed by cultural practices such as calcium spray application in the field (Rosenberger

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et al., unpublished). In contrast, much less is known about factors that affect the occurrence of soft scald and soggy breakdown, probably because of the sporadic nature of the disorders. The symptoms of soft scald (syn. deep scald, ribbon scald) are the development of sharply defined brown lesions on the skin of the apple, but which can extend into the flesh (Brooks and Harley, 1934; Pierson et al., 1971; Snowdon, 1990; Watkins and Rosenberger, 2002). Susceptible cultivars include ‘Fuji’, ‘Jonathan’, ‘McIntosh’, ‘Delicious’ and ‘Golden Delicious’. Soggy breakdown is an internal disorder, and in worst cases a complete ring of soft, brown, spongy tissue is present (Smock and Neubert, 1950; Watkins and Rosenberger, 2002). It can occur in the absence of soft scald symptoms. Cultivars that are susceptible to soggy breakdown are not always the same as for soft scald, although the causes of soggy breakdown may be identical, even if different in expression, with soft scald (Plagge et al., 1935; Plagge and Maney, 1937). Soggy breakdown is rarely mentioned in current apple literature. Both disorders are forms of low temperature injury, being worse in fruit stored below 2–3 ◦ C. The mechanism of disorder development is not known, but has been related to oxidation of unsaturated fatty acids in the surface lipids and elevated hexanol concentrations (Wills, 1973; Hopkirk and Wills, 1981; Wills et al., 1981) and may be related to abnormal respiratory metabolism in response to low temperatures during storage (Pierson et al., 1971). Major disposing factors that have been implicated in the occurrence of soft scald are over-maturity of fruit at harvest (Brooks and Harley, 1934; Tong et al., 2003; Watkins et al., unpublished) and preharvest factors such as climate (dull, cool, wet summers), light crops, large fruit, and vigorous soils (Smock and Neubert, 1950; Snowdon, 1990). Incidence of soft scald has been reported to be increased by delays between harvest and cooling (Gerhardt and Sainsbury, 1952), although responses of fruit to delay can vary with cultivar and length of the delay imposed (Brooks and Harley, 1934; Plagge et al., 1935; Plagge and Maney, 1937). Soft scald incidence is also decreased by application of the antioxidant diphenylamine (DPA), used to control superficial scald (Wills and Scott, 1982; Wills et al., 1981), or 1-methylcyclopropene (Fan et al., 1999). Initial experiments with ‘Honeycrisp’ apples indicated that

soft scald was worse at 0.5 ◦ C than at higher storage temperatures, but surprisingly, delay treatments of a week at 10 ◦ C that were applied to increase the soft scald incidence for study of the disorder, markedly decreased it (unpublished data). The objective of this study was to investigate the effectiveness of storage temperature, DPA, and pre-storage treatments of warmer holding temperatures, on the development of soft scald, soggy breakdown and bitter pit, and to determine the effects of these treatments on fruit quality. The effects of treatments were tested on fruit from three sites in the northeastern US, but regional effects are not compared because of differences in methodology.

2. Materials and methods 2.1. New York ‘Honeycrisp’ apples were harvested from a western New York orchard on 17 September 1999, and randomized into 24 lots of 40 fruit. In addition three 10-fruit samples were taken for analysis of maturity. Fruit were then transported to the Cornell University Orchard laboratory in Ithaca. Internal ethylene concentrations (IEC) were measured on the maturity samples. The fruit lots were divided to provide three replicates for each of the following treatments: (1) stored at 0.5 ◦ C; (2) stored at 2.2 ◦ C; (3) DPA-treated, and stored at 0.5 ◦ C; (4) DPA-treated, and stored at 2.2 ◦ C; and (5)–(8) same as (1)–(4), except that fruit were kept at 10 ◦ C for 1 week, prior to cold storage. DPA-treated fruit were dipped in 1000 ␮l l−1 (Shield liquid DPA 15%, Pace International, Washington) for 1 min, allowed to drain for 2 h, and placed into cold storage at the same time as non-treated fruit. All fruit were kept in plastic perforated bags during cold storage. After storage for 12 weeks, fruit were transferred to an evaluation room maintained at 20 ◦ C. After 1 day IEC, soluble solids content (SSC) and firmness were measured on 10-fruit samples per replicate. On day 7, the firmness and SSC of 10-fruit replicates was again measured, and all remaining fruit assessed for presence of external and internal disorders. In 2000, fruit were treated as described in 1999, except that a different orchard block in western New

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York was used to obtain fruit on 20 September, the storage temperatures were 0.5 and 2.8 ◦ C, and four replicates were used for each treatment. IEC, firmness, SSC, and titratable acidity were measured at harvest and after storage for 12 weeks plus 1 or 7 days at 20 ◦ C. In addition, cortical flesh from five-fruit samples was taken from each replicate at 6 and 12 weeks of storage on cold fruit, frozen in liquid nitrogen and stored at −80 ◦ C until used for analysis of ethanol. Ethylene concentrations of 1 ml gas samples taken from the core of each apple were measured with a Hewlett-Packard 5890 series II gas chromatograph (Hewlett-Packard Co., Wilmington, Delaware) equipped with a stainless steel column packed with 60/80 mesh alumina F-1 (2 m × 4 mm, i.d.) and a flame ionization detector (FID). Operating conditions were as follows: oven temperature 180 ◦ C, injector temperature 230 ◦ C, detector temperature 250 ◦ C. Flow rates for nitrogen, hydrogen and air were 45, 30, 200 ml min−1 , respectively. Firmness was measured on opposite peeled sides of each fruit using an EPT-1 pressure tester fitted with an 11.1 mm diameter probe (Lake City Tech. Products, Lake City, Canada) and the expressed juice used for SSC measurement with a refractometer (Atago PR-100, Atago Co. Ltd., Tokyo, Japan). Titratable acidity was measured on juice extracted from composite samples of segments using 0.1 M NaOH to an end point of pH 8.1 with an autotitrator (Mettler DL12, Hightstown, NJ). For ethanol measurements, frozen samples were powdered in liquid nitrogen, and 5 g samples used for headspace analysis as described by Fernández-Trujllo et al. (2001). 2.2. Michigan ‘Honeycrisp’ apples were harvested on 11 and 23 September in 2001 and 2002, respectively, from the Clarksville Horticultural Experimental Station of Michigan State University. One day after harvest, 10 fruit were analyzed for IEC, firmness, and starch index. An additional 1280 fruit were placed into 32 plastic mesh bags, each containing 40 fruit. One half of the bags of fruit were treated with DPA by immersing them in a 1000 ␮l l−1 solution for approximately 1 min. Fruit were drained for approximately 1 h then placed individually into plastic barrels (2001) or wooden crates (2002) and covered with ventilated

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plastic vapor barriers to minimize moisture loss, but ensure near ambient oxygen and carbon dioxide levels. Subsequently, fruit were handled essentially as described for the New York 1999 study with the exception that the storage temperatures were 0 and 3 ◦ C. After 12 weeks of storage, fruit were analyzed for firmness, soluble solids, background color, and IEC after 4 days at room temperature, rather than 7 days due to rapid decay development. Ethylene concentrations of 1 ml gas samples taken from the core of each apple were measured with a gas chromatograph (Carle Series 100 AGC, Hach Co., Loveland, Colo.) equipped with an activated alumina (2 m × 2 mm, i.d.) column and a FID. Operating conditions were as follows: oven temperature 100 ◦ C, injector temperature 100 ◦ C, detector temperature 200 ◦ C. Flow rates for helium, hydrogen and air were 50, 30 and 200 ml min−1 , respectively. Background color was judged according to the Cornell color chart for McIntosh which ranges from a rating of 5 for green background color to a rating of 1 for yellow background color (Anonymous, 1948). Firmness was measured manually, using a drill stand-mounted Effegi Penetrometer (FT-327, McCormick Fruit Tree Inc., Yakima, Washington) fitted with an 11.1 mm diameter probe. A hand-held refractometer (ATC-1E, Atago Co. Ltd., Tokyo, Japan) was used to measure brix. Starch–iodine indices were based on the Cornell generic starch chart, where 1 = 100% starch and 8 = 0% starch staining (Blanpied and Silsby, 1992). 2.3. Massachusetts ‘Honeycrisp’ fruit were harvested on 21 and 26 September, 2001 from the University of Massachusetts Horticultural Research Center. Ten fruit from each harvest were analyzed at harvest for IEC, firmness, SSC, and starch index. The remaining fruit were divided into four boxes of 40 fruit for each of the following treatments: (1) placed directly into 1.8 ◦ C storage; (2) kept at 20 ◦ C for 1 day, then placed in 1.8 ◦ C storage; (3) kept at 20 ◦ C for 4 days, then placed in 1.8 ◦ C storage; or (4) kept at 20 ◦ C for 6 days, then placed in 1.8 ◦ C storage. After cold storage for 6 weeks, fruit were removed to a 20 ◦ C room, assessed for presence of soft scald, bitter pit, and decay, and immediately returned to cold storage. Fruit were not exposed to warmer temperatures for more than 15 min.

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After 9 weeks of cold storage, fruit were again transferred to an evaluation room maintained at 20 ◦ C. After 9 days, firmness and soluble solids were measured on 10 fruits per treatment from each harvest, and all fruit were assessed for presence of internal and external disorders. Ethylene concentrations of 1 ml gas samples taken from the core of each apple were measured by gas chromatography (Shimadzu CG-8A Gas chromatograph, Shimadzu Corp., Kyoto, Japan) equipped with an activated alumina (2 m × 2 mm, i.d.) column and a FID. Operating conditions were as follows: oven temperature 40 ◦ C, injector temperature 110 ◦ C, detector temperature 110 ◦ C. Flow rates for nitrogen, hydrogen and air were 50, 50 and 500 ml min−1 , respectively. Firmness was measured on opposite peeled sides of each fruit using an EPT-1 pressure tester (Lake City Tech. Products, Lake City, Canada) fitted with an 11.1 mm diameter probe, and the expressed juice used for SSC measurement with a refractometer (Atago N-1EBX, Atago Co. Ltd., Tokyo, Japan). Starch indices were determined as described above. 2.4. Statistical analyses The experimental design was completely randomized with delay and DPA treatments as fixed effects. Data were analyzed by analysis of variance (ANOVA) using the general linear procedure of Minitab software v 11.12 (Minitab, Inc., State College, Pa). Disorder incidence percentages were arcsin transformed prior to analysis. The least significant difference procedure at P = 0.05 was used to test differences in treatment means.

3. Results 3.1. New York (1999, 2000) Fruit were climacteric at harvest in both years, average IEC being 10.1 and 29.7 ␮l l−1 in 1999 and 2000, respectively. In 1999, fruit were stored for 12 weeks at 0.5 and 2.2 ◦ C (Table 1(A)). Soft scald and soggy breakdown incidences were similar and were not separated during fruit assessment. Without delay treatments, the disorders were reduced by 9% when fruit were stored

at 2.2 ◦ C compared with storage at 0.5 ◦ C, either with or without DPA treatment. The lowest disorder incidences occurred in fruit kept at 2.2 ◦ C after DPA treatment. The effect of a delay of a week at 10 ◦ C before cold storage was dramatic (Table 1(A)). Soft scald and soggy breakdown incidences averaged less than 1%, irrespective of prior DPA treatment or subsequent storage temperature. Bitter pit incidence was not affected by DPA treatment, but averaged 24.5% in fruit kept for a week at 10 ◦ C compared with 13.5% in fruit without a pre-storage delay (Table 1(A)). Storage temperature affected bitter pit development only in fruit given the delay treatment. Decay incidence (17% overall) was relatively high in fruit after storage, but was not affected by any treatment (data not shown). In 2000, similar treatments were tested, except that a storage temperature of 2.8 ◦ C was used to investigate if soft scald and soggy breakdown susceptibility could be reduced by a slightly higher storage temperature than 2.2 ◦ C (Table 1(B)). Also, while in 1999 we did not distinguish injury that was internal only, i.e. soggy breakdown, in 2000, this disorder was analyzed separately. Susceptibility of fruit to either disorder was lower in 2000 than in 1999, but disorders were detected at 0.5 ◦ C without delay treatments (Table 1(B)). Soft scald and soggy breakdown incidences were reduced by storage at 2.8 ◦ C and by delays at 10 ◦ C before cold storage at either temperature. Bitter pit incidence was higher (P = 0.05) at 2.8 ◦ C (18%) than at 0.5 ◦ C (12%), and after delay treatment (22%) than without the delay treatment (8%), and the highest incidence occurred in the delay fruit stored at 2.8 ◦ C. However, DPA reduced bitter pit incidence at 2.8 ◦ C but not 0.5 ◦ C. Decay incidence averaged 5% and was not affected by any treatment (data not shown). Fruit quality was assessed in 1999 by measuring flesh firmness and SSC of the fruit after storage. These averaged 62.8 N and 13.3%, respectively, and were not affected by treatment or shelf life of 1 or 7 days at 20 ◦ C after storage (data not shown). IECs were measured only after 1 day at 20 ◦ C after removal from storage. Fruit kept at 2.2 ◦ C had 68 ␮l l−1 ethylene compared with 53 ␮l l−1 in fruit kept at 0.5 ◦ C (P = 0.031), and 69 ␮l l−1 in DPA-treated compared with 60 ␮l l−1 in control fruit (P = 0.009). No effect of delay treatment was detected. An inter-

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Table 1 Incidence of soft scald, soggy breakdown and bitter pit in ‘Honeycrisp’ apples either non-treated or treated with 1000 ␮l l−1 DPA, stored immediately at 0.5 or 2.2 ◦ C (1999), and 0.5 or 2.8 ◦ C (2000), and 0 and 3 ◦ C (2002), or after a week at 10 ◦ C, after storage for 12 weeks plus 7 days (1999, 2000) or 4 days (2002) at 20 ◦ C Treatment

Soft scald and soggy breakdown (%)

Bitter pit (%)

(A) New York, 1999 0.5 ◦ C 2.2 ◦ C 0.5 ◦ C + DPA 2.2 ◦ C + DPA 0.5 ◦ C + delay 2.2 ◦ C + delay 0.5 ◦ C + DPA + delay 2.2 ◦ C + DPA + delay

28 19 19 8 2 0 0 0

14 11 11 18 20 34 17 27

Treatment

Soft scald (%)

Soggy breakdown (%)

Bitter pit (%)

(B) New 0.5 ◦ C 2.8 ◦ C 0.5 ◦ C 2.8 ◦ C 0.5 ◦ C 2.8 ◦ C 0.5 ◦ C 2.8 ◦ C

13 0 13 0 0 0 3 0

a b a b b b b b

7 0 3 0 0 0 0 0

a b a b b b b b

8 13 5 5 13 40 22 13

d cd d d cd a b cd

38 0 26 0 3 0 0 0

a b a b b b b b

5 0 6 0 0 0 0 0

a b a b b b b b

5 7 4 3 7 9 8 12

a a a a a a a a

a b b c d d d d

c c c bc bc a c ab

York, 2000

+ DPA + DPA + delay + delay + DPA + delay + DPA + delay

(C) Michigan, 2002 0 ◦C 3 ◦C 0 ◦ C + DPA 3 ◦ C + DPA 0 ◦ C + delay 3 ◦ C + delay 0 ◦ C + DPA + delay 3 ◦ C + DPA + delay

Means are presented as back-transformed data after arcsin transformation for statistical analysis. Means followed by the same letter in each column are not significantly different at P = 0.05.

action between temperature and delay was detected however (P = 0.019); IECs in fruit kept at 10 ◦ C before storage were higher (75 ␮l l−1 ) and lower (45 ␮l l−1 ) than fruit without a delay treatment (average of 60 ␮l l−1 ) when stored at 2.2 or 0.5 ◦ C, respectively. A more detailed analysis of fruit quality was performed in 2000; only main effects were significant and are shown in Table 2. Firmness was not affected by any factor. SSC was lower in fruit stored at 2.8 ◦ C than at 0.5 ◦ C. Titratable acidities were lower after 7 days than 1 day at 20 ◦ C. Informal tasting of fruit, however, could not detect any differences between treatments,

and the importance of the small treatment effects on SSC and titratable acidity is uncertain. IECs were highest in fruit held at 2.8 ◦ C compared with 0.5 ◦ C, in fruit subjected to a delay treatment compared with no delay, and in fruit after the 7 day shelf life period. Ethanol accumulation was measured in fruit after 6 and 12 weeks of cold storage (Table 3). Ethanol accumulations were similar at both sampling times, except for an increase at 12 weeks for the 0.5 ◦ C + DPA treatment. Over all treatments, ethanol accumulations were much greater (37 mg kg−1 ) at 0.5 ◦ C than at 2.8 ◦ C (8.2 mg kg−1 ). At 0.5 ◦ C, accumulation was lower af-

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Table 2 IEC, firmness, soluble solids content, and titratable acidity of ‘Honeycrisp’ apples either non-treated or treated with 1000 ␮l l−1 DPA, stored immediately at 0.5 or 2.8 ◦ C (New York) and 0 or 3 ◦ C (Michigan), or after a week at 10 ◦ C, after storage for 12 weeks plus 7 days (New York) or 4 days (Michigan) at 20 ◦ C Main effects

Firmness (N)

Soluble solids (%)

Background color

Titratable acidity (% malic acid)

IEC (␮l l−1 )

New York 2000 Temperature ( ◦ C) 0.5 2.8 Significance

54.6 54.8 NS

11.9 11.6 **

– –

0.233 0.239 NS

60 96 ***

DPA − + Significance

54.5 54.9 NS

11.8 11.7 NS

– –

0.237 0.235 NS

78 78 NS

Delay − + Significance

54.3 55.1 NS

11.7 11.7 NS

– –

0.230 0.242 *

70 86 **

Shelf life (days) 1 7 Significance

54.9 54.6 NS

11.7 11.7 NS

– –

0.255 0.217 ***

52 104 ***

Michigan 2002 Temperature (◦ C) 0 3 Significance

65.0 63.8 NS

13.7 13.4 NS

2.0 1.5 ***

– –

51 78 ***

DPA − + Significance

64.1 64.8 NS

13.7 13.5 NS

1.8 1.6 NS

– –

66 64 NS

Delay − + Significance

64.7 64.3 NS

13.7 13.4 NS

1.7 1.7 NS

-

61 68 NS

Shelf life (days) 1 4 Significance

64.3 64.6 NS

– –

– –

– –

– –

ter the delay at 10 ◦ C (17.4 mg kg−1 ) than when stored immediately (56.6 mg kg−1 ). At 2.8 ◦ C, however, there was no effect of delay treatments. 3.2. Michigan (2001, 2002) In 2001 and 2002, the average IECs were 1.4 and 19.2 ␮l l−1 , respectively, while the starch indices were 3.2 and 7.0, respectively.

No soft scald or soggy breakdown occurred on fruit in the 2001 study, and no data are presented. In 2002, both disorders occurred only in fruit stored at 0 ◦ C (Table 1(C)). Incidences were not affected by DPA treatment, but were markedly reduced by the delay treatment. Bitter pit was not affected by any treatment. Firmness and SSC were not affected by any treatment, while background color and IEC were more

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219

Table 3 Ethanol accumulation in ‘Honeycrisp’ apples either non-treated or treated with 1000 ␮l l−1 DPA, stored immediately at 0.5 or 2.8 ◦ C, or after a week at 10 ◦ C, after storage for 6 or 12 weeks plus 7 days at 20 ◦ C

Table 4 Soft scald incidence and flesh firmness of ‘Honeycrisp’ apples harvested on 21 September (Harvest 1) and 26 September (Harvest 2) and kept at 20 ◦ C for 0, 1, 4 or 6 days before being stored at 1.8 ◦ C for 9 weeks plus 9 days at 20 ◦ C (Massachusetts)

Treatment

Days at 20 ◦ C before cold storage

Soft scald (%)

Firmness (N)

Harvest 1

Harvest 2

Harvest 1

Harvest 2

0 1 4 6

0 0 0 0

34 5 1 0

65.9 65.4 65.4 67.6

66.8 66.8 67.6 67.6

0.5 ◦ C

2.8 ◦ C 0.5 ◦ C 2.8 ◦ C 0.5 ◦ C 2.8 ◦ C 0.5 ◦ C 2.8 ◦ C

+ DPA + DPA + delay + delay + DPA + delay + DPA + delay

Ethanol (mg/kg) 6 weeks

12 weeks

40.1 18.1 52.1 7.6 14.7 14.8 18.1 4.4

53.7 4.0 80.5 8.1 8.0 4.3 29.0 4.8

bc de bc e de de de e

b e a e e e cd e

Means followed by the same letter are not significantly different at P = 0.05.

green (less advanced) and lower, respectively, in fruit kept at 0 ◦ C compared with 3 ◦ C (Table 2). 3.3. Massachussetts (2000) The only maturity factor that was significantly different (P = 0.05) between the 21 and 26 September harvests was the starch index, which averaged 7.0 and 6.5 units, respectively. The 0.5 unit decline, while statistically significant, may not be of physiological significance because most starch has been hydrolyzed at these levels. IEC, SSC, and firmness averaged 9 ␮l l−1 , 11.9% and 64.0 N over the two harvests. The major fruit assessment was carried out after 9 weeks, but an evaluation after 6 weeks at 1.8 ◦ C showed that soft scald had already developed in fruit from the second harvest (data not shown). After 9 weeks of storage plus a shelf life period, no soft scald was found on fruit from the first harvest (Table 4). However, 34% soft scald was found in fruit from the second harvest that had been cold stored without a delay treatment. A delay of only 1 day markedly reduced disorder incidence and by 6 days no soft scald was observable. Bitter pit and decay averaged 7 and 8% overall, respectively, and incidence of either disorder was not affected by harvest date or by delay before cold storage (data not shown). Firmness (Table 4) and SSC (data not shown) were not affected by harvest date or by delay treatment.

a a a a

a b b b

Means followed by the same letter in each column are not significantly different at P = 0.05.

4. Discussion We have investigated the effects of three postharvest treatments, pre-storage treatments of warmer holding temperatures, DPA application, and delay treatments before cold storage, to reduce the incidence of soft scald and soggy breakdown. Fruit from three growing regions have been used but lack of replication within regions does not allow definitive statements about regional effects to be made. Nevertheless, both soft scald and soggy breakdown are often observed in late harvested fruit in New York that are picked within the harvest period used by the industry, especially when stored at 0.5 ◦ C (unpublished data). In contrast, industry and research experience is that these disorders appear to be relatively less common in Massachusetts and Michigan; the fruit used in the present experiments had to be harvested well after the normal harvest period for the cultivar in these regions to ensure development of the disorders. The reason for differences of fruit susceptibility to disorder development is unclear. Low storage temperature increases the incidence of soft scald and soggy breakdown in ‘Honeycrisp’ apples (Table 1), consistent with the view that these disorders are low temperature injuries. Development of soft scald in susceptible cultivars can be reduced by utilizing warmer storage temperatures, e.g. 2–3 ◦ C (Smock and Neubert, 1950; Snowdon, 1990). However, two reasons exist for reluctance by industry to use such temperatures for ‘Honeycrisp’. The first is that the low volumes of fruit available because production is still limited do not warrant separate storage facilities, especially when temperatures close to

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0 ◦ C are used to maintain quality of most cultivars in air storage. The second is that while increasing storage temperatures can reduce incidence of the disorders (Table 1(B and C)), higher storage temperatures do not control their development in highly susceptible fruit (unpublished). DPA sometimes reduced, but did not prevent, development of soft scald in fruit kept at close to 0 ◦ C (Table 1). DPA also reduces but does not prevent soft scald development in other cultivars (Wills et al., 1981; Wills and Scott, 1982). Higher DPA concentrations might allow better control of soft scald and soggy breakdown, but may still be less effective for a highly susceptible cultivar such as ‘Honeycrisp’. Although DPA is registered for use as an inhibitor of superficial scald development, it has become increasingly realized that it has a broad effect of reducing incidence of other disorders such as external and internal carbon dioxide injury (Fernández-Trujllo et al., 2001; Watkins et al., 1997). Delays before cooling are cited as aggravating factors in soft scald development (Gerhardt and Sainsbury, 1952). The most effective treatment for control of soft scald in our study, however, was a delay at 10 or 20 ◦ C before storage, even at the lowest temperatures of 0 and 0.5 ◦ C (Table 1). We did not investigate a wider range of delay periods at 10 ◦ C, but fruit susceptibility was reduced markedly by as little as 1 day at 20 ◦ C (Table 4). The mechanism by which delays before storage inhibit development of soft scald is not known. Early studies on the effects of delays on development of soft scald and soggy breakdown are inconsistent and are affected by cultivar; incidence of these disorders can be increased, decreased or both depending on the season delay period (Brooks and Harley, 1934; Plagge et al., 1935; Plagge and Maney, 1937). For example, soggy breakdown incidence in ‘Northwestern Greening’ was decreased, while that of ‘Golden Delicious’ was increased, by delays at 10 ◦ C for 7–35 days (Plagge and Maney, 1937). It has been suggested that soft scald is a disorder associated with respiratory metabolism (Pierson et al., 1971) although no recent literature on this relationship exists. Accumulation of ethanol, usually an indicator of fermentative metabolism, was lowest in the higher storage temperature and in fruit that were kept at 10 ◦ C before storage (Table 3). However, in 2000, both soft scald and soggy breakdown incidences were

low, and accumulation of ethanol occurred even in fruit without disorder development. Ethanol may not be directly related to development of soft scald or soggy breakdown, or the threshold concentration for injury to occur may not have been reached in these fruit. Effects of delay on disorder development could be due to the timing of cold storage relative to the climacteric. The one year (Michigan, 2001) in which IECs of fruit were relatively low was associated with an absence of disorder development and suggests that effects of delay may be related to timing of the climacteric increase in respiration. It is interesting, however, that ‘Honeycrisp’ often does not show an autocatalytic pattern of ethylene production typical of most other apple cultivars (unpublished data). Also, IEC remained relatively low during storage (Table 2). The biochemical mechanisms for soft scald and soggy breakdown development require further research. In general, delays at warmer temperatures before cold storage of apple fruit is discouraged because softening rates and therefore loss of marketable quality can increase (Johnston et al., 2002). ‘Honeycrisp’ is a remarkable apple however, with slow softening characteristics: firmness is maintained for long periods even under air storage (Tong et al., 1999). Our data indicate that firmness and other quality factors were not affected by delays at 10 or 20 ◦ C before cold storage at least for 9 to 12 weeks (Tables 2 and 4). Informal taste panels using grower groups also indicated that no effects of treatment could be detected during these storage periods (data not shown) but effects of delays before cold storage on quality characteristics for longer storage periods are not known. The greatest concern about use of delay treatments, as well as warmer storage temperatures, is increased bitter pit development, although no treatment effect was found in Michigan (Table 1) or Massachusettsgrown fruit. Bitter pit incidence is generally increased by postharvest treatments that increase fruit metabolic rates (Ferguson and Watkins, 1989). Therefore, unless the susceptibility of fruit can be decreased by preharvest factors such as calcium spray regimes (Rosenberger et al., 2001) losses of fruit due to bitter pit may be as high as those resulting from soft scald development. Nevertheless, several New York storage operators that had sustained major fruit losses due to soft scald and soggy breakdown development in the past have utilized a delay procedure in their opera-

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tion, keeping fruit in the storage corridors for a week, with good results.

Acknowledgements This research was supported by federal formula funds, Regional Project NE-1018, the New York Apple Research and Development Program, the Michigan State horticultural Society and the Michigan Apple Research Committee.

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