‘Golden Delicious’, Pennsylvania.

1-MCP (AFxRD-038; AgroFresh) was applied to ‘Golden Delicious’/Bud.9 trees at the Pennsylvania State University Fruit Research and Extension Center (Biglerville, PA). 1-MCP was applied at either 75 or 150 mg·L⁻¹ either 1 (H-1) or 7 (H-7) d before the anticipated harvest date in 2006. In addition to the 1-MCP treatments, there was an untreated control treatment. Treatments were assigned to three-tree plots arranged as a randomized complete block design experiment with six replications. One tree within each plot was designated for fruit drop counts and the remaining two trees per plot designated for sequential sampling for fruit maturity and quality assessments after storage. The mixing and application procedures described subsequently were followed to minimize premature release of 1-MCP into the headspace in the spray tank; IAP Hi Supreme spray oil (Independent Agribusiness Professionals, Fresno, CA) was added at 1% (by volume) to a half-filled 10-L spray tank and then Silwet L-77 organosilicone surfactant (Helena Chemical Co., Collierville, TN) was added at 0.05% (by volume). After the specified amount of AFxRD-038 was added, the tank was filled with water and the mixture gently stirred using a squirrel cage-style paint stirrer attached to a cordless electric drill. Each spray treatment was applied to the point of drip immediately after mixing using a CO₂ pressure sprayer (Bellspray, Opelousas, LA) calibrated to deliver the spray at 276 KPa and fitted with a TeeJet 8004VS flat fan nozzle (Spraying Systems, Wheaton, IL).

Fruit drop was calculated as a percent of the total fruit number over time from whole-tree fruit counts made before treatment and biweekly until 21 d after anticipated harvest (H + 21). A random sample of 20 fruit was removed from the remaining two trees in each plot 7, 14, and 21 d after H for fruit maturity assessments. Fruit skin color was evaluated with a model CM-2600d spectrophotometer equipped with an 8-mm specimen measuring port (Konica-Minolta Sensing Americas, Ramsey, NJ) and reported as L*C*h values. Fruit internal ethylene concentration (IEC) was measured with a gas chromatograph (model GC-8A; Shimadzu, Kyoto, Japan) equipped with a flame ionization detector and an activated alumina column (Supelco Div., Sigma-Aldrich, Bellefonte, PA). Briefly, a 1-mL gas sample was removed from each fruit by inserting a 25-mm-long stainless steel needle through the calyx opening. Fruit firmness was measured on opposite pared sides of each fruit using a Güss model GS-14 fruit texture analyzer (QA Supplies, LLC, Norfolk, VA). Soluble solids concentration (SSC) of a composite juice sample was measured using a model PR-32 digital refractometer (Atago U.S.A., Bellevue, WA). Starch index was rated according to the Cornell Starch Chart (Blanpied and Silsby, 1992) in which 1 = 100% staining and 8 = 0% staining. Two additional samples of 20 fruits were removed from each plot at H + 14 for storage evaluations. One sample was placed in regular atmosphere (RA) storage at +1 °C for 120 d, whereas the other sample was placed in controlled atmosphere (CA) storage at +1 °C for 240 d. Storage samples were held for 7 d at 20 °C before measuring IEC and firmness as previously described and rating the incidence of fruit with superficial scald (RA storage samples only).

‘Law Rome’, Pennyslvania.

Twenty-four uniform ‘Law Rome’/M.26 trees were selected from within a mature orchard at the Pennsylvania State University Fruit Research and Extension Center in Biglerville, PA. 1-MCP was applied to the trees either 1 or 7 d before H in 2006 as the AFxRD-038 formulation at 105 mg·L⁻¹. Mixing and application procedures were as described in the previous experiment. Each treatment was applied to single-tree plots in a randomized complete block design experiment with six replications, and control and postharvest 1-MCP-treated fruit were sampled from separate untreated trees in the same orchard. Postharvest 1-MCP treatment was achieved by exposing fruit to 1 μL·L⁻¹ 1-MCP as the SmartFresh formulation (AgroFresh) in a closed chamber with a circulation fan for 24 h immediately after sampling on H + 7. There was an untreated control treatment in addition to the three 1-MCP treatments.

A random sample of 20 fruit was removed from each plot at H + 7 and H + 14. SSC, IEC, fruit firmness, and starch rating were evaluated as described in the previous experiment. The presence or absence of red skin pigment bleeding into the fruit flesh (a maturity-related defect that causes fruit to be downgraded to juice value) was evaluated on an equatorial cross-section of each sample fruit. An additional sample of 20 fruit was removed from each plot at H + 7 and H + 14 and placed in RA storage at 1 °C for 120 d. Quality evaluations included measuring IEC, and fruit firmness after 7 d at 20 °C as previously described, and the incidence of fruit with superficial scald was also rated at this time.

‘Law Rome’, North Carolina.

1-MCP was applied to mature ‘Law Rome’/M.7 trees in a commercial orchard in Henderson County, NC, 7 d before H in 2006 as the AFxRD-038 formulation either at 155 mg·L⁻¹ with a CO₂ pressure backpack sprayer or at 95 mg·L⁻¹ with a tractor-mounted axial fan sprayer. Both application methods were calibrated to deliver 3 L of spray volume per tree. In addition to the two preharvest 1-MCP treatments, there was an untreated control treatment. Mixing procedures for AFxRD-038 were as described in the previous experiments. The axial fan sprayer was configured with the jet agitation in the tank disengaged and a disc/core nozzle combination (D5/56; Spraying Systems Co., Wheaton, IL) that produced large droplet sizes in a full-cone spray pattern. Tractor speed, pump pressure (689 KPa), and nozzles were configured to achieve a spray volume equivalent to 1665 L·ha⁻¹ at the row spacing in the orchard. Each treatment was applied to single-tree plots arranged in a randomized complete block design experiment with four replications.

A random sample of 20 fruit was removed from each plot at H for assessment of treatment effects on SSC, firmness, and starch index as described previously. All remaining fruit were removed from the trees at this time; fruit from each plot were randomly assigned into groups of 100 uniform apples for imposing different postharvest treatments. Fruit from control trees were moved to either RA or CA storage with or without prior diphenylamine (DPA) or postharvest 1-MCP treatment. Fruit samples from each of the two preharvest 1-MCP treatments were placed in RA storage only but received no further postharvest treatments, a DPA drench, or a postharvest 1-MCP treatment. Fruit were treated with DPA by submerging in a 1000-mg·L⁻¹ solution for 30 s 1 d after harvest. Postharvest 1-MCP treatment was achieved by exposing fruit to 1 μL·L⁻¹ 1-MCP for 24 h as the SmartFresh formulation at H + 7 in a commercial treatment facility. All fruit were held in the same RA room until H + 21 before the samples destined for CA were transferred to a CA room (CO₂/O₂ concentrations of 5% and 1%, respectively). Temperatures in both the CA and RA rooms were –1 °C throughout the storage period. Fruit samples were removed from each plot in RA storage at 40-d intervals until H + 240. At the first removal date (H + 40), a 15-fruit random sample was held at 20 °C for 7 d before measuring fruit firmness on pared opposite sides of each fruit with a Güss model GS-20 fruit texture analyzer (QA Supplies, LLC). At each of the subsequent dates, a 20-fruit sample was removed; firmness was measured on pared opposite sides of 10 fruit per sample after 1 and 7 d at 20 °C. Fruit were held in CA storage until H + 160 and then moved to the same room as the RA fruit. The severity of superficial scald was assessed on all 20 fruit 1 d after removal and on the remaining 10 fruit 7 d after removal using the visual rating system described by Watkins et al. (1995) in which 0 = no scald present and 4 = 67% or more of the fruit surface covered with scald. Data presented are percentages of fruit affected with superficial scald (1, 2, 3, and 4 ratings combined).

Statistical analysis.

The general linear models procedure of the SAS Version 8 software (SAS Institute, Cary, NC) was used to test for block and treatment effects in each experiment. Means separations were determined using either the Fisher's protected least significant difference or the Waller–Duncan K-ratio t test multiple comparison procedures in which analysis of variance showed significant treatment effects. Percent scald data were subjected to arcsine transformation before analysis to provide a normal distribution. Single degree of freedom contrasts were used to test for effects of pre- and postharvest 1-MCP treatments, CA storage, and DPA on firmness and scald in the North Carolina ‘Law Rome’ study.

Preharvest fruit drop.

Application of 75 or 150 mg·L⁻¹ 1-MCP either 1 d or 7 d before H delayed but did not prevent, fruit drop of ‘Golden Delicious’ compared with an untreated control measured at H + 17 and H + 21 (Table 1). There was no effect of time of application or concentration of preharvest 1-MCP treatment on fruit drop. Similar reductions in fruit drop after preharvest 1-MCP treatment were reported for ‘Golden Delicious’ (Yuan and Carbaugh, 2007) and ‘Scarletspur Delicious’, but not for ‘Cameo’ (Elfving et al., 2007).

Table 1.

Main effect of preharvest 1-methylcyclopropene (1-MCP) concentration on cumulative fruit abscission per tree of ‘Golden Delicious’ in Pennsylvania, 2006.

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Fruit maturity at harvest.

Preharvest 1-MCP treatments delayed maturity of ‘Golden Delicious’ fruit in the Pennsylvania experiment. There was generally no difference between the two application timings; however, maturity was delayed more effectively by 1-MCP at 150 mg·L⁻¹ compared with 75 mg·L⁻¹. Fruit IEC and starch index were lower and fruit firmness higher after 1-MCP treatment measured 7, 14, or 21 d after H (Table 2).

Table 2.

Interaction means of effects of time of application and concentration of preharvest 1-methylcyclopropene (1-MCP) on internal ethylene concentration (IEC), starch index, fruit firmness, and skin color of ‘Golden Delicious’ apple fruit at three delayed harvest dates (7, 14, and 21 d after anticipated harvest), Pennsylvania, 2006.

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1-MCP did not affect fruit weight, fruit diameter, or juice SSC (data not shown). Fruit diameter and juice SSC continued to increase throughout the harvest period, indicating that preharvest 1-MCP sprays can be used to improve fruit size and quality by delaying harvest without the expected increase in maturity parameters such as ethylene evolution, starch hydrolysis, and softening (Yuan and Carbaugh, 2007). Preharvest 1-MCP treatments did not completely inhibit ripening of ‘Golden Delicious’; IEC and starch index continued to increase and fruit continued to soften throughout the harvest period. Although there was no interaction between the timing and concentration of 1-MCP treatment, the IEC of ‘Golden Delicious’ fruit treated with 75 mg·L⁻¹ 1-MCP at 7 d before H was 2.5 mg·L⁻¹ when measured at H + 21, suggesting that the effects of 1-MCP on ethylene action might have been lessening at this time. There was a significant effect of time of 1-MCP application on the firmness of fruit at H + 14 but not at either of the other two harvest dates. 1-MCP was without effect on the skin color of ‘Golden Delicious’ at the first two harvest dates but reduced chlorophyll degradation of fruit at H + 21 as determined by L*, chroma, and hue values (Table 2).

Fruit treated with 105 mg·L⁻¹ 1-MCP in the Pennsylvania ‘Law Rome’ study were firmer and had lower starch index values at H + 14, whereas starch index, firmness, and SSC were not different from the control at H + 7 (Table 3). Preharvest 1-MCP reduced IEC in ‘Law Rome’ fruit at H + 7 and H + 14 and also reduced the incidence of fruit with skin bleed at H + 14 in the Pennsylvania study (Table 3). The incidence of skin bleed on the H + 7 sample date was unaffected by the treatments (data not presented). Application of 1-MCP 7 d before H had no effect on starch index, firmness, or SSC of ‘Law Rome’ in the North Carolina experiment (data not shown); average values for these three maturity parameters were 3.9, 81.3 N, and 11.5%, respectively.

Table 3.

Effect of time of application of preharvest 1-MCP (105 mg·L⁻¹) on internal ethylene concentration (IEC), maturity, firmness, soluble solids (SSC), and skin bleed of ‘Law Rome’ apples at two delayed harvest dates (7 and 14 d after anticipated harvest), Pennsylvania, 2006.

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Fruit quality after storage and softening during storage.

‘Golden Delicious’ fruit that received preharvest 1-MCP treatments were firmer than untreated fruit after either 120 d in RA or 240 d in CA (Table 4). Fruit treated with 1-MCP 7 d before H but 21 d before actual harvest were 4 to 5 N firmer than untreated fruit after 120 d in RA storage and ≈10 N firmer when treated 1 d before H (15 d before actual harvest), suggesting that application times closer to harvest inhibited the loss of firmness during storage more effectively. There was a similar trend after 240 d for the CA-stored fruit; the increase in firmness over the control was greater for 1-MCP treatment 1 d before harvest compared with 7 d before harvest (Table 4). Elfving et al. (2007) also found that the closer to harvest sprayable 1-MCP was applied, the better the retention of flesh firmness was in storage, although in this earlier work, 1-MCP was not applied closer than 7 d before harvest. There was a significant main effect of time of 1-MCP treatment on IEC of ‘Golden Delicious’ fruit after 120 d in RA; IEC was reduced when 1-MCP was applied 1 d before H but was unaffected by 1-MCP treatment 7 d before H. There was no effect of 1-MCP concentration on poststorage IEC of ‘Golden Delicious’ fruit stored in RA, but IEC of fruit stored in CA for 240 d was negatively related to the concentration of preharvest 1-MCP treatments (Table 4).

Table 4.

Effects of time of application and concentration of preharvest 1-methylcyclopropene (1-MCP) on fruit quality and incidence of superficial scald of ‘Golden Delicious’ apples after 120 d storage in regular atmosphere (RA) at 1 °C or 240 d storage in controlled atmosphere (CA).^z

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Postharvest application of 1-MCP as SmartFresh reduced IEC of ‘Law Rome’ apples after RA storage in the Pennsylvania study more effectively than preharvest sprays, and application 1 d before H reduced IEC more effectively than application 7 d before H (Table 5). Firmness of ‘Law Rome’ fruit after storage was higher after 120 d storage in RA for pre- and postharvest 1-MCP treatments compared with the control; however, application 1 d before H maintained fruit firmness more effectively than 7 d before H.

Table 5.

Effects of preharvest 1-methylcyclopropene (1-MCP) (105 mg·L⁻¹ spray as AFxRD-038) or postharvest 1-MCP (24-h exposure to 1 μL·L⁻¹ as SmartFresh) on internal ethylene concentration (IEC), firmness, and the incidence of superficial scald of ‘Law Rome’ apples after 120 d storage in regular atmosphere at 1 °C.^z

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Preharvest 1-MCP sprays and CA storage were the only treatments that inhibited the loss of firmness during storage in the North Carolina ‘Law Rome’ study. The total lack of any response to postharvest 1-MCP treatment in the North Carolina study was surprising, especially because the same cultivar exhibited a significant response in the Pennsylvania study. Interestingly, fruit were exposed to 1-MCP only 1 d after harvest in the Pennsylvania study, whereas exposure to 1-MCP did not occur until 7 d after harvest in the North Carolina study. In previous unpublished work, we have found that the firmness response of ‘Rome’ to postharvest 1-MCP treatments has ranged from good (fruit 12 N firmer after 120 d in RA storage) to nonexistent. It is possible that the lack of response to postharvest 1-MCP treatment in the North Carolina ‘Rome’ study may have resulted from a problem with the commercial facility used to treat the fruit. However, this facility was leak-tested at the beginning of the 2006 harvest season and found to be gas-tight at that time. We are currently investigating the effects of delay between harvest and exposure of ‘Rome’ apples to 1-MCP in greater detail.

At the first assessment date (40 d in RA storage followed by 7 d at 20 °C), preharvest application of 1-MCP increased firmness by ≈25 N compared with untreated fruit (Table 6). The positive effect of preharvest 1-MCP treatment on fruit firmness declined in magnitude during the initial 80 d in storage; treated fruit were ≈15 N firmer throughout the remainder of the storage period. Firmness measurements of fruit in CA storage did not begin until 160 d after harvest. Fruit stored in CA were on average 2.5 N firmer than non-CA-stored fruit after 160 d in CA storage + 7 d at 20 °C, 4.8 N firmer after 200 + 7 d at 20 °C, and 6.0 N firmer after 240 d + 7 d at 20 °C. Preharvest 1-MCP treatments maintained firmness of ‘Law Rome’ fruit more effectively than CA storage in the North Carolina study. There was no difference in fruit firmness of ‘Law Rome’ after storage between the two preharvest 1-MCP treatments in the North Carolina study.

Table 6.

Effects of preharvest 1-methylcyclopropene (1-MCP) at 155 mg·L⁻¹ (155) or 95 mg·L⁻¹ (95), postharvest 1-MCP at 1 μL·L⁻¹ (POST), diphenylamine (DPA), and regular atmosphere (RA) or controlled atmosphere (CA) treatments in various combinations on fruit firmness of ‘Law Spur Rome’ apples during long-term storage.^z

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Superficial scald.

There was a significant main effect of both timing and concentration of preharvest 1-MCP sprays on the incidence of fruit with superficial scald in ‘Golden Delicious’ after 120 d in RA storage. Application of 1-MCP 1 d before H reduced the incidence of superficial scald more effectively than application 7 d before H when fruit were harvested at H + 14. Surprisingly, preharvest application of 75 mg·L⁻¹ 1-MCP reduced the incidence of superficial scald on ‘Golden Delicious’ more effectively than application at 150 mg·L⁻¹ (Table 4). Application of 105 mg·L⁻¹ 1-MCP to ‘Law Rome’ 7 d before H reduced the incidence of superficial scald in RA storage at H + 120 in RA for fruit harvested at H + 7, whereas neither application of 105 mg·L⁻¹ 1-MCP 1 d before H or postharvest exposure to 1 mg·L⁻¹ 1-MCP influenced the incidence of fruit with superficial scald in the Pennsylvania study (Table 5).

The incidence of fruit that developed superficial scald during storage was much higher in the North Carolina study compared with the other two studies. Fruit in the North Carolina study were harvested at an earlier stage of maturity as determined by higher firmness levels and lower starch index values; this difference might explain the higher scald incidence. Although scald was not observed until after 80 d in RA storage in the North Carolina experiment, there were no effects of treatment on the incidence of scald until 120 d (Table 7). Postharvest 1-MCP treatment did not influence scald development in either of the two ‘Law Rome’ studies (Tables 5 and 7). Preharvest 1-MCP treatments, on the other hand, greatly reduced the incidence of scald in ‘Law Rome’ in the North Carolina study when assessed both 1 d and 7 d after removal from RA storage (Table 7). There was a difference in how well the two preharvest 1-MCP treatments controlled superficial scald in the North Carolina ‘Law Rome’ study, although these differences were only evident after holding the fruit for 7 d at 20 °C before assessment. Application of 155 mg·L⁻¹ 1-MCP with a backpack sprayer resulted in a lower incidence of scald compared with application of 95 mg·L⁻¹ 1-MCP with an airblast sprayer, suggesting that the lower rate of 1-MCP was beginning to lose activity after 160 d in RA storage (Table 7). Preharvest 1-MCP sprays controlled scald more effectively than a postharvest DPA treatment.

Table 7.

Effects of preharvest 1-methylcyclopropene (1-MCP) at 155 mg·L⁻¹ (PRE155) or 95 mg·L⁻¹ (PRE95), postharvest 1-MCP at 1 μL·L⁻¹ (POST), diphenylamine (DPA), and regular atmosphere (RA) or controlled atmosphere (CA) treatments in various combinations on the incidence (%) of superficial scald of ‘Law Spur Rome’ apples during long-term storage.^z

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The incidence of scald was reduced by DPA when assessed after 1 d at 20 °C, although the beneficial effects of DPA were no longer evident if the fruit were held for 7 d at 20 °C before assessment at removal dates later than 160 d after harvest, and DPA was without effect on scald at either assessment time after 240 d in storage (Table 7). ‘Law Rome’ fruit that were held in CA storage developed a much lower scald incidence compared with fruit held in RA storage and fruit treated with DPA; the incidence of scald was similar in CA-stored fruit and fruit from trees that received a preharvest 1-MCP treatment.