Effect of Paper Wraps on Postharvest Decay and Disorders of Anjou Pear Fruit, 1997
Washington pears are wrapped in tissue paper at packing to protect fruit from damage during shipping. In addition, wraps are commonly impregnated with either oil, copper, or ethoxyquin, alone or in combination, to prevent superficial scald and the spread of decay, especially gray mold (caused by Botrytis cinerea Pers.: Fr), in packed fruit. The effectiveness of paper treatments in preventing spread of decay has not been formally assessed. Oil wraps were used to prevent storage scald prior to the introduction of ethoxyquin treatments, either as wraps, line sprays, or drenches. In recent years however, oil wraps have been implicated with the occurrence of other fruit skin disorders, especially calyx-end browning (CEB [= DSD]). These trials were conducted to determine the effectiveness of paper wraps used in pear packing in preventing the spread of gray mold in packed boxes of Anjou pear fruit and to assess the effects of various wraps on fruit skin disorders.
All fruits in six single replicate boxes (US No. 1, size 100) of commercially harvested Anjou pear fruit from a single grower run at each of two warehouses were wrapped in one of 7 papers (6% oil, 3% oil + copper, 6% oil + copper, Supercop [6% oil + copper + ethoxyquin], plain [dry], powdered, or copper alone) or left unwrapped. Boxes were lined with perforated poly liners. One wounded, inoculated fruit, wrapped in the same paper as the other fruit in the box, was placed in each of two locations in each box to create infection foci.
Inoculated fruit first were surface sterilized by soaking in 150 ppm sodium hypochlorite for 5 minutes after which they were allowed to dry. Fruit then were wounded twice on the cheek with a wounding tool (5 mm diameter x 3 mm deep) and 50 µL of an aqueous suspension (1000 conidia/mL) of B. cinerea was applied to each wound. Conidia were from 7-day old cultures grown on PDA (Difco, Detroit, MI). Isolates were originally recovered from decaying fruit.
After packing, boxes from each warehouse were placed in commercial CA storages at 31 ºF for 31 weeks at the respective warehouses. Fruit were kept in standard CA conditions (1.5% 02, < 1.0% CO2) for about 140 days after which they were held in regular air storage. Fruit to fruit spread of gray mold was assessed by determining the number of fruit with lesions adjacent to those that had been inoculated. Data were transformed to arcsine square-root values and analyzed with analysis of variance Minitab, Inc., State College, PA) with warehouses as blocks. Means were separated with Tukey's test (P = 0.05).
Differences in skin browning disorders among treatments were noticed when decay was being assessed. Fruit from each treatment were assessed for the incidence of each of several disorders including superficial scald, calyx-end browning, and dark skin-burn within 24 hrs after it was removed from refrigeration and again 7 days later. The proportion of fruit with each disorder was determined in a single box of fruit from warehouse 1. Two boxes of fruit were assessed from warehouse 2. In addition, scald on fruit from warehouse 2 was assessed for severity (S) on a 0 to 3 rating scale (0 = no scald and 3 = severe scald) and a severity index (SI) was calculated where SI = the sum of the proportion of fruit in each severity class multiplied by S. Proportional data were transformed to arcsine square-root values before analysis. CEB data were blocked by warehouse and analyzed with analysis of variance. Superficial scald Sl and dark skin-burn data from warehouse 2 only were analyzed with one-way analysis of variance. Means were separated with Tukey's test (P = 0.05).
Results and Discussion
Paper wraps significantly affected the incidence of secondary gray mold infections (nesting) in packed boxes of Anjou pears compared to unwrapped controls (Table 1). Aerial mycelia were observed on the surface of paper wraps covering some inoculated fruit in all treatments, but these mycelia did not always produce secondary infections on adjacent fruit. All papers containing oil and the powdered paper without oil significantly reduced the incidence of secondary decay from that observed in boxes of unwrapped fruit. However, neither copper alone or plain paper had a significant effect on nesting.
Calyx-end browning. Symptoms appeared as light brown areas with irregular margins primarily at the calyx-end of fruit and often extended about mid-way up the cheeks of fruit. Symptoms were present on fruit at the time they were removed from storage and the area affected did not increase over time. Interestingly, when PLU stickers were present in symptomatic areas, fruit skin appeared green and healthy under the stickers, and browning was not apparent.
Although, oil containing papers were effective at reducing gray mold nesting, oil may cause or lead to conditions under which CEB occurs. Symptoms were most prevalent in fruit wrapped with oil alone (Table 1). Incidence decreased with increasing copper content and was essentially eliminated with the addition of ethoxyquin and copper. No, or insignificant, incidence of calyx-end browning was observed in either unwrapped fruit or those wrapped in oil-free papers.
Superficial scald. Scald symptoms began to develop about 1.5 days after fruit were removed from storage and placed at room temperature. Symptoms increased in severity, both in area affected and darkness of marking, up to about 6 days after removal of fruit from storage. Margins of affected areas were irregular and scald extended to areas under PLU stickers.
Fruit wrapped with oil treated papers had significantly lower scald Sl values than those wrapped in oil-free paper (Table 2). Addition of copper to oiled paper appeared to further reduce the SI. Superficial scald (SI) was lowest in fruit wrapped with Supercop paper. The effect of copper added to oil was not apparent in scald incidence data collected from warehouse 1, although incidence was considerably lower in fruit wrapped with Supercop than any other paper (Table 2).
Dark skin-burn. Symptoms of this disorder were blackened blotches (about 2 to 3 cm in diameter) with irregular margins that appeared to occur randomly over the fruit surface. No dark skin-burn was observed in fruit from warehouse 1, but the incidence of the disorder was relatively high in fruit from warehouse 2 (Table 2). Copper impregnated paper wraps, both with and without oil, appeared to alleviate this symptom. Highest incidence of dark skin-burn was observed in fruit wrapped in the powdered paper. Paper with oil alone and plain paper had no effect on dark skin-burn incidence compared to the unwrapped control.
Table 1. Effect of paper fruit wraps on nesting of Botrytis cinerea and calyx-end browning in packed Anjou pear fruit after 31 weeks of storage at 31 ºF in a commercial storage.x
|Treatment||Decay (%)||Calyx-end browning(%)|
|No wrap||4.5 ay||0.0 c|
|Oil (6%)||1.8 b||58.6 a|
|Oil (3%) + copper||1.5 b||17.2 b|
|Oil (6%) + copper||2.0 b||5.3 bc|
|Supercop (oil (6%) + copper + ethoxyquin)||1.7 b||0.7 c|
|Plain (dry)||3.1 ab||0.4 c|
|Powdered||2.3 b||0.0 c|
|Copper||2.9 ab||0.0 c|
|(P = 0.001)z||(P < 0.001)|
x Fruit were
held in CA for about 140 days after which they were kept
regular air storage.
y Means followed with a common letter are not significantly different according to Tukey's test (P = 0.05).
z Significance of F statistic from analysis of variance. Data were transformed to arcsin square-root (prop.) values before analysis.
Table 2. Effect of paper fruit wraps on superficial scald and dark skin bum on Anjou pear fruit after 31 weeks of storage at 31 ºF in a commercial storage.w
|Warehouse 1||Warehouse 2|
|Treatment||Superficial scald (%)||Burn (%)||Superficial scald (S1)x||Burn|
|No wrap||96.5||0.0||2.9 ay||26.3 bc|
|Oil (6%)||18.5||0.0||1.4 b||25.8 bc|
|Oil (3%) + copper||14.5||0.0||0.9 c||1.7 d|
|Oil (6%) + copper||33.0||0.0||1.0 c||0.0 d|
|Supercop (oil (6%) + copper
|4.2||0.0||0.5 d||0.0 d|
|Plain (dry)||97.9||0.0||2.9 a||44.5 b|
|Powdered||98.9||0.0||2.9 a||75.6 a|
|Copper||67.7||0.0||2.7 a||5.9 cd|
| || || ||(P < 0.001)z||(P < 0.001)|
w Fruit were held in CA for about 140 days after which they were kept in regular air storage.
x Sl = Sum (proportion of fruit in each severity class x S). Rating was on a 0 to 3 rating scale with 0 = no scald and 3 = severe scald.
y Means in each column followed with a common letter are not significantly different according to Tukey's test (P = 0.05).
z Significance of F statistic from analysis of variance. Percentages were transformed to arcsin square-root (prop.) values before analysis.
Paper treatments affected decay and storage disorders differentially. The interaction of copper and oil was particularly apparent. Oiled paper was effective against gray mold nesting and scald. Copper in the paper had no appreciable effect on gray mold nesting, but appeared to have some effect on scald when it was combined with oil. Calyx-end browning incidence was greatest in oil treated paper and copper appeared to ameliorate that effect. In addition, although oil was not associated with dark skin-burn, copper appeared to be very effective at eliminating that disorder. Scald control was improved by the addition of ethoxyquin to the paper wrap, and would appear to allow the use of oiled paper for decay and scald control.
The cause of the storage disorders examined in this study are not known. However, their incidence and/or severity were greatly affected by the presence of oil, copper, or ethoxyquin impregnated into fruit wrapping paper. The differential effects of the materials used in the wraps suggests different causes for the various disorders. A serious look at the causal factors of these disorders and the mode of action in which the paper treatments affect them is warranted.
Dr. Peter G. Sanderson1 and Diane L. Bennett2
1Washington Tree Fruit Research Commission
2Blue Star Growers, Inc.,