Washington Tree Fruit Research Commission

Research Reports

Pear storage decay and fruit quality research (2007)

FINAL PROJECT REPORT
WTFRC Project #
YEAR 0/0
Organization Project #
Title:Pear storage decay and fruit quality research
PI:David Sugar
Organization:Oregon State University 569 Hanley Rd. Medford, Oregon 97502 541-772-5165 david.sugar@oregonstate.edu
 PDF version of report

Collaborators

R.A. Spotts, C.L. Xiao

Objectives

This research blends activities in the areas of postharvest pathology and physiology. One objective is to further develop a storage decay control program for winter pears in which diverse, independent decay control practices contribute to dependable reduction of postharvest diseases. A second objective is to develop and evaluate methods and materials for the promotion of pear quality during storage. Fruit quality research (including size enhancement) was included in this project beginning in 2006.

Significant findings

1. Postharvest decay control programs.   2. New technologies affecting pear decay.   3. Advances in postharvest management of pears.   4. Pear fruit quality enhancement.  Calcium chloride summer sprays were more injurious to Bartlett pear leaves than to Bosc, and calcium treatments did not consistently enhance Bartlett firmness or storage potential.

Methods

A variety of orchard, postharvest, and storage treatments were applied in a wide range of experiments.

Results and discussion

I. Postharvest decay control programs. 

1. A treatment program consisting of summer calcium chloride sprays, preharvest Pristine fungicide, and postharvest either Scholar or Penbotec fungicide, based on experience in this research project, offers a powerful approach to decay management. In orchards where bull’s-eye rot or side rot has been a problem, adding ziram enhances the program. Other preharvest sprays have also been effective: Flint and Topsin M, as will be shown below.  

Calcium chloride sprays in summer followed by Pristine one week before harvest increased the resistance of Bosc pears to blue mold (Fig. 1). Resistance to blue mold was determined by wounding the pears and inoculating with the fungus after harvest, then measuring the extent of decay lesion development after 6-8 weeks in cold storage. This study also compared alternative calcium programs; a late summer calcium program (3 lb. actual calcium applied 3 times in August and early September) was equivalent to a mid-summer program (3 lb. actual calcium applied 3 times in July and early August). A single-shot high dose (5 lb. actual calcium) of calcium chloride applied one week before harvest appeared to injure the fruit, and increased the amount of decay, presumably by diminishing natural fruit resistance, facilitating pathogen entry into tissue.   Fig. 1. Decay severity in Bosc pears inoculated after various calcium programs, with and without Pristine treatment one week preharvest, and with and without Scholar treatment postharvest. 

2. A two-year study of alternative decay control programs combining orchard, postharvest, and storage treatments was completed in 2005 (Table 1). Among orchard treatments, Messenger was not shown to be beneficial, while calcium chloride reduced decay. Among postharvest treatments, BioSave 110 and sodium bicarbonate (5%) reduced decay while chitosan and StorOx did not (as used in these experiments). Pears stored in LifeSpan MAP bags had less decay than those stored in standard perforated liners. Pears that had received calcium in the orchard had higher oxygen and lower carbon dioxide atmospheres in the LifeSpan bags, likely indicating a slower rate of respiration. The treatment program consisting of calcium chloride in the orchard, BioSave 110 postharvest, and storage in LifeSpan MAP was the most effective in minimizing decay incidence.


Table 1. Effects of alternative orchard, postharvest, and storage treatments on natural decay in wounded Bosc pears. 
Orchard treatmentPercent of wounds infected
 Year 1Year 2
Check6.9 a22.0 a
Messenger5.7 a16.8 a
Calcium chloride3.1 b  7.3 b
  
Postharvest treatmentYear 1Year 2
Check     3.4 bc22.2 a
Chitosan (Elexa 4)12.6 a29.6 a
Mertect     3.6 bc  8.3 b
StorOx   4.8 b22.3 a
BioSave 110     4.0 bc  5.1 c
Sodium bicarbonate    2.8 c  4.7 c
  
Storage treatmentYear 1Year 2
Check (Standard liner)6.4 a17.8 a
LifeSpan MAP4.0 b13.0 a
 Combined Effects:
 

Orchard

 Postharvest 

Storage

 % infected wounds
Year 1   
CheckWaterStandard liner 5.7 a
Calcium chlorideBioSave 110LifeSpan MAP 3.3 a
Year 2 

 
CheckWaterStandard liner44.2 a
Calcium chlorideBioSave 110LifeSpan MAP   2.1 b
 
Orchard treatmentAverage gas content in LifeSpan MAP
 OxygenCarbon dioxide
Check11.9 a3.6 a
Messenger11.9 a3.7 a
Calcium chloride13.7 b2.8 b
 

3. In laboratory tests, Scholar and Pristine had the broadest range of effectiveness among postharvest pathogens, followed by Penbotec (Table 2). Scholar and Pristine were generally effective at lower concentrations than other fungicides. These results show the excellent potential of newer fungicides to give broad-spectrum decay control. They also stress the value of knowing the target fungi in a pear orchard-packinghouse system for designing the most effective treatment strategy.

 
Table 2. Minimum concentration (ppm) of fungicides effective against major pathogens in laboratory tests. 10, 100, and 1000 ppm were tested. Dash (-) indicates no effect.
  Mertect Penbotec Scholar Pristine Flint ZiramShield TBZ
Penicillium-S10001000  10  10100-1000
Penicillium-R-1000  10  10100--

Botrytis

1000  100  10  10- 1001000

Cladosporium

1000-100  10  10-1000

Alternaria

-  100100100-1000-

Phialophora

-1000  10  10100  100-

  4.  A wide array of possible pre-harvest – postharvest fungicide combinations is available for decay control. All of the pre-harvest fungicides tested provided some decay control, even without use of a postharvest fungicide, and all postharvest fungicides provided some decay control, even without use of a pre-harvest fungicide (Table 3). However, combinations of pre- and postharvest fungicides can improve control, and broaden the range of possible pathogens to be controlled.  

Table 3. Effect of pre-harvest – postharvest spray programs on natural decay incidence in Bosc pears.

   Total decay (% of wounds infected)
  Orchard sprays Application timing relative to harvest
2004 Postharvesttreatment   Check  Ziram 1 wk   Flint1 wk  Topsin1 wk  Pristine1 wkZiram1 mo. Flint 1 wkZiram1 mo. Topsin1 wkZiram1 mo. Pristine1 wk
 None 6.2 a 2.4 a 1.3 ab 1.6 ab 1.1 a 0.5 ab  1.1 a 0.8 a
 Scholar 1.2 b 0.0 c 0.0 b 0.0 b 0.0 a 0.0 b 0.0 a    0.0 a
 Penbotec 0.6 b 0.5 bc 0.8 ab 0.3 b 0.0 a 0.0 b 0.5 a 0.0 a
 Mertect 3.2 ab 2.2 ab 2.7 a 3.5 a 0.3 a 1.1 a 3.2 a 2.1 a
 
  2005 Postharvesttreatment    CheckTopsin 1 wk Pristine 1 wk Flint 1 wk Ziram 1 mo. Topsin 1 wk Ziram 1 mo. Pristine 1 wk Ziram 1 mo.Flint 1 wk
 Water47.4 a18.0 a8.8 a33.0 a13.4 a13.2 a16.6 a
 Scholar  2.2 c  0.4 b1.4 b  2.6 b  0.4 c  2.4 b  0.8 b
 Penbotec  9.0 b  2.2 b2.2 b  1.2 b  3.4 b  1.4 b  3.0 b
 Mertect  3.2 c  1.6 b1.8 b  1.4 b  3.0 b  0.4 b  0.8 b
 Shield TBZ  1.6 c  1.6 b1.6 b  0.4 b  0.6 c  1.0 b  0.8 b

  5. Penbotec and Scholar fungicides were highly effective in controlling blue mold in pear wounds when applied up to three weeks after spores were introduced into wounds (Fig. 2). This is based on prompt fruit storage at 31 °F following inoculation. At three weeks post-inoculation, decay control was still significantly better than the control, but it was apparent that the ability to inhibit decay was diminishing. Fig. 2.  Effect of length of delay between pathogen inoculation into wounds and fungicide treatment on the severity of blue mold decay in Bosc pears, using a TBZ-resistant strain.  6. Large-scale (10 acre) plots in two commercial orchards were organized in 2005 and 2006 to compare Pristine pre-harvest treatments to standard programs. In a low-decay orchard, no difference was detected, but in a late-harvested high-decay orchard, Pristine applications reduced decay (Table 4). 

Table 4. Effect of Pristine pre-harvest sprays on decay in large-scale commercial plots, 2005.

 Percent decay
 Orchard 1Orchard 2
Pristine 2 and 1 wk pre-harvest0.4 a17.8 b
Standard program (Ziram)0.9 a51.0 a


7. In the event that two postharvest fungicides are applied (e.g., drench - line-spray or pre-size line spray – packing line-spray), the various sequences available can provide different results (Table 5). In experimental trials with TBZ-sensitive blue mold, the most effective sequences involved Scholar applied early, followed by either Penbotec or Mertect, or Penbotec followed by Scholar. 

Table 5. Effect of different postharvest fungicide sequences when the initial treatment occurs immediately after harvest and the second treatment to the same fruit occurs after three weeks in cold storage.

 Treatment applied after harvest (initial) Treatment applied 3 weeks after initial Percentage of wounds infected (Blue Mold)
WaterWater99.3 a
   
WaterMertect94.7 a
WaterPenbotec84.7 b
WaterScholar82.7 b
   
MertectWater40.7 b
MertectPenbotec14.7 c
MertectScholar13.3 c
   
PenbotecWater39.3 b
PenbotecMertect16.7 c
PenbotecScholar  8.7 d
   
ScholarWater  4.7 d
ScholarPenbotec  2.0 d
ScholarMertect  1.3 d
   II. New technologies affecting pear decay. 1. The biofumigant Muscodor albus was highly effective in suppressing blue and gray mold in Bosc pears only when inoculated fruit were held in closed containers with Muscodor at room temperature for 24 or 48 hours prior to cold storage (Table 6). Table 6. Lesion diameters (mm) at wounds inoculated with Penicillium expansum or Botrytis cinerea, held in closed containers at room temperature for 24 or 48 hours, then stored at 31°F for 2 months.
 

Penicillium

Botrytis

24 hours exposure:  
Check13.8 a 14.9 a
Muscodor albus
  1.3 b  0.0 b
48 hours exposure:  
Check18.4 a20.9 a
Muscodor albus
  2.1 b  0.2 b

 2. Laser coding may find acceptance as an alternative to stickers in labeling individual pear fruit. Since the coding is accomplished by a certain amount of injury to fruit cells, tests were carried out to determine if laser codes can become entry points for postharvest pathogens. Dip and vacuum infiltration methods with blue mold and gray mold pathogens have thus far shown that laser codes may provide a slightly higher risk of fruit infection (Table 7). In some cases (without fungicide), fungi preferentially grew on laser-coded characters.  

Table 7. Incidence of decay in Bosc pears with and without laser coding, following inoculation with decay pathogens by dipping or vacuum infiltration in solutions containing 10,000 spores per milliliter. Following inoculation, pears received either water or Scholar fungicide as a line-spray.

  Total decay incidence
 Across all inoculation methods No fungicide Scholar fungicide
  Blue mold No fungicide Scholar fungicide  Dip Vacuum infiltration  Dip Vacuum infiltration
 Laser coded 27.7 a 8.3 a 21.7 a 33.8 a 10.3 a 6.3 a
 No code 16.4 b 2.6 b 16.5 a 16.3 b   4.0 b 1.3 b
 Gray mold      
 Laser coded 25.0 a 0.6 a 26.3 a 23.8 a 0.0 a 1.3 a
 No code 23.9 a 0.6 a 31.6 a 16.3 a 1.3 a 0.0 a

  III. Advances in postharvest management of pears. 

1. Ethylene treatments were applied to Comice pears for 48, 54, 60, and 66 hours prior to cold storage. Consistent ripening to 5 lbf. or less within 7 days was found with 66 hours of ethylene plus 9 days of cold (Fig. 3). Fruit treated for 66 hours in ethylene plus 9 days cold storage were very close to 9 lbf. firmness prior to ripening, considered a minimum for long-distance shipping (Fig. 3). 54 hours ethylene exposure times did not appreciably reduce the length of time in cold storage needed as compared to the current Comice protocol: 48 hours ethylene plus 2 weeks cold storage. Fig. 3. Effect of ethylene exposure duration and length of cold storage on fruit firmness after 7 days at room temperature (ripe = ~5 lbf.).   

2. Attempts to find an appropriate protocol for using 1-MCP in Bosc and Comice pears have been frustrating. No treatment was found that extended storage life while allowing consistent, predictable ripening. Variables tested have included dosage of 1-MCP (from 10 ppb to 1 ppm), fruit maturity at harvest, and exposure to ethylene before treatment with 1-MCP. Although studies with 1-MCP may resume if new information suggests a practical application, thus far I have not seen results that would dependably sustain fruit quality without interfering excessively in the essential ripening process for pears. 

3. The relationship between harvest maturity and the length of postharvest chill necessary for inducing ripening capacity was studied in Comice pears. The date that the orchardist identified the orchard as entering the maturity range was the first harvest. Subsequent harvests were conducted weekly for 7 weeks. From each harvest, replicate groups of pears were stored at 31 °F for 5, 10, 15, 20, 25, or 30 days, then brought to room temperature for 7 days, then firmness was measured. A firmness of 5 lbf was considered “ripe”. The number of days of chill required decreased in a linear fashion with each later harvest (Fig. 4). This indicates that while the standard 30 days chill requirement for Comice applies to fruit harvested at the top of the maturity range, fruit from later harvest times require shorter chilling duration. From the equation in Fig. 4, the chilling time corresponding to any number of days after entering the maturity range can be calculated.  Fig. 4.  Relationship of harvest date (relative to the onset of harvest maturity) to the length of postharvest chilling required to induce ripening capacity in Comice pears.    

IV. Pear fruit quality enhancement. 

1. In 2 of 3 years, 5% and 7.5% urea sprays at full bloom resulted in increased tonnage of Bartlett pears size 90 or larger, while reducing yield of smaller fruit (Table 8). The effectiveness of urea sprays may be dependent on crop load; further testing is needed to understand and predict the outcome of urea sprays. It appears that the effect may be a combination of blossom (fruit) thinning and providing nitrogen to developing fruitlets at a critical time to support fruit expansion. Urea sprays at earlier bloom (20%) have not been effective.  Table 8. Effect of urea sprays at full (80%) bloom on fruit size and yields of Bartlett pear.

   2004 Average fruit weight (grams)  Equivalent # fruit per box  Tons per acre  % size 90 or larger Tons per acre size 90 or larger
 Check 189 106 23.7 26.8   6.35
 Urea 5% 229   88 17.1 57.7   9.87
 Urea 7.5% 243   82 18.7 71.3 13.30
 2005     
 Check 190 105 18.3 29.2 5.47
 Urea 5% 200 100 14.5 39.6 5.81
 Urea 7.5% 212   95 11.4 48.5 5.17
 2006     
 Check 164 122 19.2   8.9 1.76
 Urea 5% 186 108 19.4 26.4 5.17
 Urea 7.5% 203   99 17.3 38.4 6.02
 

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