Washington Tree Fruit Research Commission

Research Reports

Control of postharvest fruit rots in pears

(2011)

FINAL PROJECT REPORT
WTFRC Project #PR08-803
YEAR 0/0
Organization Project #
Title:

Control of postharvest fruit rots in pears

PI:Chang-Lin Xiao
Organization:WSU-TFREC, 1100 N. Western Avenue, Wenatchee (509) 663-8181 ext. 229; clxiao@wsu.edu
 PDF version of report

Cooperators:

Robert Spotts, Oregon State Univ. (Hood River); David Sugar, Oregon State Univ. 
(Medford); Selected packinghouses across the state

Objectives

1.      Develop preharvest fungicides and postharvest fungicides or biocontrol integrated programs for decay control.

2.      Develop pre- and post-storage integrated programs for decay control.

3.      Develop molecular-based assays for diagnosis and detection of pear fruit infection by the Phacidiopycnis fungus leading to Phacidiopycnis rot in storage.

Significant findings

·   When Pristine was applied to d’Anjou pear fruit one week before harvest, residual protection of the fruit by preharvest Pristine was still evident two months after harvest. 

·   On the fruit treated with Pristine in the field and packed one week after harvest, preharvest Pristine alone without any postharvest fungicides at packing reduced blue mold incidence by 56% in 2008, 87% in 2009, and 21% in 2010 in comparison with the nontreated control. Residual effects of Pristine were more pronounced in 2008 and 2009 than in 2010. The decline in residual effects of Pristine in 2010 likely resulted from the wash-off of residues because there was a rain event within three hours after Pristine application in the field, whereas no rain events occurred after Pristine spray in 2008 and 2009.  The results suggest that rain events shortly after Pristine application could compromise its residual effects on decay control. 

·   For d’Anjou pear fruit that were sprayed with Pristine seven days before harvest and packed and inoculated with Penicillium expansum two months after harvest, Pristine alone, without any postharvest treatments, reduced blue mold incidence by 47-70% compared with the control eight weeks after packing, indicating that residue of Pristine on/in d’Anjou pear fruit can last for at least two months during storage. 

·   The biocontrol agent BioSave alone applied at packing significantly reduced blue mold on the fruit packed one week after harvest, but 30-61% of the fruit treated with BioSave alone still had blue mold.  BioSave was less effective than postharvest fungicides Scholar and Penbotec for blue mold control. 

·   An integrated program consisting of Preharvest Pristine applied one week before harvest and postharvest BioSave applied at packing was superior to Pristine alone or BioSave alone and further reduced blue mold incidence to a much lower level (1-15%) on wounded- and inoculated fruit. 

·   The effectiveness of preharvest Pristine in combination with postharvest BioSave was reduced after the fruit had been stored at room temperature for one additional week after cold storage.  Nonetheless, our results suggest that preharvest Pristine plus postharvest BioSave could be a promising program for blue mold control when fruit are packed shortly after harvest and have not been drenched prior to storage. 

·   Residues of Scholar and Penbotec on/in fungicide-drenched fruit persisted during storage, and residual activity of Scholar and Penbotec against P. expansum can last for at least 4-6 months during storage. However, the residual activity of these two postharvest fungicides on d’Anjou pear fruit was also less consistent than that on Red Delicious and Fuji apples we previously observed.  This may be due to the differences in cuticles between apple and pear fruit, which may affect the uptake of fungicides or penetration of the fungicides. 

·   BioSave alone did not provide adequate control of blue mold on pear fruit that had been stored for four or six months after harvest. However, BioSave significantly reduced blue mold incidence on pear fruit that had been stored for two months or less.  Fruit senescence four or six months after harvest may increase the susceptibility of fruit to blue mold and thus affect the efficacy of BioSave.  Additional benefits from BioSave applied at packing were not consistent on Scholar- or Penbotec-drenched fruit for blue mold control and not present on TBZ-drenched fruit. 

·   Preharvest Pristine or Topsin applied seven days before harvest and a postharvest drench with Scholar, Penbotec or Mertect significantly reduced Phacidiopycnis rot compared to the nontreated control on the fruit infected in the field by Phacidiopycnis piri five weeks before harvest.  The efficacy of a postharvest drench with Scholar or Penbotec was generally more consistent than those of other treatments. 

·   Conventional and real-time PCR assays were developed for diagnosis and detection of Phacidiopycnis rot, gray mold and Sphaeropsis rot on d’Anjou pear fruit.  Validation with stem-end rot and calyx-end rot samples collected from a packinghouse indicated that the PCR-based assays and the isolation-based assay yielded consistent results in the identification of causal agents of decayed fruit.

Methods

Preharvest Pristine in combination with postharvest biocontrol BioSave or fungicides for blue mold control was evaluated on d’Anjou pears.  Pristine was applied seven days before harvest.  Fruit were harvested and stored in RA.  Part of the fruit was removed from RA at one week and two months after harvest.  Fruit were run through a research packingline and inoculated with P. expansum.  Part of the inoculated fruit was treated with each of the three postharvest fungicides (TBZ, Penbotec and Scholar) or the biocontrol agent BioSave after inoculation.  Nontreated fruit were used as controls.  All fruit were stored in cold storage for eight weeks and then for seven days at room temperature. 

An experiment was conducted in a research orchard of d’Anjou pear near Wenatchee. To ensure a necessary disease level, fruit were inoculated with spore suspensions of the Phacidiopycnis fungus at five weeks before harvest. For preharvest fungicide treatments, fungicides Pristine and Topsin M were applied within two weeks before harvest, and a nontreated control was included. For postharvest fungicide treatments, fruit were not sprayed with preharvest fungicides. Treatments were arranged as a randomized complete block design with four replicates, with 1-2 trees per replicate. Fruit were harvested in mid-September. Fruit for postharvest fungicide treatments were treated with one of the three postharvest fungicides.  All fruit were packed on fruit trays in cardboard boxes and stored in air at 32ºF. All fruit were visually examined for decay development (calyx-end rot and stem-end rot, etc.) every two weeks for five months, starting in December. 

Commercially harvested d’Anjou pear fruit, without use of preharvest fungicides, were either not drenched or drenched with one of the postharvest fungicides. Fruit were stored in CA.  Part of the fruit was removed from CA four and six months after harvest. Fruit were subjected to packing process and then inoculated with P. expansum.  For each fungicide-drench treatment, part of the inoculated fruit was treated with BioSave after inoculation.  Nontreated fruit will be used as controls. All fruit were then stored in cold storage for eight weeks and then for seven days at 68ºF at which time decay development was evaluated. 

Molecular-based assays for diagnosis of Phacidiopycnis rot, gray mold and Sphaeropsis rot were developed.  PCR based assays were validated using naturally infected fruit collected from a packinghouse.

Results and discussion

Preharvest Pristine in combination with postharvest biocontrol BioSave or fungicides for blue mold control 

Experiments were conducted for three years (2008-2010). For the fruit packed one week after harvest, similar results were obtained (Table 1 and Table 2). Residual protection of the fruit by preharvest Pristine was evident after harvest.  In comparison with the nontreated control, preharvest Pristine alone without any postharvest fungicides at packing reduced blue mold from 97.5% to 42.5% in 2008, from 90% to 11.3% in 2009, and from 100% to 78.8% in 2010 (Table 1). Residual effects of Pristine were more pronounced in 2008 and 2009 than in 2010. The decline in residual effects of Pristine in 2010 likely resulted from the wash-off of residues because there was a rain event within three hours after Pristine application in the field, whereas no rain events occurred after Pristine spray in 2008 and 2009.  The results suggest that rain events shortly after Pristine application could compromise its residual effects on decay control. 

BioSave alone applied at packing significantly reduced blue mold, but 30-61% of the fruit treated with BioSave alone had blue mold (Table 1).  However, preharvest Pristine plus postharvest BioSave was superior to Pristine alone or BioSave alone and further reduced blue mold incidence to a much lower level (1-15%). However, the effectiveness of preharvest Pristine in combination with postharvest BioSave was reduced after the fruit had been stored at room temperature for one additional week (Table 2).  Our results indicate that preharvest Pristine plus postharvest BioSave could be a promising program for blue mold control when fruit are packed shortly after harvest and have not been drenched prior to storage. 

For the experiment with fruit from the 2009 crop that were stored for two months before packing, the results were generally consistent with those observed on the fruit packed one week after harvest (Table 3). Preharvest Pristine without any postharvest treatments reduced blue mold incidence from 84% in the nontreated control to 25%, indicating residual effects of preharvest Pristine was still evident two months after harvest. Similarly, preharvest Pristine plus postharvest BioSave provided better control of blue mold than Pristine alone or BioSave alone for the fruit packed two months after harvest. 

Table 1. Preharvest Pristine in combination with postharvest fungicide and biocontrol agent for control of blue mold in d’Anjou pears – decay incidence 8 weeks at 32°F after packing during 2008-2010

Preharvest TreatmentFungicide applied 1 week after harvestIncidence of blue mold (%) 8 weeks at 32F after packing
2008 season2009 season2010 season
NontreatedNo fungicide97.5 a90.00 b100.0a
Scholar0.0 d0.00 e0.0f
Penbotec0.0 d0.00 e0.0f
TBZ100.0 a96.25 a95.0b
BioSave61.3 b30.00 c60.0d
PristineNo fungicide42.5 c 11.25 d78.8c
TBZ67.5 b 27.50 c76.3c
Scholar0.0 d 0.00 e0.0f
Penbotec0.0 d 0.00 e0.0f
Biosave2.5 d 1.25 e15.0e

z Values within the same column followed by the same letter are not significantly different according to the Waller-Duncan K-ratio t test at K ratio = 100 (P = 0.05).  

Table 2. Preharvest Pristine in combination with postharvest fungicide and biocontrol agent for control of blue mold in d’Anjou pears - decay incidence one additional week at room temperature after cold storage during 2008-2010

Preharvest TreatmentFungicide applied 1 week after harvestIncidence of blue mold (%) one additional week at room temperature after 8 weeks in cold storage
2008 season2009 season2010 season
NontreatedNo fungicide98.8 a 95.00 b100.0a
Scholar0.0 d 0.00 g0.0f
Penbotec0.0 d 0.00 g0.0f
TBZ100.0 a 98.75 a97.5b
BioSave70.0 b 56.25 d62.5d
PristineNo fungicide70.0 b 41.25e85.0c
TBZ96.3 a 77.50 c81.3c
Scholar0.0 d 0.00 g0.0f
Penbotec0.0 d 0.00 g0.0f
Biosave17.5 c 5.00 f23.8e

z Values within the same column followed by the same letter are not significantly different according to the Waller-Duncan K-ratio t test at K ratio = 100 (P = 0.05). 

Table 3. Preharvest Pristine in combination with postharvest fungicide and biocontrol agent for control of blue mold in d’Anjou pears in 2009-10 season (2 months after harvest of 2009 crop)

Preharvest TreatmentFungicide applied 2 months after harvest8 weeks at 32°F after packing1 week at room temp after cold storage
% decayLesion (mm)% decayLesion (mm)
NontreatedNo fungicide83.8a24.4a97.5a57.0a
Scholar0.0e0.0e0.0d0.0d
Penbotec0.0e0.0e0.0d0.0d
TBZ67.5b23.0a93.8a49.3b
BioSave55.0b15.9b70.0b46.0b
PristineNo fungicide25.0c12.3c68.8b25.6c
TBZ27.5c11.0c78.8b23.6c
Scholar0.0e0.0e0.0d0.0d
Penbotec0.0e0.0e0.0d0.0d
Biosave11.3d5.4d18.8c22.1c

z Values within the same column followed by the same letter are not significantly different according to the Waller-Duncan K-ratio t test at K ratio = 100 (P = 0.05). 

Pre- and post-storage integrated programs for blue mold control

Experiments were conducted on 2008, 2009 and 2010 crops.  Results from 2008 and 2009 crops were generally consistent. The 2008 results were reported last year.  The results on 2009 crop are presented in Table 4. Four and six months after harvest, blue mold incidences were significantly lower on Scholar-drenched and Penbotec-drenched pear fruit that were inoculated at packing with P. expansum four or six months after harvest and did not received any other treatments at packing in comparison with the nontreated control (Table 4).  However, the spectrum of residual effects of Scholar on blue mold control on d’Anjou pears was smaller on 2009 crop than on 2008 crop.  The residual activity of these two postharvest fungicides on d’Anjou pear fruit was also less consistent than that on Red Delicious and Fuji apples we previously observed.  This may be due to the differences in cuticles between apple and pear fruit, which may affect the uptake of fungicides or penetration of the fungicides. Nonetheless, the results suggest that residues of Scholar and Penbotec on/in fungicide-drenched fruit persisted during storage and that residual activity of Scholar and Penbotec against P. expansum can last for at least 4-6 months during storage. 

BioSave alone did not provide adequate control of blue mold on pear fruit that had been stored for four or six months after harvest (Table 4). However, BioSave significantly reduced blue mold incidence on pear fruit that had been stored for two months or less (Tables 1-3). Fruit senescence four or six months after harvest may increase the susceptibility of fruit to blue mold and thus affect the efficacy of BioSave.  Additional benefits from BioSave applied at packing were not consistent on Scholar- or Penbotec-drenched fruit for blue mold control and not present on TBZ-drenched fruit (Table 4). 

Research has been set up to repeat this experiment on the 2010 crops.  The fruit are currently in CA. Part of the fruit will be removed from CA four or six months after harvest. The fruit will be run through a research packing line and inoculated with Penicillium expansum.  The experiment will end in spring 2011. Results will be forthcoming. 

Table 4. Residual effects of Scholar and Penbotec on blue mold on d’Anjou pears that were inoculated at packing with Penicillium expansum and treated with BioSave, 2009-10 season

Drench treatment applied prior to storageFungicides applied at packing 4 or 6 months post drenching 4 months post drench treatments 6 months post drench treatments
% infected fruit at 8 weeks at 0ºC post packing % infected fruit at one additional week at room temperature after storage % infected fruit at 8 weeks at 0ºC post packing % infected fruit at one additional week at room temperature after storage
TBZ-R TBZ-R TBZ-R TBZ-R
NontreatedNo fungicide100.0az 100.0a 100.0a 100.0a
Scholar1.3e 1.3c 2.5de 11.3d
Penbotec0.0e 0.0c 0.0e 0.0e
Mertect97.5b 98.8a 98.8a 98.8a
Bio-Save100.0a 100.0a 88.8b 100.0a
ScholarNo fungicide61.3c 100.0a 36.3c 92.5b
Bio-Save38.8d 73.8b 25.0c 67.5c
PenbotecNo fungicide2.5e 2.5c 5.0d 5.0d
Bio-Save1.3e 1.3c 5.0d 6.3d
TBZNo fungicide100.0a 100.0a 98.8a 100.0a
Bio-Save100.0a 100.0a 92.5b 100.0a

z Values within the same column followed by the same letter are not significantly different according to the Waller-Duncan K-ratio t test at K ratio = 100 (P = 0.05). 

Pre- and postharvest fungicides for control of Phacidiopycnis rot originating from infections during the fruit-growing season 

Experiments were conducted in a research orchard in 2008-09 and 2009-10 seasons to determine whether preharvest fungicides applied at harvest and postharvest fungicide drench treatments were effective to control Phacidiopycnis rot on fruit that were infected by the Phacidiopycnis fungus five weeks before harvest.  All selected fungicide treatments significantly reduced Phacidiopycnis rot on pear compared to the nontreated control (Fig. 1). No Phacidiopycnis rot was observed on pear fruit treated with postharvest Scholar or Penbotec.  Although Phacidiopycnis rot occurred on the fruit treated with Pristine, Topsin M or TBZ, the incidence of Phacidiopycnis rot was low and was not significant among all fungicide treatments.  

The results from 2009-10 season were similar to those in 2008-09. Taken these together, it appeared that the efficacy of a postharvest drench with Scholar or Penbotec was generally more consistent than those of other treatments. 

Fig. 1. Effectiveness of pre- and postharvest fungicides in controlling Phacidiopycnis rot on d’Anjour pear fruit that were inoculated with the Phacidiopycnis fungus 5 weeks before harvest in the orchard in 2009-10. 

PCR-based assays for diagnosis and detection of Phacidiopycnis rot, gray mold, and Sphaeropsis rot in pears 

Phacidiopycnis rot, gray mold, and Sphaeropsis rot all can cause stem-end rot and calyx-end rot on pears.  The symptoms of these three diseases are very similar, particularly in the early stage of symptom development. In this project, two PCR-based assays were developed and compared with the isolation-based method for diagnosis and detection of these three diseases. 

The first PCR assay was based on specific primer sets designed based on the sequences of ITS region. One primer set per target pathogen was selected and applied in both conventional and real-time PCR in this study.  Specificity of the three primer sets against target pathogens and non-target pathogens or fungi was tested (data reported previously).  At specified annealing temperatures, amplification for each pathogen was strong and detected only with its own isolates, while no amplifications were detected with other fungi and the fruit DNA. Validation with stem-end rot and calyx-end rot samples collected from a packinghouse indicated that ITS-based PCR assay and isolation-based assay yielded consistent results in the identification of causal agents of decayed fruit (Table 5). 

Real-time PCR for diagnosis. In addition to a conventional PCR-based assay developed for diagnosis and detection of these three diseases, we also developed a real-time PCR assay.  Validation with stem-end rot and calyx-end rot samples collected from a packinghouse indicated that the real-time PCR assay and the isolation-based assay yielded consistent results in the identification of causal agents of decayed fruit (Table 5).         

Table 5. Identification of causal agents of naturally infected pear fruit using three different approaches

SamplesaSymptoms( # of samples)Causal agentApproaches
IsolationPCR-based assays
ITS-based conventionalPCRReal-time PCR
1Stem-end rot (20)Potebniamyces pyri9b99
B. cinerea10109
S. pyriputrescens111
Calyx-end rot (20)Potebniamyces pyri161616
B. cinerea444
S. pyriputrescens000
2Stem-end rot (20)Potebniamyces pyri899
B. cinerea111111
S. pyriputrescens000
Calyx-end rot (20)Potebniamyces pyri141414
B. cinerea222
S. pyriputrescens444
3 Stem-end rot (20)Potebniamyces pyri999
B. cinerea111111
S. pyriputrescens000
Calyx-end rot (14)Potebniamyces pyri899
B. cinerea333
S. pyriputrescens999
a Samples were collected from a commercial packinghouse.  At least 20 stem-end rot and calyx-end rot samples were included in each collection if available.b Number of samples in which the pathogen was inferred as the causal agent.                  

Executive Summary

This report is a summary of a three-year project conducted from 2008 to 2010. The focus of this research project was on the integration of identified decay-control tactics, including field and postharvest components, for control of major postharvest diseases.

Pristine as a preharvest spray is being implemented by growers for postharvest decay control. In this project, we further found that when Pristine was applied to d’Anjou pear fruit one week before harvest, residual protection of the fruit by preharvest Pristine was still evident during storage two months after harvest. On the fruit treated with Pristine in the field and packed one week after harvest, preharvest Pristine alone without any postharvest fungicides at packing significantly reduced blue mold incidence in comparison with the nontreated control. For d’Anjou pear fruit that were sprayed with Pristine one week before harvest and packed and inoculated with Penicillium expansum two months after harvest, Pristine alone, without any postharvest treatments, reduced blue mold incidence by 47-70% compared with the control eight weeks after packing.

The biocontrol agent BioSave alone applied at packing significantly reduced blue mold on the fruit packed one week after harvest but did not provide satisfactory control as 30-61% of the fruit treated with BioSave alone still had blue mold.  BioSave was less effective than postharvest fungicides Scholar and Penbotec for blue mold control.

However, an integrated program consisting of Preharvest Pristine applied one week before harvest and postharvest BioSave applied at packing was superior to Pristine alone or BioSave alone and further reduced blue mold incidence to a much lower level (1-15%) on wounded- and inoculated fruit. The effectiveness of preharvest Pristine in combination with postharvest BioSave was reduced after the fruit had been stored at room temperature for one additional week after cold storage.  Nonetheless, our results suggest that preharvest Pristine plus postharvest BioSave could be a promising program for blue mold control when fruit are packed shortly after harvest and have not been drenched prior to storage.

Residues of Scholar and Penbotec on/in fungicide-drenched fruit persisted during storage, and residual activity of Scholar and Penbotec against P. expansum can last for at least 4-6 months during storage. However, the residual activity of these two postharvest fungicides on d’Anjou pear fruit was less consistent than that on Red Delicious and Fuji apples we previously observed.  This may be due to the differences in cuticles between apple and pear fruit, which may affect the uptake of fungicides or penetration of the fungicides.

BioSave alone did not provide adequate control of blue mold on pear fruit that had been stored for 4 or 6 months after harvest. However, BioSave significantly reduced blue mold incidence on pear fruit that had been stored for two months or less.  Fruit senescence four or 6sixmonths after harvest may increase the susceptibility of fruit to blue mold and thus affect the efficacy of BioSave.  Additional benefits from BioSave applied at packing were not consistent on Scholar- or Penbotec-drenched fruit for blue mold control and not present on TBZ-drenched fruit.

Preharvest Pristine or Topsin applied seven days before harvest and a postharvest drench with Scholar, Penbotec or Mertect significantly reduced Phacidiopycnis rot compared to the nontreated control on the fruit infected in the field by Phacidiopycnis piri five weeks before harvest.  The efficacy of a postharvest drench with Scholar or Penbotec was generally more consistent than those of other treatments. It appeared that a postharvest fungicide drench is a better measure for control of Phacidiopycnis rot.

Conventional and real-time PCR assays were developed for diagnosis and detection of Phacidiopycnis rot, gray mold and Sphaeropsis rot on d’Anjou pear fruit.  Validation with stem-end rot and calyx-end rot samples collected from a packinghouse indicated that the PCR-based assays and the isolation-based assay yielded consistent results in the identification of causal agents of decayed fruit.

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