Washington Tree Fruit Research Commission

Research Reports

Sphaeropsis Rot in Apple (2007)

FINAL PROJECT REPORT
WTFRC Project #AH-05-510
YEAR 0/0
Organization Project #WSU Project No. 13C-3661-5366
Title:Sphaeropsis Rot in Apple
PI:Chang-Lin Xiao
Organization:WSU-TFREC, 1100 N. Western Avenue, Wenatchee (509) 663-8181 ext. 229; clxiao@wsu.edu
 PDF version of report

Collaborators

Fruit packinghouses

Objectives

1.       Determine the sources and availability of inoculum of Sphaeropsis pyriputrescens in the orchard during apple-growing season.

2.       Determine seasonal susceptibility of apple trees to infection by S. pyriputrescens in the orchard.

3.       Determine susceptibility of apple fruit at different growth stages to infection by S. pyriputrescens in the orchard in relation to Sphaeropsis rot during storage.

4.       Test sensitivity of the fungus to various fungicides including new postharvest fungicides.

5.       Determine the prevalence and incidence of Sphaeropsis rot as well as other postharvest diseases on major apple varieties under various handling systems.

6.       Evaluate effectiveness of preharvest fungicides and postharvest drench with fungicides in controlling Sphaeropsis rot. 

Significant findings

·         Over the three-year statewide survey of postharvest diseases on Red Delicious, Fuji and Golden Delicious, blue mold caused by Penicillium spp., gray mold caused by Botrytis cinerea and Sphaeropsis rot caused by Sphaeropsis pyriputrescens accounted for 32.4%, 29.4% and 18.4% of the total decay, respectively.  Sphaeropsis rot was observed in all seven counties that we sampled in central Washington State. Sphaeropsis rot was observed in 73% of the grower lots we sampled.  Sphaeropsis rot varied from grower lot to grower lot.  Instances of severe losses of fruit due to Sphaeropsis rot in storage have been observed in both Red Delicious and Fuji apples.

·         Our three-year survey results indicate that gray mold, blue mold and Sphaeropsis rot should be considered major targets for decay control. Bull’s eye rot should also be considered a target disease on Golden Delicious.

·         In 2006, 60-100% of sampled apple trees in a commercial Fuji orchard were infected by the Sphaeropsis fungus; 27-57% of the sampled dead fruit spurs or twigs were infected by the fungus. Over 90% of sampled crabapple trees were infected by the Sphaeropsis fungus.

·         In the Red Delicious orchard, crabapple trees were not commonly planted. The focus was on dead fruit spurs or twigs and dead bark. Approximately 20-40% and 0-50% of the sampled trees were infected by the fungus in 2005 and 2006, respectively; 1-16% and 0-14% of the sampled fruit spurs had pycnidia of the fungus in 2005 and 2006, respectively.

·         The results indicate that dead tissues on fruit spurs, dieback twigs or cankers, and crabapple trees were important sources of inoculum responsible for infection of apple fruit in the orchard leading to Sphaeropsis rot during storage. The results also indicate that viable inoculum of the fungus was available throughout the fruit-growing season.

·         Cankers and dieback twigs of crabapple trees were not the only sources of inoculum. Crabapple trees, if present, likely facilitated spread of the fungus from crabapple trees to apple trees in the orchard. Fruiting bodies of the fungus on apple trees were the immediate inoculum responsible for infection of fruit in the orchard leading to Sphaeropsis rot during storage.

·         Significant cankers developed on twigs inoculated in November and early spring. No significant cankers developed on twigs inoculated in June. It appeared that trees were more susceptible to infection during the dormant period and that Fuji trees seemed to be more susceptible to infection than Red and Golden Delicious.

·         Sphaeropsis rot developed on early-inoculated fruit as well as late-inoculated fruit, indicating that when conditions were met the fungus was able to colonize the fruit even in the early season and to remain latent throughout the fruit-growing season. Overall, incidence of Sphaeropsis rot on inoculated fruit increased as the inoculation date approached harvest except for Fuji inoculated in October.

·         On Red Delicious, stem and calyx infections both were common; on Golden Delicious, stem infection was more common than calyx infection; on Fuji, calyx infection was more common than stem infection.

·         Scholar, Mertect and Pristine were highly effective in inhibiting mycelial growth of the fungus, and Penbotec was effective only at higher rates. Pristine was also effective in inhibiting spore germination. The information has been used for developing pre- and postharvest fungicide programs for control of Sphaeropsis rot.

·         Ziram applied at two weeks before harvest provided inconsistent results in trials conducted in a commercial orchard (in the first year it was effective but not effective the following year).  In a trial conducted in a research block of Red Delicious, ziram was effective to control Sphaeropsis rot.  Timing of infection may affect its efficacy.

·         In the experiment conducted in 2005-06 season, Pristine and Topsin applied at seven days before harvest significantly reduced Sphaeropsis rot on apple fruit that were inoculated with the Sphaeropsis fungus at either five or two weeks before harvest. Pristine and Topsin reduced Sphaeropsis rot by 53-71% and 39-59%, respectively.

·         Timing of infection of fruit by the Sphaeropsis fungus may affect the effectiveness of preharvest fungicides for control of Sphaeropsis rot.  This needs to be further evaluated.

·         Mertect applied as a pre-storage drench treatment was consistently effective to control Sphaeropsis rot.

·         We are currently evaluating new pre- and postharvest fungicides (Pristine, Topsin M, Scholar and Penbotec) for control of Sphaeropsis rot. 

Methods

Sources and availability of inoculum of Sphaeropsis pyriputrescens were monitored in two commercial apple orchards during the apple-growing season.

Experiments were conducted four times a year to determine susceptibility of trees of Fuji, Red Delicious and Golden Delicious to S. pyriputrescens.  To determine susceptibility of apple fruit to infection by S. pyriputrescens, fruit of Fuji, Golden Delicious and Red Delicious were inoculated with the pathogen four to five times during the growing season. Fruit were harvested and stored at 32ºF for decay development. Decay incidence and infection sites on the fruit were recorded.

Effectiveness was tested of new fungicides (Scholar, Penbotec, Pristine) and other fungicides in inhibiting mycelial growth and spore germination. Ten representative isolates were included. An experiment was conducted in a commercial Red Delicious orchard with a history of severe Sphaeropsis rot to evaluate effectiveness of preharvest fungicides and postharvest drench with fungicides in controlling Sphaeropsis rot.

Results and discussion

Sources and availability of inoculum in the orchard

In 2005 and 2006, we monitored inoculum availability of the Sphaeropsis fungus in two commercial orchards (Table 1 for 2006 data). The results from the two-year study were similar.  The 2005 data were reported in the 2005 report.  In summary, in the Fuji orchard sources of inoculum likely responsible for infection of fruit included: 1) Twig dieback and dead fruit spurs. In 2006, 60-100% of sampled apple trees were infected by the Sphaeropsis fungus; 27-57% of the sampled dead fruit spurs or twigs were infected by the fungus. 2) Fuji fruit mummies on the trees.  Fifty-five percent of the mummies sampled in mid-May were infected by the fungus. 3) Cankers, twig dieback and infected fruit of crabapple. Over 90% of sampled crabapple trees were infected by the Sphaeropsis fungus.

In the Red Delicious orchard, crabapple trees were not commonly planted. The focus was on dead fruit spurs or twigs and dead bark. Approximately 20-40% and 0-50% of the sampled trees were infected by the fungus in 2005 and 2006, respectively; 1-16% and 0-14% of the sampled fruit spurs had pycnidia of the fungus in 2005 and 2006, respectively.

The results indicate that dead tissues on fruit spurs, dieback twigs or cankers, and crabapple trees were important sources of inoculum responsible for infection of apple fruit in the orchard leading to Sphaeropsis rot during storage. The results also indicate that viable inoculum of the fungus was available throughout the fruit-growing season. Table 1. Sources and availability of inoculum of the Sphaeropsis fungus in two apple orchards in 2006.

DateOrchardVarietySample Type% Trees with Pycnidia% Samples with Pycnidia
16-May-061CrabappleTwigs10096.7
FujiSpurs/Twigs8043.3
2Red DeliciousBark00.0
Spurs 00.0
21-Jun-061CrabappleTwigs9090.0
FujiSpurs/Twigs8046.7
2Red DeliciousBark202.0
Spurs 204.0
10-Aug-061CrabappleTwigs100100.0
FujiSpurs/Twigs9056.7
2Red DeliciousBark00.0
Spurs 5014.0
27-Sep-061CrabappleTwigs10093.3
FujiSpurs/Twigs10076.7
2Red DeliciousBark00.0
Spurs 5014.0

 1  In the Fuji orchard, at each sampling time, 3 dieback twigs from each of 10 crabapple trees and 3 dead fruit spurs     or twigs from each of 10 Fuji trees were sampled. In the Red Delicious orchard, 5 pieces of dead fruit-spur tissues     and 10 pieces of dead bark tissues from each of 10 trees were sampled. 

Seasonal susceptibility of apple trees to cankers caused by the Sphaeropsis fungus

We inoculated trees of Fuji, Golden Delicious and Red Delicious at four different times each year.  Some results were presented in the previous report and the experiments are still in progress.  Some available results (canker sizes at six months after inoculation) are presented in Table 2. Significant cankers developed on twigs inoculated in November and early spring. No significant cankers developed on twigs inoculated in June. It appeared that trees during the dormant period were more susceptible to infection and that Fuji trees seemed to be more susceptible to infection than the other two varieties.  

Susceptibility of apple fruit to infection by the Sphaeropsis fungus in the orchard in relation to Sphaeropsis rot during storage

In 2004-2006, we inoculated fruit of Fuji, Golden Delicious and Red Delicious at different growth stages. The 2005-06 data are presented in this report. The fruit from the 2006 inoculation study are currently in storage for decay development. We observed that Sphaeropsis rot developed on early-inoculated fruit as well as late-inoculated fruit, indicating that when conditions were met the fungus was able to colonize the fruit even in the early season and to remain latent throughout the fruit-growing season. Overall, incidence of Sphaeropsis rot on inoculated fruit increased as the inoculation date approached harvest except for Fuji inoculated in October (Fig. 1).  The Fuji fruit inoculated in October had a lower incidence than those inoculated in September.  This is likely due to low temperature in October when inoculation of Fuji was conducted.

On Red Delicious, both stem and calyx infections were common; on Golden Delicious, stem infection was more common than calyx infection; on Fuji, calyx infection was more common than stem infection (Fig. 2).      

Table 2. Susceptibility of apple trees to infection by the Sphaeropsis fungus.

Inoculation DateVarietyIsolateCanker Size in mma
AverageRange
19-Nov-04Fujicheck6.66.0 - 8.0
Sphaeropsis30.88.0- 110.0
Goldencheck7.16.0 - 9.0
Sphaeropsis9.77.0 - 18.0
Redcheck6.96.0 - 10.0
Sphaeropsis18.27.0 - 61.0
22-Mar-05Fujicheck8.86.0 - 12.0
Sphaeropsis12.66.0 - 25.0
Goldencheck6.96.0 - 10.0
Sphaeropsis10.86.0 - 18.0
Redcheck8.66.0 - 13.0
Sphaeropsis12.17.0 - 24.0
21-Jun-05Fujicheck10.46.0 - 17.0
Sphaeropsis8.55.0 - 13.0
Goldencheck6.36.0 -8.0
Sphaeropsis6.55.0 - 8.0
Redcheck7.05.0 - 10.0
Sphaeropsis7.05.0 - 10.0
20-Sep-05Fujicheck5.65.0 - 7.0
Sphaeropsis8.95.0 - 25.0
Goldencheck6.15.0 - 7.0
Sphaeropsis7.97 - 11.0
Redcheck5.55.0 - 6.0
Sphaeropsis7.65.0 - 23.0
15-Nov-05Fujicheck7.57.0 - 8.0
Sphaeropsis25.67.0 - 170.0
Goldencheck7.47.0 - 8.0
Sphaeropsis10.47.0 - 20.0
Redcheck7.66.0 - 9.0
Sphaeropsis9.98.0 - 15.0
28-Mar-06Fujicheck8.76.0 - 14.0
Sphaeropsis11.87.0 - 17.0
Goldencheck8.07.0 - 10.0
Sphaeropsis9.17.0 - 15.0
Redcheck8.76.0 - 12.0
Sphaeropsis10.57.0 - 17.0
a Twigs were inoculated and canker sizes were measured at six months after inoculation. 

 

Fig. 1. Development of Sphaeropsis rot on apple fruit after 9 months of storage at 32ºF. Fruit were inoculated with Sphaeropsis pyriputrescens in the orchard during the fruit-growing season.

 

Fig. 2. Infection sites of the Sphaeropsis fungus on the fruit of three apple varieties. 

Sensitivity of the Sphaeropsis fungus to newly registered pre- and postharvest fungicides   

In 2004 we tested sensitivity of the fungus to various preharvest fungicides. In 2005, we tested sensitivity of mycelial growth and conidial germination to new fungicides fludioxonil (Scholar), pyrimethanil (Penbotec) and Pyraclostrobin+boscalid (Pristine). Scholar, Mertect and Pristine were highly effective in inhibiting mycelial growth of the fungus, and Penbotec was effective only at higher rates. Pristine was also effective in inhibiting spore germination. The information has been used for developing pre- and postharvest fungicide programs for control of Sphaeropsis rot.      

Table 3. Effectiveness of three postharvest fungicides and Pristine against the Sphaeropsis fungus

FungicideClassConcentrationInhibition (%)
RangeAverage
MertectBenzimidazoleX/4 (label rate)100100
10-1X/495.8-10099.6
10-2X/499.5-10099.9
10-3X/489.3-10094.5
10-4X/492.2-10098.3
PenbotecPyrimethanilX/4 (label rate)95.8-10099.1
10-1X/426.7-58.249.4
10-2X/40-1.00
10-3X/40-9.40
10-4X/400
ScholarFludioxinilX/4 (label rate)100100
10-1X/4100100
10-2X/4100100
10-3X/4100100
10-4X/473.8-87.482.6
Pristine X (label rate)100100
10-1X100100
10-2X96.2-98.797.6
10-3X82.0-84.382.4
10-4X23.9-39.033.7

Pristine was tested with 3 isolates starting from the label rate. Others were tested with 11 isolates starting from ¼ label rate. 

 Prevalence and incidence of Sphaeropsis rot and other postharvest diseases

Surveys of Sphaeropsis rot and other postharvest diseases were conducted in 2003, 2004 and 2005. Decayed apple fruit were sampled from six commercial packinghouses, representing orchards in various apple producing areas including north-central Washington, the Columbia Basin, and the Yakima area. Approximately 50 decayed fruit from each grower lot were randomly sampled from cull bins, dump tanks, or sorting tables depending on packing or pre-sizing operations in the packinghouses. In this study, each grower lot represents one orchard. Twenty-six grower lots of Red Delicious were sampled during June to August in 2003; 72 grower lots (39 Red Delicious, 19 Golden Delicious and 14 Fuji) and 81 grower lots (37 Red Delicious, 19 Golden Delicious and 25 Fuji) were sampled from March to August in 2004 and 2005, respectively.

Over the three year survey, blue mold caused by Penicillium spp., gray mold caused by Botrytis cinerea and Sphaeropsis rot caused by Sphaeropsis pyriputrescens accounted for 32.4%, 29.4% and 18.4%, respectively (Table 4).  Sphaeropsis rot was observed in all seven counties where we sampled. Percentage of Sphaeropsis-infected orchards ranged from 32 to 100% with an average of 73%. Percentage of Sphaeropsis rot in the total decayed fruit within a grower lot varied from lot to lot.  Instances of severe Sphaeropsis rot were again observed on Fuji and Red Delicious fruit. Our three-year survey for postharvest diseases on apples indicated that gray mold, blue mold and Sphaeropsis rot should be considered major targets for decay control. Bull’s eye rot should also be considered a target disease on Golden Delicious.

The incidence pattern of postharvest diseases under different postharvest-handling systems was very similar in all three years (Fig.3). The percentage of gray mold in the total decay was higher on non-drenched fruit than TBZ-drenched fruit, whereas blue mold was more prevalent on TBZ-drenched fruit. There was no difference between non-drenched and TBZ-drenched fruit on Sphaeropsis rot. On TBZ-drenched fruit, blue mold showed the highest incidence followed by either gray mold or Sphaeropsis rot. On non-drenched fruit, gray mold comprised the highest percentage in the decays followed by blue mold and Sphaeropsis rot. Bull’s eye rot comprised less than 5% of the total decays with an exception of non-drenched fruit in 2004. There was no difference in bull’s eye rot between non-drenched and TBZ-drenched fruit in 2003 and 2005, whereas non-drenched fruit had a higher percentage of bull’s eye rot than TBZ-drenched fruit in 2004. 

Table 4. Mean percentages of postharvest fruit rots caused by various pathogens in the total decayed apple fruit sampled from commercial packinghouses in Washington State from 2003 to 2005a.

 YearVarietyNo. of grower lotsSph  rotbGray moldBlue moldBull’s eye rotSpeck rotMucor rotAlternaria rotOthersc
 2003Red Delicious2623.634.035.23.50.70.00.03.0
 2004Red Delicious3921.723.741.42.86.50.40.82.7
 Golden Delicious1918.029.918.830.00.20.01.21.9
 Fuji1418.832.230.24.92.00.92.88.2
 Mean 19.528.630.112.62.90.41.64.3
 2005Red Delicious3720.236.427.92.84.80.81.35.8
 Golden Delicious199.422.917.543.80.00.32.04.1
 Fuji256.317.750.65.71.52.13.712.4
 Mean 12.025.732.017.42.11.12.37.4
 Overall meand 16.928.131.713.42.20.61.75.4
a  Approximately 50 decayed fruit from each grower lot were collected from cull bins, dump tanks or sorting tables depending on the packinghouses available for sampling during packing or pre-sizing operations. Each grower lot represents the fruit from one unique orchard.b   Sph rot=Sphaeropsis rot caused by Sphaeropsis pyriputrescens.c   Includes Aureobasidium rot, Moldy-core rot, Coleophoma rot, Cladosporium rot, Phacidiopycnis rot, black rot, Cytospora rot, and other minor rots caused by unidentified fungi.d   Overall mean is the average of all varieties in all three years.

 

Fig. 3. Comparison of occurrence of common postharvest diseases between TBZ-drenched and nondrenched grower lots in 2004 and 2005.
 

Chemical control of Sphaeropsis rot 

In 2004-06, we evaluated pre- and postharvest fungicides for control of Sphaeropsis rot.  The results are summarized as follows. Ziram applied at two weeks before harvest provided inconsistent results in trials conducted in a commercial orchard (in the first year it was effective but not effective the following year).  In a trial conducted in a research block of Red Delicious ziram was effective to control Sphaeropsis rot (Fig. 4).  Timing of infection may affect its efficacy.

In the experiment conducted in 2005-06 season, Pristine and Topsin applied at seven days before harvest significantly reduced Sphaeropsis rot on apple fruit that were inoculated with the Sphaeropsis fungus at either five or two weeks before harvest (Fig. 4). Pristine and Topsin reduced Sphaeropsis rot by 53-71%  and 39-59%, respectively.

Timing of infection of fruit by the Sphaeropsis fungus may affect the effectiveness of preharvest fungicides for control of Sphaeropsis rot.  This needs to be further evaluated.

Although the Sphaeropsis fungus infects apple fruit in the orchard, the infections remain latent at harvest and decay symptoms develop only during storage.  One question we have been trying to address is whether or not the current decay-control practices are effective to control Sphaeropsis rot. In 2004-05 and 2005-06 seasons, Red Delicious apples from a commercial orchard with a history of severe Sphaeropsis rot were drenched with Mertect and stored in CA for about seven months.  We found that Mertect applied as a pre-storage drench treatment was consistently effective to control Sphaeropsis rot (Fig. 5).

In 2005 and 2006 we evaluated postharvest fungicide-drench treatments for control of Sphaeropsis rot.  The 2005 experiment was conducted on commercially harvested Fuji fruit.  The natural infection of fruit by the Sphaeropsis fungus was low in 2005.  We did not obtain reasonable data to separate differences among the treatments.  In 2006 we inoculated apple fruit in the orchard and then treated with postharvest fungicides at harvest.  The experiment is still in progress.  Results will be forthcoming.

Fig. 4.  Control of Sphaeropsis rot by preharvest fungicides.  Fruit were inoculated at five weeks (A) and two weeks (B) before harvest.  Ziram was applied at two weeks before harvest, and Pristine and Topsin were applied at one week before harvest. Fruit were stored in CA at 32ºF for nine months at which time decay development was evaluated. 

 

Fig. 5. Control of Sphaeropsis rot by a pre-storage drench with Mertect.  Fruit of Red Delicious were from a commercial orchard with a history of Sphaeropsis rot, drenched with Mertect at a commercial facility and stored in CA for seven months. 

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