1999 CORNELL FRUIT HANDLING AND STORAGE NEWSLETTER


Items of Interest for Storage Operators
in
New York and beyond

Chris B. Watkins
Department of Fruit and Vegetable Science
Cornell University
Ithaca, NY 14853
Voice: 607-255-1784; Fax: 607-255-0599
E-mail: cbw3@cornell.edu

and

David A. Rosenberger
Cornell's Hudson Valley Laboratory
PO Box 727, Highland, NY 12528
Voice: 914-691-7231; Fax: 914-691-2719
E-mail: dar22@cornell.edu

 Item

Controlling storage decays in Empire fruit during CA storage
Controlling postharvest decays in varieties other than Empire
Temperature management of apple fruit - the continuing saga
ReTain effects on McIntosh storage
DPA recommendations
MCP - new chemical of the future?

 Mention of specific trade names or omission of other trade names does not imply endorsement of products mentioned or discrimination against products not mentioned.


Controlling storage decays in Empire fruit during CA storage

Current situation:

All apple cultivars are susceptible to postharvest decays, but Empire fruit have been most severely affected over the past six or eight years. Losses have approached 15% for some lots of Empire fruit held more than six or seven months in CA storage. Non-decayed fruit in the affected lots are still firm and show no signs of internal breakdown or other disorders. Most of the decays are caused by Penicillium expansum, the cause of "blue mold". Postharvest fungicide treatment has been totally ineffective for controlling decays in some lots of Empire fruit.

Decay problems are currently more severe in some storage operations than in others. Apparently not all storages have the fungicide-resistant strains of P. expansum that are responsible for the most severe problems. However, the Empire decay problem is becoming more widely distributed each year. Where problems have occurred in the past, action must be taken this summer to minimize potential decay problems with the 1999 Empire crop.

Background:

P. expansum and Botrytis cinerea are the most common postharvest pathogens, account for most of the losses in commercial storages, and are the primary targets for postharvest fungicide treatments. B. cinerea causes gray mold. Empire fruit with gray mold come out of CA storage looking like baked apples: the fruit remain firm but the entire skin is a light brown. Gray mold can be controlled by treating fruit with diphenylamine (DPA) plus thiabendazole (TBZ) in a postharvest drench, so gray mold is most common in fruit that are moved to storage without a postharvest treatment.

Blue mold decay is most severe in fruit that received a postharvest treatment, but it can also occur in untreated fruit. TBZ is no longer effective against some strains of P. expansum, and the drenching process can spread inoculum to more fruit than would otherwise become infected. When first introduced, TBZ and the other benzimidazole fungicides were very effective against P. expansum and B. cinerea. Benzimidazole-resistant strains of P. expansum and B. cinerea were present in apple packing houses throughout the world by the late 1970's, but postharvest treatments continued to work throughout the 1980's. The postharvest treatments remained effective because strains of P. expansum and B. cinerea that were resistant to the benzimidazole fungicides showed increased sensitivity to DPA and were therefore suppressed by the DPA that was always applied with the fungicide. However, about 2% of the P. expansum isolates collected from apple storages in the mid-1980's were resistant to the DPA/benzimidazole combination. These double-resistant strains have gradually become dominant and are contributing to the current decay problem with Empire fruit.


Unique Decay-Susceptibility of Empire

If fungicide treatments have lost their effectiveness against P. expansum, why are most decay problems still limited to Empire? We do not yet have a definite answer, but it appears that Empire fruit may be uniquely susceptible to blue mold decay.

Until the recent decay problem developed with Empire fruit, most blue mold decays in apples originated at stem punctures or other wounds on the fruit. As the current Empire decay problem emerged, packinghouse operators noted that many decayed fruit had no evidence of any skin breaks or wounds. We therefore devised and completed experiments to determine if P. expansum can invade non-injured fruit through stems.

During each of the past two years, Empire fruit were harvested on the same day from six orchards in western NY. These fruit were uniformly inoculated by placing measured droplets of spore suspensions on the ends of the fruit stems before the fruit were moved into storage. Results of these experiments provided clear evidence that P. expansum can invade fruit through the stems. Invasion through stems had previously been reported for pears, but not for apples. We do not know if other apple varieties can be infected through stems, but we suspect that this is a unique attribute of Empire and that it explains why current decay problems are mostly limited to Empire.

There is still much to be learned about how and why stem infections occur on Empire fruit, but results from two years of research allow the following conclusions:

1. Infection through stems occurs only under CA conditions. Inoculated fruit held for 6 months in air storage did not decay whereas up to 69% of inoculated fruit in CA storage developed decay.

2. Susceptibility to decay varies significantly from one orchard to another, but the susceptibility ranking for the six orchards from which we collected fruit was not consistent over the two years of the study. Two orchards produced fruit that was highly susceptible to stem infections in both years, one orchard had little fruit infection in both years, and the other three orchards varied considerably in susceptibility from year to year.

3. Delays in cooling of up to 24 hr, delays in time of inoculation (12-hr vs 40 hr after harvest), and delays in establishment of CA atmosphere (1-day vs 14 days) did significantly affect the incidence of decay in inoculated fruit. Thus, allowing stems to "heal" before fruit are cooled and put into CA atmospheres did not reduce the incidence of decay.

4. Stem inoculations using spore concentrations comparable to those encountered in postharvest drench tanks resulted in up to 25% fruit infection in 1998 inoculations. The incidence of decay was higher as the spore concentration was increased, but our results suggest that signficant rates of infection can occur with inoculum rates that would be difficult to avoid in drencher solutions.

What do we do next?

There are no easy short-term solutions for preventing decays in Empire fruit. The biocontrols that have been registered for use on apples either do not work or are not available. Within several years, we may receive a registration for a new postharvest fungicide with the generic name of "fludioxonil". This product is manufactured by Novartis and has provided excellent control of P. expansum in initial trials. Novartis believes that this product can be registered for postharvest use on apples and is currently deciding whether to pursue registration.

Until a new fungicide becomes available, the best approach for controlling decays in Empire fruit will be to avoid exposure to inoculum. The following methods should be considered for reducing inoculum potential:

1. Stop drenching Empire fruit: This will avoid exposing fruit to the recirculating spore load that collects in the drencher solutions. However, fruit moved into storage without postharvest treatment will be more susceptible to gray mold decay and carbon dioxide injury. DPA treatment has been shown to reduce carbon dioxide injury. In the absence of DPA treatment, special care may be required to minimize the potential for carbon dioxide injury on Empire.

Incidence of gray mold in untreated fruit is unpredictable. Gray mold infections have been presumed to occur primarily at wounds during and after harvest. However, Empire fruit with gray mold frequently have no wounds, and the decays appear to originate from the calyx of the fruit. I suspect that gray mold on Empire apples results from calyx-end infections that occurred in the field. B. cinerea is known to infect flower sepals of kiwifruit and strawberries during bloom, and sepal infections on these fruits result in development of fruit decays only after fruit begin to ripen. If gray mold in apples results from infections that occur during or shortly after bloom, then the incidence of gray mold might be lower in a dry year like 1999 than it would be in a wet year like 1998. This hypothesis requires more testing, but it provides a basis for suggesting that gray mold may not be too severe in Empire fruit that go into storage without a postharvest treatment during the fall of 1999.

2. Sanitize storage room floors and walls during summer. Floors and walls of storage rooms become contaminated with spores that will be stirred up by forklift traffic and evaporator fans in the fall. Quaternary ammonia compounds are registered for sanitizing storage rooms. Cleaning rooms during summer can also help to eliminate odors associated with non-pathogenic molds (fungi) that sometimes develop on storage walls. Some storage odors persist in packed fruit, so cleaning storage walls and floors can improve fruit quality at the same time that it reduces the inoculum load for post harvest decay fungi.

3. When ever possible, use new bins or the cleanest of your old bins for long-term storage of Empire. Fruit that are moved into storage without postharvest treatment can still develop decay problems if exposed to high levels of airborne inoculum. In an experiment conducted in fall-winter of 1997-98, we applied different treatments to replicated bins of fruit from the same orchard block. Some bins received fungicide treatments and others were moved into storage without any postharvest treatment. When fruit were removed from CA storage on July 15, the incidence of decay in the treated and untreated fruit was similar (about 200 decayed fruit/bin). Spores for infecting the non-treated fruit must have been airborne because those fruit were never wetted after harvest. The airborne inoculum probably originated with other contaminated bins.

If you store other varieties in the same rooms with CA Empire, then bins for those fruit must also be reasonably clean to prevent contamination of the Empire fruit.

4. Sanitize contaminated bins: Bins that have been in storage rooms that contained significant quantities of decayed fruit will be heavily contaminated with spores of fungicide-resistant P. expanusm. The same is true for bins that came out of packinghouses while decayed fruit were being removed from packing lines. We know from spore trapping experiments that packinghouses are full of airborne spores of P. expansum. These spores will land on bins and be recycled back into the storage unless the bins are sanitized.

Having chlorinated water in the water dumps in packinghouses can help to sanitize bins as they are emptied, but the empty bins are likely to become recontaminated before they can be removed from the packinghouse. Running bins through chlorinated water provides no residual protection against recontamination. Furthermore, treatment with chlorinated water will not eliminate contamination that is embedded in decayed fruit and apple tissue that remain in the bottom of the bins.

Apples with blue mold decay usually sink to the bottoms of bins as the bins are emptied in water flotation tanks. These decayed fruit are sometimes left in the bottoms of bins after the bins are nested and removed from the packinghouse. Decayed fruit in the bottoms of bins can provide millions of spores for infecting the next year's crop. No sanitizing treatment (except perhaps steam) will effectively sterilize decayed fruit.

The only effective way to sanitize bins is to remove all decays, scrub out visible dirt or spore accumulations on the bin floors and walls, and then run the bin through a drencher that contains a quaternary ammonia compound. Quaternary ammonia is considered more effective than chlorinated water for sanitizing bins. The same equipment that is used to apply postharvest treatments can probably be used to apply quaternary ammonia sanitizers, but the outlets on the drencher may need to be modified to ensure good coverage of the bins.

Sanitized bins should be kept separate from bins that have not been sanitized. If sanitized bins are moved back into non-sanitized storage rooms, or if they are transported through contaminated passageways, then the bins will become recontaminated with airborne spores that are stirred up by the forklifts. Bins that appear "clean" and that came from storage rooms where decays were not a major problem can probably be used without sanitizing for apple varieties other than Empire. However, unsanitized bins that appear "clean" have the potential for recontaminating sanitized bins if they are stored in the same CA room.

Sanitizing several thousand or tens of thousands of apple bins is no small job, and the benefits have not yet been proven. However, I see no alternative for handling badly contaminated bins. Without effective fungicides for controlling blue mold, spores from contaminated bins will contaminate storages and will contribute to continued problems with postharvest decay in Empire.


Suggestions for bin sanitation at the packinghouse

If bins are not sanitized prior to the 1999 harvest, the next best alternative will be to improve bin sanitation as bins come out of the packinghouse next winter. The following approaches could be used to decrease the amount of inoculum that recycles on bins:

1. Always use chlorinated water in the flotation tank on the packing line. Be sure that chlorine levels are properly maintained and that pH of the water is near neutral.

2. Remove all decays from the bottom of bins as the bins come out of the water flotation tank. Scrub dirty spots with chlorinated water from the flotation tank.

3. Consider methods for getting empty bins out of the packinghouse while they are still wet (before they can become re-contaminated with spores of P. expansum). Spores landing on bins that are still wet from chlorinated water will probably be killed, but bins will be subject to recontamination as soon as they dry. An enclosed conveyer with positive airflow into the packinghouse might be one way to get empty bins out of the packinghouse relatively quickly and with minimum exposure to packinghouse air. The empty bin conveyer should lead directly to the exterior of the packinghouse.

4. Avoid storing empty bins in CA rooms that have not been sanitized or that have a direct connection to the packinghouse. Rooms connected to the packinghouse by an enclosed hallway will quickly become re-contaminated with spores from the packinghouse.

By now it should be obvious that we have no simple solutions for the decay problem in Empire fruit. A new postharvest fungicide may be available within several years, but it will be important to minimize the spore load in apple storages before the fungicide is introduced. Exposing a new fungicide to the high spore loads that are currently present in some storages would create tremendous selection pressure for development of resistance to the new fungicide. Very few fungicides can meet the stringent criteria for postharvest registrations, so it will be absolutely essential to use any new postharvest fungicide in ways that minimize the selection pressure for fungicide resistant strains. An integrated approach involving sanitation and effective fungicides will be essential for controlling decays in Empire fruit.


Controlling postharvest decays in varieties other than Empire

Recommendations for controlling postharvest decays remain unchanged except for Empire fruit. As noted above, we do not believe that postharvest treatments should be applied to any Empire fruit in 1999 that will be stored more than 5 or 6 months because treatment sometimes contributes to an increased incidence of decay during long-term storage. Other apple varieties that are not at risk for development of scald (e.g., Golden Delicious throughout the state, McIntosh in the Champlain Valley) can also be stored without postharvest treatment. When DPA is needed for scald control, however, we believe it is still wise to apply thiabendazole (TBZ, = Mertect 340 F) along with the DPA.

In storages that have experienced major problems with Empire decay, TBZ may be only marginally effective even on varieties other than Empire. In those situations, sanitation measures that reduce inoculum potential should help reduce decays in all apple varieties. We have not tested strains of P. expansum that have dual resistance to TBZ and DPA to determine if they are equally pathogenic on all apple cultivars. Thus, TBZ could conceivably provide some decay control on other apple varieties even when it no longer works on a very decay-susceptible variety like Empire.

Where the TBZ/DPA combination has provided acceptable control of decays in previous years, there is no reason to change procedures this year. Recommendations for applying postharvest treatments in 1999 include the following:

1. Always use DPA and TBZ together because that combination provides better control of both TBZ-sensitive and TBZ-resistant isolates than either product used alone.

2. Never use chlorinated water and DPA in the same postharvest treatment tank. Chlorinated water will break down the DPA.

3. Captan used at the full label rate may help to control isolates of P. expansum that are resistant to DPA and TBZ. Some storage operators have claimed excellent success with captan postharvest treatments, but trials with captan have provided inconsistent results. Also, captan-treated fruit may be unacceptable in some markets. Furthermore, the captan label might be revised in the near future as part of the implementation of the Food Quality Protection Act.

4. When using any postharvest treatment, follow label recommendations for rates, replenishing solutions, and maximum quantities of fruit that can be treated before the solution must be replaced.

5. Only use application equipment that has an effective agitation system in the holding tank. Otherwise, the fungicide(s) in the drench solution will settle out of solution on the bottom of the tank.

6. Rapid cooling can significantly reduce the incidence of decay that develops in storage. If CA rooms are being filled rapidly, fruit should be pre-cooled in separate rooms before it is loaded in the CA room so as to reduce the total cooling time.


Temperature management of apple fruit - the continuing saga

Problems in meeting firmness standards for fruit, particularly for Empire apples exported to Europe, has been a major issue for the New York industry. Losses of firmness en route have resulted in downgrading of the fruit and associated severe financial losses. Minimizing the risk of rejected shipments is a key to maintaining confidence in the variety, maximizing quality, and ensuring growth of the Empire apple in this critical market. Moreover, information obtained from these studies will help improve quality for other overseas markets as well as domestically.

In the 1998 Fruit Handling and Storage Newsletter, Jim Bartsch and I reported on our results during the first year of a study on temperature management during the packing process. Briefly, the study indicated that:

1. Skin and core temperatures of fruit increased significantly during the grading operation, reaching on average 63 and 45oF by the time that fruit were packed into cartons. The take-home message was that we need to maintain temperatures at 32oF in rooms holding fruit to be packed out for all varieties, and that only the number of bins needed to maintain the packing operations should be brought out from the storage rooms for warming prior to packing..

2. The cooling rate measured as half-cooling time (see definition in box) could be extremely slow - 13 hours in some instances before fruit even began to cool and then half cooling times of as much as 84 hours were measured! Forced air cooling of vented cartons reduced this time to 3 hours. Although these experiments did not include measurements of fruit firmness, the results strongly suggested that these delays in cooling might be responsible for loss of fruit condition.


Defining "half-cooling" time:
The half cooling time measures the time that is taken to remove 50% of the heat from the apple. For example, if fruit temperatures are at 72oF in a storage room at 32oF, the temperature difference between the fruit and final desired temperature is 40oF. A half cooling time of 8 hours means that it will take that time to reduce fruit temperatures by half this amount, i.e., 20oF, to reach a temperature of 52oF, and a further 8 hours to reduce fruit temperatures by 10oF to 42oF. In practice, we consider that it takes three half cooling times to "cool" a product.

This season a trial was carried out during March with the cooperation of several shippers in which fruit temperatures and changes in firmness were monitored from the time of packing until the fruit were received by importers in UK. Five packing operations were used in the trial. In two of these, forced air cooled systems were available, and in one of these, we were able to compare forced air- and passively-cooled fruit. In each of six containers, fruit in cartons on the top layer, eighth layer from the bottom), and the bottom layer, of two pallets were tested for firmness and temperature probes, which recorded temperatures every 30 minutes, were inserted into the core of an apple. Firmness measurements were made at arrival and the temperature probes recovered and downloaded.

A typical temperature profile in passively cooled fruit is shown in Fig. 1. Clearly, the cooling of fruit in the middle carton was much slower than either the top or bottom cartons. The half-cooling times for fruit in the top, middle and bottom cartons between packing and arrival were 25, 74 and 28 hours, respectively. The average firmness loss of fruit in the bottom, middle and top cartons between packing and unloading was 0.6, 1.4 and 0.3 lb, respectively, suggesting half-cooling time and firmness is related.

This conclusion was reinforced by results from one packing shed utilizing forced air cooling: half cooling times were only two hours in the top, middle and bottom cartons, and these fruit did not soften during transport to the UK.

However, in the only direct comparison between passive and forced air cooling that we were able to make, no advantage of forced air cooling on firmness was detected (Table 1). This happened despite the fact that forced air cooling provided more rapid cooling than passive cooling (Fig. 2A and B). Differences in cooling rates between cooling methods were substantial: half cooling times for top, middle and bottom cartons were 23, 31 and 15 hours for passively cooled fruit, and 2, 3 and 3 hours for forced air cooled fruit, respectively.

How can we explain the lack of relationship between cooling and firmness? On the basis of the data, one might conclude that there is no advantage of forced air cooling on Empire quality. Extensive information available elsewhere suggests, however, that this is unlikely to be the case, although the initial quality of the fruit may be a very important factor in determining measurable differences. For example, fruit that softens rapidly because of orchard based problems may respond to rapid cooling more than fruit that has a natural tendency to retain firmness.

The answer may lie not only in the effect of cooling, but temperature management after cooling and during transport. Fig. 2 shows that fruit temperatures increased during transport, starting about six days after packing. Temperatures of the fruit averaged 36.6oF in both passive- and forced air-treated fruit over the next 10-day period. It is possible, though we cannot be sure without further trials, that these elevated temperatures negated any advantage of forced air-cooling.

This research is ongoing, but clearly indicates that the issue of temperature remains a critical factor that limits maintenance of the quality of our apples. Hard data does not prove that forced air cooling is the right thing to do, but collective observations indicate that investment in such facilities should be seriously considered by all shippers.

Fig. 1 Core temperatures of Empire apple fruit in cartons in the top, middle or bottom of stacked pallets during and after passive cooling and transport.

Fig. 2. Core temperatures of Empire apple fruit in cartons in the top, middle or bottom of stacked pallets during and after passive (A) and forced air cooling (B).

Table 1: Effect of carton position on pallet on flesh firmness (lb) of Empire apples from a packinghouse (No. 5) in New York after packing, and after passive or forced air cooling and export to the UK. Each value represents the average of ten fruit in each of two cartons on separate pallets.
   

 Position on pallet
Cooling method    Top  Middle  Bottom  Pallet average
 Forced air  Start  15.1  15.1 14.5   14.9
   Finish  14.2  14.4  14.3  14.3
   Difference  -0.9  -0.7  -0.2  -0.6
           
 Passive  Start  14.7  14.9  14.9  14.7
   Finish  14.1  14.2  14.4  14.2
   Difference  -0.6  -0.7  -0.5  -0.5



ReTain effects of storage of McIntosh

ReTain dramatically delays pre-harvest drop of McIntosh, especially in the northern regions of New York, but the effects of the chemical on storage quality are not well known. Anecdotal evidence suggests that ReTain-treated fruit are firmer than untreated fruit out of storage, but reports have been varied. It is not known how important it is to keep treated and untreated fruit separate during storage.

In the 1998 growing season, an experiment was carried out using fruit from three McIntosh orchard blocks in the Champlain Valley. Trees were sprayed with ReTain, and fruit from these trees and untreated trees were harvested during the normal harvest season. One block of trees developed severe mite infestation and the ripened early. At the first harvest of this block an effect of ReTain was still found at 98 ppm and 60 ppm of internal ethylene in the control and ReTain-treated fruit, respectively, but because of the high ethylene levels in the fruit from this orchard, they were not stored under CA.

Table 2 shows the maturity of untreated and treated fruit at two harvests. A strong effect of ReTain in delaying ethylene build up was found especially on the second harvest. Surprisingly, firmness of the fruit was slightly softer in treated fruit than untreated fruit. Starch pattern indices were not affected by treatment.

Treated and untreated fruit from both harvests were stored separately under standard McIntosh storage conditions for 4 or 6 months and evaluated after 1 or 7 days at 68oF. For the first harvest, these fruit were also stored combined.

There was little effect of separate or combined storage on firmness of treated and untreated fruit during storage. ReTain-treated fruit were slightly firmer (less than 0.5 lb advantage) after the 7 day shelf life period at 68oF than control fruit but only in one of the orchards.

Our conclusion from this experiment is that it is not important to store ReTain-treated fruit separately from untreated fruit. Differences might be detected in fruit from earlier harvests when days before ethylene production are greater in fruit than was the case in this experiment. However, it is more likely that because the McIntosh variety is such a high producer of ethylene, any advantages of lower ethylene at harvest are reduced during storage. ReTain delays but does not prevent ethylene production. Similar ethylene levels were measured in commercial CA storages in which treated and untreated fruit were kept separated. While ReTain remains an invaluable tool for harvest management, its utility for maintaining quality of stored McIntosh fruit appears limited. However, lower ethylene producing apples such as Empire may benefit from ReTain treatment combined with separate storage, and trials are planned to check this possibility.

 

Table 2. Maturity of untreated and ReTain-treated McIntosh apples at harvest.
   

 Orchard number
   

 1

 2
 Harvest  Factor  Control  ReTain  Control  ReTain
 1  IEC (ppm) 9.9 0.3 0.4 0.4
 (9/15/98)  Firmness (lb) 17.9 17.3 18.4 18.1
   Starch index 4.6 4.2 4.8 4.8
           
 2  IEC (ppm) 57.7 0.2  5.1 0.1
 (9/24/98)  Firmness (lb) 16.4 15.9  17.5 17.2
   Starch index 6.2 6.1 5.5 5.4



DPA recommendations

An earlier than normal harvest is predicted in Western New York this year. This may mean that risk of scald development during storage is high this storage season. Make sure that you apply the recommended concentrations (Table 4). These are sometimes lower than labeled rates because risk of scald development is lower in New York than some other growing regions. Dave Blanpied developed these recommendations based on concentrations required to control scald, label maximums, and susceptibility of varieties to DPA injury.

Mixing of varieties with different DPA recommendations can be an issue for storage operators. If the variety with the lower recommended concentration, eg. 1000ppm, will be burned by as higher concentration, eg. 2000ppm, then the lower concentration should be used. Golden Delicious may be burned by 2000ppm and therefore if a tank load is used for both Red Delicious and Golden Delicious, then the concentration should not exceed 1000 ppm. However, if Empire, which requires only 1000 ppm, is mixed with Red Delicious, then 2000ppm can be used because 2000ppm will not damage Empire.

Finally, a reminder about the powerful effect of DPA for control of carbon dioxide injury. Our research with McIntosh, Cortland, Empire and Law Rome indicates that risk of injury by the gas is essentially zero if fruit have been treated with DPA. So, if carbon dioxide gets out of hand during early periods of storage and your fruit has been drenched with DPA you should worry less. Both No Scald (Decco, Elf Atochem North America) and Shield-Brite (Pace International LP) DPA formulations offer excellent protection against carbon dioxide injury when applied for scald control.

 

Table 3. Recommended concentrations of diphenylamine (DPA) for scald control of New York apple varieites.
 Variety  DPA (ppm)
 Cortland 2000
 Delicious  1000-1500
 Empire  1000
 Golden Delicious  1000*
 Idared  1000
 McIntosh  1000
 Mutsu  2000
 Rome  1500
 Stayman  1500
*Note that Golden Delicious is more sensitive to DPA injury than other apple varieties and that DPA retards chlorophyll loss.


MCP - new chemical of the future?

Controlling ethylene is a key to maintaining fruit quality in storage. Everything that we do after harvest, such as cooling and application of CA conditions is an attempt to prevent production and/or action of ethylene. Therefore, it is really exciting when a new chemical that affects ethylene action is discovered, as its impact on our industry may be great. This past season we have worked for the first time with a compound known as 1-methylcyclopropene (MCP), sometimes described in the trade press as EthylblocR. The compound comes as a powder, which releases a gas when a dilute base is added to the mixture. We tested effects of three MCP concentrations on Delicious, Empire, Law Rome and McIntosh stored in air and CA. Our results show that the effectiveness of MCP is affected by variety, with inhibition of ethylene production being less effective on McIntosh and Law Rome than on Delicious and Empire. Effects on firmness were quite startling - Figs. 3 and 4 shows McIntosh and Empire firmness after treatment and storage in air or CA. Fruit were removed from storage at each sampling time and kept in air at 68oF for a further 7 days. Both Empire and McIntosh softened in air storage, but MCP delayed softening, especially in Empire (Fig. 3). CA storage resulted in greater effectiveness of all MCP concentrations (Fig. 4). McIntosh apples that were producing high amounts of ethylene at harvest, however, continued to soften, indicating that higher MCP concentrations might be necessary for this variety. Another important aspect of MCP is that it markedly reduces development of superficial scald and senescent disorders.

These results are very promising. MCP has just been approved for registration for extending the life and usefulness of fresh cut flowers and potted flowering, bedding, nursery, and foliage plants. Low toxicity of the product suggests that it may be permitted on fruit and vegetables in the near future, and negotiations to steer the chemical through regulatory processes are ongoing.


Fig. 3. Firmness (lb) of McIntosh and Empire apples after treatment with MCP and storage in air at 32°F for up to 30 weeks, plus 7 days at 68°F.

 

Fig. 4. Firmness (lb) of McIntosh and Empire apples after treatment with MCP and storage in CA at 35°F for up to 32 weeks, plus 7 days at 68°F.


Acknowledgements

We thank the cooperating growers who provided the Empire fruit used for studies on stem infections by Penicillium expansum, and we gratefully acknowledge the assistance of the packinghouse operators who collaborated on studies of postharvest decays and provided and CA storage space for decay-control experiments. Research on postharvest decays was funded by the New York Apple Research and Development Program, the New York Apple Research Association, Novartis, and the Decco Division of Elf Atochem North America, Inc.

The temperature trial described in this newsletter could not have been carried out without the cooperation of shippers in the US, and the importers in the UK. Their contributions of fruit, and patience is gratefully acknowledged. The project was funded by the Statewide Program Committee Research/Extension Grants program, Cornell University. The research on ReTain was carried out with Kevin Iungerman and funded by the New York Apple Research and Development Program and Abbott Laboratories. The research with MCP was supported by Gowan Chemical Company. We thank Jackie Nock (Ithaca), and Fritz Meyer, Catherine Ahlers and Albert Woelfersheim (Hudson Valley Lab.) for excellent assistance.


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