42 Preventing soft
scald in apples Post-harvest handling key to reducing spoilage
Two of the most popular apple varieties in Canada are Honeycrisp and Ambrosia.
Research by MARGARET EVANS
People love them because of their great taste, firmness, texture and colourful appearance. Honeycrisp and Ambrosia in their prime condition are perfect for the market but keeping them that way can be a tricky balance of storage techniques and management controls. During storage, these apples are highly susceptible to a physiological disorder called soft scald, when the fine skin and underlying flesh develop ugly brown or black lesions, making them unmarketable. It comes down to temperature, and exposing the crop to low temperature too early after harvest can trigger soft scald. Now, a group of proteins
may help researchers better understand and develop the best protocols for storage to preserve these apples’ high quality.
“Honeycrisp and Ambrosia
can be particularly susceptible to soft scald,” says Peter Toivonen, research scientist at Agriculture and Agri- Food Canada (AAFC)’s Summerland Research and Development Centre. Toivonen along with colleagues at AAFC, Kentville Research and
Development Centre and Dalhousie University, Nova Scotia, have identified a group of proteins that possibly could be critical to helping the industry maintain the apples’ high quality while in storage. The goal is to now validate their findings to see if the protein group can be used as biological markers for detecting, preventing and monitoring soft scald. “Dr. Jun Song [AAFC
Kentville] has identified that these proteins are associated with oxidative stress response in the Ambrosia apple tissues,” says Toivonen. “Soft scald symptoms themselves are due to chilling injury in low temperature storage when susceptible apples are subject to some form of stress in the field (water, heat, etc.)which renders them more susceptible to develop symptoms in low temperature storage.”
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Soft scald is an issue for Honeycrisp and Ambrosia apples and researchers are trying to identify the optimal environment for storing them. DR. JENNIFER DEELL, ONTARIO MINISTRY OF AGRICULTURE, FOOD AND RURAL AFFAIRS PHOTO
Toivonen says that it is sometimes difficult predicting which orchards will be susceptible in any particular growing season and it is this uncertainty that causes problems when it comes to making decisions about post- harvest and marketing. “The disorder is considered
important in BC if an orchard has 5% or more of the fruit affected,” he says. “In the past, some orchards had a lot more (up to 25% or more) but current practices help to contain the problem for the most part. However, [2018] resulted in much more incidence than has occurred over the last several years.”
Ambrosia apples were used during experiments in which they were subjected to post- harvest conditioning treatments and then monitored for soft scald incidence in storage. “Dr. Jun Song been
conducting the protein analysis in collaboration with our research group at Summerland,” he says. “The next step is to validate the correlation with apples from a different cropping season, choosing apples from historically susceptible orchards and from apples in resistant orchards to confirm that the protein expression levels always equate to soft
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scald development in storage.” They know that a
preconditioning treatment (holding apples at 10° to 20° C for seven to 10 days) prior to placement into cold storage will reduce incidence. “Storage of apples at warmer temperatures (3° to 5° C) can reduce incidence as well, but warmer temperatures for storage causes more rapid softening, thereby reducing storage potential. Environmental conditions
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may have some influence and Toivonen says that, to date, they have been able to confirm that inadequate irrigation in the month before harvest is consistently associated with an increase in susceptibility to soft scald. So far, though, they have not determined what that threshold should be in order to avoid the onset of the condition. “A new scientist at the Summerland Research Development Centre, Dr. Hao Xu, will be investigating the issue in much more detail in the coming years to give more definitive answers to the industry,” he says. “That being said, other stresses that may be related to soil type may also correlate to increased susceptibility. For instance, it has been reported that in New Zealand excessive rainfall prior to harvest leads to increased susceptibility to soft scald in Ambrosia apples, likely due to saturation of the soil by water (i.e. drowning of the roots).” The next step in the
research will be to further their understanding of the group of proteins as markers then develop detection tools to help growers and packers become more effective and proactive at reducing or eliminating soft scald while the fruit is in storage.
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