Scientists hope to give producers the tools to predict which apples will develop disorders in storage.
Left: Dave Rudell checks stored Honeycrisp for development of scald at the USDA lab in Wenatchee. Later stages of soft scald (on the Honeycrisp) can resemble decay (on the Granny Smith). At right, soft scald in Honeycrisp.
Growers might nickname it Moneycrisp because of the high returns, but for packers the Honeycrisp apple brings the risk of big losses.
As the volume of Honeycrisp has increased in Washington State, so has the need to store the variety longer. It is prone to a range of physiological disorders, and packers can’t accurately predict which lots of fruit will store well and which won’t.
“We’ll try this and that, and you think you do everything right, and then something blows up in your face and, boom, you have a six-figure problem,” Peter Verbrugge with Sage Marketing in Yakima, Washington, said during the Washington State Horticultural Association’s annual meeting.
“With Honeycrisp, you’re guaranteed something is going to happen, and we’ll try something else next year,” he said. “As just a packer, if I look at it from the profitability aspect, I probably lost a ton of money handling Honeycrisp because we have all the issues to deal with, and we have flat charges.”
But help is on the way.
Scientists are developing predictive tools that will enable fruit packers to test apples at harvest or in storage and accurately assess the risk that the fruit will develop postharvest disorders later. With this knowledge, they could decide whether the fruit should be packed and marketed soon or could be stored longer.
Dr. David Rudell, plant physiologist with the U.S. Department of Agriculture in Wenatchee, Washington, is heading a team of scientists who are working to develop a risk-assessment tool for apple storage management with funding from a four-year federal Specialty Crop Research Initiative grant.
It would allow packers to shift from a treatment-based approach to a more economical management-based system, along the lines of integrated pest management in the orchard.
They are looking for biomarkers that result from natural changes in fruit that would show if it is predisposed to developing a disorder. Rudell said this is similar to when doctors test patients’ cholesterol and other biochemical levels to find out if they are prone to heart disease.
Rudell began by studying superficial scald in Granny Smith. In trials, some apples were treated with diphenylamine and SmartFresh (1-methylcyclopropene) to prevent scald while others were untreated. After analyzing hundreds of apple peel chemicals, he found that the chemicals differed, depending on whether the apples had scald or not. He was then able to select candidate biomarkers that might indicate if the fruit is predisposed to developing the disorder.
When Granny Smith apples were held in regular storage, the scientists saw differences in peel chemicals after eight to ten weeks, before seeing symptoms on the fruit.
In an experiment in controlled-atmosphere storage, Granny Smith apples were held at a 5 percent oxygen level. After three months, when biomarker levels rose, the oxygen level was reduced to 1 percent and development of scald was minimized.
“We were able to see it before it was coming,” Rudell said. “We discovered these changes in chemistry that are only associated with the disorder or risk of the disorder.”
Biomarkers should provide packers with better information about the fruit than just measuring ethylene or using other techniques that are not as tightly related to the disorders, Rudell said. “We’re looking directly at which will develop the disorders.”
Scientists in the project are also looking for biomarkers for soft scald and soggy breakdown in Honeycrisp, external carbon dioxide injury and firm flesh browning in Empire, and flesh browning of Gala.
Rudell analyzes extractions from peel and flesh samples using sophisticated liquid and gas chromatography-mass spectroscopy instruments. The same samples, which are frozen to -50°C, are shipped to Cornell University in New York where Dr. Jim Giovannoni and colleagues analyze them for gene expression using RNA-seq, a high-throughput sequencing technology.
Rudell said that’s given them more than 30,000 potential biomarkers to select from. Because such a massive dataset tends to crash computers, researchers at the Catholic University of Leuven in Belgium, who are experienced in handling large volumes of data, are doing the mathematical modeling for the project.
Ines Hanrahan, projects manager with the Washington Tree Fruit Research Commission, who is on the SCRI project’s advisory panel, said knowing if a certain lot of Honeycrisp apples will develop superficial scald and soggy breakdown in storage would be invaluable to packers. They store Honeycrisp at relatively high temperatures to reduce the risk of scald developing, but that aggravates bitter pit, to which Honeycrisp apples are also extremely prone. If packers knew that certain lots of apples wouldn’t develop scald, they could hold them in lower temperatures and reduce the incidence of bitter pit.
Knowing about potential storage problems in advance would also help organic producers get their fruit to market before problems develop, she said.
The scientists are also developing diagnostic tools to help packers identify disorders after they develop. Hanrahan said a number of postharvest disorders result in browning of the skin or flesh and are difficult to distinguish. For example, soft scald in Granny Smiths can easily be confused with rot. Conversely, a particular fruit disorder can manifest itself in a variety of different symptoms.
Being able to accurately diagnose a problem could help pinpoint the cause and enable packers to adjust their storage regimes. It might also help determine who is responsible and would be useful in cases where claims go to court.
The project will continue for another two years as the scientists continue to select and validate biomarkers for the various fruit ailments. After the risk-assessment tools are developed, scientists will do an economic assessment to find out if they would be cost effective.
“What we want to do is pass this technology off to someone who’s going to employ it in an extension role or a business,” Rudell said.
There are several ways that biomarkers could be used in a commercial setting. Packers might send samples of fruit to an agricultural service lab for testing, just as they might send samples for nutrient testing. Or, a packing house could purchase a simple spectrophotometer (priced under $10,000) for its quality control lab to provide almost instant results. Alternatively, volatiles in the storage atmosphere could be monitored and analyzed.
Methods of measuring gene expression in the field are also becoming available, Rudell said, which would allow a risk assessment to be done before harvest.
The Washington Tree Fruit Research Commission and AgroFresh are helping to fund the project. Plant and Food Research in New Zealand is also involved in the project.