What can physiological profiling tell us about this Cripps Pink mutation? By Anna Mouton.
Apple growers are always on the lookout for new Cripps Pink strains that can deliver higher Class 1 pack-outs. Lady in Red is one such promising mutation. Discovered in New Zealand in 1996, it develops earlier and better red colour than the original Cripps Pink.
But a potential Class 1 apple in the orchard only gets a grower so far — the fruit must maintain its quality until it reaches the consumer. This is why a new Hortgro-funded project led by Heleen Tayler of ExperiCo Agri-Research Solutions is putting Lady in Red through its postharvest paces.
A proliferation of variables
Cripps Pink is the third most-planted and most-exported cultivar in South Africa after Golden Delicious and Royal Gala, but its sensitivity to postharvest browning disorders can cause headaches. Research has shown that Cripps Pink browning is influenced by harvest maturity, storage temperature, and storage duration, so Tayler focuses on these variables.
She sourced apples from a full-bearing orchard in Ceres. “It was chosen because it’s the oldest established Lady in Red orchard,” says Tayler. “So far, we have only sampled this one orchard for one season.”
The fruit were harvested at three maturities: early-optimum (15%–20% starch conversion), optimum (30%–40% starch conversion), and late-optimum (more than 50% starch conversion).
Each maturity group was further divided to assess fruit response to 1-methylcyclopropene (1-MCP) application, storage at -0.5 °C versus 1.0 °C, and storage for 3, 5 or 7 months. The experimental layout is summarised in Figure 1.
Figure 1: Treatments applied to fruit in each harvest-maturity group.
After the initial cold-storage period, all fruit were subjected to simulated shipping of six weeks at -0.5 °C, followed by simulated shelf life of seven days at 20.0 °C.
Complete maturity evaluations were performed at harvest and after the initial cold storage, simulated shipping, and simulated shelf life. Data collection included firmness, total soluble solids, titratable acidity, blush and background colour, decay, and internal and external disorders.
“This project is not only about internal browning,” says Tayler. “It’s also about quality and about identifying other possible disorders.”
Three harvest maturities, four treatments, three storage temperatures, and four sets of maturity evaluations add up to 144 maturity evaluations. And each maturity evaluation had five replicates!
So far, so good
“The browning defects we saw in the first season were really very slight,” says Tayler. “The browning we found might not even be an issue commercially.”
Evaluations include cutting the fruit open. Tayler explains that some fruit had light yellowish discoloration internally as opposed to typical browning. Others had subtle signs of CO2 browning at the core. She did not observe any diffuse or radial browning.
Although this is good news, Tayler cautions against hasty conclusions from a single season’s data on one orchard. “You can’t make a blanket statement that Lady in Red has few postharvest problems. We need to confirm whether this just happened to be the case for that season or that orchard.”
Seasonal variation is one reason why repeating the trials is essential. “There was browning in the industry in 2022,” recalls Tayler, “but I don’t think it was a train-smash year.”
Whereas the jury is still out on browning, clear results emerged on superficial scald. Apples not treated with 1-MCP developed superficial scald regardless of harvest maturity.
According to Tayler, superficial scald on Cripps Pink is usually light brown, almost cream, but the scald she observed on Lady in Red was much darker, similar to superficial scald on Rosy Glow.
In addition, treatment with 1-MCP reduced peduncular scald while improving firmness, total soluble solids, and titratable acidity.
“I think 1-MCP is important,” says Tayler. “We also noticed that fruit treated with 1-MCP have a lower tendency for CO2 core browning. This could be due to lower respiration, but we haven’t investigated that.”
Previous research led by Dr Elke Crouch, Chair in Deciduous Postharvest Research at Stellenbosch University, demonstrated that stepdown cooling is essential for mitigating internal browning in Cripps Pink. In her trials, apples stored directly at 1 °C developed severe browning.
Stepdown cooling is not part of the Lady in Red project protocol. “The idea was not to use stepdown cooling so we could see what disorders the cultivar tends to develop,” says Tayler.
She clarifies that the fruit were allowed to cool slowly. Apples were kept overnight at about 15 °C after harvesting. Two days later, when they were treated with 1-MCP, they had cooled to 5 °C and took about a week to reach their final storage temperature.
Cripps Pink is stored above 0 °C — usually at 0.5 °C, but this project included a -0.5 °C treatment to stress-test Lady in Red. Browning was no worse at -0.5 °C, but the firmness of optimum-harvested fruit may have been better.
However, storage at -0.5 °C was generally associated with decreased firmness, total soluble solids, and titratable acidity. Tayler stresses that more data are needed to tease out the relationship between quality and temperature in Lady in Red.
A second round of trials is planned, although Tayler is worried about this season. “The orchard we chose is in the Witzenberg Valley, where they had severe hail damage. So we need to see whether we’ll have enough fruit.”
Meanwhile, initial results are encouraging. “You can’t draw conclusions at this stage, but I was pleasantly surprised at how little browning we found,” says Tayler. “I was cutting up fruit and asking, where is the browning? I don’t see any.”
What are people saying about this research?
“The question is how Lady in Red will react — different mutations are more or less sensitive to postharvest defects. In addition, when skin colour changes, skin thickness also often changes, which can affect the internal atmosphere of the fruit.”
Henk Griessel. Quality Assurance Manager, Tru-Cape.