Tracking Pink Lady apple firmness (AP01036)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

As a result of this project, growers and packers had a new fruit firmness management tool in SmartFreshTM to avoid soft Pink Lady apple outturns on domestic and export markets. Furthermore the project had investigated a number of other production and handling practices that may have impacted on fruit firmness.

Ethylene the fruits’ natural ripening hormone, had been identified as a prime factor in soft fruit outturns. SmartFreshTM was a gas that inhibited ethylene action when applied shortly after harvest to warm or cooled fruit. Fruit treated with SmartFreshTM were significantly firmer than non-treated fruit after medium and long term air and CA storage plus a simulated marketing period. In 2002 and 2003 actual trial shipments of SmartFreshTM treated fruit from 12 orchards in the Goulburn Valley were sent to the UK. In both years the SmartFreshTM treated fruit from all orchards exceeded the market specifications whereas the untreated fruit from most orchards did not meet the export standard. SmartFreshTM insured against soft fruit outturns provided the fruit leave Australia with an average firmness of 7.5 kgf and less than 10 per cent of the fruit were 7.0 to 7.4 kgf. Supplementary work to this project conducted by Dr Gordon Brown in Tasmania showed that treatment of Jonagold and Gala apples with SmartFreshTM resulted in fruit that were well above market specifications.

Overall, the fruit from the optimum harvest time was significantly firmer than the fruit from a later harvest after long-term storage. It did not seem to be linked to starch levels. It was more the fact that earlier picked fruit were firmer and remained that way during storage compared to later picked fruit.

The firmness of the fruit needed to be monitored both before and during the harvest period. If the fruit was harvested with a firmness greater than 8 kgf with less than 10 per cent of a sample population less than 8 kgf then with good post harvest management it should have outturned well after long term storage and would be suitable for export. However, in a severe drought year such as the 2003 season, caution needed to be taken in predicting outturn firmness based on harvest firmness.

Apples needed to be held at close to 0°C to minimise quality loss through increased fruit respiration. In the simulated shipping trials conducted as part of the static trials and the SmartFreshTM trials the effects of 6 weeks simulated shipping at 4°C on fruit firmness was variable. In some trials there was a significant reduction in fruit firmness at 4°C compared to maintaining the cool chain at 0°C. The response of the fruit to poor storage temperature differed between orchards. Given that shipping containers would most likely had warmer spots during transport it was possible that shipping temperature was a limiting factor to achieving firm outturns in the UK for fruit from some orchards.

There were many publications that showed the benefits of elevated calcium with appropriate nitrogen to calcium ratios on improved fruit firmness. However, the industry wanted to know if foliar sprays applied during the early fruitlet stages 25 grams to 55 grams, could correct mineral imbalances in time to achieve a normal level at harvest. In the two drought years that the higher nutrient input were trialed, there was no evidence that the early warning system wasn’t working. The nutrient levels did improve between the 25 gram and 55 gram fruitlet stages as a result of the higher nutrient input applied between the 25 gram and 50 gram fruitlet stages. However, there were also orchards on lower nutrient inputs whose fruit had similar nutrient levels 90 days after full bloom (DAFB) and at harvest. Therefore, the results from this project were inconclusive. The drought conditions were probably having a bigger effect on fruit firmness than the nutrient levels in the fruit. The nutritional status of the fruit needed to be viewed in relation to the crop load and tree vigour. It may have been possible to carry two consecutive high yielding years provided the trees vigour was reduced and the nitrogen to calcium ratio was low meaning that the calcium available for the fruit development was not a limiting factor for firm fruit. Nutritional trials were usually run over many years because the benefits of proper nutrition could take time. Two years was not long enough, particularly during drought years to fully determine the benefits of early fruitlet analysis on fruit firmness at harvest and after storage and export.

Flesh browning (FB) also known as ‘internal browning’ of Pink Lady apples was an undefined physiological condition of fruit, which was expressed during storage under certain conditions. FB was first observed in the 2000 season. The incidence and severity increased over the next two seasons being worst in 2002 season. FB was not a problem in 2003. Three types of browning were characterised in this project, Type I senescent (diffuse browning in the cortex), Type II radial (rays of browning in the cortex), Type III carbon dioxide (patches of browning and associated cavities in the cortex). The problem appears to be orchard specific, with large or misshapen, late maturing fruit being more susceptible. Seasonal variations, root disease and growth retardation methods influence the risk of getting FB. In this study, SmartFreshTM applied to Pink Lady apples harvested at commercial maturity had no significant effect on the incidence and severity of internal browning.

Fact sheets were prepared for minimising firmness loss of Pink Lady apples for domestic and export markets.