To kick start the 2017 year, APAL held its annual Post-Harvest Seminar in Adelaide, South Australia, in January, attended by over 80 people in the industry. Many topics were covered aimed at improving the way we grow, handle and store apple and pears pre-harvest in order to ensure quality going into cold storage.
Post-harvest quality starts in the orchard
While this was a day about post-harvest, from the content covered it was clear that orchard managers need to be much more aware of and engaged with the impacts of their orchard management pre-harvest than they currently are.
In the industry there is often a divide between the cold store operator and the orchard manager as growers increasingly tend to send more of their fruit to larger packing sheds where it is stored and handled in bulk. Cold store operators may not know the history of the block’s management where a certain batch of fruit came from, and growers may not get feedback about post-harvest quality and be able to relate that information back to a specific block and its management.
Yet seminar attendees were told a lot of physiological disorders seen post-harvest actually occur as the result of some condition which occurred pre-harvest. Therefore, having a solid understanding of the impacts of orchard management is critical to managing fruit quality.
Key note speaker, post-harvest specialist, lecturer and research lead at Stellenbosch University, South Africa Dr Elke Crouch, explained good quality fruit coming out of storage depended on good quality fruit going into storage.
“During handling a fundamental principle of all quality maintenance is that an apple is alive,” Elke said. “It is actually removed from the mother plant and hasn’t got any additional sources of nutrients and this little packet of energy has to last a very long time.
“Where you start in an orchard is where your post-harvest life starts – so the quality on the tree is what you are going to end up with – [storage] can’t make it better.”
Dr Hannah James, R&D Manager Australia / New Zealand, AgroFresh, endorsed this view and emphasised the need to see the process as a linked continuum.
“It can be a disconnect from the guy growing, where he hands over the perfect looking fruit to the storage guy and says to himself ‘all done’,” Hannah said. “Then six months later in storage there’s a problem with pack outs – it’s a case of ‘you did it’, no ‘you did it’.
“We must link it all and say that apples go on a journey.”
Picking at correct harvest maturity is the most important step for the orchardist in reducing risks of many physiological disorders post-harvest. Although other factors are involved, many disorders are increased when fruit is picked outside optimum harvest maturities. For example, if fruit is picked too early, it is more prone to superficial scald, bitter pit and shrivel, and if picked too late it is more likely that yellowing and internal browning as well as certain types of water core will be problems post-harvest.
These optimum dates can vary according to the storage life required and some ripening will occur during storage. When fruit is at pre-optimum levels ethylene and respiration are very low, whereas at post-optimum levels respiration will have increased so rapidly that cold storage cannot slow it down to mitigate the impact and the fruit quality suffers.
Predicting internal flesh browning in Cripps Pink
Flesh browning is one post-harvest disorder that can affect Cripps Pink. In 2003, the problem became real for Australian apple growers exporting to the UK when 35 shipping containers (approximately 650 tonnes) were rejected due to the disorder.
This triggered a research effort which found that cooler growing conditions are a driver that will increase the risk of internal browning. Other risk factors were found to include nutrition, such as low calcium and low boron, and harvesting at post-optimum maturity. Knowing if the fruit meets these risk factors can help packing shed managers ensure the fruit is appropriately handled and marketed earlier before the problem appears in the fruit, thereby avoiding any potential loss.
Applied Horticultural Research post-harvest physiologist Dr Jenny Ekman reviewed and presented the Australian flesh browning research and explained that three different types of flesh browning occur: diffuse, radial and CO2 damage (high CO2 in cold storage). The risk of developing the disorders can be predicted by calculating accumulated growing degree days (GDD) for the growing season between full bloom and harvest. However, as Jenny explained the research is particularly unclear on what happens when growing degree days fall between 1,100 and 1,400 where there is overlap of the likelihood of the disorders. So while there is some uncertainty, the research has characterised the risk of diffuse browning as less than 1,100 GDD (cold) and for the high end of radial browning of more than 1,450 GDD (warmer.)
The accumulated growing degree days in the 2016-17 season showed most regions started with colder springs than normal (except Manjimup). However, the warmer summer temperatures that followed the cold spring mean the total growing degree days were pretty much going to end up as normal overall.
Cell demography and impact on quality
Visiting Italian plant physiologist Professor Luca Corelli Grappadelli outlined the inner workings of the plant, the processes of fruit growth and development and the effect on quality attributes. Luca is normally based at the University of Bologna but is currently a visiting scientist at Tatura funded by Agriculture Victoria’s Veski program.
Apple cell demography refers to two main attributes of what the number and volume of cells are of a fruit which in turn is linearly related to fruit size. As Luca explained “the number of cells is determined by the number of cell division events. Cell numbers, size, shape and percentage of air and positioning in the fruit impact the cell demography and cell packing defines the textural attributes of the fruit and quality of the fruit.”
Two other areas covered that affect apple flesh quality were the development of dry matter and calcium uptake. Fruit with low cell numbers will have larger cells and produce larger intercellular spaces. Low cell numbers are less desirable as it affects size, texture and storage characteristics. Storage is affected as larger cells lead to larger intercellular space which allows the fruit more ability to exchange gases and also mineral concentrations in these spaces are lower which has an effect on calcium levels.
For a grower this explains the importance of timing and intensity of fruit thinning in order to set the highest number of cells in the young fruitlet.
“The more cells, the greater the fruit potential for better textural properties,” said Luca. “Research shows the cell division starts well before harvest the previous season, which puts a lot of emphasis on the fact that you are managing this year’s crop for this year’s yield but you are also managing the next year’s crop yield.”
Luca presented a yet to-be-published graph showing that varieties reach a stage at which the vegetative meristem developed at stage one commits to being floral at stage two in the previous season where the cell division of the fruit starts. The graph showed Fuji at just 80 days after full bloom would begin floral commitment and subsequently cell division for next season’s fruit and this was followed by Braeburn, Pacific Rose and Gala which happens at 100-120 days after full bloom respectively. This helped reinforce that tree management should consider next season’s fruit as well as the current one so that cell divisions are not hampered particularly with varieties such as Fuji which are usually the first to be thinned anyway to manage biennial bearing.
Participants were then presented research which had implications of calcium nutrition of the fruit. To some this was somewhat controversial as it challenged existing calcium application strategies. It was explained that the growth of the apple is largely dependent on its phloem (water & carbohydrate), xylem (water & minerals absorbed by the roots) and skin transpiration. During the cell expansion phase, both xylem functionality and skin transpiration are lost at 60 days after full bloom by which then fruit grow exclusively thanks to the phloem sap that flows into them.
As calcium enters the fruit prevalently by the xylem it was explained that post 60 DAFB very little calcium can be taken up. This point emphasises the importance of ensuring early calcium application in the season.
Diffuse browning of Cripps Pink is more common than radial browning in South Africa despite the warm temperatures. This is the opposite of the Australian experience, but likely to be linked to the historical tendency to store at -0.5oC (which they no longer do). The browning increases in second picked fruit (later picked) in longer term storage and varies by region, soil type and tree age. Higher potassium to magnesium ratios led to decreases in the browning disorder. Presented by Dr Elke Crouch, Stellenbosch University, South Africa.
Food safety risk assessment for apples is a new project funded by APAL with the Australian Research Council which aims to quantify the risk of pathogens of interest in the apple production supply chain. This was presented by Elizabeth Frankish, University of Tasmania, who said that industries now must prove that contamination of food is prevented.
Economic benchmarking of packing sheds is an APAL project funded by Agriculture Victoria where packing shed managers can benchmark their packing cost data. Presented by Russel Soderland, RIS Projects.
SmartFreshSM use for control of scald in pears was outlined by Stephen Tancred, Orchard Services, who presented the results of three trials of SmartFresh use that showed SmartFresh controlled scald similar to DPA and thus provided a suitable alternative. SmartFresh also reduced scuffing marks which normally come out after storage. This is similar to the experience in other countries where larger pack-outs have been achieved.
Pink Lady® quality worldwide presented by Andrew Mandemaker, APAL, where quality specifications are maintained to support the leading managed apple brand worldwide.
Managing post-harvest rots presented by Lee Duffy, EE Muir & Sons outlined that post-harvest losses to fruit rot are worsened when fruit is harvested during rain and not treated by fungicides, along with a general lack of attention to hygiene and sanitation.
The Pickapp offers growers an innovative way to improve packouts by reducing losses, particularly bruising caused by poor handling at harvest. This was presented by Roei Yaakobi, Tie-Up Venture.
Thanks to our key note speaker and all other speakers for presenting at the 2017 apple and pear post-harvest seminar and to everyone who attended. APAL would also like to thank key event sponsors: Tie-Up Venture, Sumitomo and Campbell Chemicals. Generous support from sponsors helps to ensure these industry activities can continue to be delivered at a high standard.
This project has been funded by Horticulture Innovation Australia Limited using the research and development apple and pear levy and funds from the Australian Government.