Attendees at APAL’s post-harvest seminar in Shepparton this week will hear from eminent biologist and biotechnologist Gabriele Berg, who is head of the Institute of Environmental Biotechnology at TU Graz. Gabriele and her team have been able to significantly increase the shelf life of apples using a combination of hot water treatment and biocontrol organisms.

What is the challenge?

Just under half (45 per cent) of the world’s harvest of fruit and vegetables is lost before it reaches the consumer due to spoilage from disease infestation or incorrect storage conditions, according to the UN’s Food and Agriculture Organisation (FAO).

Until recently, this challenge has been combated with the use of synthetic pesticides, but the industry is now seeking methods to respond to growing customer demand for healthier and more sustainable alternatives, along with the potential prohibition of currently used pesticides.

One such method, designed by Gabriele’s team at TU Graz, combines hot water treatment (HWT) with biocontrol organisms to successfully extend the shelf life of apples.

What is HWT?

Hot water treatment involves dipping apples into a 53oC water bath for three minutes, causing “heat shock” which stimulates the apple’s natural defence mechanisms and is a proven sustainable method for killing or reducing post-harvest pathogens.

However, prolonging HWT or increasing the temperature risks damaging the fruit, which is another reason a combined approach has been sought. The team at TU Graz found that combining HWT with a biocontrol agent improved results by 20 per cent over apples subjected to HWT only.

Why doesn’t HWT kill the biocontrol agent, too?

The biocontrol agent was obtained by researchers from the apple microbiome of native organic apples. While the release of plant defence metabolites triggered by HWT kills or almost completely contains harmful fungi, the natural apple-associated microbiome remains unaffected. This confirms the close connection between the plant and its microbial symbionts.

A combined approach

The research, published in Frontiers in Microbiology, concludes with three key findings:

A healthy apple microbiome is characterised by high bacterial and fungal diversity and evenness, a balanced ratio between both groups and several health indicators, while diseased apples show dysbiosis, diversity loss and dominant fungal pathogens. HWT-induced plant response diminished pathogen infection and showed an impact on the fungal composition.

Small-scale storage experiments applying Hot Water Treatment together with biological control agents provide further confirmation of the considerable potential of combining methods into one control strategy to reduce post-harvest decay of apples.
Harnessing the indigenous microbiota of fruits for a biological control approach is a promising and sustainable future strategy to prevent post-harvest decay of fresh and stored produce.
Post-harvest biocontrol products

The findings from Gabriele and her team provide an important link in the steady journey towards the development of commercial-scale biocontrol for apples and other fruit. HWT combined with biological control agents is one of many promising new, highly efficient biological alternatives over the past few years that may one day replace synthetic pesticide treatments.