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Tasmanian Institute of Agriculture

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Published: 15 May 2019

Have you ever bitten into an apple and found a brown spot? Gross.

It’s not as though that brown spot was a worm or some deadly virus or disease, but it was probably distressing enough for you to toss the apple in the bin, right?

It should come as welcome news, then, that researchers at TIA have found a way to make some cosmetically “ugly” fruit more palatable.

Mangoes have an extensive network of canals underneath their skin and in the flesh that contain resin or sap. When the fruit is infected with Resin Canal Disorder (RCD), these canals turn an unsightly shade of brown or black. While the affected mangoes are safe to eat, the discolouration causes many of us to chuck the fruit in the bin.

TIA PhD Candidate Umar Muhammad is part of a collaborative, multi-state research project within the ARC Training Centre for Innovative Horticultural Products. Emerging research into RCD has been difficult. While it’s estimated that it causes up to a 30 per cent loss in the Australian mango industry, there was no consensus of whether RCD occurs prior to or after harvest. It was difficult to find RCD samples in orchards.

So Mr Muhammad took a new approach to the problem: he learned how to spread the disease better.

He developed a method that allowed researchers access to unprecedented levels of RCD-infected fruit – inoculating healthy fruit, then injecting RCD into select groups via needle.

100 per cent of the injected mangoes developed RCD and zero control mangoes developed the disorder.

Northern Territory Research Leader Dr Cameron McConchie, of the Department of Primary Industry and Resources, said this discovery was a major breakthrough in preventing RCD.

“We discovered that RCD occurs post-harvest and that avoiding contamination is essential to prevent it.

“We did not fully understand the cause until after Mr Muhammad artificially induced the RCD bacteria into healthy mangoes,” Dr McConchie said.

The research team found that RCD can spread merely through contact with the intact skin of infected mangoes.

They also found that some mango cultivars, like Kensington Pride, are more susceptible to RCD than others.

There is still research to be done, but it appears adjustments to systems like post-harvest handling or more complex changes like developing RCD-resistant varieties may help farmers get more value from their fruit.  

TIA Associate Professor Alistair Gracie said projects like this aren’t just a way to help farmers keep their businesses profitable or improve an entire industry. They may also help feed more people.

“I’m sure there are people who joke about how important prettier fruit really is, but the reality is that it may actually help minimise food waste.

“For whatever reason, ugly or discoloured fruit is less palatable to most consumers. We may be able to change those preferences in the long run, but in the meantime the more fruit we can keep from getting tossed in the bin, the more people we’re going to be able to feed,” said Mr Gracie.

As the world population booms, we’re going to have to find new ways to feed more and more people. While it won’t solve the problem, cosmetic fixes and better post-harvest practices can help contribute to keeping food safe, sustainable and profitable.

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