What was it all about?

Improving avocado fruit quality is essential in order to continue to grow demand for Australian avocados, and so gaining a better understanding of where quality issues are occurring is important for the industry. This investment was tasked with investigating reports of declined fruit quality in late 2018. The project team assessed the quality of avocados available in Australian supermarkets over that summer, to help quantify the extent of the quality issues and identify the source of affected fruit.

During summer, avocados are mostly supplied by Western Australia, with the gap between demand and what the state can supply filled by imported fruit from New Zealand. During October and November 2018, anecdotal evidence suggested that rots were a major issue in avocados on the Australian market, with many fruit failing to meet consumer expectations. To better understand the situation, the project team measured fruit quality at retail for both Australian and New Zealand avocados. Fruit was sampled at retail stores in Brisbane and Sydney in late December 2018 and in early January 2019. In total, 31 samples (representing 310 avocados) of New Zealand fruit from five suppliers/exporters and 32 samples (representing 320 avocados) of Australian fruit from six suppliers/packhouses were assessed for internal quality.

Overall, 22 per cent of the New Zealand fruit had significant damage (mainly rots), compared to 10 per cent of Australian fruit (mainly bruising).

More specifically:

• 20 per cent of New Zealand fruit had significant flesh rots (greater than 10 per cent of flesh volume), compared to 1.6 per cent of the Australian fruit sampled
  
  
• 54 per cent of the New Zealand fruit had some level of body rots, 36 per cent had some stem-end rot, and 17 per cent also had vascular browning. This compared to 10 per cent of Australian fruit having body rots, four per cent having stem-end rots, and six per cent having vascular browning
  
  
• Most of the damage in Australian fruit was due to bruising, with nearly eight per cent of the Australian fruit being bruised (greater than 10 per cent of flesh volume), compared to only one per cent of the New Zealand fruit
  
  
• Regarding fruit age, New Zealand fruit averaged 25 days from harvest to stage five ripe, compared to 22 days for Australian fruit. Four New Zealand and one Australian sample reached or exceeded 30 days from harvest. However, fruit age did not correlate well with the level of fruit rots, suggesting other factors were contributing to the rot problem.

The project team concluded that above-average rainfall and flooding events earlier in the New Zealand growing season were likely to be the underlying cause of the high incidence of rots in the New Zealand fruit. Delays during transport and ripening, due to quarantine intervals, may have also contributed.

They noted, however, that the severity of rots can be influenced by many other pre- and postharvest practices, and encouraged all growers and packers to follow postharvest best practice to try and minimise the issue. This includes...

• Applying postharvest fungicides within 24 hours of harvest
• Using sanitisers in bin dumps
• Removing field heat as soon as possible after harvest
• Keeping fruit at the recommended storage temperature (5°C) through the cold chain
• Not exceeding maximum recommended storage times before ripening
• Ripening fruit at 16 to 18°C, and maintaining air.

The project team also noted that mature, late season fruit tends to be more susceptible to rots than earlier season fruit. If possible, they said, fruit which has a higher disease load should be harvested and ripened first. Fruit grown in the drier climate of south west Western Australia is likely to have a lower disease load than that from New Zealand, so could potentially be allowed to mature longer.