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Ongoing project

Reducing granulation in the production of Imperial mandarins (CT19005)

Key research provider: Queensland Department of Agriculture and Fisheries

What’s it all about?

This investment is establishing several on-farm trials to investigate the impact of irrigation and nutrition on granulation in Imperial mandarins. The end goal is to develop guidelines for growers that they can incorporate into their management practices to ultimately improve fruit quality.

Imperial mandarins are prone to granulation, a physiological disorder which results in dry, tasteless fruit. Unfortunately, affected fruit cannot reliability be detected by appearance or density, and when granulated fruit reaches the market it has the potential to damage the reputation of the industry. By providing growers with advice on how to minimise granulation, there is the opportunity to improve consumer satisfaction through reduced incidence and severity of granulation in mandarins, and more consistent quality season to season.

Key activities of the on-farm trials include, but are not limited to:

  • Improving irrigation practices in early fruit development
  • Reviewing nutrition requirements to support the development of young fruit
  • Researching the use of plant growth regulators and pruning timing to reduce fruit-to-shoot competition
  • Reviewing technologies for the non-invasive assessment of granulation.


A visual guide for granulation in Imperial mandarins was developed by project Australian Citrus Quality Standards – stage 3 (CT15013) along with a guide to maximum granulation standards.

The team report that growing-season treatments and monitoring for seven trials were completed. This included irrigation deficit treatments that extended into January at three trials, monitoring of flush growth and fruit set and drop at five trials, and leaf tissue sampling across all trials.

In April and May (Imperial harvest season), the team sampled and assessed fruit size, crop load and fruit granulation incidence and severity. For the irrigation trials, juice samples and skin colour assessments were made to check for any side effects due to the management practices under trial.

Results for the 2020/21 year have been analysed, alongside data collected from relevant trials funded by growers and DAF Queensland in 2017/18 and 2019/20.

A report on the developments in technologies for the non-invasive assessment of granulation in harvested fruit in the packing line was prepared by the team from Central Queensland University. 

Related levy funds

This project is a strategic levy investment in the Hort Innovation Citrus Fund