Post-harvest use of the plant-growth regulator, ethephon, to promote colour development (de-greening) in papaya (PP13006)

What was it all about?

The use of ethephon as a de-greening or ripening agent is considered by the Australian papaya industry to be critical. Fruit harvested during the cooler winter months often fails to develop the consumer-desirable, ripe skin colours, even though the fruit is at harvest maturity and internally is ripe and ready to consume. Green fruit is less marketable and consequently down-graded or discarded.

This project, which ran from 2014 to 2015, investigated the effectiveness of the synthetic plant-growth regulator, ethephon, to enhance colour development of winter-harvested papayas.

Researchers obtained 200 red and 200 yellow-fleshed papaya from a commercial crop during a cooler month of the year and divided them into four lots of 100 fruit which were allocated to one of the four treatments. One batch was an untreated control, and the others were dipped in ethephon at three different concentrations.

Ethephon was effective at de-greening and ripening winter harvested papaya fruit compared to those left untreated.

Further, the project detailed the likely residues of ethephon which remain in and on papayas following dip treatment at 100 and 200 mL/100 L of solution. Analyses indicated that a significant portion of the residues of the plant growth regulator remained on the skin but that residues in whole fruit were substantially reduced within three days after the treatment being applied.

The project team submitted the efficacy and residue data to support a minor-use permit application which seeks to have the use of ethephon on papaya approved for de-greening and ripening.