Assessing the effect of a new growth regulator on the storage life of Pink Lady apples (AP02031)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

ReTain® plant growth regulator is a commercial formulation of aminoethoxyvinylglycine hydrochloride (AVG). This compound is known to competitively inhibit the activity of the enzyme 1-aminocyclopropane-1-carboxylic acid synthase (ACS) which is the rate limiting enzyme in the ethylene biosynthetic pathway. By inhibiting the activity of ACS, ethylene mediated ripening processes can be delayed. Pink Lady® apples were sourced from two growing districts (Shepparton, Victoria and Lenswood, South Australia). These fruit were treated with ReTain® at two application times, 21 and 7 days before the commercial harvest date and harvested at two maturities; maturity 1 (starch pattern index 2, a harvest index for long term storage) and maturity 2 (starch pattern index 4, a harvest index not suited for long term storage and better suited to the fresh market). The samples were stored at 0oC and assessed for quality attributes at harvest and after 2, 4 and 6 months storage in air and after 2, 4, 6, 8 and 10 months in CA storage (2% O2 and 1% CO2).

The quality attributes assessed at each removal included internal ethylene concentration (IEC), flesh firmness, starch pattern index (SPI), %TSS, background colour and skin greasiness. Naturally occurring fruit volatiles were also measured after 6 months storage. A shelf life assessment was also carried out at 6 months for the first harvest of fruit from Lenswood, South Australia.

The results indicated that treatment with ReTain® significantly reduced the IEC of fruit from both districts which correlated to higher flesh firmness throughout storage than was observed in untreated control fruit. ReTain® treatment 21 days before harvest (DBH) resulted in an extended harvest period in both Shepparton and Lenswood which can be a significant commercial benefit for apple growers. Treatment with ReTain® 7 DBH for fruit grown in Lenswood and harvested at maturity 1 had the additional benefit of a 2 month extension of storage life due to the retention of flesh firmness. The benefits of treatment with ReTain® were maintained during the 14 day shelf life assessment. The research results showed that the main advantages of applying ReTain® for Pink Lady™ apple growers were the improvement of harvest management as well as the improvement of postharvest fruit quality.

During 6-11 June 2004, Dr John Golding presented this work at the 5th International Postharvest Symposium in Verona Italy, with funding from Horticulture Australia Ltd. (Project AP02031) and Valent BioSciences as a voluntary contribution. NSW Agriculture also supported his time in this project. His presentation entitled, ‘ReTainTM Maintains Pink Lady® Fruit Quality during Long Term Storage’, drew large interest both at the presentation and after the allotted time. Many pertinent questions were fielded, particularly fromresearchers from Europe.

This was the largest postharvest conference ever held and provided a valuable and worthwhile forum for discussion of the current trends and future directions in postharvest science. A major focus of the conference was product quality and ripening physiology. Apples were the major crop of interest at the conference with 74 presentations, but stonefruit, citrus and cutflowers were also well represented.