Strategies for control of ethylene production
Strategies that offer the prospect of improved control of ethylene production in apples include:
- Conventional breeding techniques – selection of genotypes with low production rates.
- Biotechnology – control of expression of regulatory proteins (ACC synthase and ACC oxidase) by genetic modification.
- Inhibition of regulatory proteins using pre-harvest bioregulants such as AVG (active ingredient of the commercial product ReTainR marketed by Valent BioSciences Corporation).
- Blocking the effects of ethylene using post-harvest bioregulants such as 1-MCP (active ingredient of SmartFresh SM marketed by AgroFresh Inc.
- Inhibition of ‘feed-back’ effect using ethylene removal. Apples and other climacteric fruits are responsive to accumulating levels of ethylene. Effective removal of ethylene from the storage environment can delay the rise in ethylene production in stored apples.
Conventional breeding techniques
This strategy is essentially for the longer term and is not relevant to the improvement of existing commercial cultivars.
This strategy has been demonstrated to be effective on the cultivar Greensleeves. Transformed clones grown in glasshouses at East Malling were found to have markedly lower ethylene production rates than untransformed control trees. However, further work is required to transform cultivars that are important commercially in the UK and to restrict altered gene expression to the fruit only. There are important issues to be resolved as regards public perception and acceptance of this technology.
This strategy presents an opportunity for the control of ethylene based on chemical inhibition. Earlier trials (1997-2006) carried out with ReTainR as a pre-harvest spray to delay the onset of ethylene production and to delay the harvest window for long-term storage. While ReTainR was never registered in Europe, it is used in North and South America, New Zealand and South Africa.
Advances in formulation of 1-MCP has led to the development of HarvistaTM for pre-harvest sray application for apples as a single spray or split application to extend the harvest window for up to several weeks. It is currently undergoing the process of registration in the EU.
SmartFreshTM, a commercial formulation of the potent ethylene inhibitor 1-MCP, has been used increasingly by UK growers since the product was registered for use in 2003. Efficacy of the product was tested extensively at EMR from 2000 to 2003 and there is now considerable commercial experience of using the product.
Other formulations of 1-MCP are being developed commercially in the USA and include FYSIUMTM (PACE). Recent developments with 1-MCP have seen the active ingredient incorporated into packaging and as slow release sachets (FruitbriteTM) that can be added to cartons of fruit during the supply chain. These are not currently available for use in the EU.
This strategy can provide commercially important benefits to CA-stored apples although there are concerns that the technique may not provide consistent improvement and that scrubbing systems currently available may not be cost effective.
Prior to the advent of 1-MCP the possible use of ethylene scrubbing technologies had a greater significance. Whilst both these technologies are intended to maintain a low rate of ethylene production by the fruit in the case of 1-MCP the fruit is insensitive to ambient ethylene for a significant period after treatment whereas with ethylene scrubbing fruits remain sensitive to ethylene at all times.
More recently, a range of ethylene scrubbing devices based on ozone or cold-plasma have been or are in the process of being commercialised. Some of these claim to have dual activity, both in terms of destroying ethylene and surface sterilising or scrubbing out air-borne pathogens. The capacity of the scrubber to remove the high evolution rates of ethylene from apples needs to be considered before adopting any particular technology. Other scrubbing technologies based on ambient temperature catalytic removal using palladium based catalysts and absorbers have been used to reduce ethylene in consumer packs in the retail chain.