Several rose varieties sold by European retailers suffer significant and unnecessary quality loss as a result of exposure to ethylene, a recent Dutch study has shown. With a few preventive measures, the post-harvest performance of these roses can be greatly improved. An alternative is to develop ethylene-resistant varieties. Either way, retailers will be able to offer consumers flowers with improved colour and opening and a vase life up to five days longer than today’s average.
The study of the effects of ethylene on roses was carried out in December 2012 and January 2013 by FlowerWatch, a leading Dutch centre for supply chain expertise, monitoring and development, and commissioned by Chrysal Netherlands, a specialist in flower care solutions. In the study, FlowerWatch followed a range of 25 rose cultivars exported to European retail destinations by two Kenyan growers. The researchers monitored the ethylene concentrations to which the flowers were exposed throughout their post-harvest journey from grower to consumer. They looked at the flowers’ sensitivity to ethylene as well as to ethylene inhibitor AVB, a post-harvest conditioner developed by Chrysal.
An important discovery
The most important outcome of the survey is that at least four of the 25 cultivars – all of which are common European retail products – showed significant sensitivity to ethylene. ‘This is an important discovery, as roses are not commonly considered to be ethylene-sensitive,’ says FlowerWatch’s Jeroen van der Hulst. ‘Everyone knows carnations and lilies are, but no rose trader monitors ethylene concentrations in the transport, storage and sales environment. These outcome are remarkable and definitely warrant further investigation.’
Ripe fruit and combustion engines
Ethylene often comes from external sources; for instance, it can be produced by ripe fruit and combustion engines. In an enclosed area or under the influence of higher temperatures, concentrations can increase. Allowing trucks or other vehicles into rose storage areas thus is a major threat to sensitive rose varieties. Storing, transporting or even selling the flowers near fruit – say, in a supermarket – can also have a disastrous effect on their quality. Inadequate cold chain management is another quality killer. However, ethylene can also be produced internally by flowers, particularly in response to temperature fluctuations and water stress. Says Van der Hulst, ‘In several rose boxes, we found ethylene concentrations up to 2.6 ppm. We believe this ethylene did not come from external sources, but was produced by the roses themselves. Our measurements were not extensive enough for scientific qualification, but they clearly must be taken seriously.’
Poor opening, wilting, discolouring The survey proves beyond doubt that ethylene is a factor rose traders must start taking into account. The most sensitive cultivars tested by FlowerWatch – Marie- Claire, Mariyo, Inka and Viva – suffered major quality loss even when exposed to relatively low concentrations of ethylene.
Exposure had the following effects on the cultivars in question: Poor opening (some flowers opened in the shape of a star, while others failed to open at all) Wilting (ethylene exposure led to premature wilting) (Purple) discolouring and loss of colour; Reduced vase life.
Vase life extended by 5 days
By contrast, roses protected against ethylene by preventive measures did not show any of these problems. Most importantly, their vase life increased by as much as five days. ‘Our conclusion is that protection against ethylene simply means fewer consumers will be disappointed in their purchase and the ornamental value of the roses in question will go up,’ says Van der Hulst. ‘We believe this is an important discovery for the rose market. Recent research in the USA has shown similar outcomes, but none of the American studies involved European rose cultivars. This report has the highest relevance for the European market.’
An ethylene-free supply chain
FlowerWatch and Chrysal list the following measures for ensuring an ethylene-free supply chain: Keep roses away from fruit and foliage and from areas in which these have recently been stored Keep trucks and other gasoline-fuelled vehicles out of rose storage facilities and auction halls Do not use combustion engines or gas heating in rose cultivation or storage facilities Ensure adequate and consistent cold chain management (avoiding warming) Subject sensitive roses to post-harvest treatment with an ethylene inhibitor, such as Chrysal AVB Reduce the risk of internal ethylene production by ensuring the utmost care in handling and packaging flowers (minimise touching).
‘The inclusion of AVB in the study is a significant detail, as different cultivars may respond differently to inhibitors,’ says Van der Hulst. ‘Its protective effects on carnations and lilies are widely known, but its effect on roses had never been researched until now.
Our study shows that conditioners like AVB are a viable option for rose traders.’ The active ingredient in AVB is silver thio sulfate. To reduce the negative environmental and health impact of silver, Chrysal has developed a neutralisation method by which most of the silver can be recovered prior to the disposal of any waste solution. ‘If these products are used the way they are supposed to be, they are environmentally sound,’ says Jeanet de Zeeuw, a technical consultant at Chrysal International BV. ‘AVB is commercially available and registered as an approved post-harvest treatment product in Kenya. This means that, like other registered products, it is accepted within the MPS quality certification scheme for flower growers.’
Resistance and prevention
Overall, FlowerWatch draws two main conclusions from its research. Says Van der Hulst, ‘First, the fact that some rose cultivars are sensitive to ethylene while others are not, means breeding and promoting resistant varieties makes good commercial sense. Second, as long as ethylene-sensitive varieties remain on the market, post-harvest handlers must take preventive measures to reduce damage and boost quality, vase life and overall flower value.’
Ethylene, a natural hormone
Ethylene is a hydrocarbon and a colourless, flammable gas with a faintly sweet smell. It is produced as a natural hormone by many different plants to regulate internal processes, such as ripening. Chemically manufactured ethylene is used in agriculture to accelerate ripening. Ripe fruit, in particular, produces a lot of ethylene and its production is increased if the fruit is damaged or stored in unfavourable conditions. For instance, high temperatures stimulate ethylene production, shortening the storage life of the fruit or plant in question.
As ethylene is a gas, its easily spreads from its source. This means that adequate management of ethylene levels throughout the post-harvest life of roses, or other flowers and plants, will result in fresher, longer lasting products. Different plant species produce different levels of ethylene under different conditions. Research into these effects is ongoing in many areas of horticulture.