Peony flowers (Paeonia hybrids) are herbaceous plants with large, showy flowers in white, pink, rose and red colours, and are much valued as a cut flower, especially by the Chinese community. They are members of the Ranunculaceae family, which also includes delphinium, larkspur, anemone and nigella species. Members of this family are generally very sensitive to ethylene which may contaminate the environment, as evidenced by rapid petal abscission or shattering (Woltering & van Doorn, 1988). As a family, they also tend to respond very favourably to silver thiosulphate (STS) treatment, which prevents ethylene action. A recent report from Korea has advocated the use of either STS or Chrysal-RVB® treatments to extend the vase life of peony flowers (Sim et al., 1994), although little information has been documented on the sensitivity of different peony cultivars to ethylene in the environment.

A series of trials were conducted at the Mt. Albert Research Centre to determine the effects of exposure to ethylene in the environment on the vase life and quality of several peony cultivars grown at Alexandra, Central Otago. Two cultivars,'Coral Sunset' and 'Maestro', were tested by exposure to 10 ppm ethylene for 24 hours. Two further cultivars, 'Monsieur Jules Elie' and 'Sarah Bernhardt', were screened with a range of ethylene concentrations from 0.1 to 100 ppm for 24 h, plus 10 ppm ethylene after pre-treatment with Chrysal. For all four cultivars, endogenous ethylene production (production by the flower itself), and respiration rates of individual flowers were determined daily over 1 week.

The following observations were recorded:

• 'Coral Sunset', 'Monsieur Jules Elie' and 'Maestro' were all slightly sensitive to ethylene exposure, with a vase life reduction of 1-2 days, and a reduction in time to complete abscission of 1-2 days;
• Chrysal-treated flowers opened earlier and developed into larger blooms than untreated flowers. However, the flowers often wilted earlier than control and ethylene-treated flowers. This was no doubt due to toxicity problems, as flowers had been left in Chrysal throughout the vase life period rather than having an overnight pre-treatment;
• 'Sarah Bernhardt' showed the least sensitivity to ethylene exposure, with similar vase life periods and time to complete abscission for all treatments;
• All four cultivars produced very little or no endogenous ethylene during the week after harvest. There were some traces of ethylene detected towards the end of this period for the cultivar 'Monsieur Jules Elie', but they probably arose from fungi that were causing petal rots. Respiration rates were high and declined to about half of initial values during the same period.

From this initial screening trial it would appear that peonies do not themselves produce any significant amounts of ethylene during vase life. However, some cultivars may be slightly sensitive to ethylene in the external environment, and therefore care should be taken to exclude ethylene from the packing and storage areas to ensure maximum vase life. However, vase life reduction due to exposure to ethylene was only 0-2 days for all 4 cultivars tested, and vase life was usually terminated by petal wilting and senescence (an age effect), rather than petal abscission (an ethylene effect). This behaviour contrasts with rapid petal shattering which is usually observed in response to ethylene exposure for other members of the Ranunculaceae family. Water relations appear to play a significant part in vase quality of peonies, but further recommendations can only be made after more in-depth study has been carried out.

The maturity of the flowers at harvest appeared to have a greater effect on vase life than any exposure to ethylene. 'Coral Sunset' which was more open at harvest had much shorter vase life than the other cultivars which were more tightly budded (2-3 days compared with 6-7 days). However, some peonies harvested at the tight bud stage frequently failed to open fully or were very slow to open, especially after exposure to ethylene.

References

Woltering, E.J. & van Doorn, W.G. 1988. Role of ethylene in senescence of petals - morphological and taxonomical relationships. J. Experimental Botany, 39:1605-1616.

Prepared for HortNET - June 1998